Possibility of cutting sheet metal with CNC router?

[jdurand]

Just pondering future possibilities. I have a small CNC router (30 x 20 cm) and was wondering about the possibility of cutting sheet metal on it.

I was thinking of tin plated steel as used for HVAC. I already know I can cut thicker aluminum on either this machine or my CNC mill as long as I'm careful about it lifting.

I've seen comments about glueing the sheet down with contact cement, but then there's getting it back OFF the table.

I guess I could route a custom vacuum table for each pattern, so there's no vacuum leaks where the cuts will be.

Any other ideas?

[bruce.desertrat]

I do know that carpet tape is often used for doing this with wood in CNC setups. Also, you can make a vaccum table with a top of MDF with the surface layers skimmed off. Apparently it's sufficiently permeable to air that this works well. https://makezine.com/projects/make-4...d-down-system/

[tonyfoale]

I have used vacuum holding with success. I made a post on this forum about my setup for PCBs.
Vacuum chuck for PCB milling and engraving.

For small items it is important to get as much suck as possible to generate enough force, so I like your idea of special pieces cut to avoid the cutting tracks. I do not think that using the porosity of board would give enough suck for small items, maybe fine for large sheets.
I would also suggest that you have fences around the vacuum table that will take the horizontal cutting forces. Or dowel pins as I used in the above mentioned post.

PS. For small items you will need a good vacuum, a vacuum pump or compressed air powered venturi device are OK. A vacuum cleaner may be OK for holding down large sheets of wood based board but they only reduce pressure by around 1.5 psi so if you have a piece 2" x 2" to hold down you will only have 6 lbf holding the work piece down. It will be less than that because there is always leakage. A proper vacuum pump will suck down ~10 x the vac cleaner, so even with 50% leakage you will have 30 lbf holding it down.

Compressed air vacuum pump.

Regular vacuum pump.

I think that these pumps are used by refrigeration mechanics and they are readily available and not expensive.

PPS. If your sheet metal is magnetic it might be worth considering a magnetic chuck. Special purpose electro-magnetic ones are easy enough to make from scrap transformers and epoxy resin. Make sure to feed them DC, AC has a tendency to switch the chuck off 100/120 times a second.

[baja]

Maybe spray adhesive? There are several different tackiness levels with them.

[jdurand]

I tried the carpet tape on an item long ago, just about couldn't get it off the table.

I'm so used to doing plastic and non-ferrous I forgot about electromagnets for ferrous wheel parts.

I also have a refrigeration vacuum pump for non-steel parts.

Will look into it when I get the new shop set up.

[mr herb]

I have used tape with adhesive on both sides to hold both ferrous and non-ferrous on to a CNC mill table. Set your depth I(Z) to a couple thousandths (-..002 inch) above the table, and you can break the part out of the sheet, and file or stone any burr from the edge. The tape that we used was made by 3M and I think that the number was 434. It was only a couple thousandths thick.. Clean your table off with acetone at the start, and acetone and a brass scraper to get the residual tape off when you are finished. I have made some very small parts this way..

End mills with a reverse spiral were available at one time. If you are ever offered a box of dull end mills, look for one in there, and if you find one get it sharpened.. They have a number of uses beside holding the part down

[tonyfoale]

End mills with a reverse spiral were available at one time.

Yes, they are a standard item, still available. Ideal when you want to reduce the tendency of lifting the work piece.