Alternative to lots of clamps?

[John Schreiber]

I'm building a workbench this summer, roughly in a Roubo style following Christopher Schwarz's "Workbenches" book. That involves laminating lots of Southern Yellow Pine into a massive slab for the top and big slabs for the legs. Chris recommends a clamp every six inches plus some across the edges to hold everything in place. I haven't got nearly that many clamps, or the money to buy decent ones. None of the local rental places rent anything appropriate.

Are there any tricks for working without clamps?

I could wrap a set of boards in layers of tightly stretched bicycle inner tubes. I might be able to work something out with frames made of 2x4s and wedges. Or maybe I could do something with rope.

Any good ideas?

[Jesse Cloud]

Make a bunch of wedges, about 3 inches long from scrap. Clamp one piece of the glue-up to your assembly table. In dry fit mode, add the other pieces to be glued up. After the last piece to be glued up, put pairs of wedges together loosely every few inches. Clamp a solid straight board after the wedges. Use a small hammer to bring the wedges together and act as clamps on your glueup. When satisfied, take the wedges apart, apply glue and repeat the wedging process.

The wedges should be the same thickness (or more) as your workpiece.

Almost free....

[Lance Norris]

How about threaded rod? You could make clamps with it. Take some 8/4 stock, say 2" wide by 10" long and drill a hole at each end, for 2 rods. Make 2 boards and run the rods through them and clamp your glue up between these. Wrenches and nuts will get you incredible force. Or how about drilling each benchtop board and running the threaded rod right through it. Glue and clamp.

[Bill Wyko]

Check Harbor Freight for clamps. They have really cheap clamps that are not 1/2 bad. 2 to 3 bucks each.

[Doug Shepard]

You might want to do a price comparison between getting some BowClamp Good Cauls (which will reduce the number of clamps you need) and going with all clamps.

[Peter Quinn]

I'll go out on a limb here and say that while you may get away with another method, for laminating a massive top you really need a whole lot-o-clamps. Simple pipe clamps will suffice. Course if your gonna build a nice joiners bench then your gonna want to work wood and your gonna need.....clamps!

[Joe Scharle]

Back in the 60s & 70s, all the mags were touting threaded rods thru the tops about a foot apart. Seemed to work well. I think though, that if I were to make one now, I'd give pocket hole screws a hard look.

[Lewis DeJoseph]

How about ratcheting belts?

Lewis

[Anthony Whitesell]

I've seen then and have a few of the HF clamps, but the pipe at the Borg ain't cheap. Anyone have a cheaper place or ideas to buy pipe for pipe clamps than the borg?

[Stephen Edwards]

Check Harbor Freight for clamps. They have really cheap clamps that are not 1/2 bad. 2 to 3 bucks each.


I second that motion! The HF pipe clamps that Bill is refering to work just fine and last for years. I prefer the 3/4 with the "T" handle. There's a hardware store near me that sells the pipe in 20 foot lengths. They cut it for me and thread one end of the pipe to accomodate the HF clamps. When all is said and done I get the pipes for about 1/2 the price of precut and prethreaded pipes that the borgs sell. Perhaps there's a hardware store near you that will do the same thing. It's an inexpensive way to get a decent clamp that serves the purpose.

[J. Z. Guest]

Instead of spending a lot of dough on clamps, this seems like a great opportunity to buy a Kreg Jig. The pocket screws in the bottom of the slab will not show, and when the glue is dry, you can take the screws out.

I'd rather do this than buy cheap clamps. I've been frustrated every time I've bought cheap clamps. The cheapest ones I will buy now are Jorgensen bar clamps. ($10-15 ea.)

[john bateman]

I'm building a workbench this summer, roughly in a Roubo style following Christopher Schwarz's "Workbenches" book. That involves laminating lots of Southern Yellow Pine into a massive slab for the top and big slabs for the legs. Chris recommends a clamp every six inches plus some across the edges to hold everything in place. I haven't got nearly that many clamps, or the money to buy decent ones. None of the local rental places rent anything appropriate.

