Are aftermarket leadscrew indicator spur gears available for manual lathes

My leadscrew is 6mm pitch and what appears to be an acme thread.

I would like to have a set of spur gears for my leadscrew indicator to cover all the different pitches, but have no idea if these are even sold.

Anyone know of a place they can be bought.

Keith

Does your leadscrew indicator mount to the helix angle of the leadscrew? If not you won't want plain sput gears but instead gears cut to the leadscrew's helix and the screw's pitch.

Generally the guys who make threading indicators will make their own gears.

Do you know the numbers of teeth that you would need? Or can you post photos of your threading indicator? Top view, showing the dial and it's markings and side view(s) showing any additional gearing that it may have.

If we are talking about the thread dial that tells you when to close the half-nut, then you don’t need a “set” , one gear will work for all the threads the lathe can cut. The pitch of the lead screw and the gear teeth on the thread dial will determine how many marks you put on the dial, and what positions on the dial can be use for each thread.

If you are talking about change gears that drive the threading gear box from the spindle or you don’t have a quick change box and want a “set” of threading gears, that’s a whole different subject


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Metric lead screws do in fact need multiple gears for a thread dial, the selection of which depend on the thread being cut.

PITA, and why metric lathes usually don't have thread dials.

But to answer the OP, yes you can make one, but might not be worth the trouble.

here is a scan posted by another member( Matt McGuire??) that I saved- it just so happens to show what is needed for 6mm leadscrew-

https://www.practicalmachinist.com/...92288-thread-chasing-dial-metricthread296.jpg

Well...crap!
Just ordered Martin Cleeves Screw cutting book, apparently I need schooling


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Ripper, While it is true that one gear is usually enough for a lathe that uses an "inch" lead screw to cut English measure threads, the same is not usually true for a lathe that is cutting metric threads. Here is why.

First the job of a threading dial is to determine when the relation of the thread being cut and the lead screw are in the same relative position every time that the half nuts are closed. There is a mathematical relationship between the rotation of the spindle and the rotation of the lead screw that is determined by the gears in the train between them. So this position WILL REPEAT, sooner or later. The threading dial tells you when this is happening.

English measure threads are specified in Threads Per Inch and these specifying numbers are almost always given in either whole numbers or compound numbers (a whole number plus a fraction) with either a 2 or a 4 as the denominator of the fraction. Examples: 32 TPI, 24 TPI, 18 TPI, 12 TPI, 8 TPI, 7 TPI, 5 TPI, 3.5 TPI, etc. There is never a fraction that is not a half or one or three quarters. Since the inch was a fairly long unit vs the mm that we do most metric work in, it was convenient to specify the English system (inch) threads in this manner. A 24 TPI thread would measure 0.04166666" between adjacent threads and that is not a nice number to work with. They could have used tenths, but that would have given us a sequence of 1 TPI, 10 TPI, 20 TPI, 30 TPI, 40 TPI, etc. That would be difficult for large diameter bolts like 1/2". 1/2-20 is a fine thread but 1/2-10 would be very coarse. A finer division was needed and using TPI was a good way to get that.

Most threading dials for English system lathes are based on a FOUR inch distance of travel along the lead screw. That's why they have the numbers 1, 2, 3, and 4 on them. Those numbers are INCHES. Now, if you think about it for even a short time, it is plain that any thread that is specified by a whole number of threads per inch will have to synchronize after one inch of travel. There is always a whole number of threads in a one inch interval. So moving exactly one inch down such a thread will put you in exactly the same point on the thread form as you started from (peak to peak, valley to valley, 27% along the left flank to 27% on another left flank). Rule: Whole number threads can be started at any numbered mark on the dial.

Going just a bit further, it is easy to see that if there is a 1/2 fraction in the thread spec., then at one inch of travel you will be at the 50% point of the thread form from where you started. That is the 1/2. But, if you go TWO inches along that thread, then you will again be at the same relative point. You moved 1/2 of the thread form the first inch and another 1/2 of the thread form in the second inch. These two halves add up to one whole and you are back in sync. Rule: Threads with a 1/2 fraction will sync on any even numbered mark on the dial. It takes two inches of travel to synchronize a thread with a 1/2 fraction and that applies to any 1/2 fraction: 99 1/2 TPI will sync in 2 inches, 2 1/2 TPI will sync in 2 inches, etc. for any other number with a 1/2 fraction.

Finally, although rare, the same idea applies to threads with a 1/4 or 3/4 fraction. It takes four 1/4s to add up to a whole inch and four 3/4s to add up to 3 whole inches. Rule: Threads with a 1/4 or 3/4s fraction will sync only on the same numbered mark on the dial that you started from. It takes four inches of travel to synchronize these fractions with a denominator of 4.

