Will this work? Workaround for CNC lathe turret misalignment.

[Job Shopper TN]

Hey folks. I need to bounce an idea off of some more experienced maestros. First, a little back-story:

Our shop has two slant-bed CNC lathes, both Haas, an SL-20 and SL-30 Big Bore. Both are of early 2000's vintage. The SL-20 has a bolt-on style turret, the SL-30 has a VDI40 turret. Neither have live tooling or Y axis.

We constantly have problems with these machines when using drills or other similar tools, in particular the SL-30. As I'm sure by now you can guess, the problem is alignment with the spindle centerline.

Only a few weeks ago, our maintenance man spent a day to clock the SL-30 turret in line. I double-checked him, he had every hole on the turret at no more than .002 TIR, mostly .001. Well, here we are, fixing to run a big production job, and it's been moved already. The couple of bores I could check were out .008 - per side, in what would be Y. Worse by the time you add the tool holder, ER chuck, and the tool. With some variation depending on clamping the tool, I got up to .012 runout on the drill - PER SIDE! If that were in a mill, you'd be into interpolation territory!

Pretty bad! The upside is, we can move the drilling operation to the mill, where the part is headed anyway after turning, and it turns out said drill can run a heck of a lot faster when you aren't limited to 2000 RPM...

It appears evident to me that simply re-aligning the machine won't do, as the least little thing would appear to move it. I'm kicking around a sort of workaround for this. At this point I would add, standard operating procedure for us when putting a drill in the machine is to indicate it to center. I would love to just be able to push F2 and be comfortable with it - but it just isn't so.

My idea is similar to a four-jaw chuck concept. Since the tool holder won't repeat, it needs to be adjustable.

So - I'm thinking, take two certain tool holders/blocks and bore them to have .020 or so clearance on a 1" straight shank (so, bore to 1.02" I.D.). Then add in a third pair of set screws. The holders we have have set screws on the front (X-) and top sides (Y-?). Doesn't do a dadgum bit of good when your drills are always low! So add in a third pair of set screws from the bottom.

My thinking is - pushing the tool in, and aligning the flat, with the set screws from the X- side should align the tool straight at least in the X axis, perhaps also in the Y axis (straight, but not concentric). Then, the top and bottom screws allow for adjustment of "Y", potentially allowing the tool to be indicated - as our owner says, mortus testes... dead nuts!

I'll add a final observation. As our SL-20 has a bolt-on turret, it already has a pair of set screws on both Y sides of the block. All it needs is the clearance.

I know it probably sounds horrifying to have to indicate even a simple drill, and I wish there was another way. I'm open to suggestions on any front (other than "buy a better machine", not in the budget, wish it was!), whether it deals with my concept or not. Have at it!

 

[dstryr]

There are tool holders out there with ER collets that are adjustable for true center on lathes. I have like 6 of these for my used Doosan because someone before me crashed it and I could never drill with carbide drills without it.


Dial-Ables - Home

 

[Comatose]

Wouldn't it be a better use of time to figure out why your turret moves by .008 in a couple weeks? Do you have a locating bore that's been beaten oversized? Busted bearings? Are you missing pins? Are the bolts shot? Is your maintenance guy not torquing it down enough? I don't know your turrets, but somewhere there's a root cause.

Even if you indicate in all your drills, what's to stop it moving on you once the job is up and running?

 

[D.D.Machine]

first find out what and why its going out of adjustment ... could be turret, the turret wedge or even the head stock ..
after you get it as close as you can then use screw machine tooling to dial the drills in so there is NO run out.... Put a indicator on the face of the chuck and then line up at the base of the drill and you can move the screw machine holders around to get zero run out..

the only time this will work is if the turret is only rotated out of adjustment ,, if the wedge or head stock is out it will not help.

 

[Dan from Oakland]

If you don't or can't spend the time to fix the misalignment, there are literally tons of old turret late tooling out there and the use of adjustable drill holders was pretty much standard operating procedure. Most of these used a split bushing to grab tool shanks, but there are some out there with collet noses. Smaller sizes were also pretty standard on Hardinge DV-59 2nd op machines, chuckers etc. Just an idea to consider if ya want to go that route. Here is an e-bay link to what I'm referring to.
Used B & S 1" Tool Holder USA TURRET LATHE TOOL HOLDER 1" shank *1423* | eBay

 

[Ox]

I agree with the guys above - you need to figger out why it moves so freely!

Even if you dial in your tool dead nuts, in two hours you are out again. Whats the point?

