rstermer

I've seen a number of thumbnails posted on the forum of cams set up to hold material in place and was wondering if those who have made cams for that purpose could share their knowledge. How does one decide on how much to offset the pivot point from the center of the circle? What material should be used for the cam and the pivot? Any particular diameter for the pivot pin? When is it best to add a lobe to the cam and what are the design criteria for lobed cams? Do you add a friction surface to the cam face? If not, how do you get it to lock in place? What other considerations are important? Thanks for your thoughts.
rstermer

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bobj3

HI rstermer

I'm a user of cams ,,, I have made many,many of them... from 1/2" dam. to 2" dia. and from from 1/2" high to 1 1/4" tall , I have made them with a hole saw and using dowel rod, by the way dowel rod works the best..,,, most of the holes are just off the edge of the dowel ,to get the max caming action out of them..
They work better than the wedges in most jobs..
I have but sand paper on some and that helps hold them in place or to say hold the stock in palce.
I also drill all the holes the same so I can use the same allen screw with them all/most...it's a 10-24 x 1 1/4" allen cap screw...
But I also use sq.drive dry wall screws when I need to...

I use a stop block on the chop saw so they all come out the same, the norm is 8 of each size..

Thumbs up on the cams

Hope this helps..

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Bj

rstermer

Thanks, Bob. Will any hardwood do for the dowel or do you have a preferance? For strength, it would seem you would want to leave adequate wall thickness from the edge of the cam to the edge of the pivot hole, otherwise the wall might crack. How much material do you usually leave? Also, how do you decide how far to set the cam back from the material the cam will be locking in position? Distance from center of pivot to furthest edge of cam minus an eighth? Or a sixteenth? It seems to me that the distance is a critical facor, too close and the cam won't be able to rotate far enough to effectively lock up, too far and the cam won't apply enough pressure. Finally, when setting the cams in position, is hand pressure all that is required or do you use a tool (slip joint pliers?) to lock them in place?
Thanks for the info!
rstermer

Edit: As I think about it, the optimum amount of interfernce between the the workpiece and the cam must depend on the diameter of the cam. A large diameter cam will hit the workpiece at a shallower angle, and thus generate less pressure (once everything is snugged up) per degree of rotation than will a smaller diameter cam. Also, the closer the pivot is set to the edge, the greater the pressure generated per degree of rotation will be for a given size of cam. So it is fairly complicated to get it just right. Yes?
RAS

rstermer

Link to an interesting pattern jig which uses cams as holding devices:
http://lumberjocks.com/projects/3292
rstermer

bobj3

Hi rstermer

ANy hardwood dowel will do the job but I do like Oak over the others.

Drilling the hole,,,I try and drill them about 1/4" from the edge,when the cam is used the screw hole is on the backside of the cam so to say you have alot of stock between the screw and the edge,plus because it's dowel you are drilling down in with the grain.

I have not cracked one yet and most are drilled down to with in 1/4" of the bottom of the cam...

To set the cam in place ,it just needs to cam in and lock the part in place,it takes no presser at all to lock them in place because of the cam action...

"So it is fairly complicated to get it just right. Yes?" No,, it's very easy to set them and lock them in place,,

The holding jig you posted (link) the cams could be used on it,just a quick turn on the cam and it's locked in place the screw is just a device to keep it from backing off the lock down...

Just the nature of the cam ,more you turn it (load it ) the more it can hold.

They also work great for picture frames, boxes,templates, etc. anything that needs to be held in place till the glue sets up...a quick right angle jig (see below) and some cams can lock the frame/box in place in a heart beat...

Do this pull out some 3/4" dowel rod you have on hand or just about any size you have on hand , cut off 8ea., then take them to the drill press and drill some holes for the screws you want to use...besure to counter sink the holes for the screws, find some scrap plywood and put a block of wood in the center of the scrap plywood and put down 4 cams and then 4 more, then try and move the block round you will be amazed how well the cams work and how easy they are to use...



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Bj

rstermer

Hi Bob- Thanks for taking the time to answer my questions, you are always very generous with your time and information!
rstermer

bobj3

You'er Welcome rstermer

I'm glad I could help out..

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Bj