How do you true up a CNC lathe?

[SRT Mike]

Okuma LC-40 is the machine - big sucker.

I know that it's been crashed at least once (no damage, unless it threw things out of alignment). The machine is new to me. I just turned down a piece of stock... over 5.5" it's about 1 thousandths smaller at the chuck end. Is that within normal specs? I was turning a 1.75" OD piece of 6061AL down to 1.5 (last pass was .010 DOC) so maybe there could have been some deflection causing the error?

And, the bigger problem - if I face a part, I end up with a little "teat" about 20 thousandths in diameter. The previous owner used to just put shim stock under the tools because he didnt want to have to pay to get it adjusted. In the user manual there is a process to adjust the headstock, but if .001 over 6" is normal when i turned the part, wouldn't that be throwing the alignment of the bed out? So I am thinking I need to adjust it at the turret itself? How do I do that and how do I know how much to move it? Put an indicator in a tool post and.... what? How do you figure out when you got it dead on?

And last but not least, when I just turn the spindle on and look at the chuck, sometimes it seems that it's turning slightly out of center - like it's slightly "bobbing" up and down. It may just be me thinking it is and being paranoid, but should the chuck be rotating totally true? Or is it impossible to get that? If it's out of alignment, do I just unbolt the chuck and try to true it up? I doubt the spindle shaft is out of true, because it's gotta be at least 8" in diameter (machine has a 60hp spindle, pretty heavy duty). The chuck is 12" and must weigh a ton, I am afraid of unbolting it because I have nothing to support it and I bet that sucker weighs more than Rosie O'Donnel after an all you can eat buffet!

[Adobe Machine]

Maybe what I do to check the spindle/chuck would help: I use a new 3/4" USA brand name end mill, chuck it up backwards so the collet end is facing the lathe turret ..then using a good tenths test indicator mounted 90 degrees to the chuck, measure the TIR..the USA made carbide end mill is ground to a very fine tolerance, in fact I have never found any thing as accurate..if your over .002 TIR an inch from the chuck there is a problem..actually I would not want any "wiggle" more than .0002 at one inch from the chuck..but you can calculate the total TIR over say,10 inches if your TIR at one inch is .001.

This is why I really like 6 jaw "Tru Set Chucks" that can be adjusted.

Adobe Machine (old as dirt, or older)

[Geof]

One thousandth of an inch on the diameter over 5.5 inches is not bad, especially on that diameter; that is 0.0005" on the radius. First thing to check is the machine levelled correctly; someting that size is probably going to have more than four levelling screws and it can be a devil of a job getting everything tweaked up correctly.

Also 60hp and 12" chuck implies a heavy machine, (I really need to double bold that), is it just sitting on a normal concrete slab floor around 6 to 8 inches thick? I think you are almost in the region of needing an isolated poured concrete base a couple of feet thick to get the full potential out of the machine.

Before worrying about doing anything regarding aligning the machine I think make sure it is mounted on a floor that is capable of supporting it in a stable manner. When the machine is correctly supported and levelled then start worrying about machine alignment.

[SRT Mike]

Geof,

It was a bear to get leveled! It has eleven leveling screws. It took a couple of strapping lads about 3 hours to get it right. It is just sitting on a regular concrete floor, although the floor has been down for some years, so it should be pretty stable and solid. In the machine manual, they say that a properly cured floor should be OK, or if a new floor they give foundation plans to get it perfect. I think I've gotten all I can in terms of level (used a machinists level, got it dead nuts on and made sure the weight was as evenly loaded on each leveling foot as I could). It is a big machine - I think around 25,000lbs, probably more with the many gallons of coolant, hydraulic oil and headstock oil that is in the thing, plus the toolholders (some of which weigh over 50lbs). I'm not real worried about the .001 over ~5" as much as having the turret perfectly on center. We got the machine from a shop in the same business park and he told me it cut slightly off center when he had it too, so I dont think its a level issue on that particular problem... but I'd rather not be trimming shim stock just to get the toolholders all nice and level either.

