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CNC machining of aluminum

01-24-2011, 03:39 PM
This is the first part in a dremel mount I'm making. Drew it out in CAD and created the cut paths then cut it with the router on my CNC table. The width was supposed to be 1.5" and the cut width turned out to be 1.492 I think that is due to spindle slop but really isn't too bad. I'll just program that in next time.
Cut was two operations, the center bore was first then the outer profile. Took .025" depth cuts for each pass. Got a little chatter on the narrow flat profile, I didn't program in holding tabs and it shifted on the last pass.


01-24-2011, 04:07 PM
Dan, really nice, and the tolerance isn't bad at all, forgot what size router is on your CNC and what Bit did you use

01-24-2011, 04:24 PM
I have a RotoZip1 and used a three flute 1/4" center cut end mill (carbide)

01-25-2011, 03:16 AM
a trick you can use for aluminum is to use a coated high helix flute to eject the chips... .004 per side undercut isnt bad, your probably getting it from tool deflection or backlash in your machine, or a combination of both.... generally in a cnc mill you take a rough pass, then a small finish pass to cut out the taper left from tool deflection and to get a nice finish...

in a cnc mill you use a diameter offset to adjust size, i'm not familiar with a cnc plasma/router, i think its called kerf, not sure though.

are you using any air on the cutter? carbide you either flood it, or use only air..

heres an aggressive helix endmill MSC Item Detail (http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=6261890&PMT4NO=101495439)

i'm sure that rotozip runs at real high rpms, you have any idea what rpms your running?

01-25-2011, 08:51 AM
That cutter you linked to is just about what I'm using. I have a motor speed control on the rotozip but at the lower speeds it seemed to bog down a bit. I found the best results at full speed which is probably in the 20000rpm range. I was using air to cool the bit.
Knowing how much deflection I'm getting, I can compensate for that in the CAD program and should be able to get nearly dead on. I also noticed I'm getting chatter on the Y travel. I think I need to change that lead screw. If you look closely at the narrow ends of the piece you can see the chatter which matches the thread cut on the lead screw exactly. That was a home made lead screw out of threaded rod, I'm going to replace it with 3 start 5 TPI acme screw. Can't justify the cost of a ball screw.

01-25-2011, 10:18 AM
ball screws can get expensive... you should be able to find some nice acme threaded rod.

what kind of feedrate you runnning?

01-25-2011, 10:43 AM
This two pieces of AL that I made, the one on the left was made on the CNC table, the one on the right was made by hand. The holes never lined up on the right one, the left one works great! I also used a Rotozip. On my Rotozip I can vary the speed from 15,000, 20,000, 25,000, and 30,000. The slowest speed worked the best. I though that 15,000 was way to fast, I hooked up an auto transformer up to it to slow it down, but on such a small motor the horse power went way down, and I stalled out the Rotozip.


01-25-2011, 12:01 PM
Feed rate was set to about 6" per minute. Plunge rate set to 4"pm

Kel Fab Creations
01-25-2011, 01:22 PM
Looks good! I wouldn't think you'd be able to cut anything other than wood that nice on a router table. Seems like you'd need everything more solid, heavy, and tight as on an actual mill. Seeing this makes me wanna set mine up for routing too but I do have a haas vf1 and soon to come vf4 at my disposal at work so ill probably just stick with those. I'm impressed with what you've done with router though.