turning rod smaller at one end

This topic has 9 replies, 6 voices, and was last updated 5 November 2012 at 22:16 by Nobby.

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4 November 2012 at 19:54 #102779
barry
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@barry
when im turning steel rod as i get near to the end it takes more off. Then i get the right size at the start then smaller at the end

only just got my lathe so any help pls

baz
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4 November 2012 at 19:54 #6421
barry
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@barry
turning rod smaller at one end
5 November 2012 at 09:59 #102827
Ian S C
Participant
@iansc
Hi Baz, from what I read ,the bar is a larger diameter the further away from the chuck you go. Unless you use a center, or a steady of some sort, any relitivly long bit of metal in the lathe will be pushed away by the tool, and the nearer the chuck you get, the more ridgid it becomes, and the greater depth the tool cuts. Without support, you might need two or three cuts at the same setting with a sharp tool.

Ian S C
5 November 2012 at 11:29 #102840
MadMike
Participant
@madmike
Barry waht Ian says is correct. However to help us get to the root cause of the problem some additional information would be helpful.

What diameter steel are you cutting, what depth of cut, how long is the turned length, how much of the metal is protruding from the chuck, what tooling are you using, and what machine and its condition?

More questions will undoubtedly flow but it is essential to know as much as possible to get a subjective diagnosis. IMHO.
5 November 2012 at 12:07 #102843
Bazyle
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@bazyle
Welcome to the forum Baz.

Baz
5 November 2012 at 12:12 #102844
Martin W
Participant
@martinw
Hi Baz

From your post I read it that you are getting the correct diameter at the chuck end of the work and as you move away from the chuck the bar is being turned under size, is that correct ?

What Ian says about turning bars is valid as there can, on long or thin work, be a tendency for the work to be displaced by the tool but this causes the opposite effect where the turned item gets thicker the further from the chuck.

Are you using the topslide or moving the saddle to move the tool along the work. If you are using just the topslide then check that this is running true to the lathe turning axis. If it is not true to the axis then you will turn a taper depending on the angle the topslide is offset by. The angle of the topslide can be adjusted but on some lathes it is a bit fiddly as the locking nuts are hidden under the slide .

Let us know how you get on and any more info will help.

Martin

Edited By Martin W on 05/11/2012 12:16:40
5 November 2012 at 12:27 #102845
Bazyle
Participant
@bazyle
Now to be more helpful than my first post

. A new lathe should have been set up t turn nice and parallel but might have been miss-set by a trainee, knocked, have a dead fly trapped under something etc, Also just putting a straight bar in a 3 jaw chuck doesn't mean it is sticking out dead straight, they aren't that easy.

First check. The headstock might not be pointing straight down the bed. Put a new bit of round bar about 9 in long in the chuck and check it by the chuck using a dial test indicator for the error as you rotate it. Mark and record the peak as it won't be dead true. Then go to the end of the bar and test there gently tapping until you get them to the same error in the same place (note not perfect at the outer end – the same). Now your bar is parallel to the spindle even if it wobbles a bit going round. Now run the test indicator held in the toolholder along the side then top of the bar. Any error here is the misalignement of the headstock and is the first thing to correct.

(Don't bother with expensive morse taper test bars while a beginner.)

Edited By Bazyle on 05/11/2012 12:28:25
5 November 2012 at 12:53 #102847
Nobby
Participant
@nobby
HI Baz & Guys

No mention of size of rod as Ian said a center may help . and what lathe is it ? as it may be difficult to adjust

Nobby
5 November 2012 at 21:03 #102906
barry
Participant
@barry
Hi and thanks for the replies

My Lathe is a Hobbymat MD65 which is about 20yrs old The steel diameter is 6mm the length is 12cm with 3cm in the chuck Held at one end by the tailstock. I am cutting towards the chuck Is this the right way to do it? It is the chuck end which is getting smaller, Having another look at it today I can see that the carriage moves up and down. i can tighten it up but it is then very difficult to move. When it is easy to move it has a lot of play in it Been following the manual instuctions for a couple of hours but still cannot get a happy medium. Is there a special way of doing it?

Thanks Baz
5 November 2012 at 22:16 #102922
Nobby
Participant
@nobby
Hi Baz
When you say held one end with the tailsstock , ie with a centre . The tailstock may be out of line .Adjusting the carriage . If you adjust the screws one at a time till tight then back off a little each time & lock the retaing nut that may help. I ve turned & threaded 4 mm useing a traveling steady .
Welcome to the Forum Nobby

Edited By Nobby on 05/11/2012 22:17:11
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