Thread chasing Dial

[cobbadog]

Hi Guys,
New here and looking for some help please. I recently bought my first metal lathe and it is a Chinese made one that came with no thread chasing dial. I restore vintage tractors, engines and mowers and from time to time need to make some nuts and bolts. I have searched high and low to buy a dial to suit but found I need a couple of different size gears to do the common metric size threads I need.

So what I need to know is for a lathe with a 20mm OD lead screw with a 3mm pitch;
What size gears do I require to make 1mm, 1.25mm, 1.50mm & 1.75mm metric threads?

thanks in advance for any and all help.
Cheers Cobbadog.

 

[rke[pler]

Just leave the halfnuts engaged for the whole duration of the threading operation, reverse the spindle to return to the start of the thread. Gears remain in sync with the thread so no problem, just takes a little longer.

 

[Street]

yep keep it engaged do above, but chinese POS made stuff is generally not discussed on the forum as it no good from the start, you get what you pay for.

 

[EPAIII]

With a 3mm pitch lead screw, you do not need a threading dial for the 1mm and 1.5mm threads. They will be synchronized at any place that you engage the half nuts. You literally can not get them wrong unless you remove and remount either the tool or the work.

I have not worked with a lathe with a metric screw, but I believe they usually have thread dials with some internal gearing. This is one of the things that proponents of the metric system do not talk about when they are bashing the English system which uses threads defined in threads PER inch and therefore has much simpler threading rules. I can attempt to give you some guidance for a simple dial that would work but may not be as convenient to use as the ones usually provided by the OEMs. The suggestions below assume a simple dial with the gear and the dial on the same shaft with no additional gearing between them.

The 1.25mm thread will synchronize at multiples of 5mm (1.25mm x 4 = 5mm) that are evenly divisible by 3mm. So you would need a gear that would allow you to travel one of those distances (15mm, 30mm, etc.) The obvious one seems to be 15mm and you would get that with a 5 tooth gear. That's too small. 10 teeth would give you a 30mm distance and that may be workable. If you have an even number of divisions on the dial face, you would be able to engage the half nuts on two of those lines that are 180 degrees apart as they would represent distances of 15mm.

Likewise the 1.75mm thread will synchronize at intervals of 7mm (1.75mm x 4 = 7mm) that are evenly divisible by 3mm. A 7 tooth gear would provide a 21mm distance (3 x 7mm) but I don't know if that would be practical. You may have to go to 14 teeth for a distance of 42mm. With 14 teeth for a distance of 42mm, if you have an even number of divisions on the dial face, you would be able to engage at two of them that are 180 degrees apart. So the same dial would work for both of the threads that you mention that actually need a threading dial.

You can work out other gears for additional thread pitches in a similar manner.

If you use these suggested gears you will have to wait a bit for the synchronization points. It may be faster to just leave the half nuts engaged and back up the spindle. That will work for all threads.

I would appreciate it if someone can check my logic and figures above.

Hi Guys,
New here and looking for some help please. I recently bought my first metal lathe and it is a Chinese made one that came with no thread chasing dial. I restore vintage tractors, engines and mowers and from time to time need to make some nuts and bolts. I have searched high and low to buy a dial to suit but found I need a couple of different size gears to do the common metric size threads I need.

So what I need to know is for a lathe with a 20mm OD lead screw with a 3mm pitch;
What size gears do I require to make 1mm, 1.25mm, 1.50mm & 1.75mm metric threads?

thanks in advance for any and all help.
Cheers Cobbadog.

 

[SteveBausch]

A good book for your line of questioning:

https://www.amazon.com/gp/bookseries/B00CM5MRWU

 

[DDoug]

https://www.practicalmachinist.com/vb/general/machinery-discussion-guidelines-137724/

A lathe with a 20 mm leadscrew might or might not fit the above requirements.

Why not post up a pix of said lathe ?

 

[cobbadog]

Thank you to those who have posted a positive reply, I appreciate it very much. My thoughts on this lathe is as I am a leaner driver a lower end price bracket lathe would get me started until confident enough to update to something better, but so far this has met all my requirements in making missing handles, bushes and pins for the restoration of our Vintage tractors, engines and mowers so now I feel this will do me.

I followed the link to amazon but they dont ship to Australia on that site so I will have a look on the Aussie site for the same book.

I already have a dial but need the right gear/s to suit my thread cutting and the information supplied above has been very helpful. I agree that both the 10 and 14 tooth gear would be best and that will cover those sizes and you mentioned that the lathe will already cut the other sizes but I still want to use the dial so that I dont have to stop the lathe and reverse it back to the beginning and as you mentioned this can be achieved at any interval on the dial. IS there a certain diameter that I need for the gears or just those number of teeth would suit?
I am sorry for any silly questions that I ask but I am doing my best to learn as I go

So attached, hopefully is a picture of the lathe in question and the dial I have that is suppose to suit a Sieg C2 and C3.