Are there any tricks for working without clamps?

I could wrap a set of boards in layers of tightly stretched bicycle inner tubes. I might be able to work something out with frames made of 2x4s and wedges. Or maybe I could do something with rope.

Any good ideas?

If you're talking about trying to clamp a bunch of 2x4's into a benchtop shape, I'm pretty sure bicycle tires or Kreg screws are not gonna supply the amount of force needed. If you really don't want to get some big clamps, you could glue and screw each board to the next one, driving the screws directly through the faces of each board. As long as the first board at the front of the bench doesn't have the screw points coming through at you, it shouldn't look too bad.

[Walt Nicholson]

I saw this years ago when a neighbor was making a laminated top for a country kitchen table top and (with no clamps) had to improvise. He glued his pieces together, put strong, straight 2X4s on either edge, placed 3 bottle jacks (one was a screw type from his car) in position on the 2X4s, looped and hooked some chain around them and then used the jacks to create the pressure. It was amazing how much glue was squeezed out and the finished product turned out very nice. He was great with "make do with what you got". I attached a crude drawing of what he did. ;)

[Greg Hines, MD]

If you're talking about trying to clamp a bunch of 2x4's into a benchtop shape, I'm pretty sure bicycle tires or Kreg screws are not gonna supply the amount of force needed. If you really don't want to get some big clamps, you could glue and screw each board to the next one, driving the screws directly through the faces of each board. As long as the first board at the front of the bench doesn't have the screw points coming through at you, it shouldn't look too bad.



To take this concept one step further: Glue and screw a pair of your planks together, and let the glue cure. Then remove the screws, plane and joint, then screw another pair of your timbers to this. Repeat as many times as you need to. Then cover the screw holes with the last pair of planks by clamping or wedging as described above. It will take time, but then you would avoid needing to get a lot of clamps.

That said, you are going to need some. And realistically, pipe clamps are versatile and not very expensive. I do all my clamping with some 3/4" pipe clamps, and use union connectors to join short pipes into long ones for certain projects.

Doc

[Jamie Buxton]

Nails.

Working your way across the slab, glue and nail each board to the next one. Keep the nails away from the top and bottom surfaces, so you don't hit them when you're planing the slab.

[mike holden]

How about Friends? Friends with clamps that is. Are you a member of a woodworking club? Anybody in any organization you belong to work wood? If you lived in SE Michigan, I would be happy to loan you some clamps, and some help too.
Of course, I would expect the favor returned when I build my bench/whatever, but hey! that's what friends are for!
Mike

[tom holton]

Regarding pipe clamps and the cost of pipe at the BORG. How about borrowing the pipe from the BORG. IE, buy what you need and then use it. Then return it afterward. Cleaning a little glue off it should not be a difficult task. Take advantage of their liberal return policy.

Tom

[Brian Kerley]

Regarding pipe clamps and the cost of pipe at the BORG. How about borrowing the pipe from the BORG. IE, buy what you need and then use it. Then return it afterward. Cleaning a little glue off it should not be a difficult task. Take advantage of their liberal return policy.

Tom

No offense....but that's not very ethical. As much as you like/dislike the BORGs, they should not be seen as a free rental service.

[Bill Wyko]

You might check building material salvage yards for pipe. I bought 4 roller tables 8 feet long for under 100 bucks and used them for years as an outfeed table at my business. They usually have stuff pretty cheap.

[Paul Simmel]

The problem with bottle jacks is that they need to sit upright. They don't work is they are laid down... unfortunately.

[Peter Quinn]

I buy my pipe at the borg (ssshhh...don't tell any one). For $10 I get 10', not the cheapest price in town, but they will cut it into 1/3's and thread the middle piece at no charge. I have a hand threader and pipe cutter but that's hard work. If you stay under 40" thats not much more than $3/pipe plus the cost of each clamp fixture. Way cheaper than Jorgie I-beams or Wetzlers!

