Thicker At One End Versus The Other.. ?

[BellyUpFish]

Ok, I'm still learning and on a less than desirable piece of equipment, but it is what it is..

I've noticed that when I go to turn something, the end of the turn near the chuck always winds up thinner than the end near the live center.

For instance, today I needed a piece that was 4.46mm thick and 37mm long. When I got the end near the Chuck to 4.46mm the end near the live center was more like 4.78.

What is the issue here?

 

[royesses]

Most likely your tailstock is not aligned on center with your spindle. Pulling the tailstock towards the operator by half the difference in turned size would bring it on center. You could place a dead center in the spindle and one in the tailstock and adjust until they are exactly lined up. Or wait until the more experienced guys respond to your question with valuable tips.

 

[mce5802]

The diameter of the stock you are turning will give anybody a headache, it is probably flexing away from the tool somewhat. If I read it right, it's about 1 1/2" long? And you're getting roughly .012" taper? That's a lot. If you meant 37 cm I'd say it's probably partially due to the stock flexing away from the tool. But anyway to check your tailstock alignment, put a piece of stout round stock (maybe 1 1/2 dia) as long as you can comfortably fit in the lathe between centers, and make a pass across it. Check the dia near both tailstock and headstock. Smaller at headstock, move tailstock towards you, etc. You can turn the center down leaving a larger boss on each end if u want, makes it a little faster process. It may take a few passes but you need both ends to be as close as possible to the same diameter to ensure your tailstock is aligned. Order yourself a copy of South Bend's How to Run a Lathe. Lot of good info in there for beginners, or anybody for that matter.



Edit: In case you didn't know, every lathe has two set screws near the base of the tailstock that are used to align it in this process. Can also use them to offset the ts for turning a taper. Fwiw.

 

[rafe]

Ok, I'm still learning and on a less than desirable piece of equipment, but it is what it is..

It may be what it is ,but what is it? Anyway the previous posts are a good start ....However if the ways are bad they can cause the same problem on the vertical alignment.
Setting your lathe up to its very best potential is real important and a good learning experience that will carry over into all your projects. A good machinist can do amazing things with a worn machine.
....

 

[chips&more]

Pictures would help please. And you did not say what the material was that you are cutting. It makes a BIG difference with tool cutting resistance and the material flexing to name a few. Are you using the live center for this operation or just a mention for reference?…Good Luck, Dave.

 

[BellyUpFish]

Thanks for the replies guys..

The numbers used are imaginary, as I didn't record them. I just did what I needed to do to get the parts to the size needed.

I'll try turning the longest piece I can fit. The machine could use some tuning I'm sure.

I'm making hinge pins for "Khyber pass" Ak builds. 37mm long. 4.48 at the thick spots 3.86 at the thin.

Also tried to make them look "hand made" which, with my skill set, plays into my favor.

 

[BellyUpFish]

It may be what it is ,but what is it?

It is the glorious Harbor Freight 46199..



I just did a few passes over a 12" piece and came up with .8695" starting and .8590" ending.

.0105" deviation.

 

[JR49]

BellyUpFish, Set up a DI on the side of that piece, at the tailstock end. Preload the DI and zero it, then with the tailstock hold down loose, use whatever adjustment screws are on tailstock (not familiar with that machine), adjust it towards the operator by 0.0052". Although I'm a beginner, pretty sure I'm right on this one. What say you pros? Good luck, JR49

 

[BellyUpFish]

Well I've got it down to .0025, which will do for me at this point.

Thanks for the help guys.

 

[epanzella]

If you didn't do it already you should check your headstock alignment with the lathe bed. Put a stout (1.00 inch OD or better) piece in the chuck sticking out about 6 inches and don't use the tailstock. Take a light cut on it. If there's no taper then your problem is confined to the tailstock. If there's a taper then you headstock needs tweaking. If you counteract a headstock misalignment with a tailstock adjustment, the taper will return whenever the tailstock is not used.