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Loose or bad headstock bearings.

Proxule

Ultra Member
I'm sort of leaning back to maybe bad bearing again. They seem to be running warmer than I think they should be, and used to maybe.
Did you do any upgrade of bearings when you replaced yours?
Nope I kept same tolerance and bearing dimension and numbers. Broke in accordingly and adjusted after X hours.

Spindle beerings should be 40F above ambient temp after 30 minutes or so at highest rpm. For tapered roller any way.
( none splash lube )
Any way you cut it those bearings max temp is 170F

If you are adventurous... rip your spindle out after you take end float numbers. Clean and repack / or just clean and reinstall if splash lubricant. And adjust preload and see what happens.

Spindle bearing tinkering would be my last resort. IMO

Gluck
 
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I had issues when using a parting blade (broke 3) and with chatter/cut quality over entire shafts after replacing the main spindle bearings in my Standard-Modern 9". On the SM9, the entire spindle is held in placed by a threaded ring on the outboard side that is tightened/loosened with a pin wrench.

Tightening this threaded ring with an appropriate sized pin wrench solved my issues. I basically tightened it until the spindle shaft was just starting to drag and then backed off slightly. Rinsed and repeated a few times until parting issues and shatter went away.

The threaded ring I'm talking about is #14 and teh two bearings I replaced were #15 (sealed roller bearing) and #19 (tapered roller bearing) in the below diagram

1675265554731.png
 

DPittman

Ultra Member
Premium Member
I had issues when using a parting blade (broke 3) and with chatter/cut quality over entire shafts after replacing the main spindle bearings in my Standard-Modern 9". On the SM9, the entire spindle is held in placed by a threaded ring on the outboard side that is tightened/loosened with a pin wrench.

Tightening this threaded ring with an appropriate sized pin wrench solved my issues. I basically tightened it until the spindle shaft was just starting to drag and then backed off slightly. Rinsed and repeated a few times until parting issues and shatter went away.

The threaded ring I'm talking about is #14 and teh two bearings I replaced were #15 (sealed roller bearing) and #19 (tapered roller bearing) in the below diagram

View attachment 30283
Yes my lathe spindle is held in place similarly with a threaded nut on the outboard side of things but because my lathe is not a gear drive it should be a simpler disassembly than yours. There certainly isn't any play in my bearings yet and they don't make any noise yet either so I'm still evaluating and going to consider all advice given here before I pull mine apart.
 
My didnt feel like there was any play either and certainly didnt make noise. After checking EVERYTHING else (x-slide, carriage, compound slide, etc etc etc) for looseness I mused it might be the main spindle 'preload'. So I tightened the ring a 1/8 turn and tried parting and it got better, so I progressively tightened and then finally loosened until I was happy with the cut quality and no more broken parting blades. No additional noise was heard from the bearings.

And teh SM 9 is a belt drive with 4 'steps' and a gearbox for high/low speed ranges. Pretty standard for older 9 and 10" lathes, no?
 

DPittman

Ultra Member
Premium Member
And teh SM 9 is a belt drive with 4 'steps' and a gearbox for high/low speed ranges. Pretty standard for older 9 and 10" lathes, no?
Oh could be, I'm not familiar with SM lathes and I was making an assumption (that obviously was not so right).
 

DPittman

Ultra Member
Premium Member
0.020" - 0.030" is fine. Try increasing your feed to .003-.004"/rev. and see what happens.
So I will try that eventually as I know the finish often get better with a more aggressive feed/cut rate with carbide on my lathe to the point where it is taxing the power and rigidity of my little lathe. But under what circumstances would too low of a feed/cut rate result in an intermittent surface finish where the finish got worse near the headstock? Is that possible?
 

Proxule

Ultra Member
Take reading on float prior to tinkering. Failing or failed bearings will indicate X float.
Same procedure when installing. Float is really the only real way to dial in preload. Vs. Feeling for drag.

Perhaps just a snug up of the locking collars is all that is needed ?
 

DPittman

Ultra Member
Premium Member
Usually when you have a repeat finish problem in the same local area its things like power feed drive assembly (junk in the power feed bar or screw, slightly misaligned bar or bent that is staring to choke up on the worm drive etc.)
I did have EXACTLY that problem for a while and it took me awhile to really diagnose it, and even longer to work up the gumption to tackle the issue.

