Leg vise experiences?

[Scott Winners]

I just ordered from Lake Erie and Anchora Yacht Services, have a couple or four weeks to get my act together.

My main questions regard the chop.

I am seeing a lot of folks using 12/4 stock, but then trimming the top of the chop back to half an inch or so so they can get at the workpiece. Is 12/4 really neccessary? If I really need 12/4 I will probably have to glue it up. One 8/4 glued to one 4/4 should put me in the ballpark. Is there a compelling reason I couldn't or shouldn't build the chop up to 12/4 thickness to match the thickness or depth of my benchtop, about the top 4 inches of the chop, and then run 8/4 down to the floor?

Is maple just traditional, or does it have a specific advantage over white oak or hickory? Weight maybe? I have been buying 8/4 in all three species lately for turning projects, I am leaning towards finding a piece of 8/4 that I can get some turning pieces out of and then use the not suitable for turning remainder as the chop.

I can visulaize the install, I feel darn good about it; but I would like to hear from folks that have been using them a while.

"I made my chop out of 8/4 butternut/white pine / figured walnut 25 years ago and it is great" is a valid data point. If I really need to glue up 12/4 from floor to bench top I would rather do it right the first time. "I started with an 8/4 chop but it flexed when I did ___ so I had to make a new 12/4 chop" also valid data point.

The other thing is I am old enough and wise enough to ask all y'all, what am I not asking that I should be asking? I recognize I don't know what I don't know.

Thanks in advance.

[Christopher Charles]

Hi Scott,

I have an elm chop that's probably 12/4, but that's because I got it from a friend, along with the wood for the base of my bench for the best price (free). I also have the Anchora chain and think it works great (there are some picks of the install in a thread I did of the bench build started nearly 10 years ago). From a structural standpoint 2x pine would probably be sufficient because the lever arms in the vice are short. So I would say pick anything that will suit your eye and wallet. I'm not sure what I would have done if paying for wood...

Best of luck!

[Scott Winners]

Thanks Chris, I am leaning towards 12/4 because I ass/u/me the ones before us needed it for something; but I will have to special order it and count on the order filler in the lower 48 to send me a good piece. My local guy carries 8/4 and under, he has a little bit of Brazilian something in 16/4 but it is more than $25/ bf. I will go look for your bench build.

[Michael Bulatowicz]

Hi Scott,

While I don’t have any experience with a leg vise to offer, I can tell you the following. All else about the geometry and materials being equal, the stiffness will go as thickness cubed, so 3 inches thickness will be over 3 times as stiff as 2 inches. The experience of others, as you indicate, seems to suggest the extra stiffness is a good thing.

I don’t see any reason you couldn’t laminate pieces together to get the greater thickness if you go that route.

[Prashun Patel]

My chop is 8/4 walnut and works fine.

The leg vise works best when the fulcrum is slightly wider than the thickness of the held piece. So taper your chop or plan your chain install accordingly.

Leg vise handles are lower than other vise types. While a lower handle implies greater holding power and leverage and depth capacity, it means more stooping. As I am getting older, the stooping is really wearing on me. The vise is plenty strong and I could have gone a couple inches higher with my handle without sacrificing power noticeably.

If you are planning to use it to edge plane, a makeshift deadman on the other front leg is a godsend.

[Phil Mueller]

My leg vise chop is 6/4 hard maple, which is 1/4” thicker than what Chris Schwarz shows in his Roubo bench plans. If it’s ever flexed, I haven’t noticed. It has plenty of holding power.

[Derek Cohen]

Hi Scott

If you have not read the review of the chain adjuster on my website, here is a link: http://www.inthewoodshop.com/ToolReviews/AYSLegViseChainAdjuster.html

I have the very first AYS adjuster, which Jim entrusted to me for evaluation. It have remained on my leg vise for over 8 years.It works exactly as designed, and has been completely reliable.

http://www.inthewoodshop.com/ToolReviews/AYSLegViseChainAdjuster_html_673377d5.jpg

http://www.inthewoodshop.com/ToolReviews/AYSLegViseChainAdjuster_html_5654bec3.jpg

My leg vise is also a wooden thread, although not the quality of a Lake Erie, about which I have heard excellent reports.

There is also an anti-racking mechanism I built for use with the leg vise: http://www.inthewoodshop.com/ShopMadeTools/AntiRacking.html

http://www.inthewoodshop.com/ShopMadeTools/AntiRacking_html_5ca126bb.jpg

http://www.inthewoodshop.com/ShopMadeTools/AntiRacking_html_m60bfac7.jpg

You do need a deadman ...

http://www.inthewoodshop.com/Furniture/EntryHallTableForANiece2_html_m1dd9ab31.jpg

Regards from Perth

Derek

[Michael Bulatowicz]

While a lower handle implies greater holding power and leverage and depth capacity, it means more stooping. As I am getting older, the stooping is really wearing on me. The vise is plenty strong and I could have gone a couple inches higher with my handle without sacrificing power noticeably.

Hi Prashun,

You have part of that backwards.

