cruddy finish makes for cruddy attitude

[zeeprogrammer]

I've been learning/practicing with my new lathe and I'm struggling to get a decent finish.
More fiddling and practice will no doubt improve things...but still...

I'm turning aluminum with a insert cutter. I've tried different inserts as well as a couple of ground HSS.

For the most part, what I'm getting is a spiral cut under power feed.
Manual feed was not much better...spirals were simply more variable.

I've tried moving the cutter slightly lower than center, various speeds, wet and dry, making sure all parts are locked down (gibs, etc.)
I've measured the lathe, and while it's not level...I detected no twist to speak of.
The lathe seems really solid to me. Even with untightened gibs, I can detect no movement when I push/lift on the carriage, cross slide etc.
Not like my mini that seemed to want to cross the county line.

I finally got a somewhat decent finish on manual feed but still not what I remember achieving on my mini. Not good enough in my mind.
The problem with manual feed is that as soon as I have to move my hand in order to continue turning...I get a machine mark (and some squealing...if that's a clue).

But power feed still gives me a spiral finish.

I'm aware that too fast a feed rate can result in this. The ratio of spindle speed to feed rate has to be 'high'. Too low and the cutter moves across the material too fast.

This is the PM1030 lathe. It has two feed selection knobs. One is for direction and the other...well the other has been a struggle learning too.
It is marked A B C. When the lathe is off, I sometimes cannot turn that knob. The lathe has to be on (making sure it is running slow).
I had expected 3 settings but I find that between A and B the lead screw does not turn. Same between B and C.
What I find odd though is that A appears slow, B is faster, yet C seems slow as well. I haven't measured, but it seems the same as A.
I've tried all 3.

I would expect the fast speed would probably result in spiral cuts. But the slower speeds also result in spiral (just smaller).

I talked to a fellow at the show about this and one suggestion is changing the gears in the gear box.
I haven't tried that yet. Seems odd I'd have this problem with a new lathe out of the box.

If/when I do go that route, the questions will be 'how' and 'to what'?

Any thoughts my friends?

In the meantime, I'll try some other material and keep trying different spindle speeds as well.

Currently at the 'bummed to almost frustrated' level. Got a few levels to go before I lose it entirely. 

[wagnmkr]

Sorry you are having problems Zee.

For the aluminum, what speed are you turning at and what diameter stock?

That lathe has a quick change tool post ... silly question ... is the tool holder locked in tight, and is the post locked down good? You mentioned that you got a squeal and a mark if you stopped feeding by hand. That can mean flex in the tool post/cutter. I would not expect that to happen on that lathe.
The spiral mark shows the lathe thinks it is threading something ... is there a separate knob to engage threading versus straight feed?

Have you contacted the seller? That would be my main suggestion.

Tom

[Jasonb]

Question is Zee what gear train have you got set up on the banjo? as this will affect the input speed into the feed gearbox.

Also you should be using the smaller lever in the middle of the apron to engage feed, if you use the big one on the right you will be cutting a very fine thread which could explain your spiral

You should have a speed table on a plate on the front cover of the machine and that should also be in the manual, set the gear train for the finest range and then use the ABC lever to give what you need for the job in hand. That is all I have ever needed on my slightly larger 1128

C is the finest feed, A medium and B fastest

[Dave Otto]

I was wondering about the half nut vs the feed lever also?

Zee it would really be helpful to see some pictures of the tools that you are running, If the insert tools that you are using happen to be negative rake you are fighting a loosing battle on that small machine.
It sounds to me like your tool may not be sharp and also has too much nose radius; which is why it digs in a sequels when you stop feeding. Could you post a link to what you are using?

The technique that I use when hand feeding to use both hands, when your right hand has turned the handle as comfortable the left hand takes over with out stopping the handle from turning. With a little practice you can get a nice fluid motion; much easier to do on the cross feed than on the longitudinal feed.

Dave

[Florian Eberhard]

Hi Zee

I am guessing its the spindle bearings which are not set correctly (too much play). I had quite the same when I rebuilt my schaublin lathe. I had to adjust the front bearing and i had heard it was quite a delicate thing to be done. The bearing needed exactly 0.002mm play. Now the thing is you almost can't measure that and I luckily heard from someone how to do it.
However, the point is before readjusting the bearing play, I had exactly the same kind of bad finish of what you described (at least as far as I understood it).
Although I have a different spindle bearing solution than your lathe, the effect of too much bearing play will be quite the same.

