What's new
What's new

Metric threading a pitch my lathe doesn't have available

abmaul

Plastic
Joined
Oct 10, 2012
Location
Jacksonville, Il
First off I hope this is in the correct category. I searched around and couldn't decide where to put it and this looked to be the best option.

My problem is that my lathe will cut M1.20 and M1.30 pitch threads but my chart does not show that it can cut M1.25 pitch. This is a standard lathe with an 8TPI lead screw. To cut metric threads I must change my gears from a 40 x 127 x 40 to a 40 x 127/120 x 40. Is there a way to cut M1.25 threads on this lathe? If I have to have new gears cut then so be it. I've searched all over the net and no one else I can find has this problem. Thanks in advance.
 
20.32 tpi is mighty close to 20tpi ..hmmmm

First off I hope this is in the correct category. I searched around and couldn't decide where to put it and this looked to be the best option.

My problem is that my lathe will cut M1.20 and M1.30 pitch threads but my chart does not show that it can cut M1.25 pitch. This is a standard lathe with an 8TPI lead screw. To cut metric threads I must change my gears from a 40 x 127 x 40 to a 40 x 127/120 x 40. Is there a way to cut M1.25 threads on this lathe? If I have to have new gears cut then so be it. I've searched all over the net and no one else I can find has this problem. Thanks in advance.


Is this application a short thread for your own needs? 'Might work!
 
It may be possible to cut that particular pitch exactly on your lathe, but if not, you can probably make up a gear train that will cut a very close approximation, which would be fine for anything except a precision leadscrew. Your first step is to find out what loose gears you have, and then carry out some calculations. Rather than describe these in detail and probably confuse the issue, I suggest that you get hold of 'Screwcutting in the lathe' by Martin Cleeve, which has several chapters devoted to this and related problems.

Gordon is quite right to point out the problem with your description. A M1.25 thread is very different to what you intended. To see how to designate metric threads, please see this: https://en.wikipedia.org/wiki/ISO_metric_screw_thread.
 
A 40X127/125X40 compounded train will cut a 1.25mm pitch using the "20" position of the QC gear box

What I have done is provide a 0.984252:1 compound ratio in conjunction with the "5" position on the QC to alter lead from .200" to .19685" (5mm) and then divided that by four by selecting the "20" position

.19685 / 4 = .049213 lead or 1.25mm

This would work even if there was no "5" position due to size of lathe.

On edit - it will be important to get the gears on right. upper 40 drives the 127, lower 40 driven by the 125. This actually creates a 1.0160:1 reduction ratio - the reciprocal of the 0.984252
 
Last edited:
When I encountered this problem, I found a number of discussions about it. I came to the conclusion that I needed some new gears, which didn't happen. I ended up buying a 22 x 1.25 die to thread the part. Well, then it turned out that the part was really not 22mm x 1.25, but rather 7/8"-20. (I was making a new shaft for an import boring head and the threads were too short to measure accurately).

If you need a 22 x 1.25 die, I'll make you a deal!
 
Thank you so much for all of the replies. For some reason I was not getting any e-mails when someone replied to my post. I was actually trying to search again for this same problem and came across this post I created. I actually was on the quest of just cutting 20 tpi because it is so close to the 1.25mm thread pitch. I'm actually cutting M12 x 1.25mm threads and would have just purchased a tap but this is for a tie rod and I must also cut left hand threads on one end.

Jobnoder - Thank you very much for explaining what gearing I need. I still don't fully understand how you come up with what gears to run but I will probably have some cut on a waterjet very soon. I don't understand what you are talking about on which position to use on the quick change gear box. I'll have to look how many positions my gearbox has.
 
Sounds like two things need to be done. You need to practice up on technical forum participation, and you need to know more about your particular lathe.



Thank you so much for all of the replies. For some reason I was not getting any e-mails when someone replied to my post. I was actually trying to search again for this same problem and came across this post I created. I actually was on the quest of just cutting 20 tpi because it is so close to the 1.25mm thread pitch. I'm actually cutting M12 x 1.25mm threads and would have just purchased a tap but this is for a tie rod and I must also cut left hand threads on one end.

Jobnoder - Thank you very much for explaining what gearing I need. I still don't fully understand how you come up with what gears to run but I will probably have some cut on a waterjet very soon. I don't understand what you are talking about on which position to use on the quick change gear box. I'll have to look how many positions my gearbox has.
 
