Graziano spindle issues

My Graziano SAG14 is driving me crazy with an issue when doing heavier cuts and mostly when parting off a part. I can't remember it having this in the past but I haven't been able to use it for the past couple of years due to moving, renovating etc. Maybe it got worse over time but I can't remember.

The problem I have is that I get a lot of chatter during heavier cuts, during parting I can't seem to get a straight cut after facing. The face is always concave or convex for 0.5-1mm (around 1/32"). There is no real pattern that I can find that causes it to go either way. During the cut it starts making a lot of noise, but I can't really pinpoint it to the bearings, just overall rattling/knocking. If I continue cutting, usually the tool won't cut and the force will move the part in the chuck, offsetting it with more damage as a result. If I do light cuts, nothing is wrong, surface finish is great. Also, the tool post rotates due to the high forces involved.

The tool used to part off is an Iscar with GTN insert, 3mm wide. 280-400RPM, 0.03mm/rev. Any higher feed and it will crash straight away. Parting diameter is 80mm. Material is C45 (AISI 1045).

I've checked quite a few things but it's looking like I need new spindle bearings which is pretty expensive (yes, they are available and I have a quote). But before calling it, I want to check if there's something I might have missed?

I did the following test: I turned a test piece, Ø50x250 (Ø2"x10") and checked parallelism. I measured 0.08mm which is somewhat higher but can be caused by the relative long stickout and some chatter that I had. It wouldn't explain the concave or convex surfaces that I had. Next I put an indicator on the end of the test piece and tried to lift it up. I can easily, without using much force, lift it 0.1mm (0.004") which seems like a bit too much. The force required to bend the shaft like that would be around 126kg (270lbs). That's not the force I'm exerting with my hand.
When I do the same test but measure between the headstock/bearing and chuck I measure 0,01mm. This is after re-tightening the bearings. I re-tightened them a bit and they do not warm up at 1500RPM.

I already tightened up all gibs. That doesn't seem to have an effect. I tightened the nut on the tool post but it's righthand thread so any force due to cutting or facing will easily loosen this. I'm not sure if there's something wrong there, maybe a conversion that wasn't done properly? There is no locking provision between the washer on the top and the stud. So it untightens by itself rather easily.

My idea is that the following is happening: during parting the spindle is lifted up due to the cutting force. The force is not enough to cut the material and the tool starts to surf across the surface, then when it finally grabs again, the forces are so high it rotates the toolpost. I tried measuring if any lift was happening during cutting by placing a indicator on top of the OD, but I can't really get a good measurement. The needle jumps around too much to make a real reading.

I tried another chuck because I don't like how it's slipping/moving in the chuck, but the results are equal. Strange fact is that when I measure with the mag base on the chuck and the indicator on the part, I get quite a bit of movement as well. I tried to measure between the spindle and the chuck but I can't find any movement. It's not moving on the D1-5 camlock from what I can measure. Maybe it's the chuck?

Any thoughts? Are my chucks worn or how can I check or rule-out the bearings? What about the toolpost connection, anyone had issues with that before? What about the stickout of the test piece? I figure it should be able to turn this without that much chatter but I couldn't. Last cut was 0.25mm DOC (0.01") 0.06mm/rev (0.0024"/rev) and it was still chattering, tried several inserts but that didn't make a difference.

I have a non locking turret toolpost. You could try tightening it more with some sort of lever to rule that out as I've had mine move. Odd though it might sound is there any way you could fit a test bar in the opposite end of the spindle and look for looseness there?

It's also possible that both chucks have worn slides.

Other than that it sounds like bearings.

How expensive are replacements?

volzuki said:

Strange fact is that when I measure with the mag base on the chuck and the indicator on the part, I get quite a bit of movement as well. I tried to measure between the spindle and the chuck but I can't find any movement. It's not moving on the D1-5 camlock from what I can measure. Maybe it's the chuck?

Click to expand...

I would look into this a little more. It kind of sounds like there may be some "bell mouthing" of your chuck jaws. I recently had this issue with one of my chucks. With a part chucked I could slide a .004 - .005 feeler gauge about half the depth of the jaws between the part and the jaws. I re-ground the jaws and that chuck works fine now.

As expensive as those Gamet spindle bearings are, I would investigate every possibility before changing bearings (which it sounds like you're doing). It would be a shame to replace the bearings and still have the same problem.

Ted

On the toolpost rotating and getting concave/convex cuts, would be a natural expectation - and what I've experienced.

In the situation here, I've used spacers under the toolposts so you can swap quick change holders between 3 lathes, without need for height adjustment, but found those 2 lathes with spacers would sometimes rotate under load, no matter how tight, while the direct mount on the compound was ok.

You don't say what system you use, if your toolpost has provision for dowelling, I'd probably be looking at doing that.

I've heard stories of the t-slot in the compound being pulled up resulting in the toolpost only making contact near the bolt. So there's less total contact area, and it's a smaller diameter, so the toolpost is easier to rotate.

I'd also be looking at chuck jaw contact on the bar. Maybe some thin shims at the nose to even out the contact. And, I'd be wondering how hard that piece of 1045 is.

Can you tell us the spindle bearing arrangement of the lathe and also if they get warm at all when run at higher speeds?

Concur they a bell mouthed chuck could present symptoms so if you have another or a 4-jaw try that. The toolpost/compound relationship is also a good point. Blue up one or the other and make sure they’re making good contact. I’m closing in on a fight with chatter on my toolmex TUM-35D1 lathe and in all my tests including this with chatter I haven’t rotated the toolpost yet. But I did make sure there was good contact and the t-nut wasn’t proud of the compound regardless.

Instead of checking for deflection at the end of your test piece, check it right at the chuck or spindle with the indicator base mounted on the HS, not bed or compound etc. Prying up on the spindle should result in near zero radial deflection, a couple tenths. You can measure for axial deflection by pushing on the spindle with the TS and then pulling with the TS or prying with a bar between HS and spindle flange. Again a couple tenths is all that you’d expect. Any more and you need adjustment.

Finally re: your facing cut. I’ve noticed my saddle will move under chatter so keep those issues separate. A facing cut as a test for HS alignment should be done with the carriage locked and not as a parting cut, but with a rigid sharp facing tool.

A quick note:
I own a Harrison 1330S CNC lathe.
It needed new spindle bearings .
Replacement Gamet bearings are costly.
Got quotes north of $2500+ for the pair.

Found these guys and literally the cost was half...
Good service and the bearings were real ,sealed in the original containers form Gamet UK....
If you need new bearings might give them a shout to see if they can give you a better price.

Quality Bearings Online - Deep Groove, Tapers, Precision

Cheers Ross

I have an earlier SAG 180 lathe and noticed chatter when parting off and poor finish on light cuts. Also I noticed oil squirting out from under the compound base where it attaches to the cross slide. Years of poor cleaning and dirt getting under the compound base, not to mention a good dose of corrosion in the recessed section of the base. I had to surface grind the cross slide, machine the compound base and scrape the two together for a good fit with the aid of a round 150mm cast iron flat.

It's made a big difference to the lathe performance, parting off is easy and light cuts are easy to do.

Also dealing direct with Gamet Bearings is noticeable cheaper than buying as a spare part, in the case of a Colchester Master 2500, the price was half that of Machinery 600 spares even though Gamet is part of them.

Mentioned here before but I would check out the chuck first
Or use your independent 4-jaw for testing

Peter