Low level edge clamps

[thehomeengineer]

Hi All
Yesterday I made some low-level edge clamps from aluminium for the CNC engraver at work to fit a jig plate. As the stock material is small makes it difficult to hold on the machine, as it is fitted with a vacuum table. The components need both, engraved text and holes the manufacturing process is to be, completed in two operations text then holes to save tool changing. Therefore, repeatability is required to ensure everything lines up.
The threaded cam has a 2mm throw and a M6 cap head press fitted. The main clamp is 25mm A/F. The counter bored holes are, offset to give different clamping distances when used on the jig plate.





The clamps simply push the work piece against the datum pins on the jig plate to lock in place.



Thank you for viewing
The Home Engineer

[olderdan]

The principal is well known but your version is a great improvement on the dig in style of edge clamp, nice work as usual.

[petertha]

Nice. I kind of understand these but not entirely. Is the hole in the hex off-centre in one direction or 2? (or maybe you have a dimension sketch?). I understand the eccentric action on the bolt but what prevents it from bottoming out in the axial direction prematurely, meaning before the cam action has fully displaced the hex part? In other words the cap screw feels tight but it still hasn't fully applied lateral clamping force.

[Toolmaker51]

Nice. I kind of understand these but not entirely. Is the hole in the hex off-centre in one direction or 2? (or maybe you have a dimension sketch?). I understand the eccentric action on the bolt but what prevents it from bottoming out in the axial direction prematurely, meaning before the cam action has fully displaced the hex part? In other words the cap screw feels tight but it still hasn't fully applied lateral clamping force.

Not to usurp thehomeengineer, allow me provide an explanation. This is an effective clamp, secure enough to withstand milling and drilling; be aware burying a helical [right-hand cut, right-hand helix] cutting edge can pull the plate up. One technique uses right-hand cut with a left-hand helix to generate down force.

Off center in one axis is sufficient. Knowing the amount, it moves the hexagon laterally an equal amount on any face; one needs to pick that which locks against the part before the cam goes over center. The rail or hard stop of opposite side does the rest.
A bi-axial offcenter would produce same result, without benefit, as the cam's rotation is in the entire round bearing area. They could be round instead of hexagon; moving the same distance, but too little contact area for dependable clamp action.
A commercial version is known as Mitee-Bite

[petertha]

ok, maybe I need to start at base principles. I mistook the rail for the part. And now I see the dowel pins which are acting as fixed stops. So dumb question, if the hex is acting on the rail with clamping pressure by screwing in the eccentric, could you not just as well clamp directly against the part? Maybe this example is illustrating thin stock, but I mean just in principle?

[Toolmaker51]

ok, maybe I need to start at base principles. I mistook the rail for the part. And now I see the dowel pins which are acting as fixed stops. So dumb question, if the hex is acting on the rail with clamping pressure by screwing in the eccentric, could you not just as well clamp directly against the part? Maybe this example is illustrating thin stock, but I mean just in principle?

Likely thehomeengineer and I will both agree generating low profile lateral motion is akin to how a vise works. If, by "clamping against the part" you mean to push a clamp against the workpiece with a thumb while clamping, will have only a fraction the mechanical advantage a cam produces.
By selecting the 'correct' face of the hexagon, maximum force will be near the clockwise apex of cam rotation. At least one face might not contact at all, probably one or two won't allow enough rotation to let cam turn sufficiently.
So in principle, just pushing would register location effectively, minus effective clamping. The sketch might illustrate this better than a mere description.
[click on this to view at size]
Numbered sides simulate increased amount off center from cam screw center to edges of hexagon. Turning the screw [which is press fit in cam] causes shift in position of hexagon, both toward and away from intended clamp surface. One of the faces will press heaviest on workpiece when screw+cam rotate in the bore of hexagon.
Quick action like this is used in production vises; using a screw to approach size, a cam to actuate clamp action. Only the cam needs to be opened and closed to exchange parts.

[petertha]

I understand now. Thanks for taking the time to explain.

[thehomeengineer]

Hi petertha and thank you to Toolmaker 51
Great explanation on how the clamps work.
I was teaching last night so did not get a chance to reply to the question (sorry) but you have done a great job in explaining the clamps. These clamps like you say clamp really well, to well in fact that the point contact of the dowels against the work piece has marked the material which is unacceptable. So a second flat piece of stock will be used to prevent this damage (like toolmaker51 stated this is like a vice). Will add some photos of the setup later.
The advantage of these clamps is, the top surface of the material is accessible to the cutting tool and setting up a vice is time consuming to position and create the datum’s on this machine. The jig plate with its evenly known positioned dowel holes are simply loaded in to the machines programme. This is not to say I have not used a vice on the machine or other clamping methods but this is just easier for this type of work. Before I made these clamps, the work piece was, originally held down with vinyl tape. Once I sort all the niggly issues this should be a vast improvement.
The hole in the Hexagon is 1mm by 2mm off centre for your reference.
Thank you again for your interest and toolmaker51 for all your help and explanation
The Home Engineer

[thehomeengineer]

I simply moved the flat stock to the opposite side to stop the pin damage when clamping as the Hexagon is flat anyway.

[DIYer]

Thanks thehomeengineer! We've added your Edge Clamps to our Clamps category,
as well as to your builder page: thehomeengineer's Homemade Tools. Your receipt:

Edge Clamps by thehomeengineer

tags: clamp