Cutting metric threads with an imperial lead screw and a thread dial indicator.

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bearhunter

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Not sure where I picked this up, maybe right here?

It works great, with both back gear and quick change gear box models.

https:// youtu.be/HXt4TWa382Q

I left a space just after the forward slash marks.

I have always just left the clamp nuts engaged and stopped the machine at the end of the cut. It works but if you need to thread right up to the shoulder, you need to thread in reverse, which is a pain in the butt.

This method is much easier and you can easily thread right up to the shoulder.
 
That works if your lathe has gear settings for metric threads... many do not... my lathe does not.
 
guntech said:
That works if your lathe has gear settings for metric threads... many do not... my lathe does not.
Click to expand...

That would make sense.

Both of my lathes are capable of cutting metric threads, one is a back gear model and the other has a quick change gear box with metric settings.

I usually use the back gear lathe but I have tried cutting metric threads with the quick change model. Seems like it works fine.
 
guntech said:
That works if your lathe has gear settings for metric threads... many do not... my lathe does not.
Click to expand...

i expect your lathe has more settings than listed and because the inch is defined by the metric system, many will be metric. you could make a scratch pass with every different combo and measure, or count the gear teeth and use excel to calculate
 
scott585 said:
i expect your lathe has more settings than listed and because the inch is defined by the metric system, many will be metric. you could make a scratch pass with every different combo and measure, or count the gear teeth and use excel to calculate
Click to expand...

I wonder where the settings are hiding? Threading from 4 threads per inch up to 224 threads per inch are visible. The owners manual shows absolutely nothing for metric, no actual gears to change, no 'conversion' to do. The few times I need to thread metric I rent time on a metric lathe.

Please explain how the inch is defined by the metric system. That's a new one for me... On the metric/inch equivalent charts I have - nothing ever matches up to the exactness that would be required for threading.
 
My Asian lathe made in the later 1980's with imperial lead screw and dials came with an 86:91 combo gear and chart that after a gear change allows me to cut a variety of metric threads. But a lot of earlier lathes from some point and back did not automatically include such a gear and thread chart option. I'm not sure when this feature became more common. Guntech, I assume here that your lathe is one of those from the "Before Time"... :d

The normal method when doing this due to the odd nature of the setup is that one would normally not open the half nuts. The method in Tom Lipton's video on how to work around this is a clever idea. It injects a bit of real world practical timing into the process. He's still using the same teeth all the time. I LIKE it!
 
My lathe was new in 1971 ... and shortly after discontinued.

but I am still interested in how the inch is defined by the metric system...
 
My 1971 Myford ML7 long bed with an imperial lead screw and gear box has the ability to cut metric threads with a conversion kit consisting of change gears and a quadrant
 
My mid 90's Taiwanese lathe has both an imperial & a metric guide riveted to the machine. Requires a gear change before the shifting transmission to work tho.

Guntech, there is an inexpensive book available in a series of british publications for hobby machinist, I think it is titled "Threading on a lathe for amateur's". Last I seen them available was in a Busy Bee store. The author very much explains the correlation between threading with an imperial lead screw. He provides mathematical formula's on how close to a usable tolerance can be attained with imperial machines.
 
fingers284 said:
Guntech, there is an inexpensive book available in a series of british publications for hobby machinist, I think it is titled "Threading on a lathe for amateur's". Last I seen them available was in a Busy Bee store. The author very much explains the correlation between threading with an imperial lead screw. He provides mathematical formula's on how close to a usable tolerance can be attained with imperial machines.
Click to expand...

Many years ago I tried threading for a 1.5mm pitch for fitting a barrel... it was not accurate enough for me and a painful method. Maybe if you want to cobble some sort of almost metric thread...?


Either thread on a metric lathe or if you have the gears and chart for metric threading use that...
 
guntech said:
Many years ago I tried threading for a 1.5mm pitch for fitting a barrel... it was not accurate enough for me and a painful method. Maybe if you want to cobble some sort of almost metric thread...?


Either thread on a metric lathe or if you have the gears and chart for metric threading use that...
Click to expand...


I recently pulled a barrel from a sported 98 Mauser action. It was very tight, to the point I was worried it had been set with LocTite.

It wasn't.

Once I got the friction weld? broken, the threads on the tenon were actually quite sloppy in the receiver.

The threads on the 98 should have a 2.00mm pitch, which is very close to 12 TPI.

It's not unusual to find this sort of thing on older barrel swaps.

I removed that barrel because the rifle just wouldn't shoot well, no matter what I did.

I replaced it with a slightly cut back milsurp 98 bbl, chambered for the 8x57js. This wasn't just a normal twist in. This barrel had a "bulge" on the face of the tenon and looked like it had come off an early 29 inch barreled rifle. The bulge had to be cut off to reface the tenon and of course that meant the chamber had to be reamed and the shoulder cut back.

Not a big deal but it takes time.

The rifle went together well. The action is a BRNO marked VZ24, so I installed a set of BRNO 21H double set triggers and mag well assembly that was given to me by a now deceased gunsmith from Burns Lake. Don't remember his last name. First name was Bill. His shop was in a discarded highway tractor trailer. Nice fellow and knowledgeable.