Quite early in my lathes life I had crashed the carriage into the headstock for one of the reasons people do such things. Ever since that time engaging the power carriage feed was not as smooth as it use to be and the lathe definitely started to growl and strain near the headstock. It seemed okay near the middle of the ways and it became really noticeably poor when threading. I knew something wasn't right in the carriage feed mechanism but didn't want to disassemble until I got my other lathe up and running.
In the end it was a slightly tweaked/bent shaft for the gear that meshes with the worm gear just as you described. After all said and done, the job really wasn't that bad and I had wished I had repaired it much sooner as it fixed the issue 100%.
I don't believe my present issues are related to that but I'm really great at being wrong so we will see eventually. :rolleyes:
 
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DPittman

Ultra Member
Premium Member
Do you have any issues with parting?
Well sort of....being a light little lathe there has always been potential for issues but I only have done a bit of parting recently. And come to think of it, I do believe that too was not as smooth as it used to be. I was just chalking it up to not holding my tongue right.
 

YotaBota

Mike
Premium Member
I'm going to guess you checked the tool height about a zillion times.
What is the finish if you turn a short piece a couple of inches from the chuck?
Experimenting with parting sounds like a good plan as well, on a 1" bar I part at about 300rpm and use lots of lube. Make sure your parting blade is 90deg to the work.
A second set of eyes could help as well, who's close to you that needs a coffee?
 

DPittman

Ultra Member
Premium Member
I'm going to guess you checked the tool height about a zillion times.
What is the finish if you turn a short piece a couple of inches from the chuck?
Experimenting with parting sounds like a good plan as well, on a 1" bar I part at about 300rpm and use lots of lube. Make sure your parting blade is 90deg to the work.
A second set of eyes could help as well, who's close to you that needs a coffee?
Thanks, I do have alot of things to check out. Unfortunately no one is really "close" to me but I did have the pleasure of meeting and having @Kelly McLaughlin
in my shop last week but I was not aware of my issues then.
 

Dabbler

ersatz engineer
After reading this thread (several times) it is loaded with all kinds a great suggestions.

Bit I think you need a diagnostic path rather than a fix-it path. (no offense intended).

What I suspect is your material and your insert are not compatible. If you are cutting 1018, for instance, and your feed/speeds are off and the insert is for harder materials, all the heat from cutting is going into the insert. At some point, the insert is hot enough to affect the cutting zone. Material from the cut can weld to the insert affecting the cut and the chip enough to ruin the surface finish.

Do you have some 10L14 or other free cutting steel? it'd be worth a try,

I'd start with a piece of aluminum and a nice sharp tool. Turn it as per your mystery metal. If you have excess play in the headstock, you will see poorer surface finish and a smaller diameter near the chuck. I suspect your diameter will be fine, and the finish will be consistent over the length.
 

DPittman

Ultra Member
Premium Member
Spindle beerings should be 40F above ambient temp after 30 minutes or so at highest rpm. For tapered roller any way.
( none splash lube )
Any way you cut it those bearings max temp is 170F
Thanks those spec are helpful.
I tightened the ring (ever so minimally though) on the outboard spindle that loads the bearings and ran the lathe for 30 mins and while I believe the bearings are running warmer than they were, they definitely are below that 40° temperature increase threshold. On with more experimenting.
 

PeterT

Ultra Member
Premium Member
Agree with @Dabbler Mystery metal is not what you want to be playing with trying to diagnose a problem like this. You could have a perfect setup & still have finish issues depending just how mysterious it is, so temporarily eliminate it altogether as a variable. Aluminum like 6061 is pretty cheap, use a sharp tool & it will show up deviations quite visibly because there is less cutting forces involved. 12L14 or free machining steel is a good option as well if you have it. Start with a fresh insert or cutting edge... eliminate those variables too, they are easy to nail down before experimenting.

If you start seeing some repetition consistency like worse patch as a function of carriage position to bed, or only with a certain powerfeed gear combination, or powerfeed vs no powerfeed... then the results will dictate what to focus on. My PF bar has a slot that runs the length, it engages worm key. But it can fill with grunge, or have a nick & now you have some slight resistance or micro interruption to smooth carriage traversing that may reflect on finish. You might be able to feel this by hand which is another good reason to PF & no PF.

Other things to check are maybe you have a funky tool holder assembly. Try a different one. My old ones have a slight radius in the corner where a tool shank will ride up slightly vs being flush on the bottom, which means its not supported correctly well even though the set screws appear are tight.
 

Downwindtracker2

Well-Known Member
I changed my headstock bearings when I changed the belts. I had 3 tenths on the old ones, so I adjusted the new ones to the same. I had to buy a good 1/10 Mitutoyo dial indicator. I used a 6 foot 2x4 and pried up. My lathe is like the one above used simple Timken bearings. Prying up is sometimes used in industry to check preload.
 

jcdammeyer

John
Premium Member
I've been perusing old copies of Home Shop Machinist and I found an article on surface finish while turning. His example was along the entire length but his reasoning behind it made sense.