I'm guessing that your guy just isn't balling down on the bolts enough? Maybe they are to spec on the trq wrench, but maybe that's just not enough? I understand that you run risk of stripping out holes maybe, but it seems to be worth the risk to me at this point?

Or maybe you take heavy interrupted cuts frequently?
Doo you know what fer jobs went through it in the last cpl weeks?
Maybe need to back off on some of those cutting parameters?


Option:

If you can get your hole spotted with the turret as is, you can likely put your drill in a Floating Reamer Holder.
I doo it regularly, and you can hold tight tols with a common twist drill that way.


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Think Snow Eh!
Ox

 

[deljr15]

is it possible that the taper pins are damaged/loose and the indexing plate is moving?

 

[Bobw]

I've got an old Wells Index, and the head kept knocking off...

After about the 3rd scrap job, finally pulled the studs....

Over years of torqueing, and most likely over torqueing, they had reached that yield point..

Torque 'em down and the head would move, torque again.. Move... Rinse repeat...

The moral of the story... Check the bolts holding the turret to the coupling. You shouldn't be
moving around like that.

 

[ewlsey]

I've seen similar issues on Haas lathes. If you run big insert drills the machines will actually push themselves out of alignment. But, this is alignment in X/Z.

Have you pulled the turret completely apart? I'll bet there is a bunch of crud in the curvic that prevents it from fully clamping. Does it hold size on OD or ID turning?

You can test that. Just set up your indicator on the turret along the "y" axis and whack the turret with a dead blow hammer. If the indicator needle moves, your curvic is not fully engaged.

 

[Ox]

I've seen similar issues on Haas lathes. If you run big insert drills the machines will actually push themselves out of alignment. But, this is alignment in X/Z.

Have you pulled the turret completely apart? I'll bet there is a bunch of crud in the curvic that prevents it from fully clamping. Does it hold size on OD or ID turning?

You can test that. Just set up your indicator on the turret along the "y" axis and whack the turret with a dead blow hammer. If the indicator needle moves, your curvic is not fully engaged.

He mentioned that they indicated every (most?) stations and were all good. If it was just gunk, I wouldn't think that they would get all good results, and then get all bad results a week later?




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Think Snow Eh!
Ox

 

[Gobo]

Another vote for finding out WHY it is moving. Do you have a swing crew that just is not fessing up to unintentional impacts? Something I have seen done once before is make a drill bushing with the bore intentionally off center by 10 or 15 thou. Then just rotate the drill bushing in the turret and move your X axis until you are on center. Just be aware that the set screws holding the bushing in your turret will probably not be sitting on a flat on your bushing. It works well for small drills. Never tried it for something big.

 

[Job Shopper TN]

First - WOW. This is why I come to Practical Machinist! Thank you all for your input. I'll address everything I can thus far. I'm amazed!

On squaring the headstock:

I never realized how much that may be biting us in the rear until now. Yes - the further away from the headstock you move, the further off-center you get... as soon as the machine gets an opening, hopefully in a couple of days, I will see how straight it is. As you all have said, I wouldn't be surprised if it's out. We are... lacking, in thorough preventative maintenance and checks like that.

I will report back when I get this done. I've read about doing it, so it should be simple enough to check. Fixing it, well, we'll cross that canyon when we drive up to it. Ha!

On the turret moving:

Good questions all-around. As far as I've been able to research, Haas lathes do not have any taper pins for alignment. Only the cap screws, which all have nominal bolt clearance. The former boss was here about a year ago and told me how much he wanted to put a couple of dowel pins in the turret to fix it, but... I guess that opens you up to possibly more expensive "crunches".

But, when the bolts tightened, the turret does not move in any way. In fact, even with all two-dozen-ish screws snugged, the turret won't move from a hammer blow. As far as torque, well, basically they are as tight as a man can get them with a normal hex key. Now, I say it won't move - from a hammer blow is the key... The leverage on a boring bar or turning tool in a heavy cut I'm sure would apply a much different force, unfortunately the right kind to rotate the turret.

As far as why, I really am not sure how it could've happened. I do have an idea, I believe after we had the turret lined up, we ran a large job, a piece of 12" A2. Did a lot of heavy cutting, up to 100% spindle load on the machine... that by itself could have done us in.

I will note, though, that we have not run any jobs with interrupted cuts.

All great information! I'm not the boss of the place, in fact right now I'm the programmer, but I have passed this info to him. It's a situation we certainly need to correct... I'll talk to him tomorrow about how quick I can check some things out on the machine.