By the time I've bought enough straps or bike tubes or chain or threaded rod or basically anything I don't already own it has cost me more than pipe clamps and left me with an often inflexible dubious work around I may be disinclined to utilize in the future. The inescapable fact is building a laminate counter top takes a lot of clamping pressure, and pipe clamps are the cheapest way to get it.

I have several 30 Ton bottle nose jacks, and my father has several steel I-beams along with various other bits of steel. I have considered building a vertical press when I find that box of round tuits. Use a steel I beam top and bottom, put one I-beam between the jacks and the wood, screw wooden cauls to the faces that press against the wood to protect the work, use 1/2" steel plate with double holes spaced every to inches to form the ends and allow connection to the i-beams, etc. Imagine 90 tons of clamping pressure being exerted with the twist of the wrist!

When I wake up from this vision I reach for a pipe clamp.

[Johnny Kleso]

I lam'ed my bench with cheap eBay clamps

The sellers names is My Deals Direct

I got like seven 36" clamps for about $25
These clamps where bowing like crazy but I did not even joint the 2x4s before glue up..

You can read more here
https://home.comcast.net/~rexmill/projects/bench/bench.htm

https://home.comcast.net/~rexmill/projects/bench/bencha3_small.jpg

These are HF clamps here
https://home.comcast.net/~rexmill/projects/bench/new_small.jpg

[Richard M. Wolfe]

John beat me to it. I don't see what would be wrong with just screwing one board to the next. The screws would be buried deep in the top and shoudn't pose any problems. Clamp one place tight, put a couple or three screws there, move the clamp(s) down and repeat. The only thing would be having screw heads showing on the outside boards, and one way around that could be to countersink and cover with a plug - either matching face grain or suitable contrasting, providing the screws are spaced properly.

[Chris Friesen]

You might want to do a price comparison between getting some BowClamp Good Cauls (which will reduce the number of clamps you need) and going with all clamps.

The cauls will spread out pressure, but there is no way you'll get *enough* pressure. When face-gluing boards to make a bench slab, to get anywhere close to the recommended pressure requires a lot of clamps.

As for the screw method, you'll need to plan the location of the screws carefully so that they don't interfere with holes for dogs/holdfasts/vices/etc.

[Mike Cutler]

The cauls will spread out pressure, but there is no way you'll get *enough* pressure. When face-gluing boards to make a bench slab, to get anywhere close to the recommended pressure requires a lot of clamps.

As for the screw method, you'll need to plan the location of the screws carefully so that they don't interfere with holes for dogs/holdfasts/vices/etc.

Chris

I'm not sure that I agree 100% with limitation you put on the BowClamps.
One of the glueups I did with the Bowclamps is a padauk table top 7 feet long, 42" wide and 1 1/2" thick. I used an epoxy resin, System Three, as the adhesive. Everything would appear to be fine with that top.
The Bow Clamps will put a lot more pressure on the edge than you might think. While the pressure applied using a PVA glue is important. So is applying pressure equally.
Personally, I think the Bow Clamps, with an epoxy adhesive, would work very well for this glueup. Using epoxy with a high temperature hardner, kept on ice, would give John the pot life and assembly time necessary to do the glueup in one step.
We would have to ask Craig to see if there would be enough pressure for a PVA glue in this application thouigh. He would be the best source.

[Peter Quadarella]

My vote is that Bowclamps would be fine.

[Frank Drew]

I guess I'm a traditionalist like Peter Quinn. A woodworking shop will always need clamps and any clamps I bought early continued to be useful for years afterwards. Pipe clamps became my least favorite but they were my first clamps, were relatively cheap, and they can provide lots of pressure, more than the f-style clamps.

[Chris Friesen]

Chris

I'm not sure that I agree 100% with limitation you put on the BowClamps.
One of the glueups I did with the Bowclamps is a padauk table top 7 feet long, 42" wide and 1 1/2" thick. I used an epoxy resin, System Three, as the adhesive. Everything would appear to be fine with that top.
The Bow Clamps will put a lot more pressure on the edge than you might think. While the pressure applied using a PVA glue is important. So is applying pressure equally.
Personally, I think the Bow Clamps, with an epoxy adhesive, would work very well for this glueup.