Thanks once again, Cobba

 

[gbent]

I don't think metric lead screws commonly used to threading dials. That is why you don't have one.

Learn to thread by reversing the motor.

Higher value machines had lead screw reverse on the carriage.

 

[James H Clark]

Cobbadog: I believe you forgot to read the rules at the top of the forum. The owner does not allow these types of machines discussed and this thread will be locked. I would offer some friendly advise that you take this question over to the HomeShopMachinist forum. It will be a much friendlier environment there. Please read the the rules at the top of this forum.

JH

 

[Matt_Maguire]

Keep your powder dry guys, I suggest the OP edit the first post & remove the chinese business. I wouldn’t remove the pictures though.

A metric tread dial “meters” off a distance, and the dial can be in thirds or quarters using several different changeable worm wheels. Or the dial can be thirds & quarters with selectable internal gearing… Either way metering off a length with a machine tool IS a professional question if there ever was one. Also if you’re building machinery that needs to meter off a length for cutting or dividing mechanically it’s good to know how.

EPA had it right in post #4, if the op is still struggling I can attach some reference tomorrow.

Good luck,
Matt

 

[fusker]

I have not worked with a lathe with a metric screw, but I believe they usually have thread dials with some internal gearing. This is one of the things that proponents of the metric system do not talk about when they are bashing the English system which uses threads defined in threads PER inch and therefore has much simpler threading rules

This is not correct. On my polish lathe (TUE-40) the lead screw has 6 mm pitch (IIRC) and there is a normal dial with no extra wheels.
If I want to do imperial pitch (inches) I have to add/exchange a set of gear wheels to reduce lead shaft revolutions and in this case I can't use the thread dial.
To avoid confusion, take rkepler's advice (#2), that's what I do anyway.

Yes, there is a lot of metric/imperial bashing. I grew up with inches but gradually went metric. I think both systems are really O.K. as long as you don't mix them up. The rules are the same with each of the units.
Just my .02 euros,
fusker

 

[EPAIII]

From the board's guidelines, "Larger and/or higher quality Asian machines that might be used in manufacturing or job shop setting are ok to discuss." With a 20mm x 3mm lead screw, it sounds like it may fit within that exception. But I am not the one to decide. I did not mind posting my prior answer even though it took around 15 or 20 minutes of my to compose. This was time that I could have been using for profit making purposes.

As I see it, it is an interesting question and the answer is not trivial nor can I remember it being discussed here before. If it has been, it could not have been over discussed. I am interested in the construction of metric threading dials, both for lathes with metric lead screws and for lathes with English lead screws and either precise ratio of approximate ratio transposing gears. So I was happy to donate a few minutes thought to the OP's question which brought my understanding of the situation a bit further toward my ultimate goal here. Ultimately I would like to design and make a completely universal threading dial. It would probably be electronic and would only use one gear for any lead screw and thread combination: English-English, English-metric, metric-English, and metric-metric. I feel that would be a useful thing and possibly also profitable.

As far as I can see, the only things that matter in the OP's question are the lead of the lead screw (3mm) and the lead of the thread that is being cut. The type of lathe, country of manufacture, the diameter of the lead screw, size of the lathe, or it's suitability for professional use are all completely immaterial. The answers would apply to any lathe of any size or capability that has the same lead screw lead and that is cutting the same thread. IMHO, that should qualify the question for discussion here or in any professional forum. It is not a waste of time to think of such things. And anyone who does not want to contribute is completely free to ignore it. I have had time constraints and unreasonable bosses and can completely understand their possible reasons for doing so. On the other hand, I think most of us can benefit from a discussion of this type: I certainly have already done so.

And I repeat my request for anyone that is capable, to check the math in the answers that I posted above. Metric threading dials DO exist and they generally have multiple gears that must be changed for different threads. Surely there are some members here who are acquainted with the use of these metric threading dials.

https://www.practicalmachinist.com/vb/general/machinery-discussion-guidelines-137724/

A lathe with a 20 mm leadscrew might or might not fit the above requirements.

Why not post up a pix of said lathe ?

 

[EPAIII]

OK, that is interesting to know. It makes me wonder if some metric lead screw pitches need multiple gears in the thread dial and others do not. I would love some more information on your thread dial: number of teeth in the gear, is there any internal gearing or just a shaft, how many divisions are on the dial, how are those divisions used, and are there any metric threads that it will not work with? I ask this because I would love to work out the math for it so I can see how it is working. And does it work well enough, does it come around to a sync point fast enough for it to be useful? Or do you just wind up working with the half nut closed and back up the spindle between cuts.