To test if that's the case, you can try to machine something supporting it with the revolving center. This will reduce the bearing play in the front bearing. (I think all those type of lathes have two tapered roller bearings)

If you get quite some improvement (but probably not perfect finish) you should disasseble your spindle, clean everything, probably lap the rear bearing seat on the spindle (in case the bearing sits very tight) and then reasseble everything. It may also be a good idea to put some good quality bearings in it (timken, skf or similar) instead of those chinese bearing of unknown quality.

Hope you can sort it out then,
Cheers Florian

[zeeprogrammer]

@Tom - I'd tried different speeds. Stock is 1/2" aluminum. Keep reading...I made some progress.

@Jason - well well well. I did not realize the little lever also engaged the lead screw. I was using the big-un which is what I was familiar with on the mini. That made a huge difference. And thanks for explaining the ABC differences. Yes, the tables are there. I haven't been able to figure them out. I'll work on that.

@Dave - One of the inserts I tried is supposedly 'matched' to what I'm doing. But what surprises me is your comment about 'too much nose radius'. I was trying what I believe is a bigger radius nose thinking smaller would be worse. I'd like to know more about this. As for the hand work...I implied I was stopping the wheel when changing hands...but like you I switch from one to the other. I got decent on the mini. Need more practice here.

@Florian - That was probably THE thing I'm hoping not to hear. Brand new lathe out of the box. If I have to deal with bearing play, lapping, etc....I'll probably need to bribe someone to visit me and help.

Back @Jason. So it appears using the little lever uses a different gear ratio between the lead screw and spindle than the big lever. Right? Why are there two levers? For that reason...to get a different set of speeds using the lead screw? Or is the big lever more relevant when threading.

Thank you all so very much. I've made progress. My level has moved from 'bummed to frustrated' to somewhat bummed (only in that I don't have it perfect yet).

  Thanks!!!

I need to think more about the squealing when I stop the carriage.
I have the cross slide locked so I can't simply pull the cutter back.
I first stop the carriage then stop the motor then can loosen the gibs to pull the cutter back.
The squealing occurs after stopping the carriage and before stopping the motor.
Should that happen? Am I doing it wrong? Or if I'm not doing anything wrong...is it about the setup?
Seems I didn't lock (tightly) the cross slide when I was using the mini.

[Jasonb]

Back @Jason. So it appears using the little lever uses a different gear ratio between the lead screw and spindle than the big lever. Right? Why are there two levers? For that reason...to get a different set of speeds using the lead screw? Or is the big lever more relevant when threading.

That sounds like the main problem as by using the big lever you were cutting a fine screw. When the smaller lever is used that goes through more gears in the apron so the carrage moves less for a given rotation of the leadscrew when turning along the lathe axis. It then goes through a further 2:1 reduction when the little lever is moved the other way for facing cuts so will move at half the rate. Generally if you set the gear train for the slower of the two feed groups shown ( should be supplied with that setup) then you will find that 99% of facing can be done in position A and turning along the lathe in position C.

When you get to the end of turning the work down have one hand on the carage handwheel and the other on the lever, disengage feed and move carage back towards tailstock end slightly this should stop you squeeling. most of the time the cross slide should not need locking.

[Florian Eberhard]

@Florian - That was probably THE thing I'm hoping not to hear. Brand new lathe out of the box. If I have to deal with bearing play, lapping, etc....I'll probably need to bribe someone to visit me and help.

Well yeah, its a brand new lathe out of a Chinese Box

Setting tapered roller bearings is not difficult since they are not very sensitive on preload (like angular contact bearings are.)
All you have to do when mounting them is to first tighten them until the spindle starts to turn with resistance (only turned by hand!)
Then you loosen up the nut again and screw it against the bearing by hand. Then you tighten it again only a tiny bit, with very few force. If you did this, you can run your spindle with the motor and then the bearings should not reach more than 50°C after half an hour of running it. If they get hotter, you need less preload, if they stay completely cold, you can try what finish you get and if its ok, you can go with that setting, otherwise you should tighten the nut a little more.

