Tracking down cause of chatter - what is proper gib adjustment?

[NegativeNines]

I have a MicroMill2000 CNC purchased directly from Taig. As I learn how to use it and try new things, I have run to an issue with chatter which I think is abnormal.

Cutting 6061 with a 1/4" 2 flute Carbine flat end mill and ~.01-.02" DOC, 10500rpm is fine (at any feed, up to 30ipm), but once you take it to .03" or greater DOC, chatter city, it sounds like an angry banshee.

Unless I'm calculating something wrong, I got 687sfm for 10500rpm, 1/4" . UltraTool (EM mfg) says up to 1500sfm. Taig recommends 500ish sfm, but even at 6500rpm I have the same issue, it's actually worse with less RPM.

So this makes me think I have a fundamental rigidity issue.

I feel I have work piece rigidity under control, the piece is mounted a large "screwless" vise with 4" wide jaws. The 28lb vise is secured to the table by 2 clamps being held down with 1/4-20 hardware. I don't think it's moving.

The tool is being held in the appropriate ER16 collet, with the flutes brought up to just below the collet opening. With 1" long flutes there is maybe 1.125" of exposed end mill, the rest of the EM shaft being inside the head stock.

So now, in trying to investigate other rigidity issues, I have two questions.

Question 1) What is the proper gib adjustment for X and Z where you have the loosen one, tighten the other, system? I find plenty of info on how to do it, but nothing says to what specification, feel, whatever, you are supposed to adjust the gibs to? Just enough so you can't detect play with your human senses? Adjust until something binds and then back off 1/30th of a turn? What are you actually aiming for?


Question 2) I can detect the absolute slightest amount of play in my head stock. I can wiggle the male threaded portion where you would attach the collet nut and feel a very, very, tiny amount of play. But, the fact I can detect it makes me think that might be too much. Is this the case?

[900steve]

Here is the procedure I use for adjusting the Taig CNC leadscrews:
Taig Mill Setup

I actually found that most of my backlash was due to the coupler between the stepper motors and the leadscrew. I tried to minimize the gap where you can see the plastic tubes in the middle of the coupler, also, making sure the nut tightening the coupler to the leadscrew is not too tight or too lose.

regarding the play you feel in the spindle, this doesn't sound right. maybe that's something you need to bring up with Taig or wait until someone with more experience chimes in.

In 6061, i have pretty good luck running 15-20 IPM, at .02" DOC with a 1/4", 2-flute endmill, but I can't recall which pulley, maybe the 2nd or 3rd from the fastest spindle speed. I'm sure I can go faster, but I have not increased my DOC because this chipload feels and sounds good to me. Typically, with these smaller machines high feedrates and smaller DOCs are needed due to the relative lack of rigidity.

-steve

[Jeff-Birt]

If you can feel play in the spindle than you should me able to measure it too. I would start by measuring run-out. Do you have the collet properly snapped into the closing nut? If you over-tighten the closing nut you can distort it as well. Are you using any coolant? If not your likely to ruin your end mill by chip welding, especially at the high speeds your running the spindle.

In general I would recommend slowing the spindle way down and starting over. At high speeds the spindle motor is producing far less torque and the belt has far less capture on the spindle pulley. You could be intermittently slipping the belt which would cause all sorts of issues. Keep in mind that calculating feeds/speeds in not an exact science. Machine rigidity, available power, and bit geometry all play a huge factor.

Take a look at: [nomedia="http://www.youtube.com/watch?v=RKludUU2f6c"]YouTube - ‪30 IPM in .375 AL.AVI‬‏[/nomedia] as I recall the spindle was about 5000 RPM.

The gib adjustment is done by feel. First take the stepper motors off so you can turn the screws by hand. You need to adjust the gibs until you start feeling a slight amount of drag. At this point you should also not feel any 'wiggle' to the table. Tightening them past this point will not help.

[NegativeNines]

Here is the procedure I use for adjusting the Taig CNC leadscrews:
Taig Mill Setup

I actually found that most of my backlash was due to the coupler between the stepper motors and the leadscrew. I tried to minimize the gap where you can see the plastic tubes in the middle of the coupler, also, making sure the nut tightening the coupler to the leadscrew is not too tight or too lose.

regarding the play you feel in the spindle, this doesn't sound right. maybe that's something you need to bring up with Taig or wait until someone with more experience chimes in.

In 6061, i have pretty good luck running 15-20 IPM, at .02" DOC with a 1/4", 2-flute endmill, but I can't recall which pulley, maybe the 2nd or 3rd from the fastest spindle speed. I'm sure I can go faster, but I have not increased my DOC because this chipload feels and sounds good to me. Typically, with these smaller machines high feedrates and smaller DOCs are needed due to the relative lack of rigidity.

-steve

Thank you Steve, I will take another look at the stepper motor couplings, since I haven't really inspected this since I assembled the machine.

[NegativeNines]

If you can feel play in the spindle than you should me able to measure it too. I would start by measuring run-out. Do you have the collet properly snapped into the closing nut? If you over-tighten the closing nut you can distort it as well. Are you using any coolant? If not your likely to ruin your end mill by chip welding, especially at the high speeds your running the spindle.

I will have to measure run-out then. I have admittedly never done it before, so I'll do some searching before I bother asking the exact procedure.

I am running dry cuts on aluminium for the most part, sometimes using alcohol as a coolant. I notice I get a good amount of heat in my end mill, collet, and collet nut, but not in the work piece. Is this an indication of something other than me probably needing coolant?

In general I would recommend slowing the spindle way down and starting over. At high speeds the spindle motor is producing far less torque and the belt has far less capture on the spindle pulley. You could be intermittently slipping the belt which would cause all sorts of issues. Keep in mind that calculating feeds/speeds in not an exact science. Machine rigidity, available power, and bit geometry all play a huge factor.

Take a look at: as I recall the spindle was about 5000 RPM.

The gib adjustment is done by feel. First take the stepper motors off so you can turn the screws by hand. You need to adjust the gibs until you start feeling a slight amount of drag. At this point you should also not feel any 'wiggle' to the table. Tightening them past this point will not help.

Thank you, more to consider.

[NegativeNines]

So I measured run out by putting a ball end tip if a dial indicator on the exposed shank of a 1/4 end mill. I measured .0008-.0010" run out while manually spinning the spindle by the pulley on top. I could also measured .0005" of deflection just by pushing/pulling the spindle pulley side to side with light torque.

Are these numbers high? Within acceptable limits? A possible cause of chattering?