Cam lobe profile question

[Rich Purdum]

I'm looking for any suggestions and maybe a drawing on the cam portion of a hand lever cam clamp. Since this site discards "cam" as a 3 letter word I can't handle the resulting 500+ posts that show up with "clamp", so if this has been dealt with already my apologies.

I'm making a hand lever cam clamp for a saw vise. I've got a 1/2" diameter, 3/8" thread barrel nut which will be inserted into this "lever" on the user end of the vise. A 3/8" bolt will come in from the back side of the vise. I can do this via trial and error but thought I would ask here before embarking into the unknown. I've done a mock up in cardboard but I'm not comfortable as to how it will operate in the real world.

[Mark Dorman]

The basic thing to me is how much travel do you need. If you have a 1/2" from center to edge and you need 5/8" when clamped you offset the hole 1/8" in one plane. The cam action takes place because the hole is off center. The end can be round and dosn't need a profile like a cam lobe on a camshaft.

[Rich Purdum]

Mark, thanks for the diagram. The "open" state of the saw vise is fairly narrow, say maybe 1/8" or less, so the travel required is very small. Based on your drawing, I'm guessing all I need to do is ensure 1/8" or a little less distance between the center of the pivot point and the "open" and "closed" edges of the "cam" (which is basically what shows on your drawing). I'll give it a shot later today.

[Jonathan McCullough]

Cam clamp mechanisms from Lee Valley. I've bought some but haven't put them on my saw vise yet.

http://www.leevalley.com/US/wood/page.aspx?p=45034&cat=1,43455,61994

http://www.leevalley.com/US/images/item/woodworking/clamps/05j5101i2.jpg

http://www.leevalley.com/US/images/item/woodworking/clamps/05j5101s5.jpg

[Rich Purdum]

J

That's basically what I'm shooting for except from wood and shop made. I've got the barrel nut and a long bolt to pull with so if I can get the correct profile on the cam portion of the clamp and the correct placement of the pivot point, cut a slot for the bold, I should be good to go. The store-bought route is my backup plan.

If it works I'll post the results back to this thread.

Rich

[Jim Koepke]

My solution to such was to have the cam movement to be more than needed and the surface it clamped against to be flexible. This insures enough movement for the item to open and enough pressure to keep it closed.

Not sure if I have any of these things still in use. For me, they tend to be temporary solutions for an immediate problem.

jim

[Dale Sautter]

My solution to such was to have the cam movement to be more than needed and the surface it clamped against to be flexible. This insures enough movement for the item to open and enough pressure to keep it closed.

Not sure if I have any of these things still in use. For me, they tend to be temporary solutions for an immediate problem.

jim

Dittos to that Jim... I've made/used wood ones in the past in a pinch, but for longevity, it's hard to beat Rockler:

http://images.rockler.com/rockler/images/58252-01-500.jpg

Rockler cam clamps (http://www.rockler.com/product.cfm?page=10602)

The clamps that Jonathan McCullough linked to look nice too... well, most any/everything from Lee Valley does as well. :)

[Jim Koepke]

Found an old setup out in the shop.

This one was to index a piece that was being routed for a lap joint. It has a sliding dovetail key to transfer the movement to the piece being held in place.

157570

jim

[Steve Branam]

Hmmm, I've been thinking about some kind of flat cam with an axle that drops into a dog hole as an alternative to using wedges to secure a board flat to the benchtop against the planing stop. Maybe I'll give this a try. Make a couple with different diameters and ranges of travel.

[Jim Koepke]

Hmmm, I've been thinking about some kind of flat cam with an axle that drops into a dog hole as an alternative to using wedges to secure a board flat to the benchtop against the planing stop. Maybe I'll give this a try. Make a couple with different diameters and ranges of travel.

I have done things like this. If the handle is long enough and situated advantageously, then a short dowel can be used in another dog hole to secure the lever in tension.

jim

[Rich Purdum]

Mark

I followed your circular lobe design with off-center pivot point and it seems to be working. I was concerned about the flex in ipe which is somewhat brittle. I cranked down on the cam, then backed it off, slid a blade in and "clamped it" down and it seemed fine.

Below are thumbnails of the clamp and the vise. It was all made from ipe scrap left over from a big deck project. The jaws are 22" long (that's the longest 4x I had left). The center position of the lever seems to be getting even pressure over the length of the jaws. We'll see how well it works in practice. I may need to redo the pivot blocks which hold the two jaws together to get a larger space in the open jaw position.

The vise itself

http://i563.photobucket.com/albums/ss75/RichPurdum/Miscellaneous%20projects/th_CRW_5948_RJ.jpg (http://i563.photobucket.com/albums/ss75/RichPurdum/Miscellaneous%20projects/CRW_5948_RJ.jpg)

Clamp open

http://i563.photobucket.com/albums/ss75/RichPurdum/Miscellaneous%20projects/th_CRW_5949_RJ.jpg (http://i563.photobucket.com/albums/ss75/RichPurdum/Miscellaneous%20projects/CRW_5949_RJ.jpg)

Clamp closed

http://i563.photobucket.com/albums/ss75/RichPurdum/Miscellaneous%20projects/th_CRW_5951_RJ.jpg (http://i563.photobucket.com/albums/ss75/RichPurdum/Miscellaneous%20projects/CRW_5951_RJ.jpg)

Mounted on bench with blade

http://i563.photobucket.com/albums/ss75/RichPurdum/Miscellaneous%20projects/th_CRW_5950_RJ.jpg (http://i563.photobucket.com/albums/ss75/RichPurdum/Miscellaneous%20projects/CRW_5950_RJ.jpg)

Rich

[Rich Purdum]

Edited my post from yesterday to add pics but that does not bump the date on the post, so see "It's working" above if you are interested. Thanks to all for the inputs.

[harry strasil]

You might consider some kind of large diameter washer like a fender washer to prevent wear in the main piece from the cam being used, the cam is the expendable easily replacable piece after all.

[Rich Purdum]

Jr,

I was just lazy...there is a fender washer out of the photo on the workbench which will get installed once I get the beast tuned up. Ipe is so hard it is difficult to think about it wearing out but why take the chance? And my thoughts exactly on the cam. A bit of time on the band saw and you've got a new one for the price of some scrap.

Rich

[Mark Dorman]

Rich,

Glad it worked for you. Thats a good looking saw vice. I'll be making one this fall and yours gives a good idea of what I want to do.

Mark