Oh sure, if you're going to use epoxy then things are different. It's also more expensive, especially since the bench top involves a lot more glue surface than a regular table.

As for the bow clamps...according to the manufacturer they're designed to give even pressure with 150lbs of force on each end. That's okay for edge gluing (especially with epoxy), but not ideal for face gluing.

For PVA, Franklin recommends 100psi in softwoods. The Roubo is 4" thick and 8' long, for a total of 38000 lbs of force recommended by the glue manufacturer. Pipe clamps every 6" will give maybe half that much. On the other hand, the vertical glue lines aren't going to see serious stresses, so it's certainly possible to get an acceptable bench top even if the glueline strength is less than the theoretical max.

[Mike Heidrick]

I am about 40 miles north and have some clamps, maybe I can help you out. You probably want to do this part of the project right the first time. I have a bunch of clamps and all kinds - Parallel, F-clamps, pipe clamps. We should be able to clamp it up.

http://i39.photobucket.com/albums/e169/BloomingtonMike/clamps2.jpg

[Mike Cutler]

Chris

Thanks for the info. I had no idea that bench was that big. Wow!:eek:
No matter what method used, the glue-up is going to be interesting. That's a lot of surface area for each laminated section. It's going to take some doing, that's for sure.

Mike

[Art Mann]

Go to the Titebond website and read what they recommend as clamping pressure for maximum strength. You will find that it will take pipe clamps every 6 or 8 inches tightened very tightly to even approach that level of pressure. Bowclamps or other cauls will spread the force out evenly (which is unnecessary in this application) but they will not manufacture force out of thin air. You simply need a lot of clamps to apply enough force over such a large surface area. I have seen many glued up benches - even commercial ones - where the glue has turned loose and a crack developed in the top. It is a common failure.

[David DeCristoforo]

As usual, a lot of "creative solutions" and some "sound advice". My favorite of the creative solutions is to glue and screw the boards together one at a time. The "best" of the "sound advice" is get the clamps you need. The only good "Alternative to lots of clamps" is lots and lots of clamps. No such thing as too many clamps. Of course, there is also my "famous truck bumper" clamping system which involves laying your boards on saw horses against the side of your shop and backing your truck up against them. But, obviously, this requires a truck and if you can't afford enough clamps, you probably can't afford a truck either.....

[Peter Quadarella]

OK I went to titebond's website and did the math. According to this website:
http://www.taunton.com/finewoodworking/toolguide/toolguideallabout.aspx?id=2992
A heavy duty I-beam clamp can exert up to 7,000 lbs of force. For softwoods, Titebond recommends 100-150 psi. Using 100 psi as a minimum, for a 4" thick x 96" long glue up = 38,400 pounds of force required across the whole glue up. Using four, 4' long bowclamps on a side (2 side by side and on top of each other, since there is 4" of thickness), you would have 8 clamps x 7000 pounds each = 56,000 pounds of force.

Did I miss something? Perhaps a limitation might be in the bowclamp, which only spreads the pressure evenly up to a maximum, and then starts putting a bit more on the edges. This would depend on the material used in the bowclamp - with a stronger or weaker wood this could be tweaked.

[Art Mann]

Yes, you missed something. You missed the error in the Fine Woodworking magazine web page. 7000 pounds of clamping force from one clamp is preposterous. Go to the Bessey website and see what force a top quality K-body clamp will provide. If I remember correctly, it is 500 or 600 pounds. Think about it. Do you really think a single wood clamp can apply enough force to lift 2 midsized cars off the ground at the same time?

[Peter Quadarella]

I honestly have no idea, that's why I ask you people with experience :).