You only have to lap the rear bearing seat if you cannot move the rear bearing by hand (ideally with a little resistance)
Lapping the bearing seat on the spindle is quite easy, all you need is a lapping ring (made from aluminium), some lapping compound, a micrometer to check the size of the bearing seat from time to time.
And depending on how much you have to remove quite some patience.

Florian

[Florian Eberhard]

The squealing occurs after stopping the carriage and before stopping the motor.

That should definitley not happen. And sorry to say this, but this is also a hint for too much bearing play.
I think what happenes is the following:
You machine a diameter and the machining forces push the spindle away from the lathe tool. When you stop the carriage, the spindle wants to move back into the centered position and there the workpiece rubs over your cutting edge and makes that squealing noise.

Florian

[Jasonb]

How much of your 1/2" bar is sticking out the chuck? too much and the bar will flex away duringthe cut and rub when you stop even with perfectly adjusted bearings.

It will also tend to rub as the "thread" you cut with the wrong lever is flattened out by the stationary tool

Are you cutting dry or with lubricant?

[zeeprogrammer]

@Jason - Thanks! I managed a pretty decent finish. My hopes for the future have risen tremendously.

@Florian - That's very helpful information. I learned quite a bit and will keep that information tucked away.

For the moment I am 

(You all know me by now...I get to know the valleys just as much as the peaks. Short visits to both...but frequent.)

Just saw your last post Florian. I'm not so sure. I can understand that more with deeper cuts where the cutter is really pushing but this occurs even on the lightest cut.
I'm thinking rubbing. Possibly not centered properly. Possibly cheap index.
I'll keep an eye on it.
I do want to investigate the spindle play though. Even if built well enough...shipping etc and cause changes.

Also Jason...A couple of inches (probably too long). I cut up to about 3/8 away from the chuck. It's near the chuck end that squealing occurs. Dry and wet (WD40) but less so with WD (which I would expect).

Going to play some more with it. Also want to try some brass, steel, and stainless.
(No fluid with brass. Some cutting oil for the steels.)

[10KPete]

Make sure there is a bit of a radius on the end of the cutting tool. If the point is sharp, it will show the feed rate. Radius wants to be much larger than the feed rate to minimize the height of the 'groove'.

Pete

[philjoe5]

Zee,
I own 3 lathes, 2 imports, 1 USA made.  They are 2, 10 and 71 years old respectively.  All give good finishes on steel, aluminum, brass and cast iron.  If I chuck a 1" round bar x 12 inches long and put a dial indicator against it and pull the bar toward me, they all deflect the bar 0.001" or slightly less.  That much play does not appear to affect finish.  If that's what you're getting I'd look elsewhere.

A reasonably sharp tool set on the spindle center should give a good finish with a feed rate of 0.002"/rpm, 400 rpm on a 1" round projecting NMT 1 inch out of the chuck.  Plus, if you take a cut of say 0.025" and wind the carriage back toward the end of the work while under power you should only just barely see a spiral cut.  If you get a pronounced spiral cut I'd check tool tip for sharpness, and height on centerline.

Good luck with solving this issue, we've all gone through this.

Phil

[jadge]

Zeeprogrammer: You might find this thread (on another forum) of interest:

http://www.model-engineer.co.uk/forums/postings.asp?th=51900

If nothing else it will explode the myth that inserts must be run hard and fast to get a good finish. They can be, and for some materials must be, but not for all materials.

Andrew

[zeeprogrammer]

Thanks very much my friends. I think I'm getting a handle on this.

Andrew...that was a very helpful and interesting link. Thanks!
Are you the same Andrew as the author?

[gerritv]

Hi Zee

I have a KC1022ML lathe, similar to the Grizzly G0602 and your PM1030 (except mine isn't variable speed of course).

I suspect there are several issues at work here, so best to not get too dramatic about spindle play and changing gears int eh gearbox etc until other things are taken out of the equation.