This rifle shoots 196 grn Oryx bullets in moa or less at 100ys at 2600fps or so my Magnetospeed tells me.

When the old 308 chambered barrel had been installed and tightened, some deforming of the threads, both on the tenon and in the receiver occurred. I had to clean up the internal threads on the receiver, which I always find to be a bit of a challenge and do in reverse, because I can't see what's happening inside.

There is a thread cleaning tap available, just like the taps offered by Brownelle's for cleaning up revolver frame threads. IMHO, it's not worth bothering with as I so seldom have to do this clean up.

This long post is just to make people aware of what can occur when the "close enough" mentality is enabled. Sometimes it works and sometimes the next person in line has to fix the job.
 
guntech said:
.......but I am still interested in how the inch is defined by the metric system...
Click to expand...

Too many folks thinking that things need to constantly change.... :)

An interesting read on standards of lengths we typically use on a daily basis...

https://www.nist.gov/pml/weights-and-measures/si-units-length

I had not realized that there was originally a difference between English and American yards. A little more searching seems to indicate that it's a preciously small difference. Like 2 parts/million?

But it is enough that I see from following a couple of related links that the US Survey Office has stuck with the old standard so that the old property surveys did not need to all be re-done or otherwise converted or cause confusion over when a survey was performed and in which units.

So... just how old are your vintage Starrett or B&S micrometers? They may be reading in the older units! :d
 
bearhunter said:
The threads on the 98 should have a 2.00mm pitch, which is very close to 12 TPI.
Click to expand...

I believe it is the other way around...

The threads on older M98's are 12 tpi , which is very close to 2.00mm pitch only cut with a 55 degree tool rather than a 60 degree.

There isn't a metric thread on a Mauser 98 that I am aware of.

There is also a 11.5 tpi thread out there...
 
All the lathes with imperial lead screws use a one piece two part ratio change pulley to adapt for metric. Or they stack the two gears on a keyed bushing that then goes on one of the banjo shafts. The two popular options are 100:127 and 86:91. With that ratio change in the mid point some of the usual combos will cut useful metric threads.

But hey, if you have easy access to an all metric lathe then that trumps trying to find gears to fit your lathe.

But then we need to either never unlock the half nuts or we can use Tom Lipton's trick if we're running slowly enough.
 
guntech said:
I believe it is the other way around...

The threads on older M98's are 12 tpi , which is very close to 2.00mm pitch only cut with a 55 degree tool rather than a 60 degree.

There isn't a metric thread on a Mauser 98 that I am aware of.

There is also a 11.5 tpi thread out there...
Click to expand...

I'm just going by the thread guage, which indicates 2.00 mm. The pitch on the take off barrel tenon was 12 tpi, but over it's entire length, it was slightly off the pitch inside the VZ24 action.

That leads me to assume that the smith cut the threads sloppy on purpose, so that it would snug up properly on the shoulder.

The sported 8mm barrel fit the 2.00 mm pitch guage without gaps, fitting to the bottom of the threads.

I may have it backwards but the difference was enough.

Maybe the person that fitted the 308Win bbl just did a sloppy job?
 
bearhunter said:
I recently pulled a barrel from a sported 98 Mauser action. It was very tight, to the point I was worried it had been set with LocTite.

It wasn't.

Once I got the friction weld? broken, the threads on the tenon were actually quite sloppy in the receiver.

The threads on the 98 should have a 2.00mm pitch, which is very close to 12 TPI.

It's not unusual to find this sort of thing on older barrel swaps.

I removed that barrel because the rifle just wouldn't shoot well, no matter what I did.

I replaced it with a slightly cut back milsurp 98 bbl, chambered for the 8x57js. This wasn't just a normal twist in. This barrel had a "bulge" on the face of the tenon and looked like it had come off an early 29 inch barreled rifle. The bulge had to be cut off to reface the tenon and of course that meant the chamber had to be reamed and the shoulder cut back.

Not a big deal but it takes time.

The rifle went together well. The action is a BRNO marked VZ24, so I installed a set of BRNO 21H double set triggers and mag well assembly that was given to me by a now deceased gunsmith from Burns Lake. Don't remember his last name. First name was Bill. His shop was in a discarded highway tractor trailer. Nice fellow and knowledgeable.

This rifle shoots 196 grn Oryx bullets in moa or less at 100ys at 2600fps or so my Magnetospeed tells me.

When the old 308 chambered barrel had been installed and tightened, some deforming of the threads, both on the tenon and in the receiver occurred. I had to clean up the internal threads on the receiver, which I always find to be a bit of a challenge and do in reverse, because I can't see what's happening inside.

There is a thread cleaning tap available, just like the taps offered by Brownelle's for cleaning up revolver frame threads. IMHO, it's not worth bothering with as I so seldom have to do this clean up.

This long post is just to make people aware of what can occur when the "close enough" mentality is enabled. Sometimes it works and sometimes the next person in line has to fix the job.
Click to expand...

Bearhunter you must be referring to Bill Mackereth, didn't know he had passed away. Good guy and like you said , very knowledgeable.
 
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