In any statics situation (i.e. when things aren’t moving, such as when you have something clamped in the vise) the sum of all forces and the sum of all torques must be zero.

This indicates that the total force applied by the screw is shared between your workpiece and the base, with the sharing determined by how far each is from the screw. Force times distance for each (the work and the base) must be equal, so if the screw is closer to the work the force on the work must be greater because the distance is smaller.

Therefore, a higher screw increases the clamping power but reduces the capacity.

[ken hatch]

Scott,

I've used chops made of 12/4 and ones made of 8/4 with a 4/4 lamination, functionally there is no difference. At that thickness wood used makes almost no never mind, pick something cheep and/or looks good.

ken

P.S. On the portable benches I've used 8/4 Red Oak or Beech chops with no problem.

[Jeff Ranck]

I laminated two 8/4 pieces and ended up with a chop that was about 3.25" by the time I was done. I cut the top of the chop at something in the neighborhood of 60 deg. rather than the 45 deg. I have seen others do. I like the look better and I can bring my saw to a steeper angle when needed. I used maple because I like the look, not because I was worried about any strength issues.

I can't figure out why the photo is rotated. It shows fine in my desktop. Sorry.


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[Prashun Patel]

Michael, then I've had it wrong all this time. The screw should be as high as one can stomach in terms of sacrificing depth.

[Joshua Lucas]

I used 8/4 Hickory and it has absolutely no flex. 12/4 might be necessary if you're using pine but for most hardwoods it's pretty overkill.

[fritz eng]

Be aware that you may have to adhere a non-slip material on the jaw(s) of your leg vise to secure the work piece. I probably erred in building my leg vise using only 6/4 material. I am considering adding stiffeners as a result.

[Scott Winners]

Yay!! Data! Appreciate it.

I did find my c.2010 Chris Schrawz workbench book last night. In 2010 he used one piece of 8/4 maple for the chop with no objective reasons provided. Same author, c2020 workbench book he laminated two pieces of 8/4 maple face to face for a finished chop ' about 3 1/4 inch thick', again with no objective data or rationale.

I guess I should pencil up a drawing and figure out how much force can be applied by the screw to the chop before the chop begins to flex. That's the fundamental reason for a thick chop, yes? Crank it down hard enough the chop flexes the the jaw face goes out of parallel with the bench face and then the work slips.

That is exactly the problem with my current vise that is going away. When I crank it down hard enough the moving jaw pivots on the low edge of the clamped work piece, the mouth opens and my workpiece slithers away.

[Scott Winners]

I think we can model a vise chop as a simple beam with a point load. The screw ought to be able to generate enough force to ignore gravity. Simple drawing attached. The beam calculators I have access to on a timber framing website only have design values for structural beams 5x5 inches and up for floor joists and top plates and etc.

I am going to have to dig a little bit for design values to plug in to the calculator, fiber stress in bending, modulus of elasticity, that sort of thing. Once I have those I can plug and chug with the data points in this thread to see if there is any consistency, I should be able to say something like "folks who can generate 12 psi on each sqin of the clamping face with no deflection of the chop have no comlaints. Folks who can only generate 8 psi per sqin..."

I do need the width of your chop top and bottom. If you have 2" thick chop that is 2 inches wide at the stop block at the bottom and 12 inches wide at the bench top, on the beam calculator your beam is 2x2 inch section width. I'll run everything on 36" tall chops (36" long beams) for apples to apples, shorter beams with the same section width will be stronger.

Do not despair, I actually enjoy math problems like this because there is an actual good reason to solve the problem. A needlessly thick chop means we are limiting our maximum jaw opening.


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[Jim Matthews]

My only input on the design is to avoid having the protruding parts at the height of your pockets.

[Michael Bulatowicz]

Michael, then I've had it wrong all this time. The screw should be as high as one can stomach in terms of sacrificing depth.
Prashun,

Not necessarily; by the time the screw is 3/4 of the way up the chop, you're already getting at least 3/4 of the screw's total force on your workpiece (more if you have the work low in the vise rather than at the toe). A few inches up or down on a typical leg vise height won't make much difference in clamping force (but will have some effect).

Placement of the screw will have more effect on comfort and capacity than on clamping force.

There are definitely diminishing returns as you raise it higher and higher. I'd say, rather, that one should place the screw as one judges based on the tradeoff between convenience/comfort, clamping force capability, and capacity. Where the "right" placement ends up seems to involve too many factors to make a recommendation without knowing about the person and their work.

Then, there's the relationship between chop thickness, toe-in angle, and flex that can limit the maximum practical clamping force independent of the screw, say if toe-in becomes toe-out due to too much force applied for the chop design. Deflection is going to be based on the ratio of length to thickness (modified by width) and will also depend on screw placement. I can go into more detail if it's helpful.

[Joe A Faulkner]

I don’t recall seeing many 12/4 leg vise chops. Most seem to be 8/4 which in My experience is adequate. I did line the face with leather. I’m not too concerned with chop deflection. In terms of species, I think maple is easier to work than hickory and the closed grain helps in having a smoother finish. I have no regrets in going with maple.