Essentially he suggested that as the tool feeds along the work it pulls ahead away from the leadscrew driving flank until it hits the other one, stops and the lead screw catches up and then it starts again. He found if he provided drag on the system with the handle it was less of a problem. Tightening the gibs also helped.

Now the issue might only show up half way because near the head stock both the bed and the lead screw tend to be worn more. So as the tool bit drops ever so slightly it grabs more, is pulled towards the head stock until the lead screw catches up.

Not saying this is happening but it might be something to look into.
 

trevj

Ultra Member
I've been perusing old copies of Home Shop Machinist and I found an article on surface finish while turning. His example was along the entire length but his reasoning behind it made sense.

Essentially he suggested that as the tool feeds along the work it pulls ahead away from the leadscrew driving flank until it hits the other one, stops and the lead screw catches up and then it starts again. He found if he provided drag on the system with the handle it was less of a problem. Tightening the gibs also helped.

Now the issue might only show up half way because near the head stock both the bed and the lead screw tend to be worn more. So as the tool bit drops ever so slightly it grabs more, is pulled towards the head stock until the lead screw catches up.

Not saying this is happening but it might be something to look into.
Gibs, and overhang would have been my first suggestion. The cross slide can be locked down, if not already. I almost always just leave the compound at whatever angle it was last used at. But some guys want it straight pointed at the chuck (which baffles me some, on a small lathe, as you already have the ways pointed that way) or, if you are working at sneaking up on very fine tolerances, putting it at around four degrees from parallel to the bore, gives you aprox one tenth of the infeed, that you put in to the compound screw. Do the trig and get back to me with exact numbers, if you need them. It's a pretty handy and simple, useful thing once in a while! Trig too!

A close look at the QCTP Holder, for a radius in the back of the slot, throwing things off would not hurt, though I kinda lean away from it as 'cause'. Easy to whistle a chamfer on the cutter holder, to account for it if there.

Counter to all the advice that one gets to have the tool on exact center height, I would suggest experimenting with a touch lower, or higher, to see if that changes the cut conditions. Taking a look at a chart that explains edge treatments, will explain better than I will, but if the edge treatment includes a purposely beveled or rounded off edge, plus a layer of plating, you may not be cutting with the part of the edge, that you thought you were!

A question I have used a lot when training apprentices... "Did you do the Math?" Typical carbide speeds are right around 4 times the revs that HSS cutters are happy at. Surface feet per minute!

Not all edge treatments on Carbide inserts will give good results on light cuts or at slower speeds. Feed rate depends on the radius of the cutter tip. A larger tip Rad., and you can use a larger feed rate. The trade is that a larger tip Rad., will also put more force in to effect, pushing against both the work, and the cross feed. Pretty much every tool catalog show the expected optimum cutting conditions that the maker expects to produce the best return on investment for a shop owner. Lots online too, if you know what insert you have. Also found on the insert pack, often, if you have that

My usual advise to a newb, is to stay away from 1018, as it takes speeds and feeds that seem pretty scary, to get really good results on a consistent basis, vs many (usually not very much!) more expensive metals you can buy. 12L14 is almost as nice as Brass to cut, 4140, 4340 and similar have a pretty good machinability rating too. 303 for stainless. If buying aluminum for turning, I REALLY like dealing with 7075 in the higher -T numbers, even with it's ability to corrode in some circumstances, while you watch! :) 6061 is cheap and available get -T4 or -T6, 2024 if you can find it, again, at he higher temper numbers.

Chatter is akin to music. It's a series of vibrations, that complement the ones before and after. Some times, you happen across the cut conditions that make that funky music, and the way out, is to change the cut conditions.
 

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
Gibs, and overhang would have been my first suggestion. The cross slide can be locked down, if not already. I almost always just leave the compound at whatever angle it was last used at. But some guys want it straight pointed at the chuck (which baffles me some, on a small lathe, as you already have the ways pointed that way) or, if you are working at sneaking up on very fine tolerances, putting it at around four degrees from parallel to the bore, gives you aprox one tenth of the infeed, that you put in to the compound screw. Do the trig and get back to me with exact numbers, if you need them. It's a pretty handy and simple, useful thing once in a while! Trig too!

A close look at the QCTP Holder, for a radius in the back of the slot, throwing things off would not hurt, though I kinda lean away from it as 'cause'. Easy to whistle a chamfer on the cutter holder, to account for it if there.

