[dinnese]

Machine: Swiss Star SB16 (2006 Model)

Material: 3/16 RD. 17-7 S.S.

Operation: Head 1- Turning a .0393 dia. +.0000/-.0005 x .975 Long tapering up to a .125 dia. +/- .0005 dia. x 1.0 Long (Total O/A Length 2.114).

Insert: Mitsubishi DCGT 32.51MJ VP10RT (.015 Nose Rad.)

Feed and Speed: 8000 RPM at .0005 IPR

Problem: .010 to .015 Total Runout on the .0393 dia.

[SirDenisNayland]

Your insert rad is way too large for a turning of that diameter in SS (or any material if you ask me), its pushing too much rather than cutting, you want almost zero radial load and it to all be axial, at that diameter there just isn't enough material to take the load you're subjecting it to. Take it down to .004 or .002. Also try firming up your guide a bit, but if only the small diameter is running out then I would put a large wager down that its your insert that is the issue.

Cheers.

[dinnese]

Thanks alot for the advice. I'll try reducing down to a smaller nose radius in the morning. I'm just concerned about the insert chipping out or not lasting on such a large cut. ( I'm going from a .1875 dia. to a .0393 dia. in one cut due to swiss style type machining). Do you still think I'll be Ok.

[ProProcess]

Thanks alot for the advice. I'll try reducing down to a smaller nose radius in the morning. I'm just concerned about the insert chipping out or not lasting on such a large cut. ( I'm going from a .1875 dia. to a .0393 dia. in one cut due to swiss style type machining). Do you still think I'll be Ok.

The DOC is ok.
The other issue you may have is material stress.
As you turn the material away, you relieve the stress and the part goes wacky.
If that is the case, there is not much you can do except try material from a different mill.
Good luck.

[SirDenisNayland]

Thanks alot for the advice. I'll try reducing down to a smaller nose radius in the morning. I'm just concerned about the insert chipping out or not lasting on such a large cut. ( I'm going from a .1875 dia. to a .0393 dia. in one cut due to swiss style type machining). Do you still think I'll be Ok.

Yes DOC is fine, you're only about .06, I've pushed similar inserts (that is the size and type, not brand, chipbreaker or coating) over .1 without issue and at higher ipr as well. Just make sure your tool is well centered and I don't think you should have any issue at all, unless like proprocess mentioned you're running into material stress issuesn

[dinnese]

Re-Programmed to compensate for a .004 Nose radius. Still have .010 to .012 runout on the .0393 dia.

[CitizenBrian]

Try lower rpm's. 8000 at that length could be too much.

[SirDenisNayland]

Try lower rpm's. 8000 at that length could be too much.

This could be a possibility, but at that diameter hes only doing 83sfm.. granted I've done less and typically don't push my machines past 5000 just because of spindle wind up and down, which leads to time loss in some cases, but is only a real concern for me due to my production necessities.

Where exactly does the runout start? right at the beginning of the .0393" diameter, or somewhere along the taper portion?

Could be even with the smaller rad that the tool just isnt sharp enough and you're still getting unwanted pressure.

Problems like these are wonderful, so many variables that could lead to the issue (chair)

Best advice I can give is to make one change at a time and measure the results, don't go making multiple changes at once because you won't know what exactly made the difference.

[SirDenisNayland]

also this just popped into my head and is something to consider if such is the case:

most star machines come equipped with a spring-loaded knockout ejector system, a real gimmicky pain in the butt piece of crap system if you ask me.

I am not familiar with the SB16 so this may or may not be the case for you.

Now, you could be picking off on the .0393 diameter which could be causing your problem because even if you are picked off right near the taper there is the heavier and longer end of the part whipping around at a few thousand rpm which could cause your run out.

On the other hand, I can assume you are picking off on the .125 diameter, but that leaves you only .164" of land before you run into the cutoff, but this is personally where I would pick off anyway.
IF this is the case, you've got 2 inches of part inside your subcollet under pressure from your spring ejector, which could be actually bending the part. Im going to assume you've got some sort of extended nose pickoff, but even with that depending where your ejector is sitting, that poor little .0393 diameter can be under some pretty strong pressures.

