End mill pull out with PDB.

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01-23-2013, 07:24 PM
btu44

End mill pull out with PDB.

I have read on this forum that other people were also having pull out issues so here's how I fixed it.

Before I installed Tormach's PDB, I was able to remove aluminum at a rate of about 3 cubic inches with a little bit of tolerance for chatter. This was using a 1/2" 3 flute aluminum rougher.
After installing the PDB, tool pull out got much worse. I was only able to remove aluminum at about 1.7 ci and had no tolerance for chatter. So any time saved with quicker tool changes was more than lost in lower MRR.

How I fixed tool pull out was installing a LYNDEX R8 collet. Unfortunately it took alot of fitting to get it right. When I first installed the new R8 collet, I wiped prusian blue on the taper of the collet. It showed that only a very small area of the taper was contacting the spindle. So using a 3M deburring wheel and a diamond lap, I was able to get 100% taper contact. This took most of the day and a least 30 check and recheck with the blueing. But after all that hand work the run out was .008" TIR 6" from the collet. So after another half day of hitting the high spot of the collet, I got it to about .0005" of TIR at 6".

Now I can use full spindle power and am back to a MRR of 3.1 ci and have good tolerance for chatter with out any tool pull out. I even did a worst case test were the cut was so deep at almost completely stalled the spindle...still no pull out. I'm not sure if it's the harder material of the LYDEX collet or the 100% taper contact that has fixed the problem but it was definately worth the effort.

I would be interested to hear how other peoples collets fit. Prusian blue can be purchased at auto parts stores but dark lip stick can used instead. It doesn't 'read' as easy but works OK. I think it is the reason some people have this problem and others don't.

Barry
01-24-2013, 02:41 PM
neilw20

Often, something softer can grip better better as it conforms/deforms to the surface.
I had a hand made mild steel taper in an old machine and it gripped exceptionally well, but I had to careful not to damage it.
Another method to rough things up microscopically is to get a piece of carbide, a 12v power pack with a capacitor across the output and spark many times on the hardened surface. Stronger sparks? Larger value capacitor. Put a 20 or 30W bulb in series with supply so as not to damage with a full short. Put the capacitor after the bulb.
This also works very well on lathe chuck jaws when needing to hold hard material, that would normally slip with heavy cutting.
01-25-2013, 06:57 PM
mike sr1

Quote:

Originally Posted by neilw20

Often, something softer can grip better better as it conforms/deforms to the surface.
I had a hand made mild steel taper in an old machine and it gripped exceptionally well, but I had to careful not to damage it.
Another method to rough things up microscopically is to get a piece of carbide, a 12v power pack with a capacitor across the output and spark many times on the hardened surface. Stronger sparks? Larger value capacitor. Put a 20 or 30W bulb in series with supply so as not to damage with a full short. Put the capacitor after the bulb.
This also works very well on lathe chuck jaws when needing to hold hard material, that would normally slip with heavy cutting.

You think a lot like I do Neil, that should work well.
I am thinking about a rig we used to electro etch stainless lines with in the dairy, I would think anything that would take the high polish finish down a bit would really help.
I also thing getting the collet to seat over the entire surface would help as well, I havent checked mine but having it pinch at the bottom 1/8" inch would put all the clamping pressure on the first 1/8" leaving the rest of the surface not clamped tightly and then it could wobble slightly, and if anything moves it will come loose eventually, an old machinist told me that years ago.

BTU pretty much covered this in his post and in much better detail.

It would be interesting to see if dykem on the clamped shank surface would show an uneven pattern as well.
01-26-2013, 02:42 AM
tbaker2500

Thank for the heads up btu44. I'll file it away for when I get my PDB.
01-26-2013, 10:23 PM
Spinnetti

Good stuff. I don't have hard data, but mine seem to pull out mighty easy. I tried cleaning surfaces well and scuffing the tts holder, and making the spring stack tighter, but still works out. More to try.. I have a spare TTS collet, so maybe I'll try that and see if results are any better
01-27-2013, 01:16 AM
btu44

Was messing around in the garage today and thought I'd make a vid of some test cuts. The cuts at the end are heavier than was possible before the PDB.

TTS Pull Out Test - YouTube
01-27-2013, 01:52 AM
SCzEngrgGroup

Quote:

Originally Posted by btu44

The cuts at the end are heavier than was possible before the PDB.

That makes no sense.... The PDB can't possibly enable heavier cuts, unless you were under-tightening it before. You can get the drawbar MUCH tighter manually than the PDB can.

Regards,
Ray L.
01-27-2013, 02:52 AM
btu44

Quote:

Originally Posted by HimyKabibble

That makes no sense.... The PDB can't possibly enable heavier cuts, unless you were under-tightening it before. You can get the drawbar MUCH tighter manually than the PDB can.

Regards,
Ray L.