[Michael Bulatowicz]

Hi Scott,

I would be happy to help with the calculations if you would like. I have a good deal of experience with mechanical analysis.

Michael

[Prashun Patel]

Nice. Thanks. I don’t know bout your fancy math ;). I just know my old back don’t like stopping. The leg vise is easily the most powerful of my vises and I suspect up or down it will be plenty strong.

[Michael Bulatowicz]

It appears you already knew the most relevant information, then:).

Should you choose to adjust your setup, you now also know that you won't compromise on clamping force.

[Jim Ritter]

Here are are some real world numbers on what one of my leg vises is capable off. If you can’t see the dial it is 1600 PSI.

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In answer to your problem Scott of the top of the jaw opening up, there is an adjusting nut at the end of the chain that makes it easy to dial in just the right amount of toe in so at full pressure the jaw is possible.
full disclosure I am the vender of the chain kit. I’m just here to answer questions, I hope that is ok.
Jim

[Scott Winners]

A couple items and then I will have to leave this be for a few days.

I have written down on my Monday to do list the phone number for NELMA so I can order the grading guide for northeast and great lakes USA. Can't do beam calculations without knowing what grade lumber you are using. Local to me none of the hardwood from the NEMLA area has grade stamps on it. Hopefully the person I get on the phone can tell me how to find the grading rules that are supposedly free .pdfs on the website, I couldn't find them.

I did do a beam calculation with a 5x5 inch hickory timber. For beams and stringers, hickory, (american) beech and birch all use the same table. So imagine a select structural grade hickory beam 5x5 inches and three feet long. Set two anvils on your driveway so the outside edges are three feet apart, set the beam across them. Set one of your hands on one of the anvils and under the beam. Have a friend lower a Toyota Corrola or similar 2800 pound item on the beam 12 inches down from the end of the beam over your hand, 24 inches from the other end, a point load. The beam will not fail, and will only deflect 0.029 inches.

I don't know of anyone using a chop five inches thick. At some amount of force the threads on the screw and nut will fail.

All: Please keep your data points coming. "My chop is 2.5 inch thick maple, four inches wide at the floor, 12 inches wide at the benchtop, no issues" is all I really need.

Michael B:

There are many things timber framers are willing to do if an engineer trusted by both the builders and the building inspector signs off on the blueprint, but the timberframers would not attempt if an engineer hadn't signed off. I am not a timberframer. I did spend most of my free time last winter learning about it. And this beam is an unusual situation in the load comes and goes and comes and goes, much more rapidly then seasonal snow load.

I have to get the grading book in, find reasonable design values for material I can get, and I have to leave the through hole for the vise screw out of the beam width. If the chop is two inches wide at the bottom stop block and the through hole for the vise screw is two inches on center there is no beam, from a timber framers perspective.

In say 2-3 weeks I should be able to write up reasonable beam calcs, makes sense to start with hard maple. When I get to the end of all that you or anyone else who feels qualified is cordially invited to look it over and say because of x, y, and z this item is actually 30-50-200% stronger than calculated.

Jim R:

Your posts come up in my search results here often, glad you are still around. I have wanted a wood screw face vise since I used one in Junior High shop class, and can finally justify it as my current vise wracks too much to do the thing I am trying to do now. My suspicion is the AYS chain system on the parallel guide is going to meet 75-90% of my needs. I saw a new thing recently since I last watched all the leg vise videos on you tube. If you were to interent search "Jay Bates leg vise" and kick over to the "videos" tab of your search results you should find a 22 minute video near the top of your results. If you open that and pause it six seconds in you will see a wedge on the floor that will probably tell you all you need to know.

I am planning to do both, just run the AYS chain system routinely (It is still, after eight years, good enough for Derek Cohen for heaven's sake), and have the system from Jay Bates video ready to go.

[Michael Bulatowicz]

Hi Scott,

When designing based on acceptable levels of deflection, strength becomes a non-issue unless you’re using very stiff and brittle materials (think ceramics). Far more important is the elastic modulus and the geometry. If, however, you want to order the grading guide and run the calculations for your own edification, I won’t try to dissuade you.

For the screw, there will be a pull-out strength based on the effective shear area of the threads; that said, it’s not as simple as the calculations might lead you to believe. Going by just the shear area formula, one would conclude that more threads engagement is always better. However, as long as the screw maker has done their job properly and in the case that the material of the screw and threaded hole are identical you’ll generally get very close to maximum strength on a coarse thread with 4-5 threads engagement (more for fine threads). This is because the materials deform under load (the screw stretches, for example) and the first 4-5 threads end up taking most of the load (highest load on the first thread, less on the second, and so on).

The screw is unlikely to be able to apply a large enough load to break any reasonable chop design, particularly if the chop has been designed for appropriate stiffness. This includes under cyclic loading as well as static loading. Put another way, I’d recommend you design the chop for the stiffness you want and let the strength take care of itself.

If I understand your goal correctly, you’re interested in whether you can get away with using locally available lumber for a high-performance chop rather than ordering something. I am confident that you can; I am willing to help.

