Besides the electrical problems I’ve been having this weekend I’ve been trying to cut my first real things from Aluminum. I did a rough cut a long time ago, but now I need to actually mill some things.
I made these 4 holes with a 3mm bit and they came out pretty well, nice and shiny on the insides there and the machine sounded good. So I moved on to this larger inner profile you see in the center, all went well for a while then the bit broke.
I tried again later in the day with reduced DOC and feed rate, and the same exact thing happened in the same spot. I noticed that this is where the gcode starts raising and lowering the bit to create triangular tabs.
This made me think that perhaps I have a spindle alignment problem, since raising the bit shouldn’t really cause an issue like this. Sure enough there’s a little bit of light between my square and the bit.
I get out the measure and it appears that I have about 0.003" off in about a half inch of travel in both the X and Y directions.
Any idea how this came about? Or how to fix it? I’m betting this is causing my issue, as the bit rises for the tab it bites into the side of the wall of the cut and breaks the bit.
I hate triangular tabs in aluminum (at least with a single flute endmill). Ever since I switched to flat tabs I have had far less issues.
The angle in x is probably a result of the combination of the eccentric nuts, and other tolerances. A sag in Y is likely to to spindle sag. It should certainly be minimized if possible. It just takes tweaking and time. Maybe some shim stock wedged in the right locations.
I have some shim washers I can try and insert in some strategic locations I guess.
Just thinking about you Ben, saw this post. That’s kind of crazy excessive Left to Right. Let me think on this one.
You jumped in with Eric and I right at first. You have the better spindle clamps, but think there is more adjustment in your X/Z than what is available in the current cut.
Front to back, some is expected, we can only work so much magic with Al. 
reason I always tell people to not go over the 800w. But that left to right is too much.
Also notice your going off one spot on that chopped up MDF, not a great reference I believe. Throw that Al. sheet in there and reference off it (if it’s a full sheet), or reference off the X axis. MDF swells and bends as time goes by, and the smaller the width, longer run, the worse things can get.
All my machines are sitting on a full 4x4 sheet, uncut.
Reference off your material. That should help. Guess your using something of my F&Ss. Do recall brother cutting metal ain’t like cutting wood. Anyone can cut wood… metal takes getting intimate with a machine, from a 2 ton mill to a desktop thing that shouldn’t exist, both will do it with class but not till after a few bruises and cuts… takes a few endmills. Which…
Brings me to the reason I was thinking about you. I’ll post on your controller post.
I’m going to try loosening my spindle clamps tonight and see if I can get rid of that X offset.
I’ll try and figure out if I can mount my dial indicator off of the X axis somehow in such a way as I can actually measure against the bit…Not sure its going to be that straight forward.
Agreed that alu is definitely a different beast for sure. Figured I should probably spend some more time truing my machine as I’ve had a number of crashes lately that probably sent things out of whack anyway.
The spindle clamps you have should make it close to impossible for it to be out of square with the Z C-bean but absolutely worth checking.
Hmm so if not them then I guess adjust the eccentric nuts to modify the x z alignment then?
Ok so before taking the machine apart my wife very right suggested that I measure everything again.
Turns out this is all just a bad collet! The spindle runout on my 1/4" collet is close to 0.007", this completely explains the 0.003" variation as I move up and down the length of the stickout of the bit.
I switched to a different brand of collet that I had for 1/8" bits and measured again, this time 0.002" runout.
So it appears I just have rubbish collets! Anyone got any suggestions on a source for a good 1/4", 1/8" and 3mm, 4mm and 5mm collets?
Anyone tried the precise collets ones? http://www.precisebits.com/products/equipment/er11_collets.asp?tsPT=!!!ER!!!COLLET!!!ER11!!!PG!!!
@Eclsnowman you said you use square tabs? What height and width are you using? Also does the really slow plunge (5) into aluminum not give anyone else the jitters?
I use 4.00mm wide x 0.8mm high tabs.
Hsmworks in solidworks which is what I use doesn’t do automatic tab generation. This means creating tabs is not super easy, but you get a lot of control by manually generating them via profile sketches.
Thanks man will give that a go. The 2mm ones I jus dd were a bit beefy 