[Peter Quadarella]

Curious as to why FWW got it wrong I did a search. It turns out, I misunderstood what Taunton was talking about. They weren't incorrect, they were talking about industrial I-Beam clamps. Here's an example:
http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_18556_18556

I'm not sure if that's clamping pressure tho - but I could imagine something out there that could apply that pressure. Not for wood though, as you corrected! :)

[David Bodkin]

I'm also busy doing the same thing. I think your cheapest alternative would be to screw the boards together as mentioned above. I'd screw the boards together and then put the last edge on the back side of the bench when you're done and that way no one will notice the screws. Just make sure you keep track of where the screws are so you won't hit them if you put holes in your bench top. FYI you're going to need lots and lots of glue. :D

[Peter Quinn]

I think the only clamp that will even approach that kind of force is a jorgie I-beam or a wetzler. The Jorgies are listed at 7000# load limit. Its between you and your hands to decide if you can cause these clamps to actually exert that kind of pressure in use.

http://www.adjustableclamp.com/bl-7200.htm

If the theory that 38,400psi is required is correct then you only need 5 jorgies! I can tell you from experience that you are going to need a heck of a lot more than 5 of any clamp!

Lets all start working on plans for that hydraulic clamping press.....

[Art Mann]

The theory says 38,400 pounds, not 38,400 pounds per sqare inch. That is more than I would have guessed, but we are talking about a huge surface area. I like the screw idea better than trying to do that much clamping.

[Jim Andrew]

I built the french style bench from that book, and from another plan I noticed that their top was drilled and threaded rod installed and left in the bench top. So I did that. I had every clamp I own besides the bolts, and it came out pretty well.

[Jeff Bratt]

I fail to see what that clamp at the referenced link has to do with woodworking...
The 7,000 pound rating comes from the Jorgenson website - although it's unclear exactly what it applies to...

The last test of clamping pressure in FWW (#194) indicated that those I-beam clamps (Jorgenson, etc.) could produce between 800 and 1900 pounds of force each - depending on who was cranking the handle. Pipe clamps were measured from 600 to 1500 pounds each. Now, maybe if you slip a pipe over the crank handle of a Jorgie and jump on it a couple times...

[David DeCristoforo]

"...maybe if you slip a pipe over the crank handle of a Jorgie and jump on it a couple times..."

Doesn't work. Either the handle will bend or the pin that keeps the screw and jaw together will shear or the end of the screw will break or all of the above. My old friend (and former employee) Earl bent and sheared at least a third of my HD Jorgensen bar clamps with his huge mitts alone.

[John Schreiber]

Thanks all for the tons of information here. It goes well with the tons of clamping pressure I need.

Cheap Clamps: I've got nothing against cheep, but not in clamps. Glue ups are hard enough and I can't stand for things to start slipping when they shouldn't. I just wont take a chance there.

Pocket Screws: Unless I put them in the top and the bottom, the pressure would be uneven, and I want to start with a flat bench.

Wedges: I think it could be done with wedges. In fact, I drew up a fixture which would work very nicely. It would hold everything in place for the glue-up and should allow for the job to be done quite quickly. The problem with wedges is that I don't have any experience with them and I don't have a feeling for the angles needed or what the friction would be like. It's still a possibility though.

Threaded Rod: That would work. Could leave rod in place or take it out. I do worry about aligning everything, but with some jigs I'm sure I could get that right.

Friends: Thank you for the kind offer, especially Mike. If I had any good friends who were woodworkers locally that would be a definite possibility. I don't have much time each day, so I'd probably have to borrow for a couple of weeks. I don't mind borrowing or loaning to good friends though, but I hate to hit up acquaintances and try to make friends for the purpose of borrowing.

Screws through the face of each board: I think this is the winner. I would want to take the screws out before going on to the next board though. I don't want to leave metal in the slab in case I decide to modify something later. With each board clamped for four hours and a total of 24 laminations for the top, it's going to take a while, but it would work and the price is right. It also makes the stock preparation less demanding (no fitting of thick sub-assemblies to each other) and it's a gradual controlled process where I won't mess up a whole bunch of wood at once. I could cover the last set of screw holes with a fitted strip and I'd be done.