Michael

[Dave Anderson NH]

Jim Ritter, You are allowed to answer technical questions and offer advise. You just can't tout your website or link to it unless it is a photo illustration of your comments. Thanks for asking.

[Scott Winners]

Hi Scott,

When designing based on acceptable levels of deflection, strength becomes a non-issue unless you’re using very stiff and brittle materials (think ceramics). Far more important is the elastic modulus and the geometry. If, however, you want to order the grading guide and run the calculations for your own edification, I won’t try to dissuade you.

I agree with you here. On all the models I tried Fiber stress in bending (FSB) and Modulus of Elasticity (MoE) were the key components to stiffness. Is MoE the same as elastic modulus? I am not knowledgeable enough to assume it is.

Anyway, when I piled weight on my model beams they all eventually failed in horizontal shear, but it was high FSB and high MoE that limited deflection before shear failure.

I need the grading guide so I can tell what I am looking at. I did all of my computer modeling based on select structural grade, but there may not be any select structural eastern hardwood in all of Alaska today, I won't know until I have the grading guide in my hand. If it turns out what I can get my hands on is grade I then I will go back to the models.




For the screw, there will be a pull-out strength based on the effective shear area of the threads; that said, it’s not as simple as the calculations might lead you to believe. Going by just the shear area formula, one would conclude that more threads engagement is always better. However, as long as the screw maker has done their job properly and in the case that the material of the screw and threaded hole are identical you’ll generally get very close to maximum strength on a coarse thread with 4-5 threads engagement (more for fine threads). This is because the materials deform under load (the screw stretches, for example) and the first 4-5 threads end up taking most of the load (highest load on the first thread, less on the second, and so on).

The screw is unlikely to be able to apply a large enough load to break any reasonable chop design, particularly if the chop has been designed for appropriate stiffness. This includes under cyclic loading as well as static loading. Put another way, I’d recommend you design the chop for the stiffness you want and let the strength take care of itself.

I think the screw threads are the weak link in the system. They are probably strong enough. A big enough timber I will load directly onto sawhorses from my truck, cut whatever joints it needs, and put it on the ready to assemble stack while my leg vise is nice and warm and dry inside the house. I guess I am doing exactly that, designing the chop for minimal deflection and expecting the screw threads to be strong enough for any piece of wood I am likely to ever put in there.


If I understand your goal correctly, you’re interested in whether you can get away with using locally available lumber for a high-performance chop rather than ordering something. I am confident that you can; I am willing to help.

Michael

That's pretty close. My goal is to not have to do this twice. One and done, lifetime vise, won't have to replace it. I have identified five contenders for my vise chop. All the below values are for select structural grade.

Red Maple, no suprise, 1300psi FSB, 1.7 million psi MOE
Doug Fir, king of the west, (but not the DF-Southern grown in AZ, CO, NM, NV or UT) FSB 1300, MoE 1.7
The Beech-birch-hickory group, FSB 1450, MoE 1.7
Southern Yellow Pine FSB 2400, MoE 1.9
Yellow Poplar FSB 1000, MoE 1.5

Sitka Spruce I cannot afford, but it is probably otherwise a contender with good FSB and MoE in larger cross sections. I don't have design values for Sitka Spruce at 8/4 or 12/4, when I saw the price I stopped looking for the design values. I have never seen SYP for sale up here.

Rabbit hole: Red and white oak are traditional chop materials with very high Shear strength, they can take more weight than any of the above before they too eventually fail in shear, but they deflect more. White oak FSB 1200, MoE 1.1. Northern Red Oak FSB 1200, MoE 1.1. Mixed oak FSB 1150, MoE 1.1

Having run a bunch of stiffness calculations I am planning on a 12/4 chop, planed flat to assumed 2.75 inch thickness. It will be eight inches wide at the floor. It will widen as it rises 23.5" to the horizontal center of the screw and be 10 inches wide there, and then widen to 12" width at the bench top about 10" higher than that.

In the beam modeling I did all five of those were showing 0.02 inches deflection at 12/4, when I dropped back to 1.75" thickness (8/4 planed flat) the deflections ranged from 0.07 to 0.11. So 8/4 is good enough, 12/4 should improve my stiffness dramatically. At least at the one loading point I tested for - 500# uniformly distributed.,

If I did the math right and Lake Erie sends me a screw as long as the one they sold me (they have a great reputation, I just don't have my personal screw to measure against my bench), but I should have a max jaw opening of about 12.25" with a 12/4 chop, or 13.25" jaw opening with an 8/4 chop. I think 12.25 inches jaw opening is plenty.

The 12" width at the top is not set in stone. Local birch just doesn't grow that big without also having notable center rot. If I find a beautiful beautiful piece of hickory that is only 8 inches wide I will probably not use it for a chop.

For now I am looking for a 12/4 billet 12" wide and 36 inches long from one of my top five.

[Scott Winners]

I guess I have enough of a plan for Michael or anyone else with a background in higher mathematics to take a shot at it. From a timberframe perspective, for a building, this simply doesn't work. The big hole in the middle of the chop to pass through screw divides the chop into two spindly little beams that will struggle to hold up a case of beer without unacceptable deflection. But face vises work, I don't dispute that.

