SS Panel Clamps

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BuckeyeDennis
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Re: SS Panel Clamps

Post by BuckeyeDennis »

larryhrockisland wrote: Sun Jan 09, 2022 4:14 pm
BuckeyeDennis wrote: Sun Jan 09, 2022 1:55 pm
  • Start with a straight edge on an MDF template.
  • Use trig and a spreadsheet (or a CAD system) to calculate arc offsets from the straight edge. Generating an offset calculation every few inches along the straight edge.
  • Use calipers to lay out the offset points on the template.
  • Bandsaw and sand the template smoothly to the arc points.
  • Use the template with a router and a pattern bit to transfer the curve to the actual cauls.
This might be easier and quicker. Stumpy Nubs starting at 4:15 minutes
https://youtu.be/KdeUBuCOBBQ

There are lots of other videos out there, this was pretty easy to find, I still like messing with CAD though.
For sure, the “bow” technique can generate a nice smooth curve, with no math or computers required. It’s unlikely to be a true semicircle, but who knows, it might actually be better for generating even clamping pressure. Even if using a bow to generate the curve, I’d still make a master template, and then transfer the curve from that template to all of the cauls. For me, that’s both faster and more consistent.
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Re: SS Panel Clamps

Post by larryhrockisland »

edflorence wrote: Sun Jan 09, 2022 8:31 pm My Shopsmith panel clamps have seen a lot of use over the years and they do a great job. Occasionally, though, I have needed cauls longer than the panel clamps and the way I learned to make them is dead simple. No math, no measuring. Start with a 1x2 or 1x3 as long as you need and stand it on edge with a spacer under the center. The spacer is a scrap piece about 1/8 to 1/4 thick. With the spacer in place, clamp both ends down to a table or bench. Then set a scribe tool (which can be as simple as a pencil with a thickness of tape wrapped around it to get it to the right height) to match the gap between the table and the raised center of the caul and keeping the pencil on the bench top, scribe the caul from one end to the other. This makes a nice arc. Release the clamped ends and bandsaw and sand.
I like the scribing method, thanks. Any trouble with the 1x wanting to lay over when you tighten them?
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edflorence
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Re: SS Panel Clamps

Post by edflorence »

larryhrockisland wrote: Sun Jan 09, 2022 10:23 pm
edflorence wrote: Sun Jan 09, 2022 8:31 pm With the spacer in place, clamp both ends down to a table or bench.
I like the scribing method, thanks. Any trouble with the 1x wanting to lay over when you tighten them?
No, not as I recall. I laid a piece of plywood across two sawhorses and set the 1 by on it with the spacer under it and clamped the ends a bit at a time, back and forth until both ends were snug to the ply.
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Re: SS Panel Clamps

Post by larryhrockisland »

[/quote]
No, not as I recall. I laid a piece of plywood across two sawhorses and set the 1 by on it with the spacer under it and clamped the ends a bit at a time, back and forth until both ends were snug to the ply.
[/quote]

Thanks
Larry Hargrove
Rock Island, Ok
1981 Mark V 500>510>520(98922)
19?? Mark V 500>Power Pro headstock 556176 06-17-11 factory exchange program original serial unknown
1957 Mark V 500 (350389)
1953 10ER
Another 10ER
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Bandsaw, Jointer, other goodies
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SS 6” Belt Sander w/power stand 1970’s?
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algale
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Re: SS Panel Clamps

Post by algale »

edflorence wrote: Sun Jan 09, 2022 8:31 pm My Shopsmith panel clamps have seen a lot of use over the years and they do a great job. Occasionally, though, I have needed cauls longer than the panel clamps and the way I learned to make them is dead simple. No math, no measuring. Start with a 1x2 or 1x3 as long as you need and stand it on edge with a spacer under the center. The spacer is a scrap piece about 1/8 to 1/4 thick. With the spacer in place, clamp both ends down to a table or bench. Then set a scribe tool (which can be as simple as a pencil with a thickness of tape wrapped around it to get it to the right height) to match the gap between the table and the raised center of the caul and keeping the pencil on the bench top, scribe the caul from one end to the other. This makes a nice arc. Release the clamped ends and bandsaw and sand.
Ed, this is a really interesting technique, and not just because it is elegant in its simplicity. I think it answers Dennis' question about whether an arc of a circle of radius X is really the most efficient curved shape to ensure equal downward pressure from the center of the caul outward to the ends when clamping force is applied.

If you draw an idealized curve on a board that is not under clamping stress and then cut out that curve, there's no guarantee that the board will flatten out when used as a caul and placed under maximum clamping stress.

When done Ed's way, however, you put the board under stress first then define a perfectly flat and straight plane across the bottom of the caul by scribing that perfectly flat line across the bottom of the caul while is under maximum stress. When it is relaxed, that straight line will assume whatever curve it wants to take on; but it should flatten back out perfectly when the same clamping stresses are applied to it.
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Re: SS Panel Clamps

Post by KCollins »

Ed that is genius. Well done sir.
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JPG
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Re: SS Panel Clamps

Post by JPG »

Not sure how significant the caul internal stress will play out when used to clamp other boards with individual stress contributions.

Seems plausible though.

If one is "good" with a hand plane, the inverse of the tape trick would also work. (successive strokes of diminishing length)
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Re: SS Panel Clamps

Post by edma194 »

The bow method described sounds as good as any other to me. Wood is not that kind of precision substance that will flex in a predictable manner, and I doubt it matters. I'm not sure this curve matters so much except as a way to guarantee the clamping surface of the board has not deformed into a concave shape that would negate the clamping action away from the end.
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JPG
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Re: SS Panel Clamps

Post by JPG »

The cauls exert pressure from BOTH sides in hopefully an equivalent manner so bowing should NOT be an issue.
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BuckeyeDennis
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Re: SS Panel Clamps

Post by BuckeyeDennis »

JPG wrote: Mon Jan 10, 2022 11:00 pm The cauls exert pressure from BOTH sides in hopefully an equivalent manner so bowing should NOT be an issue.
That raises an interesting point. If both cauls used for a particular clamp have the same stiffness, and an identical smooth curve, then when under pressure the curved clamping faces will be drawn into a straight line (flat plane, actually). If either the stiffness or the curve is different, the clamping faces will draw into a non-straight curve, and the panel glue-up won’t be flat.

Which suggests a good test for the cauls: clamp pairs of them together without workpieces, and then check the clamping-surface straightness with a good straightedge. It’s also another argument for making all of the cauls from one template. And unless you can ensure that the template is perfectly symmetrical, the ends of both the template and the cauls should be marked (or “specialized”), so that the ends always match in use.

I take my Shopsmith clamps apart to store them, and when I use them I reassemble them with arbitrary caul pairs. But the caul ends are specialized, so at least the orientation is always consistent.
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