Banding on finish when using powerfeed on G0602

[steamer]

Show us a picture of the tool mounted ........please..... ;D

 

[steamer]

Preferably up against a piece of stock..........

 

[Jasonb]

I'll say it again why do we need to see the tool if the OP says its fine when fed manually

"do a cut without the powerfeed. Results were as good as I could get it manually but no banding"

J

 

[mzetati]

because the forces applied to the (possibly dull) cutting edge would be much greater than those applied to a (possibly) better tool, to say nothing about the (possibly) lower feed rates when feeding by hand.
The brass workpiece shows a lot of metal being pushed towards the HS, instead of being cut: that COULD be a sign of a bad tool.

Marcello

 

[Ken I]

I have the same problem with my no name brand lathe.

Although it is nowhere near as bad as in the photos - more cosmetic finish changes rather than any real depth to the banding - but a few tenths of a thou to be sure.

Definitely leadscrew pitch.

I have tried snugging everything up to no avail.

However I have noticed that with the screw nuts closed (machine stopped) I can rock the carriage back and forth about 0.5mm - its not play in the half shells or the leadscrew - and it feels like a spring.

If I power feed (without cutting anything) if I load the carriage handwheel, I can see a momentary hesitation and again this "springyness" in the connection to the leadscrew.

Something is wrong here - going to strip it and see what I find.

I will be watching this post closely.

Ken

 

[steamer]

Gotta agree with Marcello here. I am suspect that it's dull, ill positioned , ill shaped or all of the above.

Though I would suspect hand feeding will be at a higher feed rate than .0024"/rev!

The added cutting force from a higher feed rate may be taking up the slack in the machine that wouldn't take up otherwise.

It's just a hypothosis....

WE need to eliminate it because WE'RE not there to look at it ourselves Jason.

It's exceptionally difficult to trouble shoot someone elses machine from half way round the world.

Leave no stone unturned. I promise I'll not complain if you tell me I was wrong later ;D

Ken, I'm intriqued with your statements.....seems to be a theme here.

Dave

 

[steamer]

Something else to check may be leadscrew alignment, either up and down or front to back with respect to the halfnuts


Dave

 

[dalem9]

my guess their is play in the head stock bearing and a high spot on one of the drive gears. Only a guess Dale

 

[Mosey]

Off the point a little, but maybe interesting anyway... when I got my first South Bend heavy 10 back in 1990+-, I got similar rings in the finish when turning a bar. After lots of frustrating attempts to find the culprit, I called South Bend and spoke to an old timer- Mel- who was the guy who tested the lathes before they went out the door. Mel said "yup, it's what we call here a "ring-turner"". He said "they don't know what causes it, but if I ever figure it out, he'd like to know". Well I did figure it out. It was poor HS tool tip shape, height, and finish, any or all at a time. I switched to carbide indexible inserts, which are correct shape and finish of course and never got a ring again.
I guess Mel is gone by now.

I guess I should add that the problem seems to be that the chip starts to form, then welds itself to the work, then breaks off, then the cycle repeats. What I was seeing was the ring of welded broken chips.

 

[dalem9]

with machine off engage feed drive turn chuck by hand and see if there is a tite spot.just to rule out a gear that is bored off center Dale

 

[wannasteam]

:bow:

Thanks for all the input and thoughts. Very muchly appreciated.

I'm at work now and I will have a look at a few things when I get home tonight.

Just a few thoughts and comments from me:

I have a 7 x 12 asian lathe that I've had for about five years and get very good results even tho my saddle is quite "baggy".

I've had very good results finish-wise using both hand sharpened HSS tooling, indexable tooling and carbide tools. I am using the same tools on the bigger lathe.

I very strongly suspect that the problem is somehow related to the connection between the leadscrew and the cutting tool. I say this because if I hand feed as slow as what the leadscrew gives, I get very good results, although not with the same uniformity as one would get from powerfeed. To me, this eliminates the tool itself as the culprit.The banding occurs from heavy cuts, light cuts and very light cuts.

The pitch of the banding is the very nearly the same as the pitch of the leadscrew which indicates a problem somewhere in that system.

Again, thank you very much for your input, ideas and thoughts.

Cheers

Joe

 

[Niels Abildgaard]

File a slot in end of leadscrew,disengage geartrain,engage powerfeed and try with an electric screwdriver.
Good luck and enjoy the feeling when localizing problem

Regards

Niels.

 

[Jasonb]

File a slot in end of leadscrew,disengage geartrain,engage powerfeed and try with an electric screwdriver.
Good luck and enjoy the feeling when localizing problem

Regards

Niels.

As this is a brand new lathe I would strongly advise NOT to do this, if it needs to go back or replacement parts are required you could invalidate any warrantee.

Jason

 

[Richard1]

Cutting a slot in the end of the lead screw is probably not a good idea. If there is a way to drive it independently of the gear train without damaging it, it might tell us something.

Richard

 

[Ken I]

This is the banding typical on my lathe.

Still haven't figured it out.

In this case I think it looks cool but generally not.

Ken

 

[steamer]

Jason's right....no modifications please......

Dave

 

[mzetati]

Joe,

now we know the tools have no faults, I'd try to remove some of the other variables: would You get bands if cutting forces were zeroed? a felt tip pen in the toolpost might give an answer.
Can You fit a hand crank to the spindle? Powerfeeding by arm would let You sense eventual tighter spots, while cutting, while moving parts with the tool retracted, no tight spots at all, ...
If You do that with the gear cover removed You might actually see the reason of them.

Marcello

 

[steamer]

Additionally, if you have an accurate arbor, or a piece of ground stock that you can put in a 4 jaw and tram it, you could put an indicator on the toolpost and up against the bar and see if we can measure what's going on.

Dave

 

[Jasonb]

Looking at the Grizzly manual teh gear on teh end of the leadscrew is retained by an Allen socket screw, either drive this with a hex driver or replace with a hex head bolt and use a nutdriver or socket, thats a non invasive way of cranking the leadscrew by hand.

One other thing I was pondering, if the OD of the leadscrew has minimal runout but what about the root of the thread could it be possible the leadscrew deflected while the thread was being cut?
Would need something narrow on teh end of teh DTI to measure but worth a try.

J

 

[Mosey]

Seems to me that as this is a new lathe, and you have eliminated user error, it is a problem of the manufacturer, and should be given to them to solve. What I mean is that you might inform them of the problem and ask them to fix it. if it means their replacing or repairing the machine, so be it.