The above is one of the hidden advantages of using English (inch) measure.

Now METRIC threads: the pitch of metric threads is NOT measured in threads per mm or threads per cm or threads per decimeter (100mms), or threads per any metric dimension. Metric threads are measured and specified in the straight forward distance between one thread and the next: they are usually specified directly in mms. This is due to the rather small size of the millimeter. One thread per mm would be around 24 TPI, two threads per mm would be around 49 TPI, and it gets really fine from there. There would be very little use for 3 threads per mm. And coarser threads would be require fractional numbers of threads PER mm. That wouldn't work. You could use threads per centimeter, but it would still get arkward for low numbers. And threads per decimeter (100 mms) would be really large numbers. In short, "threads per" just does not work well for metric measure. SO, they decided to use just mm (or mm per thread which is mathematically the same thing) to specify metric threads. And they wanted a nice, numeric sequence instead of numbers with 5 or 10 decimal places and difficult values to remember. So they went with tenths of a mm (0.1mm) and twentieths of a mm (0.05mm) in determining that sequence of numbers. But this is an entirely different type of mathematical sequence than that generated by using a "threads PER" type of sequence. One is, more or less a geometrical sequence (8, 16, 32, 64 TPI) while the other is, more or less an arithmetic one (0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, etc.)

While a 0.1mm thread, and a 0.2mm thread and a 0.5mm thread will all synchronize in 1mm, a 0.3mm one will take 3mm and a 0.7mm thread will take a full 7 mm. A 0.45mm thread (yes that is used) will take 20mm to synchronize.

It is due to the use of two different types of mathematical sequences to specify the threads that making a threading dial for an English lathe is a lot easier than making one for a metric lathe.

Another problem is the range of lead screw pitches that are used for metric lathes. I have seen a metric lathes with 3mm, 6mm, and even 7mm and fractional mm (2.5mm) lead screws. WHY would you ever use 7mm????????? Insane, but it has been done. If you take two examples from above, a 0.45mm thread and a 6 mm lead screw, you have a real problem making a dial to use to synchronize it. In some cases, it may be easier to make a threading dial for use with an English lead screw and transposing gears making metric threads.

I know I will get flamed for saying it, but English threads make a lot more sense. A LOT more.

ripperj said:

If we are talking about the thread dial that tells you when to close the half-nut, then you don’t need a “set” , one gear will work for all the threads the lathe can cut. The pitch of the lead screw and the gear teeth on the thread dial will determine how many marks you put on the dial, and what positions on the dial can be use for each thread.

If you are talking about change gears that drive the threading gear box from the spindle or you don’t have a quick change box and want a “set” of threading gears, that’s a whole different subject


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Click to expand...

You will find that using a thread dial to cut metric threads on a lathe with a metric lead screw and an indicator is a 1st class PIA. Cutting metric threads is much easier on BOTH a metric and an inch lathe if the lead screw is only engaged once with the half nut. Now, this task is much easier if you use a lathe that has a reversing lead screw, a spindle brake and a multi-fix threading tool. These tool holders come in both internal and external varieties. These tool holders have a lever that retracts the tool at the end of the cut and will accurately return the tool to the exact original position for the beginning of the next cut. These tool holders are expensive, but they make single point threading a pleasure and they are fast to use.

Paul?? -Great reply, I’ll read it again after more coffee, I may have wasted $15 on the book
Thanks for taking the time to write it up.

Posts like this( minus my incorrect BS) make this place worth coming to, lately it’s been pretty easy to get lost in all the noise and wonder why you bother login in.


Keith (another Keith , not OP)

Edit: Steve- I agree with use of the retractable cutting tool. I have the licensed copies from Create Tool in B size. The quality is very high and they take a lot of stress out of threading to a shoulder. I think they we $800 for the inside and outside tools.



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Thanks for the replies everyone. Never expected such a response.

The Martin Cleeve book is what I used to learn screw cutting, definitely worth a read.

I personally have never found metric screw cutting to be a PIA. So long as my thread dial has the correct divisor for the thread in question, it's very easy. My leadscrew indicator gear has 15 graduations in a full turn, i.e. 15 turns of the leadscrew rotates the indicator once. So I basically have every single graduation (6 mm), every 3 graduations (18 mm), and every 5 graduations (30 mm). Any thread pitch that will divide exactly into those distances can be cut with my indicator.
However, there's a bunch of other metric pitches (that the gearbox can do) that my indicator won't cover.