You will need to digest the gear train charts to sort out the feed rate issue. It really sounds as if the default setup is for threading, not feeds. Can you post a link to the manual so we can guide you better. Some photos from your new camera might help as well :-)

The rh lever on your apron is for carriage feed, the small one is for cross slide (facing) feed. So use the RH one for what you are doing at present.

Re: squealing, are there any signs of the material rubbing against the tool? Try marking that face with blue, do a small cut and then look to see if the blueing is gone. It could be clearance

The last thing you want or should need to do is mess with the spindle bearings. From everything I have read PM checks their stuff before shipping. The odds of this being an issue is very slim regardless of where the lathe was made.

Gerrit

[jadge]

Andrew...that was a very helpful and interesting link. Thanks!
Are you the same Andrew as the author?

One and the same - Andrew

[zeeprogrammer]

Still making progress. I got what I consider a good finish on aluminum. After dropping the cutter slightly I also got a real nice finish on brass.
I still have a bit of squealing when I stop feeding and leave the motor on. But it depends on the speed of the spindle. Seems to squeal within a small intermediate range.
Slower or faster is quiet.

A bit troubling though...as I changed the spindle speed I could feel the lathe shake like something is out of balance.
One time, the shaking was what I would consider significant then later could not find the speed where that occurred although some shaking was still noticeable.

I took the chuck off and the shaking reduced considerably. Slight shaking at high speed (over 1500 rpm).
I'm pretty sure the chuck was installed correctly...that is I matched the marking on the chuck to the marking on the flange.

I can try other positions but is this usual? How concerned should I be?

Thanks

[Tennessee Whiskey]

You may have to indicate the chuck true to the spindle. Indicate the OD of the chuck, or, better yet, a known round piece of stock tightened in the chuck.

Cletus

[Jasonb]

You should not get a vibration from the 3-jaw, more common on the 4-jaw when the work is an odd shape

[Vixen]

The Vee belts on some Chinese products are not as good as they could be. Some are distorted out of round, some have bumps on the Vee were they were spliced during manufacture. Observe the belts carefully and check they are running smoothly and not jumping in time with the vibrations. Dont get your nose too close.

Mike

[zeeprogrammer]

You may have to indicate the chuck true to the spindle. Indicate the OD of the chuck, or, better yet, a known round piece of stock tightened in the chuck.

I setup a .0005 test indicator and a piece of 1/2" bar from a printer.
Lowered test indicator and zeroed it.
Turned chuck (by hand) and needle swung just over 5 marks in both directions (0.0025mm)

Seems okay, no?

Since I was set up...I moved the indicator out by 4". Needle swung -3 to 5.5 marks.
Average difference of 1.25 marks or .000625mm.

So that's the tilt in Z (up and down) which doesn't seem too bad. Could be sag too.

At some point I need to measure front to back but I don't think any of that explains the shaking.

It's very noticeable at around 700 rpm. Next to nothing below that and very very slightly above it.
Returns to shaking at around 1500 rpm but not as bad as at 700.

At some point I'll try the 4-jaw chuck too.

Just saw some posts come in...

@Jason - is that also true if the 4-jaw is not holding anything?
@Mike - I switched the belt to high speed yesterday and hadn't noticed anything. I'll take another look. Should probably test with the belt at low speed too.

Thanks everyone.

[gerritv]

If the lathe shakes without the chuck mounted then it must be pulleys or belts, it can't be the chuck. V belts, US or Chinese made are notorious for having lumps. If the belt is too tight the lumpiness will be exacerbated. Too loose you get slippage but that is usually a better thing than too tight.

[Jasonb]

The rh lever on your apron is for carriage feed, the small one is for cross slide (facing) feed. So use the RH one for what you are doing at present.
Gerrit

Sorry gerrit, can't agree with that, Zee's lathe is the Weiss Machine WM250VF as sold by many companies.