If such is the case try running just head1 and parting off a part and catch it before it falls (so you can make sure its not damaged when it drops into the chip tray/conveyor) and see if the same runout is exhibited. If its not then your ejector may be the issue.

Just one more thing you can look into. Like I said, I hate these damned spring-loaded ejectors and I've made it a goal to eventually replace them with an air cylinder system. Citizens all have an air cylinder with adjustable valves for the knockout extend and knockout retract to control their force. Some of the higher end models come with a servo driven knockout system where you can actually command a position and feed for the knockout, which can be quite handy.

Ive had issues on my stars where the knockout has marred parts because at the end of the cycle, when the spindle stops, the ejector doesn't come to an immediate full stop and would rub the face of my glass-like part, screwing it up.

Stupid buggers.

[dinnese]

Thanks guys for all the advice. I did remove the ejector assembly unit ( I am only using air blow) so I know that it's not interfering with the part. I'm picking off as close to cut-off as I can on the .125 dia.(with an extended taper nose collet). The runout is at the beginning of the .0393 dia. and straightens out as it gets closer to the .125 dia.

[micky316]

I do loads of small diam pins in 316 and 303 front turn diams anything from .5mm upto 1.2mm anything upto 75mm long I normally run at 4500rpm constant and feed .02mm per rev I use a .1 rad VCEX or a sharp precitool type front turning insert only because the job calls for that corner rad , a .2 dcgt works just as well .replace the ejector with a hollow one with a thru hole larger than your pick up diam ,set the airblow high and on ejection hold for G4 U1.5 and blast it out , I dont get any problems with running out check it chucks it out ok though you may need to play about with where and how it blasts it out
Mick

[PixMan]

There doesn't seem to be a tooling problem so much as there's a mechanical issue.

I would look closely at three things. Start with how much out-of-round is in the raw stock, just how snug the guide bushing might be, and double-check the tool for being on center.

In regards to out-of-round condition, even with a rotary guide bushing machine you will get about 60% of that which is in the stock transferred to the workpiece. Running it snug is required. My test is can I just barely turn the stock in the guide bushing with two hands on it (one on either side of the guide bushing trying to rotate the stock.) It should slide back and forth with a little less effort than that.

BTW, the VP10RT grade is only OK for that material. It's really better in austenitic stainless, titanium and some other high temp alloys. The precipitation hardening stainless steels actually machine better with straight steel-turning grades. I used a Walter DCMT32.5.5-PF4 in grade WPP10 for some of that and got amazing results.

Hope this helps.

[SirDenisNayland]

While I know you have a lot of experience Pixman, the things you are describing are for roundness issues, not so much tapering and runout, deflection which is the issue he has described. I do understand that runout can be a biproduct of roundness issues. While lack of material roundness and a guide that isn't tight enough can have affects on straightness, the fact that his largest diameter is flawless leads me to believe that both of those are a non issue. Inherent material stress aside, it seems pretty evident that the turned part is experiencing unwanted load in an other than axial direction which points to a tooling issue in my opinion, possibly as simple as being off center which you did mention and several of us have, so I would largely believe that not to be the issue either as I'm sure the OP knows how to set a tool.

If its not being bent from the pickoff or ejection, then it can only be happening at the point where the part is turned: a tooling issue. Or as has been mentioned, inherent material stresses which would be a real big problem but is just about the only other possibility.
Speaking of which, does anyone know of methods to check for such a thing without going through a trial and error elimination of variables such as what's going on here?

[PixMan]

Sorry about that. You are correct in that I've mis-read the problem.

I agree with you Sir Denis, it does appear to be some sort of internal stress. That material is one that should be pre heat-treated and then tempered back as a means of stress relief.

[lukehonor]

I've run a similar job on my Tsugami BE20. We run a 304 S.S. job in which we turn 1/8" bar stock down to .055" in one pass. The shaft is approximately 1.2" long. I had an out of roundess problem as well and I solved this by using a Kennametal DCMT insert with approx .004"-.008" nose radius. I ran my spindle speed up to 8000 and fed around .002"-.004" per rev (maybe less, can't remember).

WIth such a small turn diameter, it is very critical to make sure your tool is on center. If I had to bet, I would say your tool is off center.

Good Luck to you!