Just like alot of things, tighter doesn't always mean more clamping pressure.
I think I've increased clamping surface area and it's why the improvement.
But all I can say is I'm not a newbie at this, I've done work that required alot of roughing on the PCNC1100 and I know how to tighten a draw bar.
01-27-2013, 03:29 AM
SCzEngrgGroup

Quote:

Originally Posted by btu44

Just like alot of things, tighter doesn't always mean more clamping pressure.
I think I've increased clamping surface area and it's why the improvement.
But all I can say is I'm not a newbie at this, I've done work that required alot of roughing on the PCNC1100 and I know how to tighten a draw bar.

Well, I gotta wonder if there are some funky collets floating around out there, as there have been a number of people having pull-out problems lately. I've been using TTS with several different machines, and several different collets for years. I've never experienced pull-out, either working manually, or with my PDB, which tightens the drawbar to 30 ft-lbs. If the collet and spindle are as they should be, tighter should be better, and a PDB should make no difference, other than convenience.

Regards,
Ray L.
01-27-2013, 07:09 AM
tbaker2500

Nice.

Quote:

Originally Posted by btu44

Was messing around in the garage today and thought I'd make a vid of some test cuts. The cuts at the end are heavier than was possible before the PDB.

You mean heavier than possible before you got the collet mating fully?
01-27-2013, 11:05 PM
btu44

1 Attachment(s)

Cool, glad you like it.
Yes...the first cuts were my tried and true roughing parameters before the new collet. It left a little in reserve for full width cutting that can happen in a profile and some chatter. The last cuts would have pulled out badly before fitting the new collet.

Here's something some of you may find interesting. In the picture you can see were the tool was deflecting till it started breaking though the material. I measured it with an indicator at .012". Something nice to know when leaving material for finish cuts.
01-28-2013, 05:58 AM
tbaker2500

Wow. Nice pic. Time for some stub length tooling, eh? :-)
01-28-2013, 06:49 AM
neilw20

After the finish cut, feed back across and intermittently push down firmly on the head while cutting. You will be surprised how much a column actually flexes!!
09-30-2014, 06:37 PM
popspipes

Re: End mill pull out with PDB.

I think I will get some Prussian blue today and see what I can do with my collet setup, in my opinion this is the main problem with pullout.

Quote:

Originally Posted by btu44

I have read on this forum that other people were also having pull out issues so here's how I fixed it.

Before I installed Tormach's PDB, I was able to remove aluminum at a rate of about 3 cubic inches with a little bit of tolerance for chatter. This was using a 1/2" 3 flute aluminum rougher.
After installing the PDB, tool pull out got much worse. I was only able to remove aluminum at about 1.7 ci and had no tolerance for chatter. So any time saved with quicker tool changes was more than lost in lower MRR.

How I fixed tool pull out was installing a LYNDEX R8 collet. Unfortunately it took alot of fitting to get it right. When I first installed the new R8 collet, I wiped prusian blue on the taper of the collet. It showed that only a very small area of the taper was contacting the spindle. So using a 3M deburring wheel and a diamond lap, I was able to get 100% taper contact. This took most of the day and a least 30 check and recheck with the blueing. But after all that hand work the run out was .008" TIR 6" from the collet. So after another half day of hitting the high spot of the collet, I got it to about .0005" of TIR at 6".

Now I can use full spindle power and am back to a MRR of 3.1 ci and have good tolerance for chatter with out any tool pull out. I even did a worst case test were the cut was so deep at almost completely stalled the spindle...still no pull out. I'm not sure if it's the harder material of the LYDEX collet or the 100% taper contact that has fixed the problem but it was definately worth the effort.

I would be interested to hear how other peoples collets fit. Prusian blue can be purchased at auto parts stores but dark lip stick can used instead. It doesn't 'read' as easy but works OK. I think it is the reason some people have this problem and others don't.

Barry
10-01-2014, 07:02 PM
BAMCNC.COM

Re: End mill pull out with PDB.

Here is what I did as a test.

https://www.youtube.com/watch?v=z5hM7ORrGOg

Then afterwards I ran a 1/2" 3FL ZrN Helical Brand endmill into 7075 Aluminum at 1" DOC and .100" step over at I think 4000rpm (well, started that high) and 18ipm, not sure on the MRR of that, but I stopped it, as the load meter pegged - No Pull out. Editing video for it today, should be on YouTube tonight.
10-01-2014, 07:28 PM
SCzEngrgGroup

Re: End mill pull out with PDB.

Quote:

Originally Posted by BAMCNC.COM

I ran a 1/2" 3FL ZrN Helical Brand endmill into 7075 Aluminum at 1" DOC and .100" step over at I think 4000rpm (well, started that high) and 18ipm, not sure on the MRR of that, but I stopped it, as the load meter pegged - No Pull out.

Odd, because that's an MRR of only 1.8 cu. in./min. The machine is capable of nearly twice that.

Regards,
Ray L.
10-01-2014, 08:07 PM
BAMCNC.COM

Re: End mill pull out with PDB.

I didn't feel like looking up the torque curve, and am sure I had too high of an RPM. I do know that I broke the e-stop off while doing it too. I probably chickened out as I'm use to machining Titanium only.