I ordered the 2X system from Lake Erie, so I have to drill a 3.0 inch hole through the chop and the through the vise leg for the screw. Smaller holes should take less strength away from the chop (and the vise leg), so I don't see any point in analyzing what larger holes would do to the system, though an engineer might, and I will not dissuade them from doing that.

The undercarriage of my bench is all 4x6 nominal Doug Fir. For my next (bigger) bench I will be using an 8x8 timber for the vise leg. Drilling a 3" hole in the 5.5" wide face of the vise leg feels kinda creepy. My expectation is my current 4' bench will be my sharpening station once I have a bigger shop space and a 6-8 foot workbench. The new/expensive vise I am installing now will migrate to the new bench. The craptastic vise is fine for saw sharpening. When I build the longer bench I can use a 3" through tenon for the side stretcher centered under the vice screw hole and also drill vertically for the AYS chain without doing much in the way of damage to the side stretcher or the vise leg.

I will put pics of my vise leg here, and then discuss:



The side view of the vise leg is the first picture. Relevant you can see my craptastic home center vise at the top, and then double pinned the 5.5" face of my side stretcher. The side stretcher is shoudlered on the visible face down to the perfect 3x5 leg within the nominal 4x6 Doug Fir leg I started with. Below that is a vertical 2x6 with grade stamp showing and a through hole, that is part of the bottom shelf so parts don't fall off the shelf, and then a bit below that is the end grain of the through mortise for the front stretcher.

If I could pull the side stretcher out in a vacuum you might think I was using half lapped joints, or recognise it as a bare faced tenon in situ. My plan is to cut nominal half inch deep shoulders for the vise nut, same as for the side stretchers, so I don't weaken the back face anymore than it already is.

Second pic is the face surface of the vise leg with probably a pretty good approximation of layout. I don't have any of the parts here to actually do the final layout but I am probably within a quarter inch or so.

From the top my crappy current vise, the horizontal 2x4 DF stud with the grade mark on it is the front surface of my top. Headed down from there a 3" circle to pass the vise screw, below that a hole I think at 5/8 or 6/8 to pass the AYS chain, my best guess at clearance for the AYS sprocket above the side stretcher, then the end grain of the side stretcher visible on the face. The chain hole is also spaced to not require any drilling of the vise nut from Lake Erie, I hope. The drawn mortise for the parallel guide starts 1.25" below the side stretcher (hopefully enough room for the second AYS sprocket), passes through the through knot and then bites a notch in the front stretcher tenon about 1" deep. Below that I have about 8" of exposed leg surface unadulterated. I started this bench in Dec 2018 and finished in Jan 2019, the through knot I can move maybe 1/8 or so with my thumb, I plan to hammer it out and then get a saw in there to cut the parallel guide mortise.

AYS chain is to pass through the chop just below the screw, through the front leg without messing up the Lake Erie nut, bend over a sprocket to a vertical hole to be drilled in the side stretcher, hit another sprocket, and then run along the top of the parallel guide to the end of the guide. I will likely attach some sort of dust ruffle out of cheap plywood to keep dust and crud off the screw and chain.

Jaw depth, from bench top surface to top of screw is going to be about 8.5 inches. Bench height is 34 inches.

I am fine with this, 8.5" jaw depth, 12.25 max jaw width, for heavens sake. If I am working even a 24" piece of 8x12 I'll fasten it to the bench top with holdfasts, longer pieces of 8x12 won't even be coming in the house.

For the chop my current plan is 12/4 stock planed flat to 2.75" in any of Red Maple, Southern Yellow Pine, Yellow Poplar, the beech, birch, hickory group or Doug Fir (not Southern - D Fir S). Continuing with the chop, I plan to start half inch off the floor at 8" width and taper evenly to 10 inch width at the center point of the vise screw, 24" off the floor, 23.5" up the chop. Above the centerpoint of the vise screw I envision more taper with the top increasing in width to 12" at the bench top about ten inches above the screw center.

About. Since the vise leg on my next bench is going to be 8x8 (probably white spruce or Doug Fir) I don't see a good reason to make the bottom the chop less than 8" wide. If an engineer of some kind can say making the width at the bottom 10 inches will make the the chop 16.58% stiffer because Orion gnu theta omicron I will make it ten inches at the bottom. I am not married to having a twelve inch wide face at the bench surface either. Realistically, 12/4 stock greater than 10" width end to end and select structural grade is going to be hard to find, and it is going to be rift sawn in my budget.

Have at it fellas. We have three MDs here that I know of here, and I don't know how many engineers. I am just a trogdolyte who knows if I build it stout it will last. I failed Calc I twice; calc II, Ochem and calc based physics once each. All of my degrees are in the social sciences.

[Michael Bulatowicz]

Hi Scott,

That’s plenty of information for some analysis.