Lastly, to dstry - about how much do those tools run, say an ER32 chuck? I could not find pricing on their website. Thanks for the link, I swear there's a tool for everything nowadays.

 

[Ox]

100% spindle load should not effect the turret - unless you have your tool hanging WAY out, then ... maybe... <???

As far as torque, well, basically they are as tight as a man can get them with a normal hex key.

CHEAT!
Got a 1' long pc of 3/4" EMT?
(What self respecting Maint man doesn't?)

Tighten to break/strip/round, and back off a RCCH.


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Think Snow Eh!
Ox

 

[chucker]

Before you bore out your tool holder I would try to use an adjustable drill sleeve. They are basically an eccentric sleeve that you put in your tool block then you would put your drill in it, then you can turn the sleeve and move the drill in the Y axis. check out page 8 from the link below.

http://www.innovativetoolsales.com/drilling_brochure.pdf

 

[chip_maker]

Do you do heavy O.D. roughing on these machines?

Everyone I know with a haas lathe can't keep them aligned for very long.

I think it's more of a design flaw/poorly designed turret.

As far as I know, there isn't anything that you can really do about it (other than replace the machine with something more rigid).

 

[Job Shopper TN]

Alright folks, I have some results. I took a 3" piece of aluminum and skimmed a length about 8" long, without support, using a sharp aluminum insert. Much to my surprise, it was straight as an arrow! Straighter, in fact. Averaging my measurements, it was straight within one to two tenths, cylindrical within the same. I was very surprised.

So... that isn't the issue.

I will ask our maint. guy about torqueing the screws some more, and will be doing some looking into eccentric drill bushings as has been suggested. That looks like a much better way to go! I'll have to look at Chucker's PDF tomorrow when I have a decent internet connection.

I'm envisioning holding our 1"-shank ER chucks in a round, 1.5" diameter bushing with an I.D. eccentric by about .015". The ER chuck would be secured via its own flat, set screws in the bushing... not sure about holding the bushing in the tool holder. If I put flats on it, it will index at certain points... but, I say that without looking at aforementioned PDF!

We're on the right track, folks! Awesome.

 

[Ox]

Alright folks, I have some results. I took a 3" piece of aluminum and skimmed a length about 8" long, without support, using a sharp aluminum insert. Much to my surprise, it was straight as an arrow! Straighter, in fact. Averaging my measurements, it was straight within one to two tenths, cylindrical within the same. I was very surprised.

So... that isn't the issue.

You just checked the straightness of the spindle to the Z axis rails.
That test had nothing to doo with the turret.

You mentioned about a long drill being out of square earlier?
You would need to run your indicator - mag'd to the chuck and touching the turret top plate (face and/or side) and jog in X and Z to see if you get any taper there.

Then there is the radial (Y axis?) alignment that is apparently the big issue for you.


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Think Snow Eh!
Ox

 

[EnderDRM]

"Everyone I know with a haas lathe can't keep them aligned for very long."
bingo

 

[Job Shopper TN]

You just checked the straightness of the spindle to the Z axis rails.
That test had nothing to doo with the turret.

You mentioned about a long drill being out of square earlier?
You would need to run your indicator - mag'd to the chuck and touching the turret top plate (face and/or side) and jog in X and Z to see if you get any taper there.

Then there is the radial (Y axis?) alignment that is apparently the big issue for you.


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Think Snow Eh!
Ox

I see what you mean, Ox. I guess the main thing I found is that at least my spindle isn't out of kilter with the machine, as you say. That way it don't progressively get worse the further away you get, haha. Baby steps...

Now, what you mention about the turret being square, that is interesting. I will check that in the morning. Ideally, across the front face of the turret, the thing really out to be dead straight, no indicator movement, when jogging X... and the same in Z, on the O.D. of the turret.

I'll take a look tomorrow at that. I'll also, just for the sake of diligence, try to run an indicator in and out of the turret bore itself to check for Z straightness... As old as the machine is, it may be some of these toolholders, or perhaps the bores themselves, could easily be bellmouthed, or just plain worn... As far as I am aware, all of the toolholders came with the machine when it was bought new!

 

[ewlsey]

I see what you mean, Ox. I guess the main thing I found is that at least my spindle isn't out of kilter with the machine, as you say. That way it don't progressively get worse the further away you get, haha. Baby steps...

If the turret is out of square, a longer tool will runout much more than a short tool. But, the runout will be in the X, not the Y.