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South Bend 10L, uneven cut

scooternut

Plastic
Joined
Nov 30, 2017
Location
Washington, PA
New South Bend 10L owner here.

I'm still learning proper setup and this old lathes quirks. I intend to do a 2 collar test later to help with a taper that I'm seeing over a long cut. The ways do have some detectable wear, but not horribly so, and the saddle does have visible wear on the underside. I have leveling feet on the way, I noticed that the rear leg is not in contact with the floor, so perhaps my question is premature.

Problem, see pic attached. The tool dug in to create that "thread" while returning with the carriage hand wheel. As if using the hand wheel moved the tool closer to the part. High speed steel from overseas, 10L14 1/2 round, 5c collet set up in the spindle, slowest speed and slowest auto feed, .003 depth of cut, cross slide zeroed and backlash removed.

What could be the cause of this spiral? Shouldn't the carriage return without backing off the cross slide? Sorry, I'm very new and learning all that I can.

IMG_3233.jpgIMG_3182.jpg
 
" Shouldn't the carriage return without backing off the cross slide?"

Basically, no. For a variety of reasons, lathes are not infinitely rigid. So in any practical application
it's standard procedure to not drag the tool across a cut you just made. The corollary to this is,
if you can do that and not make hardly any impression on the surface you just created, that's a
very good lathe.

Does not take much to move the cutter a few thou. Before you level up your lathe, do this:
Put a piece of stock in the collet (or chuck) extending out a couple of inches. Touch off on the
stock with a good dial indicator.

Then just *lean* on the headstock of the machine with your hand. See what the dial gage does.

This is one reason that old timers holler at novice operators who hang out this way while a cut is in progress.

Be sure both legs are load-bearing before you start the two collar test. The machine won't be nearly as
fussy after you do this.
 
That textbook tool you ground is really sucking for you in that QCTP with that presentation, compounded by large radius, too light DOC and the small diameter workpiece.


Look up "3 grind tool" and try that.
 
There is flex in every part in the machine between the tip of the cutter and the floor.

You can stop the lathe at the end of cut then return to the right and restart and make another cut and you will remove more material.

This is due to the force of the cutting pushing back on everything.

Look close at the end nearest the chuck.

In the photo it looks like the OD is smaller there.

Likely because you stopped the carriage movement but spindle still turning allowing it to continue cutting while the flex pressure is reduced by the cutting.

Normal stuff.

Try using power feed with smallest feed rate and lesser depth of cut.

If you need to be dead on you may need to experiment with tool shape that works better as well as sneaking up on final or finish cut.



Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 
Something is loose. Either the carriage is not riding correctly on the bed and is cocking a bit when rewinding the carriage back to start with the hand wheel or the cross feed casting is loose of the carriage (loose gib) or the compound is loose (Gib). In essence, every moving element must be adjusted so that its motion is ONLY in its intended direction. To test these things, you should use a dial indicator bearing on the suspect casting and manually with force try to move this casting in all the unintended directions and look for movement on the dial indicator. Do this for every element. You'll find your fault(s). Remember, it is an old lathe and may very well be worn out everywhere. You won't know until you do this test. Get back to us with your findings and we can suggest the correct remedies. Lastly, a level bed means a straight bed. Sure your bench should be level, but it is the bed that must be straight and this is adjusted with shims on the bed to bench mounting bolts, not the bench legs. To do correctly you will need a Precision level, not your hardware store special.
 
That textbook tool you ground is really sucking for you in that QCTP with that presentation, compounded by large radius, too light DOC and the small diameter workpiece.


Look up "3 grind tool" and try that.

Funny you mention that. I was getting WAY better finish on my mini lathe with a tool that I ground in the way that I think that you are referring to, though 5/16 bit. It was the first tool that I ever ground. I just bought some new 3/8 bits to make another. The one that I used above I actually found in a full Kennedy box that I bought, likely from an apprentice based on the contents. It sucks, develops a burr too easily, though I did not feel a burr after the above cut.
 

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Something is loose. Either the carriage is not riding correctly on the bed and is cocking a bit when rewinding the carriage back to start with the hand wheel or the cross feed casting is loose of the carriage (loose gib) or the compound is loose (Gib). In essence, every moving element must be adjusted so that its motion is ONLY in its intended direction. To test these things, you should use a dial indicator bearing on the suspect casting and manually with force try to move this casting in all the unintended directions and look for movement on the dial indicator. Do this for every element. You'll find your fault(s). Remember, it is an old lathe and may very well be worn out everywhere. You won't know until you do this test. Get back to us with your findings and we can suggest the correct remedies. Lastly, a level bed means a straight bed. Sure your bench should be level, but it is the bed that must be straight and this is adjusted with shims on the bed to bench mounting bolts, not the bench legs. To do correctly you will need a Precision level, not your hardware store special.

I picked up a used Starrett 98 level just a few days ago to assist me with this. Facebook is good for some things! I do intend to learn the proper way, been reading all the posts, watching all the videos.

This is the first that I'm reading to shim at the bed/ leg mounting bolts. Though, I do understand that later SB have a leveling adjustment in this location.
 
Something is loose. Either the carriage is not riding correctly on the bed and is cocking a bit when rewinding the carriage back to start with the hand wheel or the cross feed casting is loose of the carriage (loose gib) or the compound is loose (Gib). In essence, every moving element must be adjusted so that its motion is ONLY in its intended direction. To test these things, you should use a dial indicator bearing on the suspect casting and manually with force try to move this casting in all the unintended directions and look for movement on the dial indicator. Do this for every element. You'll find your fault(s). Remember, it is an old lathe and may very well be worn out everywhere. You won't know until you do this test. Get back to us with your findings and we can suggest the correct remedies. Lastly, a level bed means a straight bed. Sure your bench should be level, but it is the bed that must be straight and this is adjusted with shims on the bed to bench mounting bolts, not the bench legs. To do correctly you will need a Precision level, not your hardware store special.

I get .020 vertical movement at the compound when I pull the entire front assembly upward at the apron. Seems the cutting forces are down only here though? No movement when pulling up at the far side of the carriage. The rack did have shims to the bed, I was sure to return them.
 

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That textbook tool you ground is really sucking for you in that QCTP with that presentation, compounded by large radius, too light DOC and the small diameter workpiece.


Look up "3 grind tool" and try that.

Good call, missed that huge nose radius. It really is the textbook "How to Run a Lathe" book tool grind.

jrr_toolbit.jpg
 
I raised the lathe today and put four feet firmly on the ground. This really helped consistency with the Starrett 98 level. I was able to get a pretty consistent reading up and down the ways, at least to the installed chuck. If I remove the chuck, like I was installing 5C, the reading gets very wonky up near the headstock.

I'll let things settle a bit, level again, then run the 2 collar test.
 
Thank you everyone.

I was able to get the taper under control with just a few tweaks on the leveling feet.

I ground a new 3 grind tool with almost no radius, but did polish it up on a fine stone. I was getting pretty nice finishes with it.

Thinking I'll just leave the 5C setup out of this equation based on the way off Starrett 98 readings up close to the headstock. Makes sense in my mind that this is where the bed/ saddle wear shows itself. At least I know that I'm cutting straight the first 7 inches out from the chuck.

Thinking I'll need to realign the tailstock now.

Thanks again everyone.
 

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Nice job and good call on not using the 5C set up for your test....what you did is fine.

I'm sure in actual use your 5C set up will be fine too.
 








 
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