SS Panel Clamps

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KCollins
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Re: SS Panel Clamps

Post by KCollins »

A lot of good info coming out of this thread thanks guys.
Kevin Collins

1x Mark 7 - 520
2x Mark 5 - 510
1x 1956 Mark 5 - 500 in need of restoration
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algale
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Re: SS Panel Clamps

Post by algale »

BuckeyeDennis wrote: Sun Jan 09, 2022 10:33 am ***
Real-world check

I just measured my own 48" Shopsmith double bar clamps. They are 2-1/8" tall in the center, and 2" tall at the ends of a 47" chord. (Beyond that they have a relief cut for the clamp hardware.)

Plugging those numbers into the curvature calculator, I get a 184' radius of curvature. That's a big difference, and I suspect that it's causing your problem. I dunno where the numbers came from on the sketch that you linked, but they definitely don't match my Shopsmith clamps.
Oh my goodness! Someone's going to need a really, really big compass to draw that curve!

The numbers are so huge that I keep thinking "he must mean inches not feet."

Which reminds me of the scene in Spinal Tap where their manager gives instructions to an artist to build them an 18 foot high "Stonehenge" prop but on the sketch he gives the artist (on a napkin) he writes it as 18" instead of 18', resulting "in a Stonehenge in danger of being crushed by a dwarf."

https://www.youtube.com/watch?v=zg5Ovdu6bOE
Gale's Law: The bigger the woodworking project, the less the mistakes show in any photo taken far enough away to show the entire project!

larryhrockisland
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Re: SS Panel Clamps

Post by larryhrockisland »

KCollins wrote: Sun Jan 09, 2022 11:33 am Are these still needed?

Overall - 1-1/8" X 2 X 41
At the Crank End there is a recess narrowing the end to 1-5/8" for 2-3/4" - I can provide a picture if you'd like.
The holes are cut in half and are 1/2" in diameter.
On both ends there are 2 half holes that are 3-1/4 and 4-1/4" from the end.
The remaining half holes are from the end 6-1/2", 8-3/4", 11",13-1/4",15-1/2",17-3/4", 20", 22-1/4".
Thanks KCollins. Can you check the dimension on end opposite the crank end? I think it will be 1-7/8" based on Dennis and JPG's information.
Larry Hargrove
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BuckeyeDennis
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Re: SS Panel Clamps

Post by BuckeyeDennis »

The radius of curvature on my clamps really does work out to approximately 184 feet, or 2,209 inches.

Given that a different online radius calculator reportedly gave different results than the one I linked, I checked the calculated radius using some simple trig. The results agreed. The calculator I linked also matched the results from Larry's CAD program.

Algale, I agree that a compass isn't a very practical approach to drawing the arc! (I do have a 150 foot landscape tape measure, but it would be darned hard to find a smooth flat surface that long to work on. :rolleyes: ) I'd do it something like this:
  • 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.
Now here's another question: do we really know that the profile is in fact a circular arc? I suspect that it is, just because that makes it fairly easy. But I doubt that a circular arc is optimal for equalizing the vertical clamping pressure across the width of a panel.

But even if it's not the optimal profile, it's a lot better than a straight clamping edge. The Woodpeckers panel clamps are straight, and they don't draw the glue-up flat without some external persuasion. Starting at about 5:30 in this Woodpeckers Deep Dive Video, you can watch Jeff Farris explain why, and demonstrate how, he gets his board edges into vertical alignment by literally whacking them with a mallet.
edma194
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Re: SS Panel Clamps

Post by edma194 »

The curve is there to re-direct the tension on the clamp boards 90° towards the panel being glued up. If I make my own boards I planned to sand a slight curve into them, it shouldn't take much and the shape of the curve shouldn't matter much. Cutting the board at an angle from either end and sanding down the point where the angles meet in the center will probably do the job because the curve is so slight.
Ed from Rhode Island

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algale
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Re: SS Panel Clamps

Post by algale »

BuckeyeDennis wrote: Sun Jan 09, 2022 1:55 pm The radius of curvature on my clamps really does work out to approximately 184 feet, or 2,209 inches.

Given that a different online radius calculator reportedly gave different results than the one I linked, I checked the calculated radius using some simple trig. The results agreed. The calculator I linked also matched the results from Larry's CAD program.

