View Full Version : 1st Project: threading dial. Suggestions?

02-21-2004, 07:29 AM
......Now that I have my lathe setup and leveled, I've decided I'd like to make a new threading dial. The guy I bought the lathe from gave me a well used one. The dial is rather small and the gear is worn a bit concave.

I bought a helical cut gear from Logan Actuator and have a design in mind and it will have about a 1.25" dial face.

What my basic need is, is confirmation of my thinking on initial indexing of the dial. I believe I'm correct, but I've sure screwed the pooch on other stuff I felt secure about before :-)

Once I have the unit made and attached to the side of the apron, if I have the gear engaged with the leadescrew and then close the halfnuts I can then scribe a mark on the housing face and dial face, right? If the machine was running, the halfnuts would engage at this point, as they ARE engaged now while stationary.

The current treading dial has 4 marks at 90 degrees around it's face with just a '1' & a '2'. If I planned on doing multiple threads at some point in the future, how should the dialface be marked?

Once this is settled all I have to decide is if I want to make the housing from aluminum or steel :-).


02-21-2004, 08:28 AM
There was an article, years ago, in HSM about making a threading dial. I imagine our ever-obliging host, Neil, would be glad to sell you a copy of the back issue.

But aside from that, your logic sure sounds reasonable to me....

My South Bend dial has 8 lines, numbered every other line:

1 <line> 2 <line> 3 <line> 4 <line>

[This message has been edited by SGW (edited 02-21-2004).]

G.A. Ewen
02-21-2004, 09:01 AM
The numbered index lines on the dial depend on the (1) pitch of the lead screw, (2) the number of teeth on the gear. For example, if you have an 8 tpi lead screw driving a 32 tooth gear there will be 4 numbered lines. (you can put lines between these if you wish but don't number them) On the same lead screw if you had a 16 tooth gear there would be 2 numbered lines.

02-21-2004, 01:55 PM
Your method for scribing the first index mark on the dial face is correct, however before you scribe the mark make sure you turn the spindle over by hand enough to take up any backlash in the gear train and leadscrew/halfnuts. A little clockwise pressure against the carriage hand wheel to simulate pressure between work piece and cutting tool would probably help too. The easy way to scribe the remaining marks would be as follows: set up a dial indicator to measure carriage travel. Disengage the halfnuts and move the carriage exactly 1/2 inch and scribe the next mark. Repeat this for each succeeding mark until you return to the original mark. Number every other mark, and you're done!

[This message has been edited by Carl (edited 02-21-2004).]

Paul Alciatore
02-21-2004, 04:45 PM
The article on Threading Dials by Peter F. Lott was in the May/June 2000 issue of HSM. I reread it recently and can tell you it is an excellent source of information on this subject. He discusses the theory and provides rules for different kinds of threads with different lead screw pitches, even odd ones like 9 TPI.

As for aligning the dial with the lead screw / half nut, your procedure is good but I would strongly recommend that you incorporate a means of readjusting this alignment into the design of the dial. This will facilitate adjustment in case of wear or half nut replacemenmt. This could simply be an accessable set screw on the gear that can be loosened to allow resetting the alignment.

Paul A.

John Stevenson
02-21-2004, 05:41 PM
Myfords alter the zero setting on their threading dial by using spacing washers on the mounting stud, simple and cheap but it works.

John S.

Paul Alciatore
02-21-2004, 06:44 PM
Yea, seems like that would work with the SB too.

Paul A.

<font face="Verdana, Arial" size="2">Originally posted by John Stevenson:
Myfords alter the zero setting on their threading dial by using spacing washers on the mounting stud, simple and cheap but it works.

John S.</font>

J Tiers
02-21-2004, 10:50 PM
<font face="Verdana, Arial" size="2">Originally posted by Paul Alciatore:
Yea, seems like that would work with the SB too.

Paul A.


The set screw works pretty well............

02-22-2004, 01:45 AM
Just a note:

Some threading dial gears are MADE concave!

02-22-2004, 05:43 AM
......Thank you all for your replies.

Carl, good deal about taking out any play. I don't know if I'd have thought of that, and it's an obvious thing to do.

SGW, I guess those other lines are for catching the thread on multiple threading jobs? In other words the 8 lines represent the 8 teeth in a i" length of the leade screw? Concieveably then an '8 start' thread is possible with the right pitch. AM I thinking right here? (I'm new, it's all magic to me right now :-)

CCWKen, okay well! I didn't know that. I figured it was worn. I'll have to look closely at it to see if it was made that way. Seems reasonable as more of the tooth could bear that way.

I'm getting a nebulous hold on the fact that the leadescrew for threading will turn at various speeds when threading, to drive the carridge, and therefore the thread dial can turn faster and/or slower.

Each mark on the dial (up to 8?) represents a place that the halfnuts will engage the leadescrew, right? I guess I need to re-read the Southbend 'How to' book and a couple other sources rather than have everyone repeat info readily available.

Again thanks for the replies. Books are good but having people who've been there and done that run it past me is better. A different slant or explaination sometimes clicks easier too.


02-22-2004, 01:34 PM
Threading dials are marked in half inch intervals because all even number threads will pick up at half inch intervals. This makes every other line(the numbered ones) a one inch interval and all odd number threads will pick up at one inch intervals. For multiple threads you will have to use a marking pen and mark engagement points between the existing lines. For two start thread with an even tpi lead the pick up point for the second thread will be exactly half way between the existing half inch interval marks. For a two start thread with with an odd tpi lead the first thread will start on a numbered one inch interval line and the second thread will pick up on the unmarked half inch interval lines. For four start threads with an even tpi lead you make three evenly spaced marks between each half inch interval mark, label the existing half inch interval marks "A" and the marks you drew in between with labels "B" "C" "D". The first thread will pickup on all lines marked "A", the second thread will pickup on all lines marked "B", the third thread picks up on "C", The fourth thread on "D". For four start threads with an odd tpi lead, draw a line between each existing half inch interval mark. Label the existing numbered lines "A", Label the next line that you drew "B", label the next existing un-numbered line "C" and label the next line that you drew in "D" The First thread will pick up on "A", the second thread on "B" the third thread on "C", and the fourth thread on "D",.The above information will work for an 8 tpi leadscrew or multiples there of (like the sixteen tpi leadscrew on 9" chinese lathes). It will work for two start threads on a lathe with a four tpi leadscrew, but not for a four start thread because of the lack of extra engagement points between the half inch interval marks.