This is not correct. On my polish lathe (TUE-40) the lead screw has 6 mm pitch (IIRC) and there is a normal dial with no extra wheels.
If I want to do imperial pitch (inches) I have to add/exchange a set of gear wheels to reduce lead shaft revolutions and in this case I can't use the thread dial.
To avoid confusion, take rkepler's advice (#2), that's what I do anyway.

Yes, there is a lot of metric/imperial bashing. I grew up with inches but gradually went metric. I think both systems are really O.K. as long as you don't mix them up. The rules are the same with each of the units.
Just my .02 euros,
fusker

 

[cobbadog]

Not sure if I should say anything more on the topic after the riot act being thrown at me. Never knew that this was based around certain makes and model machinery for this I apologise it was not intended. I was guided to this forum from another one and simply posted what I thought was a reasonable question.
Cobba

 

[fusker]

No worries, cobber. Most people here are quite soft spoken and you will learn to live with the others (there is an ignore function which I use a lot).
EPAII, will have a closer look on the TUE40 and will let you know.
Regards, fusker

 

[DDoug]

Not sure if I should say anything more on the topic after the riot act being thrown at me. Never knew that this was based around certain makes and model machinery for this I apologise it was not intended. I was guided to this forum from another one and simply posted what I thought was a reasonable question.
Cobba

"Riot Act" ?

Give me a break.

If your post get's locked by the site owner (for violating those rules they
had written) would you be upset then ?

Seen this many times, hence my suggestion (no "riot act" here, please
go back and re-read my post).
Post get's locked, OP get's all butt hurt, and post's yet again a flaming
diatribe of why their post should not have been locked.

 

[awake]

cobbadog,

It's hard to be sure from the picture, but I'm not seeing a lead screw at all - unless perhaps it is under a cover near the top of the ways? There is a handwheel on the end that suggests that may be where the leadscrew resides.

But if it is covered like that ... 1) I'm guessing your half-screws are actually 1/2 screw, which may or may not cause some issues, and 2) you're going to have a hard time mounting any sort of simply thread dial where you can read it. The pinion on the thread dial has to engage the lead screw - if it is up under a cover, the pinion is going to be pointing up, and the dial is going to be on the bottom - unless you come up with some sort of geared setup.

As for the thread dial you showed in the picture - I wasn't sure if you were just showing an example of a thread dial or if you wondered if it might work for you. If the latter, then at the risk of stating the obvious - no. No way that little gear is going to engage a 3mm pitch lead screw. It was made for something like a 16 tpi or 1.5mm lead screw.

 

[Matt_Maguire]

And I repeat my request for anyone that is capable, to check the math in the answers that I posted above. Metric threading dials DO exist and they generally have multiple gears that must be changed for different threads. Surely there are some members here who are acquainted with the use of these metric threading dials.

As I mentioned in post #10, you had it right in #4. If the pitch to cut is a multiple of the leadscrew pitch you don’t need a thread dial at all. I believe your calcs are right (didn’t do the fractions/ratios though). The dial in post #7 appears to be 16T gear and 16 divisions on the dial.

Attaching what I have below, RE: metric dials.

The leadscrew appears to be covered so a thread dial would either have to go down thru the saddle apron or somehow translate from under the guard… I don’t know about that part of the problem.

Good luck,
Matt

 

[fusker]

Had a closer look at the TUE-40.
Max. turning length 1000 mm, max. diameter 200 mm (300 when bridge is removed).
Lead screw pitch 6 mm, thread dial 24 lines for a full revolution, cog wheel 24 teeth (direct,no gearing). The dial has every second line in double length, and every 6 lines is marked (0 - 6 - 12 - 18 - (0)). Not as clearly marked as on most inch-type dials I have seen.

One difference between english/american and most european users is the first group prefer to speak of TPI (turns per inch) where the second talk of millimeters per turn! To a european, the english seem to have turned the question upside down. I know at least one person who is still at times a bit confused by this.

When cutting imperial (inches) I exchange two gear wheels 'in front' of the gear box (we call it the Norton box) and as stated above I must keep the half nuts closed all the time (using the reverse switch). Other than that, it's all quite easy. There is a table screwed on to the norton box and the lathe can cut metric, imperial and DP (diametral pitch).
I don't think it possible to switch between imperial and metric with these rather primitive mechanical means unless you change either the lead screw or the two mentioned gear wheels. This could be done with an addition to the norton box - but you would still have to keep the half nuts closed.
Obviously, an electronic solution is now used on modern lathes (TUE-40 is dated 1952).

Matt: I've never seen a geared dial before. Thanks for enlightening me. A good idea but not sufficient to change between inch and millimetre.
Regards, fusker

 

[metlcutr55]

even my little grizzly 7 x 14 has a half nut, and a threading dial. I do remember a lodge and shipley I ran about 40 years ago, it was beat, and the night foreman was unsure about being able to use the halfnut on full marks, half marks, even or odd numbers only etc. so he told me just put a black mark on the "1" and use that all the time. would that work for you?