With regards to the question of having the chop tapered from 10 inches at the screw to 8 inches at the floor compared to leaving it at 10 inch width the whole way, there won’t be much difference—maybe a couple percent at most. This is because the parallel guide is applying a load near the centerline of the chop rather than distributed all across the width, so the extra material on the sides of the hypothetical 10 inch base width is almost completely uninvolved in load bearing. I’d say go for the taper.

The wooden nut will help distribute the load on the leg, but I’d suggest some lateral reinforcement of the leg: it looks to me like you have a crack running up and down the leg from the mortise. I can’t say how deep it goes, but it’s a weak point that will be exacerbated by the 3 inch hole. There are a number of ways to go about it, but the basic idea would be to reinforce as if you’re trying to clamp the crack shut.

Regarding leg stiffness and strength, as long as the crack doesn’t cause a problem you’re not likely to notice the difference before/after boring the hole: for a vertical load, for example, it’s still going to be about 95% of the present stiffness after you install the vise screw, the chain assembly, and the parallel guide. If the wooden nut is attached well, you should actually have a slight increase in bending stiffness.

[Scott Winners]

The two pictures I posted of the vise leg yesterday were taken yesterday.

I looked at a few pics from Jan 2019 in my phone, edited them to upload and now I can't find them in my phone while it is connected to my PC. The crack around the knot was not there when the joinery was freshly cut.

During the build I did split open two or three of the offcuts from my 4x6 legs and stretchers and found pretty consistent 20% Moisture Content, occasionally a 19% would show up, using a homeowner 2 pin meter for firewood. The 4x6 is homecenter Doug Fir with the S-GRN icon included in the grade stamp - Surfaced Green.

Extreme humidity swings in my shop, I see 25% RH at 64dF this minute (I have a sensor out there), 6-9% RH at 55dF is common when it is colder out. Summer time highs for say Jun and July will be 70-80% RH and 70-80 dF.

I do think this is a potentially serious stress fracture, exacerbated by both the front and side stretchers having been drawbored about 1/8 inch, at a weak point in the grain. I had to put those knots somewhere, I picked through a lot of 4x6 to get the ones I did buy. Plus the clear wood probably moved more than the knot wood as the leg dried down.

I do not -have- to put the parallel guide there, nor am I married to a particular size or shape. The more I lower the guide, the more of the through tenon for the front stretcher will be cut away.

I guess the next thing to do is hammer out the knot and try to see how deep the surface crack reaches. I'll try the big fat one centered in the side stretcher too, one of these pics is of the vise leg from the back side of the bench with part of the shelving out.

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[Scott Winners]

And a closer view of the back side of the vise leg with the side stretcher coming in from above. I don't like it.

[Scott Winners]

With a bit if time to stew on it, the one thing I am least likely to do is take this bench apart to replace the vise leg. I just don't want to put that much effort into it. I glued the pegs in.

While I am shopping for a 12/4 chop, I will also be looking for 8x8 timber to make legs for the next bench, I feel a whole lot better about drilling a 3" through hole in an 8" timber face. I will look for 8x6 to keep some max jaw opening. Maybe I will find an 8x10 that could be resawn into a pair of 8x5.

I am open to input from everyone on where to put the parallel guide in the leg I have. I am probably going to install it and see if it breaks.

For the math wizards participating, I am most interested in what the "ideal" arrangment would look like. How thick a chop from what wood drilled where, that sort of thing. I do like my front stretcher location very much. It is about 4" off the floor, so I can hook my workboot under it when planing, and the space between the top of the stretcher and the underside of the benchtop is good for wedging my leg in when I want to clamp myself to the bench.

For the future ideal bench with the 8x_ legs at the vise end I would be OK with turning a 4x6 on its side to make a side stretcher. That should free up some vertical space for the screw and the parallel guide to move around.

I am not wild about having the parallel guide pass through the front stretcher tenon. But I would be willing to haunch the front stretcher tenon in the vise leg, If i can keep the bottom 3" of the tenon length at like 5-6 inches I should be able to drawbore the stretcher down and in to the leg mortise, then the upper half of the tenon could ride in a mortise maybe three inches deep.

[Tom Bender]

Fritz has hit on a key, you need grippy surfaces. My Maple jaws were problematic. Adding leather faces made a big difference. Deflection is not a problem when you only have to grip gently.

Jeff shows a tapered chop. It could be tapered more. Bending stress is maximum at the screw and much less at the top. You could taper starting slightly above the screw hole.

One complication to all your calculations is the twisting stress when you load one end (east west, not top bottom).

Definitely consider gluing up to get whatever thickness is needed.

[Scott Winners]

I think I am committed on everything now, I did get my chop blank today. It has no grade stamp on it. By hand (I have not taken a class and am not certified) with the WWPA grading book open I have confidently graded it to select structural Joist and Plank, it is (beautiful) Doug Fir, 3.5" thick (16/4) nominal, 13" wide and I bought a piece 9 feet long for $100. It might be Doug Fir "S" from the southern states, Utah and New Mexico as above, but I have never yet seen that grade stamp on construction lumber at the higher volume big box stores here in town.