So, I'm ordering a bunch of square drive #10 x 2-3/8" ProMax Washer Head Screws from McFeely's and when the wood is ready, I'll start clamping with screws.

[Paul Simmel]

John,

Lots of screws is not an alternative to Lots of Clamps. Clamping force is most definitely an issue with this sort of application, and screws wont even approximate the force needed.

I'd revisit the threaded rod idea. But you'd need blocks between the washers and nuts which would help distribute the clamping force. Like maybe 3.5" by 6" hardwood.

[Greg Hines, MD]

I would agree that screwing your bench together would be a last resort, but it is better than nothing.

I still think you need to invest in some clamps, or borrow some from the Creeker that offered. You are going to find your options limited in doing any meaningful woodworking without a decent set of clamps, and this sounds like the opportune time to invest in some. Tractor Supply company, Woodcraft, Lowes, Home Depot all run sales from time to time for their pipe fixtures, then you just need to get the pipe. Irwin even makes clamps that do not need threads on the ends of the pipe if you were to purchase longer pieces and cut them down to size.

Doc

[Cliff Rohrabacher]

How about threaded rod?

Yup the easiest bestest is threadded rod.

Use 4 washers, 4 nuts , Two rods per clamp, & two hunks of hefty lumber per clamp with a hole in either end. A rod on either side of the glue up, shove the rods through the limber toss on some washers and tighten the nuts and off ya go to the races.

[Peter Quinn]

clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps,!!!!!:D:D:D


You have to have clamps! With no disrespect meant I wonder what you intend to make on that big bench when it is finished, and will you not need clamps for that work? I have more than 150 heavy duty clamps but no proper bench and I seem to get by, but I feel if I had one proper bench and no clamps I would be lost.

Please cheer with me now: CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, !!!:D:D:D

[Jim Becker]

If it's not already been mentioned, Bow Clamps. See our Manufacturer's Forum for the same.

[Glen Blanchard]

clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps,!!!!!:D:D:D


You have to have clamps! With no disrespect meant I wonder what you intend to make on that big bench when it is finished, and will you not need clamps for that work? I have more than 150 heavy duty clamps but no proper bench and I seem to get by, but I feel if I had one proper bench and no clamps I would be lost.

Please cheer with me now: CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, !!!:D:D:D

Peter - Let me see if I understand this. You are a firm believer in clamps - is that what you are trying to say? Sheesh - quit being so subtle and state your mind. ;)

[Chris Friesen]

Lots of screws is not an alternative to Lots of Clamps. Clamping force is most definitely an issue with this sort of application, and screws wont even approximate the force needed.

Actually, a pair of screws every 5" or so would probably do just fine. A single #10 screw tightened to around 20 inch-lbs gives around 500lbs of clamping force.

(Edit: On reflection, the numbers above may be for a machine screw. The threads on a wood screw are higher angle and so more torque is needed for the same clamping pressure. Still...20 inch-lbs isn't all that much, so I bet we could still achieve 500lbs at higher tightening torque.)

[John Schreiber]

clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps,!!!!!:D


You have to have clamps! With no disrespect meant I wonder what you intend to make on that big bench when it is finished, and will you not need clamps for that work? I have more than 150 heavy duty clamps but no proper bench and I seem to get by, but I feel if I had one proper bench and no clamps I would be lost.

Please cheer with me now: CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, !!!:D

I can't argue with a persuasive argument like that :D:D:D:D:D.

It's mostly a financial thing. With two really good vises (which should last forever and then some), some hold downs and a load of southern yellow pine I'm dropping about $500. That blows my budget for this year. I do have about a dozen clamps of various sizes, but only four of them are big enough to reach across a bench top. If I spent that much in clamps, I might have 15 clamps.

Maybe next year it will be clamps, but I also want to get a table saw. I'm cheap and because of that I'm going into this relatively slowly.

