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Forum topic by TMcG posted 01-22-2012 04:16 PM 3559 views 0 times favorited 13 replies Add to Favorites Watch
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TMcG

182 posts in 1659 days


01-22-2012 04:16 PM

Topic tags/keywords: clamping woodriver cauls

So I bought a couple of sets of these a while back when they were on sale and just used them for the first time yesterday and I gotta admit that they didn’t quite do what I expected them to.

Now, this is almost certainly operator error, but my expectation was that they would align/flatten a panel glue-up so that cauls were not needed etc..

That was not, sadly, my experience.

I guess my question is, is there some obvious reason why not ? The 2×4’s are too soft to exert the neccesary pressure maybe ?

Any/all guidance appreciated

tony

-- http://wood.mcgivern.org


13 replies so far

View CharlieM1958's profile

CharlieM1958

15699 posts in 2877 days


#1 posted 01-22-2012 04:43 PM

Tony, I don’t think it’s you.

Just looking at the design, I don’t see how these could exert much pressure. If all the boards were perfectly staright to start with, this would probably do a decent job of holding things in position, but there is no way it’s going to straighten any slightly warped boards or pull together gapped joints.

-- Charlie M. "Woodworking - patience = firewood"

View Ben's profile

Ben

302 posts in 989 days


#2 posted 01-22-2012 04:45 PM

I would guess the pine is too soft. Try a harder wood like oak, maple or cherry. Another way to possibly use the pine would be to cut a slight bow on bars. Maybe take what you have and put a slight curve on them with a sander. That way, as you clamp down, they will press down more at the center of your piece.

-- Welcome to downtown Coolsville, Population: US! --Hogarth Hughes

View richgreer's profile

richgreer

4524 posts in 1733 days


#3 posted 01-22-2012 04:49 PM

I have the ShopSmith version of these clamps and they work very well. I also have another set of similar clamps where I made my own wood pieces (like this set). The ShopSmith set comes with it’s own wood.

3 points

- I don’t think 2×4 lumber is right for this. Too soft. I used hard maple when I made mine.

- It is very important to cut this wood with a slight bow in it. I estimate that my boards bow in about a 1/16” in the center – but I have never measured it. FYI – I think the best way to make the bow is with a hand plane. Note, the bow side goes against the wood you are clamping up.

- The set I made from a kit does not have springs in the end pieces. I can’t tell if yours has springs. In my experience, not having the springs makes them much harder to work with.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View Ben's profile

Ben

302 posts in 989 days


#4 posted 01-22-2012 04:50 PM

Some old style bar clamps used a notched system like that with notches to adjust where the clamp seats. Maybe you could ditch thie plastic and cut some boards with notches like that. Seems to me the plastic could give out

-- Welcome to downtown Coolsville, Population: US! --Hogarth Hughes

View Hanman's profile

Hanman

58 posts in 990 days


#5 posted 01-22-2012 04:50 PM

It’s hard to say, what are these clamps made out of? They look like flexible plastic, which I would think would be almost impossible to get the amount of clamping pressure you were hoping for. If I’m wrong, then really the only other problem would be the pine is too soft like Ben said. I’ve never used these before and have always wondered how they worked, keep us posted if you figure em out.

-- It is amazing what you can accomplish if you do not care who gets the credit. - Harry S. Truman

View TMcG's profile

TMcG

182 posts in 1659 days


#6 posted 01-22-2012 05:13 PM

Charlie; The boards are all straight and jointed, it’s those 1/16” or so slip ups or downs that seem to be the issue I was thinking these would avoid

Ben; That was my suspicion as well, should have thought about it a bit more rather than just robotically doing what the instructions said I guess. The caul idea is also a good one. The plastic could be an issue over time I guess but it’s that injection moulded stuff, pretty hard when it’s brand new.

Rich; Bowed cauls, as for Ben, makes sense when you think about it, why is it that’s always after the fact ? :-) They do have springs that keep them closed, as it were, I think they would be impossible to use without the springs

Hanman; The notched pieces are that hard injection molded plastic but the clamping mechanisms themselves are metal, as are the clamping screws.