Counter to all the advice that one gets to have the tool on exact center height, I would suggest experimenting with a touch lower, or higher, to see if that changes the cut conditions. Taking a look at a chart that explains edge treatments, will explain better than I will, but if the edge treatment includes a purposely beveled or rounded off edge, plus a layer of plating, you may not be cutting with the part of the edge, that you thought you were!

A question I have used a lot when training apprentices... "Did you do the Math?" Typical carbide speeds are right around 4 times the revs that HSS cutters are happy at. Surface feet per minute!

Not all edge treatments on Carbide inserts will give good results on light cuts or at slower speeds. Feed rate depends on the radius of the cutter tip. A larger tip Rad., and you can use a larger feed rate. The trade is that a larger tip Rad., will also put more force in to effect, pushing against both the work, and the cross feed. Pretty much every tool catalog show the expected optimum cutting conditions that the maker expects to produce the best return on investment for a shop owner. Lots online too, if you know what insert you have. Also found on the insert pack, often, if you have that

My usual advise to a newb, is to stay away from 1018, as it takes speeds and feeds that seem pretty scary, to get really good results on a consistent basis, vs many (usually not very much!) more expensive metals you can buy. 12L14 is almost as nice as Brass to cut, 4140, 4340 and similar have a pretty good machinability rating too. 303 for stainless. If buying aluminum for turning, I REALLY like dealing with 7075 in the higher -T numbers, even with it's ability to corrode in some circumstances, while you watch! :) 6061 is cheap and available get -T4 or -T6, 2024 if you can find it, again, at he higher temper numbers.

Chatter is akin to music. It's a series of vibrations, that complement the ones before and after. Some times, you happen across the cut conditions that make that funky music, and the way out, is to change the cut conditions.

I'll second @Dabbler s comment. I think all 3 of us are brothers from another mother in many ways but not in others.

One potential difference prolly inherited from my own mother is my curiosity. To be truthful, I think Dabbler shares that trait. @trevj maybe, maybe not - I don't know him well enough yet. Anyway, the point here is that I am never happy with rules and standard ops. I wanna know why and I need to understand the underlying physics. For me, it isn't enough to know what works or doesn't. Although I never taught machining, I have done a lot of teaching. The very best students were not those that did as they were told or memorized the rules. They were the ones who questioned the rules and sought to understand reality vs observation or rote.

@jcdammeyer raises some excellent points. In particular, I love the musical analogy. Although my choice of the word Aanalogy isn't the right word cuz they really are one and the same thing. Both involve vibrations with harmonics.

If I combine @PeterT s thinking with those of @jcdammeyer, I am immediately impressed by the possibilities. Previous discussions on here have explored what really happens as a lathe tool makes a cut. Perhaps the most important (in my mind) is the fact that the tool does not really cut right to left - it cuts mostly circumferentially with the vast majority of the cutting forces applied downward onto the top of the tool. Moreover, this cutting isn't really cutting it is more like a peeling action that pushes and deforms the metal above the tool. The deformation depends on the tool geometry, metallurgy of the part, feed, speed, lubrication, etc etc etc. The high speed video Peter provided a while back were simply amazing but only served to reinforce my thinking on the matter.

If you followed this post thus far, I am grateful. Because now I can get to my point which has also been discussed before.

I think we can all agree that the feed forces are very low compared to the cutting/deformation/peeling forces. None the less, these feed forces are real and are there. In my mind, whether or not @jcdammeyer's theory is possible boils down to how these forces manifest themselves and to what extent they govern the overall process. Perhaps, the peeling action rips enough adjacent metal away from the leading edge of the tool to allow it to momentarily advance beyond the pressure of the lead screw. In fact, for some metals I could even imagine moments in time where this process vibrates around causing all kinds of finish issues.

Of interest to me though is the fact that I've never seen this on my own lathe. That's not to say that it's not there - only that I don't see it. My carriage handwheel always turns very smoothly. But that could be both the momentum of the wheel and the speed of my eye. It is well known that the eye and brain turn discreet 30hz images into smooth motion.

I think it's also worth thinking about the impact of lightly worn ways. Mine are induction hardened and show no visible or measureable sign of any wear at all. But that isn't the case for most ways. I think that any wear will show up as a high or low tool height. Depending on the diameter of the part, this could have a minimal to major impact on the cutting/deformation/peeling process.

I'm quite interested in knowing what @DPittman learns in his experimentation. At the same time though, I agree completely with @Dabbler - a diagnostic path is much superior to a hit and miss approach.

Sorry for the long post.
 
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