Algale, I agree that a compass isn't a very practical approach to drawing the arc! (I do have a 150 foot landscape tape measure, but it would be darned hard to find a smooth flat surface that long to work on. :rolleyes: ) I'd do it something like this:
  • 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.
Now here's another question: do we really know that the profile is in fact a circular arc? I suspect that it is, just because that makes it fairly easy. But I doubt that a circular arc is optimal for equalizing the vertical clamping pressure across the width of a panel.

But even if it's not the optimal profile, it's a lot better than a straight clamping edge. The Woodpeckers panel clamps are straight, and they don't draw the glue-up flat without some external persuasion. Starting at about 5:30 in this Woodpeckers Deep Dive Video, you can watch Jeff Farris explain why, and demonstrate how, he gets his board edges into vertical alignment by literally whacking them with a mallet.
What angle are you seeing between the two radii that form the arc?
Gale's Law: The bigger the woodworking project, the less the mistakes show in any photo taken far enough away to show the entire project!

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BuckeyeDennis
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Re: SS Panel Clamps

Post by BuckeyeDennis »

algale wrote: Sun Jan 09, 2022 2:34 pm
BuckeyeDennis wrote: Sun Jan 09, 2022 1:55 pm The radius of curvature on my clamps really does work out to approximately 184 feet, or 2,209 inches.

Given that a different online radius calculator reportedly gave different results than the one I linked, I checked the calculated radius using some simple trig. The results agreed. The calculator I linked also matched the results from Larry's CAD program.

Algale, I agree that a compass isn't a very practical approach to drawing the arc! (I do have a 150 foot landscape tape measure, but it would be darned hard to find a smooth flat surface that long to work on. :rolleyes: ) I'd do it something like this:
  • 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.
Now here's another question: do we really know that the profile is in fact a circular arc? I suspect that it is, just because that makes it fairly easy. But I doubt that a circular arc is optimal for equalizing the vertical clamping pressure across the width of a panel.

But even if it's not the optimal profile, it's a lot better than a straight clamping edge. The Woodpeckers panel clamps are straight, and they don't draw the glue-up flat without some external persuasion. Starting at about 5:30 in this Woodpeckers Deep Dive Video, you can watch Jeff Farris explain why, and demonstrate how, he gets his board edges into vertical alignment by literally whacking them with a mallet.
What angle are you seeing between the two radii that form the arc?
1.2 degrees, for my 48" clamps.
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dusty
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Re: SS Panel Clamps

Post by dusty »

Does this represent what is being discussed here?
Clamp.jpg
Clamp.jpg (49.94 KiB) Viewed 1321 times
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BuckeyeDennis
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Re: SS Panel Clamps

Post by BuckeyeDennis »

Close, if you're talking about the measurements that I took of my 48" clamps. The main difference is that the "height" of the arc was 1/8" on my clamps. (I actually measured a 2-1/8" total caul height in the middle, and subtracted the end height to arrive at the 1/8" arc height). It appears that you have the arc height dimensioned as 1/2".

Of little consequence, I measured the caul heights across 47" of arc, not 48". That will cause a slight difference in the calculated radius.
KCollins
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Re: SS Panel Clamps

Post by KCollins »

larryhrockisland wrote: Sun Jan 09, 2022 1:31 pm
KCollins wrote: Sun Jan 09, 2022 11:33 am Are these still needed?

Overall - 1-1/8" X 2 X 41
At the Crank End there is a recess narrowing the end to 1-5/8" for 2-3/4" - I can provide a picture if you'd like.
The holes are cut in half and are 1/2" in diameter.
On both ends there are 2 half holes that are 3-1/4 and 4-1/4" from the end.
The remaining half holes are from the end 6-1/2", 8-3/4", 11",13-1/4",15-1/2",17-3/4", 20", 22-1/4".
Thanks KCollins. Can you check the dimension on end opposite the crank end? I think it will be 1-7/8" based on Dennis and JPG's information.
I come up with 2" on the money.
Kevin Collins

1x Mark 7 - 520
2x Mark 5 - 510
1x 1956 Mark 5 - 500 in need of restoration
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