[J. Z. Guest]

Actually, a pair of screws every 5" or so would probably do just fine. A single #10 screw tightened to around 20 inch-lbs gives around 500lbs of clamping force.

I agree with Chris, and if it can't be done with 500 lbs. worth of force, the fit of the parts being clamped should be re-evaluated. ;)

[Craig Feuerzeig]

Actually, a pair of screws every 5" or so would probably do just fine. A single #10 screw tightened to around 20 inch-lbs gives around 500lbs of clamping force.


You're still only effectively clamping an area, about the size of a silver dollar, with each screw. What you end up with, is some areas with excessive pressure...and the rest with no clamping pressure at all.

It'll work just fine... and most importantly its cheap. Nothing wrong with that. But as with any glue-up, I believe, your main concern should be equal pressure everywhere for the best bond.

Now every glue-up is different... and no solution works for everything...but if it's bone crushing force you need, there's a good chance you need to re-visit your joint preparation.

Simply adding up the total pressure is quite frankly a waste of time without a method of spreading that force. For starters you have no idea, in all reality, how much pressure you are exerting. Knowing how much force your clamps could withstand before breaking is interesting... but not really helpful. I have a 4 ton press in my shop...but I can't laminate a sheet of plywood with it because it exerts that pressure on a surface area about the size of my fist.

Also clamping pressure is not cumulative that way. Tightening one clamp to 200 pounds... is simply not the same as 2 clamps side by side each exerting 100 pounds. Furthermore, if one clamp is tightened to 101 pounds , and a clamp right next to it is only tightened to 100 pounds... then the second clamp is doing nothing at all. The tighter clamp does all the work, in terms of area being affected.

Another point that I think needs addressing is that wood compresses when too much pressure is applied over too small an area. How many times have you cranked your clamps down hard... left things to dry... and when it comes time to take the clamps off... they seem to come loose way to easily? As time passes and the material gets compressed, the amount of pressure being applied reduces. Your clamps don't tighten themselves to compensate.

[michael osadchuk]

.....I encourage you to explore the use of wedges as an alternative to clamps and to pay attention to the distribution of clamping pressure delivered to the glue line via "cauls" of one form or another.......

I don't know any "numbers" of pounds of pressure per square inch that a wedge can deliver but wedges were used a lot more historically and the screws that we use, whether as screws themselves or in the screw mechanism in most of our clamps, are acting as continuous wedges. In the occasional modern 'heavy duty' use I see - such as 'levering' a stubborn end of deck or flooring plank against its neighbour, it seems that a lot of pressure is being delivered by a wedge.

There is a two page article by percy w. blandford "clamping with wedges" in Fine Woodworking #93: he recommends starting with wedges cut with a one inch rise per 6 inches of length and using a pair of "opposing" or "folding" wedges at each clamping location; probably leave the edge surfaces of the wedges "sawcut" rough to prevent slippage but a slippery edge will make it easier to drive the wedge(s).

my understanding of the distribution of clamping pressure is that it radiates from the clamp/wedge toward the glueline at a 45degree angle on either side of a perpendicular line from the clamp to the glue line (eg. if gluing a couple of 2 by 4s edge to edge, with out any cauls between the clamp and the glueline, the clamp force is distributed to a 7" length of the glueline; add another 2 x 4 on edge to act as a caul and this same total force is distributed along a 13-14" length; add a slight bit of a convex shape to the edge of the caul (a la Bowclamp) adjacent to the workpiece and you will be gain further clamping pressure (if going this route of a slightly curved caul, you probably want to use two for the length of a longer benchtop glue up).......

..... wedges are cheap and easy to make; make them th full height of your laminations for stability and better distribution of clamping pressure....... I would be cautious and just laminate two pieces (and successive already glued up sections) at a time in order to keep everything aligned and resist the tendency for the pieces being glue to bow up.....

good luck

michael

[Peter Quinn]

I wish we were neighbors, because I spent all my money on clamps and have none left for wood to make a bench! With a one year old baby it seems my woodworking tool budget has for the time being been reduced to $0.