I’ll give all that a try and post an update.

Thanks
tony

-- http://wood.mcgivern.org

View doncutlip's profile

doncutlip

2832 posts in 2214 days


#7 posted 01-22-2012 05:28 PM

I have a set of these too, bought them at a sale a while back. Just used them on a project and like you I simply followed the directions. I didn’t get a perfectly flat joint either, had to sand things down a bit. I like the ideas here too, good reason to buy my first hand plane.

-- Don, Royersford, PA

View Chipy's profile

Chipy

374 posts in 1252 days


#8 posted 01-22-2012 05:52 PM

It looks like this clamping set is made of plastic if it is the case there has to be flexing going on here.I also don’t see any way for this clamp to exert pressure in the middle of the panel.I also would suggest putting some wax paper under the culls to prevent attaching the culls to the work piece I believe that there is no silver bullet when it comes to gluing up panels.I rarely have had panels stay aligned through the glue up process I just accept the fact that I will probably have to do some planing or belt sanding after glue up.I have been toying with the idea of building a clapping bed similar to a veneer press but I am not sure that would completely fix the problem either.

View Jorge G.'s profile

Jorge G.

1526 posts in 1134 days


#9 posted 01-22-2012 06:20 PM

It is not you, I bought a set as well and it was a PITA to make them work. What I did was placed the panel on the rails, clamp the rails with regular clamps to hold the rails flat to the panel and then attach the V clamps to the ends….way too much work, might as well just use the clamps alone. Now I am using the Veritas clamps and those do work.

-- To surrender a dream leaves life as it is — and not as it could be.

View casual1carpenter's profile

casual1carpenter

353 posts in 1134 days


#10 posted 01-22-2012 07:01 PM

I think richgreer hit the nail on the head. Those clamps would provide pressure similar to culls and try to help level the field. But they will also flex or crown the wood they are attached to. I ran across an advert / video awhile back for a bow-clamp, bow-cull, bow-flex or something, the guy was essentially presenting a cull with large radius bow on one edge similar to what rich said. The way he tried to sell his product, description, and methods explained just why your question came up. If you do go the hand plane bow route, you might consider putting near identical bows, perhaps a flush trim bit and a pattern. Then I would assemble the clamp and using say a flat 3/4 plywood drop, test the clamps to normal clamping force. Check for gaps at the ends, if gaped too much bow. Sorry I can’t figure a way to check for not enough bow. Good luck with it.

View CraigFeuerzeig's profile

CraigFeuerzeig

5 posts in 2029 days


#11 posted 01-23-2012 08:04 PM

That would be mine… bowclamp.com. Thanks for looking.

-- Bowclamp "good caul"

View RONFINCH's profile

RONFINCH

142 posts in 1583 days


#12 posted 01-23-2012 09:23 PM

While the clamps are not the cat’s meow for clamping up panels, I use them and have decent success with them. I do use additional clamps to make sure there is ample pressure to get the job done. I’m happy with the way the clamps “assist” in keeping the panels “flat”.

View Viktor's profile

Viktor

447 posts in 2077 days


#13 posted 01-24-2012 12:56 AM

First, the cauls need to be bowed. How much you can establish experimentally.

Second, you can control the pressure you exert on the faces of the boards (thought cauls) by changing the angle between the arms of the clamp. (Make the cauls thicker, it will make them stiffer too, which is a plus).

On the figure:
If the screws are equally tightened (F1 on both figures) the “vertical” force on the top figure (F2) is be about 4 times the “vertical” force on the lower figure (F3). F2 = 2xF1; F3 = 0.5xF1.

If your angle approaches 180 deg, you could exert enormous force on the cauls. Your limitation thought is the tensile strength of the clamp arms.

You probably noticed the same effect when using scissor car jack. It is hard to rotate the screw at the beginning when the jack is flat, and easier at the end (with the same car on it) when the angle between the arms change.

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