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QT15 getting taper - what do I do first?

kb0thn

Stainless
Joined
May 15, 2008
Location
Winona, MN, USA
So I am finally getting to the point of making parts with my QT15. I made a 0.25" long part a few weeks ago and it was good. Last Friday I started running a 2" long part and I am seeing about 0.003" taper on OD over 1.9" length. I didn't crash between those two jobs, so I am assuming the taper is caused by the previous owner / transport / etc. Machine is level.

What should I be looking at first?

Thanks
 
Need to crack the headstock bolts loose and adjust it to pull out the taper.

Chuck up on a largish bar of aluminum for the test cuts (Ø 2.5" or so) to minimize any deflection from the part when performing this check. Use a DNMG or VNMG insert to minimize tool contact on the backside of the insert. Take a cut with the machine and check for taper using a micrometer. After you determine the total taper amount and if the front of the part is large or small, mount a test indicator in the machine and put the indicator tip on the front diameter of the part relative to the direction of expected movement from the headstock.

Loosen the big bolts and then adjust taper using the "push-pull" bolts at the rear of the headstock. Move the headstock an exact known distance (I used .010") and lock it down and take another test cut. Record taper amount difference from first cut. You can then calculate the relationship between your indicator movement and taper amount over the distance. Move required distance on indicator and take another test cut. Should be really close if you did it right.

I was able to get my 10N indicated in within .0002" on diameter over 5" distance on third test cut. Done.
 
You can offcourse program a tapper to correct it but the proper way to fix it is to adjust the main spindle.
I am nut sure how it looks on a QT15 but I guess do like this.
1, take a bar around 2-3" in diameter and maybe 4-5" long and do a fine cut.
2, Measure both ends
3, put an inicator at the end of the bar.
4, loosen the spindle (Probably 4 big bolts)
5, adjust on the adjusting screw as much as it differ devided by 2
6, tighten spindlebolts and start over until you are happy with the result.

Done this two times on our ST30ATC when it was new to me and after a minor crash.

EDIT: Phil was first :)
 
First thing to do is to take the cover off and measure the allen bolts you will need to loosen. I have a QT15 and had to do this twice now. I think it takes near an 18mm allen driver. I had to order a 1/2" drive allen driver from Mcmaster before I started.
 
What dia. is your part?

1.5625" diameter on the long part, and with a short 2.225" diameter shoulder. I have jaws and everything on the machine for 2.25" diameter bar. I was planning on using that material for the test cuts.

Gotta go out there and find some big bolts, I recon.

Thanks
 
One thing assumed in this thread is that you got the machine leveled up correctly. That must be done first to insure there is no twist in the bed.
 
Sorry I did not notice that he said it was leveled. It just came to mind since I understood it to be a new machine to him.

I am pretty sure you check for twist by mounting a precision level to the turret and tramming Z and make sure the bubble stays put.

ewlsey put a video series on youtube on aligning a cnc lathe and I think the first one was on leveling.

Complete CNC Lathe Alignment - Part 1 - Leveling - YouTube
 
Managed to get the sheet metal off and expose the headstock. Which bolts do I want to loosen? I am assuming the D bolts are the bolts to actually adjust the position.

Thanks you guys!

20170427_110641_labeled.jpg
 
Nice Picture! You loosen the A bolts then of the B bolts, the top two, one is a pusher (set screw) and one is a puller. Use these to pull or push the back end of the housing in the direction you want.
 
Nice Picture! You loosen the A bolts then of the B bolts, the top two, one is a pusher (set screw) and one is a puller. Use these to pull or push the back end of the housing in the direction you want.

Any idea of the torque spec for six A bolts? Got three loose so far with the big 450 ft/lb impact. They were quite tight. Working on trying to find an impact or breaker bar or torque multiplier to fit in for the back screws. It occurs to me that I probably need to get them quite tight again once I get things adjusted.

Thanks
 
Woohoo!

I'm not pro that can do it in 3 passes. And I didn't use an indicator. But after 8 test cuts and adjustments I have it so I am about 0.0004 difference in diameter over 3". Which is good enough for what I want to do right now. Since I haven't crashed the thing yet, I'll save doing a better alignment for after that.

For reference of anyone else who finds this thread:
14mm hex bit to loosen the 6 vertical SHCS. You are going to need a breaker bar and a cheater pipe.
6mm hex on the set screw adjuster.
10mm hex on the SHCS adjuster.

Now the bad news for me is that my guy who took the door off is gone for the next week. So I have to figure out where he put the parts and how to put the sheet metal back together. Or leave it off and start diagnosing why my tool eye isn't at the right elevation.

Thanks y'all!

-Jim
 
I have not run across much twist in qt15's. they have a pretty short and rigid bed that is not prone to twisting.
when I taper a 15 I usually just loosen the headstock bolts then tighten them right back down without making any adjustments. 9 times out of ten it will be real close after that.
 
when I taper a 15 I usually just loosen the headstock bolts then tighten them right back down without making any adjustments. 9 times out of ten it will be real close after that.

That's because the jack screws were left tight. Once you loosen the bolts, it kind of relaxes back to the nominal position. I prefer to leave the jack screws loose. It makes a little more work to line it up, but if the machine crashes, I want the thing to move. If it can move, it's less likely to break.

The manual for my ancient Slant Turn 15 specifically warned not to leave the jack screws tight. I've never seen that advice in any other manual, but it makes perfect sense to me.
 
Harding takes the adjustment bracket off when they ship the machine.
in 40 years I lost a total of 4 spindles to crash. 2 of those where bars hanging out the back 2 where upper cuts to a 3jaw chuck. don't think jack screws where the deciding factor in any of them.
but your point is a good one and I agree with the premise
 
and since we are talking g crash abatement.
both the 3jaw upper cuts where done with the spindle turning counterclockwise. you hear all the time how that is just fine. I think it's all bad, your exposing your bed to upward forces they can't handle as well as downward.
both those wrecks split the -x- dovetail. one cost me 20k to fix just that, the other went to the dumpster.
 
Did you mean to say clockwise? M3? I used to work with Okumas and we ran them M3. I've seen two crashes crack the X axis box way. One also bent the spindle. In one case they sent the whole machine to Charlotte. The other one they sent the whole carriage. To be fair though, we were running a chuck about twice as big as the stock chuck. There's little you can do to stop a 24" chuck spinning 1000 RPM.

But, I still run my machines M3, and always have. M4 does seem a little safer, but M3 is much more convenient.
 
I don't do M's
I mean counterclockwise looking at the face with the tailstock at your back.
yep
everyone wants convenience
pay me now
pay me later.
 








 
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