I have been contemplating a vacuum hold down system for while but can’t think of a way to have both a spoilboard with dog holes and Matchfit clamping slots and a vacuum hold down system. I am not really able to lift a full 4’*4’ vacuum table onto my normal spoil board for when I want to use that hold down method. I could set up with a half sized vacuum table if I had to but I am wondering about the use of a pressure foot instead of a vacuum table.
There are two reasons for me to use a vacuum table - not having to worry about traditional clamps but much more so to make sure sheet goods are flat on the mill. Virtually every sheet of plywood I have seen has flatness issues and I suspect that any sort of fancy corner joint in cabinetry will show evidence of cuts that are too deep or too shallow from a slightly warped sheet stock material. Some down pressure for flattening the stock can be supplied by using a downcut milling cutter but I do not know how effective that is.
I recently ran across a picture of a pressure foot and I am curious to find out if anyone here has used one of these puppies? How much down force are they providing while still being able to roll over stock freely? How likely are they to hang up if they run into a groove that has been cut on a previous cutter pass? Are they affective for straightening out warped stock or are they used simply to keep stock down when using upcutting endmills?
I had to Google to find out exactly what a pressure foot was. After seeing a brief description, I had similar questions to yours. It might be useful for sheet metal and other similar stock and only if you cut a small groove. I would assume larger grooves would catch the ball bearings as you suspect. Forget it for any relief work.
And since pressure is only applied under the spindle, your warped plywood would still warp further out of the foot/spindle. I would think there is only a small use case where this is useful.
I’ve been using double sided tape for plywood up until now. But all of my cuts have been through cuts. So even though I also noticed some warpage , it didn’t matter if I cut deep enough.
Oh, and what I have also been doing, with some success, is making sure the warped plywood is placed concave up. That way, I just need to clamp the sides. Doesn’t work in all cases though.
Yes, relief work was never in the picture for obvious reasons and yes, cutting through the stock doesn’t pose a problem when the stock isn’t totally flat.
It’s all about joints in drawers and cabinets. The joints that I plan on using make a lot of use of 1/2 depth cuts in 12 mm plywood and even 1/2 mm can cause issues by making the joints sloppy. I also use a bunch of 6mm stock which is even worse for flatness but all cuts on that stock is through cuts so the warped stock isn’t causing any issues.