Where to next?

For those who haven't seen it (was posted in another thread), here is an example of my "chatter".

This is about .62 axial, .02-.025 radial and 45IPM @ 2500 RPM ... with a 1/2" 3FL YG-1 alu-power end mill. The same spec 3/8" end mill does the same thing. This will even chatter on a finish cut if it is run too fast.

Apples to apples (same cut parameters above), I can rough 65 IPM with conventional cuts with little to no chatter. General vibration starts to limit me at that point.

Running across the fixed jaw area of the vise (X+) is where the sound is most pronounced. Difficult to get the visual, so crank the sound.
 
Yikes. That ballscrew isn't looking very well fitted from the factory. Still a lot better than mine, but you'd think they could do a little better.

Did the aluminum parts run without the column shims come out any better?
 
macardoso said:
Yikes. That ballscrew isn't looking very well fitted from the factory. Still a lot better than mine, but you'd think they could do a little better.
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Yes, it is embarrassing. On top of that ... Pro-Cut CNC put it together with the screws bent to hell. I need to take them back out and maybe put some more time into straightening, but it just seems like a waste of time at this point. I saw @shooter123456 got a nice set of ballscrews/ballnuts in ... may have to upgrade to those!

What I have is doing the job though, so maybe not.

Did the aluminum parts run without the column shims come out any better?
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I only had time to get it back together and X Y axes dialed back in.

Column/head tram was checked and I also adjusted the Z gib as it was a little too tight. I was only getting indicator movement every .002 or so while jogging in .001 increments. Sizes were coming out okay, so I left it alone for a bit. Pretty sure the chip cover is staying off now for easy access to the bottom Z gib screw. I put a zeroed indicator on the spindle and backed the Z gib up until there was a smidge of nod movement, about 1/2 to 3/4 turn or so. Then I locked it down back at zero. I must have overtightened it when troubleshooting the chatter last time.

Next, most likely tonight I will get the column shims out, clean the surfaces, lock it back down and run some sacrificial aluminum to see what happens.
 
bakrch said:
I saw @shooter123456 got a nice set of ballscrews/ballnuts in ... may have to upgrade to those!
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I saw those and boy did they look nice. Quite pricy tho. Perhaps on my next CNC build :)

bakrch said:
Next, most likely tonight I will get the column shims out, clean the surfaces, lock it back down and run some sacrificial aluminum to see what happens.
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Let us know how it goes.
 
macardoso said:
I saw those and boy did they look nice. Quite pricy tho. Perhaps on my next CNC build :)
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For sure, that is my thought on the matter as well.

Too bad I didn't get the original parts for the Pm-25, wouldn't mind converting it back to manual after my next build.

Let us know how it goes.
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Will do. Based on what I have laying around, cuts will be something like .31 axial, .04 radial, 60IPM 2500 RPM with the 3/8" end mill. I will take videos with the shims in and out, same cut parameters.
 
bakrch said:
For sure, that is my thought on the matter as well.

Too bad I didn't get the original parts for the Pm-25, wouldn't mind converting it back to manual after my next build.



Will do. Based on what I have laying around, cuts will be something like .31 axial, .04 radial, 60IPM 2500 RPM with the 3/8" end mill. I will take videos with the shims in and out, same cut parameters.
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My old ones may fit your machine. If you are interested, we can talk about rehoming them.
 
bakrch said:
Nothing was loose, or even close to coming loose at all ... which surprised me. All that stood out was shoddy work on the double ball nuts. Here is a short (crappy quality) video that I took.


My backlash has between .002-.003 in X and Y since the day I got it, which is explained by less-than-perfect preload. Not the greatest but have been able to make decent parts using compensation. I would have liked to take them apart, but the key screws are ground too far down.
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Late response (just noticed the thread again), but those ballnuts are terrible. You've got to do something about them!

Measure the distance between the ball nuts. Then drill out the key screws with a cobalt drill and get some belleville washers from CrackMaster Carr that make up a stack just slightly longer than the nut gap.

Put the ballnut back on with the washers between them. Should just barely not line up the keyways. You then preload the nuts by compressing the springs and install new (unshagged!) keys and screws. Even if the keys waller out a bit the springs will take up the slack.

If the screw holes are too damaged during removal you can use roll pins & loctite to anchor the keys. Anything would be better than what was in the video you posted.

-R
 
shooter123456 said:
My old ones may fit your machine. If you are interested, we can talk about rehoming them.
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My machine has a production date of 5-2017. If yours is reasonably close to that I think it's worth a shot!

spumco said:
Late response (just noticed the thread again), but those ballnuts are terrible. You've got to do something about them!

Measure the distance between the ball nuts. Then drill out the key screws with a cobalt drill and get some belleville washers from CrackMaster Carr that make up a stack just slightly longer than the nut gap.

Put the ballnut back on with the washers between them. Should just barely not line up the keyways. You then preload the nuts by compressing the springs and install new (unshagged!) keys and screws. Even if the keys waller out a bit the springs will take up the slack.

If the screw holes are too damaged during removal you can use roll pins & loctite to anchor the keys. Anything would be better than what was in the video you posted.

-R
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I should just throw them in the bin!

I suppose that doesn't sound too difficult. I need to run a few parts (and test my new spindle motor), so when I am done it will come apart for some measurements.

Thanks for the help guys!
 
Finally got a few minutes to snap a video conventional milling. Everything is trammed and shimmed. Absolutely perfect.


Physically pushing/ twisting the column helps on the climb cut, so my theory is the backlash slightly bouncing the table in climb direction + floppy column(torsion) = synergistic effect of chatter. Remove or improve one of those elements and it goes away.

Also, starting with 0 chip and it ramping to full chip load(conventional) is helping stabilize it relative to starting full chip and decreasing to 0 (climb).

Time to fix with belleville washers like @spumco mentioned above to test the theory.
 
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