The spindle shaft (for the 1" or so that it's visible) runs straight as an arrow but the chuck does seem to very very slightly "bob" up and down. It may have been just my imagination though, combined with noticing a distinct bobbing when I had a part that may not have been centered as well as it could be.

I can get by with shims for now, but some day (soon) I will try to fix the turret issue - just have NO idea how to go about it!

[Geof]

Originally Posted by SRT Mike Geof, It was a bear to get leveled! It has eleven leveling screws. It took a couple of strapping lads about 3 hours to get it right. It is just sitting on a regular concrete floor, although the floor has been down for some years, so it should be pretty stable and solid...... I can get by with shims for now, but some day (soon) I will try to fix the turret issue - just have NO idea how to go about it!

Do you have a Forklift? A big one? And is the machine in a location that you can drive the forklift past it carrying a maximum load?

If you have three yeses to these questions put your level on the lathe ways and watch it while you drive the forklift past slowly. If it doesn't move I will concede your floor is solid enough.

On the turret alignment don't be surprised if it is simply a matter of loosening the mounting bolts, there are probably 6, 8 or 10 around a circle about 5 or 6 inches in diameter at the center of the turret, and then just bashing the turret one way or the other until it is aligned (with a plastic or lead hammer) and then tightening the bolts.

I know this sounds horribly crude but when you think about it mounting the turret just with a friction grip on bolts with a bit of clearance is a good idea. Under normal operation the friction from the bolt tension is more than enough to take the cutting load; after all the tools are only held by friction from the set screws.

And when the inevitable crash occurs you want a grip that fails without causing damage; or which minimizes damage. If you bash the turret into a spinning chuck and the turret can slip maybe 20 thou it has absorbed some of the impact in slipping. This is better than something with an absolutely solid connection. Think about automobile design with controlled crumple to absorb impacts; the same principle applies.

[SRT Mike]

Originally Posted by Geof Do you have a Forklift? A big one? And is the machine in a location that you can drive the forklift past it carrying a maximum load? If you have three yeses to these questions put your level on the lathe ways and watch it while you drive the forklift past slowly. If it doesn't move I will concede your floor is solid enough. On the turret alignment don't be surprised if it is simply a matter of loosening the mounting bolts, there are probably 6, 8 or 10 around a circle about 5 or 6 inches in diameter at the center of the turret, and then just bashing the turret one way or the other until it is aligned (with a plastic or lead hammer) and then tightening the bolts. I know this sounds horribly crude but when you think about it mounting the turret just with a friction grip on bolts with a bit of clearance is a good idea. Under normal operation the friction from the bolt tension is more than enough to take the cutting load; after all the tools are only held by friction from the set screws. And when the inevitable crash occurs you want a grip that fails without causing damage; or which minimizes damage. If you bash the turret into a spinning chuck and the turret can slip maybe 20 thou it has absorbed some of the impact in slipping. This is better than something with an absolutely solid connection. Think about automobile design with controlled crumple to absorb impacts; the same principle applies.

Dont have a big forklift, but I certainly believe the lathe could tweak a little when a heavy load went by it... I dont know if I would say the floor is the best it could be, but it is what it is The building is only 5 years old and I ain't about to jack up the floor and pour a reinforced pad for this lathe So, what I have to work with is what I have.

I'll give the turret bolt thing a shot. I guess my concern is that if I put it on tool position 1, for example, and get it lined up, and if it's not exactly on center, then the rest of the tools may still be off. I can envision spending hours trying to get it just right tapping this way and that

The manual says the maximum weight for tools is 22kg which is about 50lbs, and the OD bar holders are 2.5" diameter and it uses 1.25" turning tools (which require a 1.25" spacer). So you can imagine this is a BIIIIIG sucka! I wonder if I may need to use some sort of engine hoist to take off the weight a bit before banging on it with a lead hammer... I bet the turret weighs several hundred pounds bare, would probably require a jackhammer to move it! heh..

Thanks for the comments Geof, I appreciate it.