hi can anyone help me , wot size (NM) would you need to cutt 18mm birch ply?
any help would be grate
You have to take more than just the motor size into consideration... the spindle, the integrity of the machine, also the depth of cut per pass, desired finish. There's also this thing called chip loading that I understand the basics of, I think masters of machining have to know this to maximise job efficiency, I know you don't want to burn up bits or material and I look for signs of both when I tweak speeds.
If you want to cut 3/4 birch in one pass you'll need a pretty good setup.
I have just finished building a CNC router that I use to cut plywood, plastic, MDF and aluminum. It is constructed out of 8020 aluminum extrusions and some parts made of 1/2" aluminum plate. The drive system is R&P (CNC router parts), the linear motion is V rails and I am using a Porter Cable 690 router.
The machine will rapid as fast as 750 ipm, but I have my rapids set at 500 ipm because it seems to fit best with the size of the machine.
When I cut 3/4" birch plywood I use a 2 flute, 1/4" carbide up-cut spiral endmill from Amana Tool. I am currently running the endmill at 27500 RPM, taking passes at 1/4" DOC and cutting at 120 ipm.
I am sure that I could push the endmill faster, but I need to perform some more testing. I use a simple method of testing my cutters. I program a zig-zag pattern with legs 2" to 4" long (depending on the material). Each leg of the zig-zag is cut at a different speed. For plywood I would probably start with 30 ipm, increasing the speed 30 ipm for each leg. That way I would end up with cuts at 30,60,90,120,150... etc. I simply watch the machine and the cuts. Once the cuts start to degrade in quality, or the machine starts to indicate that it is being over driven, I stop the test and inspect the cuts. It is usually fairly obvious what the best cut speeds are.
I hope this helps.