Leg vise experiences?

[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
ChopStress_1800LbScrewLoad_1575LbWorkpieceLoad.png

[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.