One-off measuring tool for internal thread

[clockworkcheval]

My lathe is a venerable 60 - 70 year old Schaublin 102VM, excellent precision, but which has several components that follow no known industrial standard. I need a light dog drive plate for small work between centers. Even if you can get one buying is prohibitively expensive. To make one I need to machine the inner thread of the spindle nose thread, which is given as M 37,6x3. So the thread top is 60 degrees, but the thread shape is nowhere close to e.g. a M 40 standard thread shape. So I decide to copy the thread on my old face plate. A good way to copy is to place 2 steelballs opposite 1 steelball in the thread and to work the new thread to the distance between the balls in the existing thread.

I decide to abuse a simple digital caliper for this purpose. I grind two parallel hollow flats on the outside of the measuring jaws.

To this purpose I mount my PROXXON grinding spindle on my WABECO milling machine. The calipers are simply fixed to an angle plate. For the light grinding involved this proves to be sufficiently stiff. The small diameter 2,5 mm steel balls are attached to the grooves with a bit of slow curing 2 component glue. I mount the calipers with the steel balls in the still soft glue carefully inside the internal thread to be copied and hope for the best. After a night curing the thing comes out OK. The double balls have not set at 3 mm distance but at the double 6 mm but that is also fine. The balls don't fall of immediately and my one-of measuring tool seems to be capable to last the probably maximum 10 measurements to be taken. And the calipers are still fit for regular use.

 

[Carbuilder]

Very cool idea. It takes balls to modify a calliper like that!

 

[clockworkcheval]

Actually 3 small balls and a € 10,- caliper, but thank you!

 

[cds4byu]

Isn't 37.6x3 almost the same as 1 1/2-8, which is a standard lathe chuck thread? I'd be shocked if the actual thread isn't 1 1/2 -8.

 

[clockworkcheval]

I'm afraid you might be shocked then. The basic design of the Schaublin 102 is about 90 years old, and at the time Anglo-American influence in Switzerland was much more noticeable in luxury ski-resorts than in Swiss Industry. Moreover Schaublin has always fully relied on its own design solutions. In fact Fréderic Schaublin told me 50 years ago when I investigated an engineering apprenticeship with them that any new design engineer or manufacturing engineer had to start a couple of years in their service department in order to see with their own eyes and understand the results of inadequate design and/or customer abuse. See the attached sketch of the spindle nose.

 

[cds4byu]

OK. I stand corrected.

 

[Joe]

My lathe is a venerable 60 - 70 year old Schaublin 102VM, excellent precision, but which has several components that follow no known industrial standard. I need a light dog drive plate for small work between centers. Even if you can get one buying is prohibitively expensive. To make one I need to machine the inner thread of the spindle nose thread, which is given as M 37,6x3. So the thread top is 60 degrees, but the thread shape is nowhere close to e.g. a M 40 standard thread shape. So I decide to copy the thread on my old face plate. A good way to copy is to place 2 steelballs opposite 1 steelball in the thread and to work the new thread to the distance between the balls in the existing thread.

View attachment 134855

I decide to abuse a simple digital caliper for this purpose. I grind two parallel hollow flats on the outside of the measuring jaws.

View attachment 134861View attachment 134862View attachment 134863

To this purpose I mount my PROXXON grinding spindle on my WABECO milling machine. The calipers are simply fixed to an angle plate. For the light grinding involved this proves to be sufficiently stiff. The small diameter 2,5 mm steel balls are attached to the grooves with a bit of slow curing 2 component glue. I mount the calipers with the steel balls in the soft glue carefully inside the internal thread to be copied and hope for the best. After a night curing the thing comes out OK. The double balls have not set at 3 mm distance but at the double 6 mm but that is also fine. The balls don't fall of immediately and my one-of measuring tool seems to be capable to last the probably maximum 10 measurements to be taken. And the calipers are still fit for regular use.

View attachment 134859View attachment 134860

Very elegant, KISS applied, I like it.
John

 

[ajoeiam]

snip


To this purpose I mount my PROXXON grinding spindle on my WABECO milling machine. The calipers are simply fixed to an angle plate. For the light grinding involved this proves to be sufficiently stiff. The small diameter 2,5 mm steel balls are attached to the grooves with a bit of slow curing 2 component glue. I mount the calipers with the steel balls in the soft glue carefully inside the internal thread to be copied and hope for the best. After a night curing the thing comes out OK. The double balls have not set at 3 mm distance but at the double 6 mm but that is also fine. The balls don't fall of immediately and my one-of measuring tool seems to be capable to last the probably maximum 10 measurements to be taken. And the calipers are still fit for regular use.