I really do like the screw idea.

[John Schreiber]

I appreciate the discussion here. I found this article (http://www.ukuleles.com/Technology/bridgeglue.html) which references a letter from a "adhesives technical person" at Titebond. It helped me understand better.

As I understand it, the idea for clamping a glueup is to bring the surfaces into contact with each other so that a very thin layer of glue remains between two pieces with no gaps. Then hold it still while the glue cures.

So, the first role of the clamps is to bring the two pieces of wood together. If the surfaces don't match perfectly, clamps can force the pieces together. The amount of force required depends on the fit. With hide glue and a near perfect fit, a rubbed joint (no clamping force) will work. A poor fit, like two unplaned boards might require the full 100 - 200 psi. Two really flat surfaces can get buy with much less pressure.

First I'm going to try to measure the clamping pressure of a screw to see what it actually is.

Then I'll do some tests to see how far that clamping pressure extends. My guess is that the force extends at roughly a 45° angle from the screw head. The washer head screw is about 1/2" d. The board being clamped is 1 1/4" thick. That means each screw should clamp roughly a 3" circle.

I'll keep you informed.

[John Schreiber]

I wish we were neighbors, because I spent all my money on clamps and have none left for wood to make a bench! With a one year old baby it seems my woodworking tool budget has for the time being been reduced to $0.
Darn good idea. Wanna move?

[Chris Friesen]

I appreciate the discussion here. I found this article (http://www.ukuleles.com/Technology/bridgeglue.html) which references a letter from a "adhesives technical person" at Titebond. It helped me understand better.

If you haven't already, it might be worth looking at the FWW article "Get Serious About Clamping" where the author (a material science guy, if I recall correctly) did a bunch of experiments and basically concluded that for maple the strongest joints were when the wood was clamped at 50% of the compression strength of the wood, or something like 1200psi.

However, for a workbench we have so much glue area that we don't need anywhere near the ultimate strength.

[Brad Shipton]

Keep in mind the specified pressures are to develop maximum bond. That means a finite glue line thickness and it takes a great deal of pressure to ensure that. Also, remember there are lawyers and safety factors used to create those specs. Chris has it bang on. You should not require ultimate capacity unless you were planning to park your car on top. I was given a free glulam 3" x 24" wide x 7' long and wanted my bench 36" wide, so I jointed some extra 12" wide pieces of glulam stock and used 5 pipe clamps and four Besseys to glue it together. I do have a 7" tall skirt all around, but it has been beat on for over a year and glue failure is by no means the problem. Me and glue or stain, now thats a diff story. If you are bent on gaining the ultimate capacity you might want to consider an epoxy instead of PVA. Many of those only require 10psi to develop the rated capacities. We used that in a school retrofit design for this exact reason. In that case we needed the ultimate strength of the adhesive. Personally, I would not put a screw or nail anywhere near the bench if you want to install bench dogs, but thats me.

Brad

[Dennis Peacock]

clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps, clamps,!!!!!:D:D:D

Please cheer with me now: CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, CLAMPS, !!!:D:D:D

I think even "I" get that hint. ;)

[Randy Klein]

I'm doing a very similar bench as yours and have just purchased the LV alum bar clamp special offer (http://www.leevalley.com/wood/page.aspx?c=2&p=57673&cat=1,43838) for my glue up of the top.

I have the Bow Clamps and used those and jet parallel clamps for the legs and stretchers. The joints were really tight and snug in dry fit. But I don't think I was able to apply enough pressure to fully overcome the hydraulic resistance of the glue.

Nothing has fallen apart, but it just seems like there should have been a smaller glue line. Time will tell I guess.

[John Schreiber]

Just in case anybody remembers this old thread, I did the experiments to see if screwing and gluing would work. It did. Details at http://www.sawmillcreek.org/showthread.php?t=115222.