I do have one new thing to consider for your build. I was looking at 12x12 this morning thinking I could pull off a 3x12x36 vise chop blank and then resaw the remainder into two work bench legs at 6x9x36. I plugged SPF into my beam calculator at 12/4 and it is on par with the top five at 12/4 (2.75 actual) but pretty noodly when thinner. If you are stressing out about drilling the Moby Chop Blank that your grandpa planted when he was a wee boy you could do a practice run with a Spruce Pine Fir chop at 12/4 and have probably a pretty good leg vise for a little while. I am not suggesting it as a long term solution, but it would give you a practice run and it should work good for a while.

I still do not have a clear understanding of how a vise chop is stressed compared to a table top or a beam or a column. There is some subtle stuff going on in there. There are lots of folks gluing up to thicker stock for chop blanks. At the end of the day I don't know how a chop is stressed, and I don't have enough confidence in my glue up skills to go for it, so I bought a thicker piece. My oldest glue up is 25 months old. It is holding up good for now, but I definitely want my vise chop to last longer than 25 months.

Thanks especially for all the input early on, there is more years of experience with leg vises posted in this thread than anywhere else on the internet I could find. SMC for the win, as usual.

[Prashun Patel]

I respect the quest for complete analysis. However, my leg vise is far from optimally designed. Cheap hardware, moderately thin walnut chop, nothing but shims on the floor to prevent racking.

It is still miles ahead of other vises in terms of holding power.

I had holding issues before but they were 100% resolved by increasing the handle leverage, lining the top of the jaws with horse butt, and always making sure the bottom is shimmed wider than whatever I'm holding. This amount wider is quite flexible, it can handle a great amount of skew if the work piece is thinner than the wedge by a lot.

You'll be fine.

[Tom Vanzant]

Well stated Prashum. The idea is to hold the workpiece, not crush it or tear your bench apart.i

[Michael Bulatowicz]

I still do not have a clear understanding of how a vise chop is stressed compared to a table top or a beam or a column. There is some subtle stuff going on in there.

Hi Scott,
The false-color image below shows a map of the stress on an example chop design approximating the design you've proposed. The units are in psi. For our metric friends, you can multiply by approximately 101325/14.70 to convert to Pascals or divide by 14.70 for pressure in bar.

This is for an arbitrarily chosen 1800 pound-force load on the screw (1600 pounds on the workpiece). As you can see, the greatest stress by far is on the through hole for the screw, but even then is not approaching the maximum allowable stress for the wood. This could be further mitigated by adding a chamfer or better yet a radius to the entrance and exit of the hole. You can expect a similar distribution near the through hole in the bench leg.

So, a long way around to saying, "Prashun is correct and you shouldn't worry about it."

If you truly want the chop as robust as possible, start the tapering a couple inches below the bottom of the screw hole (i.e. keep the chop full width above that point) and a small radius to the entrance and exit of the hole. However, the analysis shows that neither of these is necessary at your planned chop thickness.

Regards
Michael
449932

[Scott Winners]

Thanks Michael! Just carry it full width a couple inches below the screw hole before the taper. That sounds doable and leave a lot of flexibility for those who want to do swoopy stuff.

I do appreciate the false color image. In my mind's eye I could see the beam, first flexing a little bit longitudinally and then starting to cup up around the screw as it gets loaded up. It makes intuitive sense to me that keeping the chop full width for a little ways below the screw is going to help the chop resist cupping into a bowl shape as the load increases. But I never would have come up with the shape of that yellow part.

As far as the chamfer/ round over, do you have a suggestion on size? I know I have a quarter inch round over with a guide bushing on it for my router. I think I can get a 3/8 roundover to fit the chuck, my router is not very big.

Also, will it make a difference if I layout the screw hole all perfect and then bore six holes evenly spaced around the circle, chisel out the waste and end up with a hexagon screw hole with rounded corners? I think I am just going to order a big bit and only sweat drilling one hole instead of six.

And I thought of an advantage to gluing up a chop. If you have three pieces of 4/4 that have been sitting around your shop a year or two they are probably pretty well acclimated. You could glue up, shape your chop and go without having to worry about it moving much in service. Best to cut all the pieces from the same board I think, or at least the same species. I ripped the offcut of my Doug Fir so I can get my next set of bench legs out of it. On the center of the freshly sawn face I measured 20% MC. I think I should leave this chop a little fat (maybe 3.10 - 3.20 ish) for another ten years or so before I take it down to 2.75" after it is done moving around.

[Michael Bulatowicz]

Hi Scott,

For the roundover, it’s not critical; 1/4 inch is perfectly fine. 3/8 might actually be worse because of how it changes the load distribution from the screw—I don’t think it’s worth buying a new bit.

A “rounded hexagon” hole would increase the stress a bit, but not enough to matter. That said, if I were to tackle those holes myself I’d drill a pilot hole all the way through the center, of appropriate size to guide a 3 inch hole saw coming in from each side, perhaps chiseling out waste as I went to make room for the hole saw to eject sawdust more efficiently.

Three pieces of 4/4 will certainly reach equilibrium moisture content much faster (before glue-up) than one piece of 12/4; it might also be easier to find 4/4 with better grain orientation for seasonal stability.