Let's take an easy one, 4 mm. The first number that will divide into, and which is divisible by 6, is 12 (that 2 leadscrew turns to be back "in sync"). Therefore any gear with an even number of teeth will do - 2,4,6,8..........

Now lets try a 7 mm pitch. The first number that will divide into, and which is divisible by 6, is 42 (that 7 leadscrew turns to be back "in sync"). So an indicator gear of 7 teeth or 14 teeth would do.

To cut a long story short, I've went through all the pitches my gearbox can cut and I'd need the following extra indicator gears to be covered for everything - 10, 12, 14 and 16. It's a bit surprising that lathe manufacturers don't supply these as standard to cover the screw cutting gearbox capabilities. Maybe I can make my own "rough" gears. After all, I'm not needing a perfect gear tooth shape for a precise mesh with the leadscrew, just an indication that I'm in the correct sync with the leadscrew before I close the half nuts. Next is to see if my dividing head can get me there with those numbers so I can cut the gears.

Keith.

mancavedweller said:

Thanks for the replies everyone. Never expected such a response.

The Martin Cleeve book is what I used to learn screw cutting, definitely worth a read.

I personally have never found metric screw cutting to be a PIA. So long as my thread dial has the correct divisor for the thread in question, it's very easy. My leadscrew indicator gear has 15 graduations in a full turn, i.e. 15 turns of the leadscrew rotates the indicator once. So I basically have every single graduation (6 mm), every 3 graduations (18 mm), and every 5 graduations (30 mm). Any thread pitch that will divide exactly into those distances can be cut with my indicator.
However, there's a bunch of other metric pitches (that the gearbox can do) that my indicator won't cover.

Let's take an easy one, 4 mm. The first number that will divide into, and which is divisible by 6, is 12 (that 2 leadscrew turns to be back "in sync"). Therefore any gear with an even number of teeth will do - 2,4,6,8..........

Now lets try a 7 mm pitch. The first number that will divide into, and which is divisible by 6, is 42 (that 7 leadscrew turns to be back "in sync"). So an indicator gear of 7 teeth or 14 teeth would do.

To cut a long story short, I've went through all the pitches my gearbox can cut and I'd need the following extra indicator gears to be covered for everything - 10, 12, 14 and 16. It's a bit surprising that lathe manufacturers don't supply these as standard to cover the screw cutting gearbox capabilities. Maybe I can make my own "rough" gears. After all, I'm not needing a perfect gear tooth shape for a precise mesh with the leadscrew, just an indication that I'm in the correct sync with the leadscrew before I close the half nuts. Next is to see if my dividing head can get me there with those numbers so I can cut the gears.

Keith.

Click to expand...

And you don't think that's a PIA?

steve-l said:

And you don't think that's a PIA?

Click to expand...

As far as manual lathe work goes, not at all. Of course the initial learning of thread cutting and how the leadscrew indicator gear relates to different pitches requires a little effort, but that's a one time task. In any case there's absolutely heaps of stuff people doing machining need to learn.
If learning the above is an issue then I'd consider learning how to use a rotary table and indexing plates to be an issue too, and many other things in machining that require a little study and calculation.

I do a one-off job of making up a quick reference chart for each thread pitch and the associated leadscrew gear needed. Stick it on the wall.

The spur gear will be easy and quick to change out.

Start thread cutting, disengage half nuts at end of thread cut, wind carriage back, advance thread depth, re-engage half nuts, repeat until done.

So no I really don't see how that's such a PIA.

My Harrison lathe came with a set of thin spur gears mounted on the shaft of the threading indicator and a little chart telling you which gear to use for each thread and which number on the dial to close the nuts on.
The rest of the gears live on the shaft when not in use.

EPAIII said:

While it is true that one gear is usually enough for a lathe that uses an "inch" lead screw to cut English measure threads, the same is not usually true for a lathe that is cutting metric threads. Here is why. ....

Click to expand...

Long post, but a useful one! VERY useful! Thank you!

NOW.. I better understand the WHY of what Mssr. Henri Rene Bruet was up to inside that "special apron" when he built the HBX-360-BC... AKA "Grand Master of the weird-gear cult"

From Wiki:

The leadscrew engaged with a worm wheel instead of the usual halfnuts. The apron gear system could engage every metric and imperial thread directly and automatically. The leadscrew could be disengaged for each cut without losing register. This made it easy to turn and thread directly against an endstop, even into blind holes.

Click to expand...

Next best solution is waaaay cheaper, though. More wideley used as well.

Simply don't disengage the 'arf nuts atall.