# Thread Dial on Mini Lathe not Turning?



## RMS (Dec 9, 2010)

Hey Guys,

I am just learning about screw cutting, and this dial is supposed to turn when the half nut is not engaged, so what is making this turn when not engaged and what stops it when it is engaged? 

Anyone have issues with the mini lathe's thread dial not turning at all? Any suggestions on how to fix or adjust?

Thanks,
Rob


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## techonehundred (Dec 9, 2010)

Nothing stops the dial from turning, when the half nut is engaged, the apron moves the same speed as the dial is turning. Everything is in sync, so the pitch of the leadscrew that would turn the gear is in the same relative distance from the half nuts and thus moves forward at the same speed. It is much easier to see on older lathes where the gear on the dial is out in the open.

Hope you can make some sense out of this.


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## RMS (Dec 9, 2010)

techonehundred  said:
			
		

> Nothing stops the dial from turning, when the half nut is engaged, the apron moves the same speed as the dial is turning. Everything is in sync, so the pitch of the leadscrew that would turn the gear is in the same relative distance from the half nuts and thus moves forward at the same speed. It is much easier to see on older lathes where the gear on the dial is out in the open.
> 
> Hope you can make some sense out of this.



OK, I get the drift a little better now. I guess maybe now to get my dial to spin when the half nut is not engaged I may need a shim "read somewhere" to align it better basically this dial is always in contact with the lead screw. Maybe mine as with others some tweaking is needed.

Thanks!


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## Ken I (Dec 10, 2010)

On some lathes the dial can be swung out of engagement when not in use.

That indicator is supposed to tell you when to engage the leadscrew - all good and well but the information supplied can be misleading.

Particularly when cutting odd pitch (anything that is not an exact multiple of your leadscrew pitch or metric off an imperial screw or vice-versa).

Personally I long ago gave up using the indicator - simply had too many disaters.

I now screw cut in reverse - away - from the chuck so I don't have to disengage the nut - I then simply go from forward to reverse until the job is done.


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## Lew Hartswick (Dec 10, 2010)

Ken I  said:
			
		

> Personally I long ago gave up using the indicator - simply had too many disaters.



 That sounds like a coward's way out to me. 
The Clausing /Metosa lathes at school have 20 numbers on the threading dial and a 
little chart on the apron where the half nut lever is to tell how to use them. 
"for even number of threads ANY number" , "For odd threads 1,3,5,etc." "For half
threads [I forget never used it  ]"  
  ...lew...


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## mklotz (Dec 10, 2010)

USING THE THREADING DIAL

Some folks are confused by which marks to use on the threading dial on their
(assumed Imperial) lathe. Of course, you're always safe restarting on the
same dial mark on which you started but that means you'll spend a lot of time
'waiting for your number to come up'.

It's pretty easy to think through. Most dials have four numbered marks
labeled, unsurprisingly, 1-4. Between these marks are smaller, unnumbered
marks.

[Aside: A consequence of the four numbered mark dial is the fact that the
gear that meshes with the feed screw will have a number of teeth which is four
times the tpi of the feed screw, i.e., an 8 tpi lead screw will have a 32
tooth gear on its thread dial. This is worth knowing if you intend to build a
threading dial for a lathe that lacks one. Since there's no load on this
gear, a perfect match to the helix angle of the lead screw is not needed. Any
old gear with the right number of teeth can be pressed into service.]

The numbered marks almost always correspond to a carriage movement of one
inch. (However, you should confirm this by actual measurement on your lathe.)
By deduction, the unnumbered lines must then correspond to a carriage movement
of one-half inch.

Now, suppose I'm cutting an even-numbered thread (e.g., 32 tpi). If I move the
carriage by one-half inch, the tool will reenter the thread perfectly. If I
move the carriage one inch, the tool will also reenter. Therefore, I can
reengage the half-nuts on ANY line on the threading dial.

If I'm cutting an odd-numbered thread (e.g., 13 tpi), the tool will not reenter
the thread if I move one-half inch - I have to move one inch. Therefore, I
must reengage the half-nuts on ANY NUMBERED LINE on the dial. (If I started
the thread on an unnumbered line, I would then reengage on unnumbered lines but
that is generally too difficult to remember in the 'heat' of thread cutting and
should be avoided.)

If I'm cutting a half-fractional thread (e.g., 11-1/2 tpi), the tool will only
reenter the thread every two inches. Therefore I must reengage the half-nuts
on ONLY THE ODD NUMBERS ON THE DIAL (1 and 3) or on the even numbers (2 and
4). It's a good idea to decide on one of these options and always stick with
it. I always start the thread on 1 and then use either 1 or 3 to reengage.

Rarely, a lathe can cut a 1/4 thread (e.g., 1-1/4 tpi). This thread will only
repeat every four inches so, in cutting such a thread, one would reengage the
half-nuts on the same mark one used to start the thread.



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## 4156df (Dec 10, 2010)

Marv,
Super post. Useful information well explained. Thanks.
Dennis


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## RMS (Dec 10, 2010)

Ken I  said:
			
		

> On some lathes the dial can be swung out of engagement when not in use.
> 
> That indicator is supposed to tell you when to engage the leadscrew - all good and well but the information supplied can be misleading.
> 
> ...



So then I can assume you would just take a bit more time aligning the start point on every cut, and that having this dial is not a "Real" big deal then.


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## RMS (Dec 10, 2010)

4156df  said:
			
		

> Marv,
> Super post. Useful information well explained. Thanks.
> Dennis



I agree! Thanks here also.


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## Andrew_D (Dec 10, 2010)

I take an even easier approach...I always start on "1"...all the time, all threads.

Sure, it takes longer waiting for the dial to spin around, but I'm not doing production here......

Andrew


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## Ken I (Dec 11, 2010)

Lew Hartswick  said:
			
		

> That sounds like a coward's way out to me.



I know how it's supposed to work - but between mistakes and the occasional impropperly closed nut (which puts you off pitch) I have ruined a fair number of bits - and this has happened on any number of different lathes (TOS, Graziano, Colchester, Myford etc. etc.) so its not just my POS Chinese lathe.

So now I always screw cut in reverse - away from the job - with the tool in upside down.

Particularly when working in a blind bore or to a shoulder.

This allows me to be sure that I have properly engaged the lead screw in the right place - if you've ever crossed a thread on the last cut you'll know what I mean.

I can also run at higher rpm's for better cutting speeds. When working towards a shoulder you daren't go too fast - unless your lathe has an auto-disengage stop - my cheapie doesn't.

Engage the nut - roll the chuck by hand to check you are in the right place - set to depth - turn on - stopping is no longer critical as you are going away.

You obviously start from an undercut at the shoulder or the bottom of the blind bore. With an uspide down internal threading tool you are working on the "away" side of the bore.

I Don't always do this but when working on a part that has several hours invested in it already I tend to go the ultracautious approach - I don't disengage the screw - just keep going from reverse to stop to forward etc. etc.

No screw up is possible (excuse the pun).

Ken


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## RMS (Dec 14, 2010)

I got my thread dial fixed! ;D I loosened it up, started the lathe and wiggled it into the lead screw and the dialed started turning (was happy) then tightened it back up. As you might guess this is all new to me but having fun learning, so thank you all!

Rob


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