From teh manual you will see that the small lever does feeds and the large one on the right is for screwcutting



Also see this thread where someone had the same issues with a coarse feed and finally realised what I was saying was correct

http://www.model-engineer.co.uk/forums/postings.asp?th=125683&p=1

And if you look at page 32 of the manual you can see how the right hand lever engages the half but but the small lever moves a gear that is in constant mesg with the lead screw by a wormwheel and transfers this movement via various gears to move the carrage along via the rack or across via the cross slide screw as I said earlier

http://busybeetools.com/content/product_manuals/CX706.pdf

[Jasonb]

I setup a .0005 test indicator and a piece of 1/2" bar from a printer.
Lowered test indicator and zeroed it.
Turned chuck (by hand) and needle swung just over 5 marks in both directions (0.0025mm)

Zee, check what dial indicator you are using. A 0.0005 indicator is generally an imperial one where one division equals 0.0005" or 5tenths of an inch not 0.0005mm

Provided all jaws are in/out the same amount you should not get vibration from a 4-jaw

[zeeprogrammer]

I setup a .0005 test indicator and a piece of 1/2" bar from a printer.
Lowered test indicator and zeroed it.
Turned chuck (by hand) and needle swung just over 5 marks in both directions (0.0025mm)

Zee, check what dial indicator you are using. A 0.0005 indicator is generally an imperial one where one division equals 0.0005" or 5tenths of an inch not 0.0005mm

Provided all jaws are in/out the same amount you should not get vibration from a 4-jaw

Sorry about that. Units are inches. Numbers are correct.
Thanks.

Seems I've been getting my units mixed up more ever since I got the 3d printer. 

[Allen Smithee]

A 0.0005 indicator is generally an imperial one where one division equals 0.0005" or 5tenths of an inch not 0.0005mm

ITYM "5 tenths of a thou" (half a thou; 0.0125mm)

AS

[Jasonb]

Thanks AS, I went back and  added the "of an inch" after I wrote just 5tenths, should not have bothered maybe I should just have said it's an imperial DTI

[gerritv]

Jasonb, I stand corrected. I would not have known the matching model numbers in EU, (and I have learned to avoid BusyBee for pretty much everything by experience, both price and quality :-)

I guess more important is for Zee to spend some quality time with the manual :-)

Gerrit

[zeeprogrammer]

I guess more important is for Zee to spend some quality time with the manual :-)

Hee hee. Thought I had. But again...what I read isn't necessarily what was meant.

In this case, I thought the small lever was to select feed for cross slide or lead screw and to use the big lever to engage it.
It didn't occur to me that it was 'select AND engage'.

[Dave Otto]

Hey Zee

Maybe this is what you are seeing on your lathe https://en.wikipedia.org/wiki/Critical_speed
My lathe has a small vibration a 665 rpm (not variable) mostly unnoticeable without a chuck mounted Mount up the 6" 3 jaw and it is pretty pronounced put the 8" chuck on it and I just skip that speed.
This is on a very well made German toolroom lathe with good belts and bearings.

Dave

[zeeprogrammer]

Hey Zee

Maybe this is what you are seeing on your lathe https://en.wikipedia.org/wiki/Critical_speed
My lathe has a small vibration a 665 rpm (not variable) mostly unnoticeable without a chuck mounted Mount up the 6" 3 jaw and it is pretty pronounced put the 8" chuck on it and I just skip that speed.
This is on a very well made German toolroom lathe with good belts and bearings.

Dave

Thanks Dave. I was moving in that direction. It occurs at about 600...so I could avoid it.
Just trying to make sure I'm not missing something.

I did get good finishes...and it was easier than when I had my mini-lathe (in part because of my experience with the mini). So I'm kinda happy.
I expect better performance out of a $2000 machine than a $500 but I'd be foolish to expect performance that a $10000 machine would provide.

I'm doing okay here.

[crueby]

Glad you are getting it sorted out, sure that every machine has its own personality and quirks. You should be starting on the Stanley engine any day now.

[zeeprogrammer]

You should be starting on the Stanley engine any day now.

 

[crueby]

You should be starting on the Stanley engine any day now.

 

 

[mklotz]

In this case, I thought the small lever was to select feed for cross slide or lead screw and to use the big lever to engage it.
It didn't occur to me that it was 'select AND engage'.

Yes, and in an absent-minded moment, pushing the lever the wrong direction can damage a nearly finished part - DAMHIKT.

The mnemonic I keep in mind is...

UP towards the crossfeed screw engages the crossfeed screw.

DOWN towards the axial feed rod (my lathe has separate feed rod and leadscrew) engages the axial feed