Shopsmith clamps

[Kevin]

Anyone happen to know how much curve is built into the face of these clamps?
I'm thinking maybe 1/16".

[SwampDonkey]

No idea here. I have similar clamps that have hard plastic mold for the metal contact and used scrap birch I finished so excess glue won't soak into the wood from the clamped piece.

Do you mean 1/16" bend per inch of curve? When the clamp is closed tight on one end, how much gap is open on the end? Half the length of end gap divide by rail length. (Assuming both rails are curved equally). You looking to buy them or have them already? Might make a difference on whether you can measure them. :D  Different lengths will probably have different arc radii. Or do you mean how much rise above horizontal in the middle of the rails?

[Kevin]

I was thinking of making a set where I could use C clamps on the ends.
When you close the two rails the center touches first.
Looking at the picture I'm guessing that there is 1/16"to 1/8" rise in the center of each rail from the end.

[flip]

I have a few sets of these and I did not build any tweak into them.  I don't believe they need any or at least I have not found the need to pre spring them.  Remember, the idea behind these is to push the boards together AND hold them flat.  If you have warped boards to begin with these won't cure that problem.  They work very well IMHO.

[SwampDonkey]

Yeah, Kevin you don't need much rise. The ones Metalspinner and I got are not very expensive and work well. I didn't even plan any rise in my wooden rails, seems to be fine. I don't think I could clamp enough pressure to bend the rails I have anyway. :D

[Kevin]

The problem I've had using straight boards on their edge and clamped with C clamps on the outside is the center boards don't get enough pressure and there can be a difference of 1/16" in the boards near the center of say a 32" door panel.

[Hilltop366]

I have made some out of  1x5 ish hardwood boards and cut the ends back to put bolts through the ends, it worked ok but then my cabinet maker friend was telling me to taper them and it worked much better. ( I just ran them through the jointer starting in the middle and cutting deeper as I got closer to the end in each direction) I found bolts through the ends were a lot easier to use than trying to hold two boards and a c clamp and the wider boards will take a lot of strain. I also put my pipe clamps on in an alternating pattern (one up then one down) which also helps.

I have never tried these but they look quite interesting.

http://www.leevalley.com/en/wood/page.aspx?p=31181&cat=1,43838

[Kevin]

It looks like those clamps act as bar clamps for side to side pressure only.
I really need something that applies up and down pressure.

[SwampDonkey]

I guess you mean the Lee Valley clamps, eh? The way they work in your picture at the beginning of the thread is side pressure as well as up and down. But, I guess you know this. By looking at the handles in your picture, your not going to be able to get a good grip for clamping unless it's a spoked handle and it fits the palm and maybe a touch bigger. I can't really tell too good from the picture. The ones we have use a wide handle you can leverage with the thumb on one end and the 4 fingers on the other.

Metalspinner has a thread in here somewhere with what we use. They come with plastic ribs which you mount on your own rails, any length you want. I think he used rails with a slight bow for extra down pressure. Been a couple of years back during the winter as I recall where to start looking. :D

I used them on my marquetry coffee table.

[metalspinner]

They are really good clamps.  I don't remember if the bow in them was on purpose or not. :  

For those you pictured, Kevin, dead flat or a 1/32" crown would best. Just make sure to put a little finish on them before the first time you use them.

https://forestryforum.com/board/index.php/topic,28870.0.html

https://forestryforum.com/board/index.php/topic,29392.0.html

[Kevin]

That's not bad, I'll be near  a Woodcraft store in a couple of weeks and I'll have a look at those.
Thanks again.

[Hilltop366]

From what I gather from the Leevalley write up is that the clamps will apply side pressure and hold the top/bottom flat and not let it bow. One advantage is, it is like putting two clamps at once (one top and one bottom) which cures the problem of the pipe clamp pulling things out of flat when a lot of pressure is applied on only one side. They also seem to have a fine thread on the clamp screw which should give a good clamp pressure. It would be nice to hear from someone that has used them.

The Woodcraft clamps look like the ticket for you to apply pressure from all sides.\
Of coarse a big drum sander would be handy as well. ;D