Hmmmm - - - "soft glue" - - - - please - - - - what did you use? (silicone maybe?)

 

[clockworkcheval]

It is a two-component polyurethane glue. The trade-name of this glue in The Netherlands is 'Bison Kombi Power'. I learned to appreciate it while still sailing because it is resistant to seawater, oil and gasoil and is useful from minus 30 to plus 100 degrees Celsius. It will glue together many boat-materials like Stainless Steel with Polyester. And quite important stays 'soft' for 15 minutes, thus allowing time for exact positioning the parts to be connected. Full curing time is 24 hours.

 

[SmithDoor]

Most Machinist just use male thread. The same as spindle thread. You can feel the thread till you right death.
I have a male thread that matches my spindle for making chuck backing plates.

My backing plates are from weight set my son left behind.
In download section you see photos of how did this job.

Dave

My lathe is a venerable 60 - 70 year old Schaublin 102VM, excellent precision, but which has several components that follow no known industrial standard. I need a light dog drive plate for small work between centers. Even if you can get one buying is prohibitively expensive. To make one I need to machine the inner thread of the spindle nose thread, which is given as M 37,6x3. So the thread top is 60 degrees, but the thread shape is nowhere close to e.g. a M 40 standard thread shape. So I decide to copy the thread on my old face plate. A good way to copy is to place 2 steelballs opposite 1 steelball in the thread and to work the new thread to the distance between the balls in the existing thread.

View attachment 134855

I decide to abuse a simple digital caliper for this purpose. I grind two parallel hollow flats on the outside of the measuring jaws.

View attachment 134861View attachment 134862View attachment 134863

To this purpose I mount my PROXXON grinding spindle on my WABECO milling machine. The calipers are simply fixed to an angle plate. For the light grinding involved this proves to be sufficiently stiff. The small diameter 2,5 mm steel balls are attached to the grooves with a bit of slow curing 2 component glue. I mount the calipers with the steel balls in the still soft glue carefully inside the internal thread to be copied and hope for the best. After a night curing the thing comes out OK. The double balls have not set at 3 mm distance but at the double 6 mm but that is also fine. The balls don't fall of immediately and my one-of measuring tool seems to be capable to last the probably maximum 10 measurements to be taken. And the calipers are still fit for regular use.

View attachment 134859View attachment 134860

 

[clockworkcheval]

Hi Smithdoor, I very briefly considered to first make a male thread that matches the spindle. But upon first feeling and then approximately measuring how very loose the fit between outer and inner thread is, I decided to just copy the inner thread. See sketch of measurements.

 

[ajoeiam]

Most Machinist just use male thread. The same as spindle thread. You can feel the thread till you right death.
I have a male thread that matches my spindle for making chuck backing plates.

My backing plates are from weight set my son left behind.
In download section you see photos of how did this job.

Dave

I was a total noob at it but I got bit once using a gauge to determine the thread.
Make sure you have at least 2 teeth on the testing gauge (and if you don't check using other measurements!!!!).
So I cut a 3 tpi where it should have been 2.5 tpi.

In my defense the thread gauge only had a single tooth (with 2 valleys) making it sorta challenging.

Part of my education - - - sure didn't make my boss happy though!!!!
That was for a hydraulic cylinder repair and the shaft was some 4" chromed and hardened IIRC.
It was an interesting job!

 

[ajoeiam]

It is a two-component polyurethane glue. The trade-name of this glue in The Netherlands is 'Bison Kombi Power'. I learned to appreciate it while still sailing because it is resistant to seawater, oil and gasoil and is useful from minus 30 to plus 100 degrees Celsius. It will glue together many boat-materials like Stainless Steel with Polyester. And quite important stays 'soft' for 15 minutes, thus allowing time for exact positioning the parts to be connected. Full curing time is 24 hours.

Thank you very much!!

(Not enough years left for my projects never mind for all the mistakes to get them all done!!!!!!!!! LOL)
Learning from others is very important for me!!!!!!!!!!!

 

[SmithDoor]

I has also surprised when first heard of using a plug too back in 1970.
But work ever time. It is like go and no go gauge.
If think that surprising machine shop have a board full of nuts both RH & LH in NC & NF. They use that instead of thread wires.

FYI I use thread wires for threading.

Dave

Hi Smithdoor, I very briefly considered to first make a male thread that matches the spindle. But upon first feeling and then approximately measuring how very loose the fit between outer and inner thread is, I decided to just copy the inner thread. See sketch of measurements.

View attachment 134943