I’m wondering what work-holding strategies people use for blocks of aluminium.
I have the threaded table and on the table I use a sacrificial surface that I faced flat. I use this when milling large flat pieces where I have holes or similar features that can be used for clamping the aluminium to the bed.
However, if I am milling a billet with no holes I’d prefer to cut raw stock somewhere near to size so the edge contour is just cleaning up the part rather than milling it out of a bigger block and slotting all-around to cut the part loose. I have a couple of vices but don’t use them that often as I struggle with strategy for blocks that need an edge contour.
I notice with the ‘big’ machines folks will just clamp the block in the vice with parallels and then after milling the part and around the edges, flip the part and face off the extra 1/4" of stock. However, this strategy isn’t really doable on the Nomad due to the length of time to face off the extra material.
Thanks. I’ve used the superglue trick on thin pieces of material but is it strong enough for holding down a 1" block of aluminium while the interior is pocketed and then the edges contoured? IME I have to bolt aluminium down pretty well given the forces exerted on milling it.
The surface area of the tape contact (and glue joint) determine the strength, and the load is determined by the aggressiveness of the cut as well as how far from the tape/glue joint the cut is being made. If it is a 1" cube, I would have doubts. If it is a 1"X1"X1mm thick piece being engraved, I would go for it.
You can get better hold several ways. I tend to use more tenacious adhesive, such as 3m 467 adhesive strip. Removal is a bit more difficult, but can be done without solvents. Solvent makes it a lot easier. You can directly superglue the part down, but that may require accelerator to get a good bond and will likely need acetone to remove the part. Again, how well these work in practice depends on the machining forces and strength of the bond.
You can also make low grips to minimize the need for follow up work. Toe clamps (see Total Guide to CNC Jigs, Fixtures, and Workholding Solutions for Mills about 2/3 of the way down-- Poweredge is one brand) are real handy, and I have one with the working edge thinned to a knife edge so it can grip within maybe 0.5mm of the bed. One of these and a couple flat-head screws sharpened to a knife edge so they sit the same height work well.
The traditional setup uses bars that look like parallels, but are trapezoid in cross section to knifedge grab a part in a vise. (I can’t find a picture with a quick search. It shows up in a lot of introductory machining texts. I made a set in trades class many, many years ago)
You should be fine with the CA and tape trick. The Nomad is probably not going to be running fast or hard enough in aluminum to break the bond.
Another option would be the machining wax Carbide 3d sells for this purpose, which holds very well and will not stick to your endmills, but I find it is messy and frankly annoying to use.
Yes, it should be plenty strong to handle that. I mill aluminum parts up to 0.5in thick with this method with no issue and it is on par with a vise. Plus, if John Saunders (NYCCNC) uses it in his shop with their milling machines, it should be plenty fine for us hobby machinists.
Also, Vince around here uses it on billet material 2-3in thick too. Paging Mr. @Vince.Fab, to the front desk please.
You guys covered everything pretty well. I’ve used that method successfully 100% of the time but most of my parts have the advantage of surface area.
One option is using an mdf wasteboard with a slight pocket and superglue/tape your material into. A tight fit will do wonders dealing with the side loading. Cons - you’ll go full width contour on the very bottom but that’s easy enough to deal with in cam.
Keep in mind the strength in superglue/tape setups comes from a putting a good amount of force on the part during the curing time.
Just chiming in on that last part to add more. Adhesion strength is directly related to the surface area bonded so you want a thin layer on all parts of the masking tape. Similar to applying wood glue in woodworking where you want to apply it and then smear it all over the wood, I recommend doing something similar with the CA glue to ensure it is evenly distributed.