I know how forums work. It has to be something in my settings that wasn't e-mailing me. I've subscribed to my own thread and it is now working (should be set up as default that way in my opinion). Thank you polish avenger.

I know my lathe but just couldn't remember how many gears I had on it (I'm not a full time machinist). It has A,B,C,D,E and 1 through 8 on my quick change levers.
 
It does help to look at your lathe before you ask questions.
I know how forums work. It has to be something in my settings that wasn't e-mailing me. I've subscribed to my own thread and it is now working (should be set up as default that way in my opinion). Thank you polish avenger.

I know my lathe but just couldn't remember how many gears I had on it (I'm not a full time machinist). It has A,B,C,D,E and 1 through 8 on my quick change levers.
 
Quote from above : The 20 tpi will work.

It may , depending on how many threads are engaged .
The lead error is .0008" .
A good example is the difference between a Japanese Standard bicycle axle ( 10 x 1 ) , and a Campagnolo axle ( 10 x 26 )
The difference in lead is .0009" . When mixed , the lock nuts thread on by hand . They are about 5/16" thick .
The bearing cones , which are 1/8" longer ( about 7/16" ) , start by hand but need a wrench to turn before they are fully engaged .
It kinda works , but it's a pain to adjust , and it's just not right .
Now a tie rod ; aren't you turning both ends at the same time , with poor fitting threads ?
 
abmaul, we can continue if you like on the 1.25mm pitch opening question. It would be handy for both of us to know what threads the gear box on your lathe will cut in those forty positions. If you have instead decided on 20tpi, there is no need to continue.

Don't feel bad about not being a full time machinist. The last time I was one of those was in 1972.:)
 
When you have a lathe with imperial threading, and fit the transposing gears to cut metric pitches, You end up with many odd pitches, that can be made. Often the lathe makers use what they consider the common threads, but may not be common based on the asia/europe common usage.

Without knowing your lathe this may or may not be usefull, but look anyway. If you want 1.25 pitch and it is not listed, see if there is a double thread that is, example 2.50 pitch, so the 2.5 pitch needs a gearbox setting of the levers/knobs whatever of the 10tpi setting, then just double that setting to 20tpi and it will cut a 1.25 pitch. Just because it is not on the chart does not mean it isn't in the gearbox. It just means they did not list it.
 
Another solution which will also require a new (smaller) gear is to change your gear train to: 40-127/120-32 and set the QCGB to 24tpi.

Code:
[FONT=Courier New]The math looks like:

(Stud Gear)                   (Transposing Driver)                  1
--------------------     X    -------------------    X     ---------------------     X    25.4  = New Metric Pitch
(Transposing Driven)          (Screw Gear)                  (QCGB Thread Pitch)


  40         120           1
----   X    ----    X    ----  X  25.4 =   1.25mm
 127          32          24
[/FONT]

With any new gear you are considering, make sure you check whether it will fit in your lathe and you can adjust the quadrant to make the gear train mesh properly.
 
I still don't fully understand how you come up with what gears to run but I will probably have some cut on a waterjet very soon.

Ask your waterjet guy what he is capable of, both in terms of positional tolerance and straightness/draft. I suppose if you just need temporary gears to get you through this project, waterjet might work, but my experience in working with a talented waterjet guy tells me that waterjet is simply not good enough to cut gears to final shape, or, if possible, would be more costly than other processes.

Full disclosure -- a fair part of my business is cutting gears on a milling machine :-).

Regards.

Mike
 
You sir are an idiot. You get on this site with 29 posts and call one of the sharpest guys on the site, a guy with over 17000 posts, the majority of witch are to help someone out, an asshole! Yes, there are some assholes on this site and you are one of them.

Are you in love with john? It was very valiant of you to swoop in to his rescue. 50,000,000 posts or just one doesnt matter.
 
Are you in love with john? It was very valiant of you to swoop in to his rescue. 50,000,000 posts or just one doesnt matter.

And you are the top competitor for the Idiot of the day award.
Since you have nothing of interest to contribute put a cork in it.
 
Are you in love with john? It was very valiant of you to swoop in to his rescue. 50,000,000 posts or just one doesnt matter.

No love, I don't even know him. Lots of respect for what he has to say though. I have been a machinist for over 30 years and more often than not I learn something from his posts. If you have nothing productive to say you may want put your keyboard aside and read a bit more, you might learn something.
 








 
Back
Top