+1 also on the use of vise chop facing material. I used leather for a few years (quite a bit better than bare wood) and occasionally had issues with slipping if I didn’t crank the vise down enough. I just switched to the cork/nitrile rubber “grip liner” from Lee Valley. Initial impressions are excellent—much better grip and greatly reduced need for clamping force. We’ll see how well it holds up (it’s only been a few weeks), but so far I see no signs of wear even after holding a few 5/4 x 10-20 inch x 8-10 foot rough sawn red oak boards for initial reference edge planing and sawing to length.

[Prashun Patel]

I tried re-reading but could not determine conclusively: Is that df piece you show in post 33 your 12/4 chop? The perspective makes it look more like 8/4. If I were going to laminate a chop and were concerned about stability, I'd probably think about it like a bench: a bunch of small 3" wide flatsawn strips turned on their side and glued up to make a quartersawn plank. This also increases your choice of materials; you can use flatsawn portions of the boards.

I haven't done any calcs, but my general experience has been that this kind of glue up works better in the long run than gluing wide things face to face. Apologies if I misunderstand your pic or intentions.

One thing I always do is discard portions that are very close to the pith. Your sections don't have to be strictly QS; I use rift sections, just trying to keep their angle as vertical as possible.

[Scott Winners]

I tried re-reading but could not determine conclusively: Is that df piece you show in post 33 your 12/4 chop? The perspective makes it look more like 8/4.

My chop blank is 3.5 x 13x 40. The cat litter is a 45# box. Running low on TP during a lockdown is undesirable, running out of cat litter before spring would be unbearable. The first few bench planes to the right of the blank are 4, 4 1/2, 5, 5 1/2.



One thing I always do is discard portions that are very close to the pith. Your sections don't have to be strictly QS; I use rift sections, just trying to keep their angle as vertical as possible.

Pith is not explicitly mentioned in the Western Wood Products Association (WWPA) grading guide for regional wood products in structural grades. Chops fall in the Joist and Plank heading, 2-4 inches thick, and width greater than 5". For select structural and grade #1 splits, a crack passing through the plank face to face, are limited to a length equal to the width of the board. In my limited experience with Doug Fir pith is very undesirable in a plank that needs to still make grade decades in the future.

[Michael Bulatowicz]

I tried re-reading but could not determine conclusively: Is that df piece you show in post 33 your 12/4 chop? The perspective makes it look more like 8/4. If I were going to laminate a chop and were concerned about stability, I'd probably think about it like a bench: a bunch of small 3" wide flatsawn strips turned on their side and glued up to make a quartersawn plank. This also increases your choice of materials; you can use flatsawn portions of the boards.

I haven't done any calcs, but my general experience has been that this kind of glue up works better in the long run than gluing wide things face to face. Apologies if I misunderstand your pic or intentions.

One thing I always do is discard portions that are very close to the pith. Your sections don't have to be strictly QS; I use rift sections, just trying to keep their angle as vertical as possible.

Excellent points, Prashun.

I hadn't considered the benefits of effectively manipulating the grain direction for the lamination--I'll have to use that idea in my own work. Thank you.

Laminating as you describe should indeed increase strength in addition to stability.

Scott, when it comes to the strength think of it this way: in a solid piece, a crack is able to keep growing until it splits the part. The weak point represented by the start of the crack travels through the board in a continuous fashion, and the crack can grow right along the weak area. In a lamination, the cuts and glue lines interrupt the weak points, stopping any individual crack from passing through the glue line unless it manages to start a whole new crack in the adjoining piece, which is less likely because the weak points of the individual pieces probably don't line up with each other.

Then, as Prashun pointed out, there are significant benefits to seasonal stability for effectively quarter-sawn grain in the lamination. These benefits will hold long after the laminated chop has acclimated to your shop and are likely to be valuable given the extreme swings in humidity you’ve mentioned.

[steven c newman]

My Leg Vise consists of an old 1/2" Pipe Clamp....runs through a 2 x 6 Sycamore chop, then through the bench's leg. Has a 2 x 2 block of scrap down at the bottom....Chop is faced with the nail pouch of my old nail bag rig....

K.I.S.S........

[Scott Winners]

Steven does have a point.

Likewise I suspect I will have confidence in my glue up skills before this enormous piece of Doug Fir is done seasoning. But to get the confidence I need to do structural glueups, I need to put glueups in service, to put them in service I need a vise to hold the table aprons while I cut tenons on them and etc to put the panels into service.

I do accept glued up pieces as an important component of current woodworking. We don't have a lot of big trees, we have plentiful high quality glue. For a table top we can buy cheap crappy plywood, baltic birch or marine plywood from the botique store, pay through the nose for a single wide piece at high risk of wood movement, or learn to make essentially homemade plywood where we have access to excellent adhesives and can choose our own wood.

Given the vise chop is subject to bending stress on both the vertical and horizontal axes ( I think) , would it make sense to put some pieces in flat sawn and some others in quartersawn? And some rift pieces too, why not.

Recall no one in this thread has complained about their 8/4 maple chop.