Hi All,
I posted this on the PM site, but I thought some of you might like to see it...so here it is
Some of you may know of my Waltham Lathe (http://www.lathes.co.uk/waltham/index.html)
The lathe takes a W20 collet. OK they predate Schaublin....so is it really
In reading the 1909 Brochure, it states that the thread is a "Ratchet Type" with a pitch of 1.6667 mm and a diameter "equal to the diameter of the body of the collet"
see page below
As I have 1 original collet, I can confirm that the body is 20 nm but the tips of the threads are worn and difficult to measure. It is made of cast iron...consistant with the brochure
Now I scored some W20 collets on the bay recently and they measure thus
You will notice the thread is 19.7 mm, not 20mm
Well, looking at the sorry threads in the draw bar, I came to the conclusion that the bar had to be repaired to make it functional again. 100 years and soft threads = alot of wear.
I Decided to be pragmatic and thread the bar for the "modern" W20, and see were this all ended up.
I decided to insert a piece into the bar via silver solder and then thread the original draw bar. I could have just made a new draw bar....well ..I didn't.
Making the insert, just prior to parting off. Material is 1144sp
Setting up the draw bar in the lathe with a steady rest. The handwheel end is pressed on and is too big to go into the spindle. Additionally, a shaft collar was made up to grip the bar in the 3 jaw. The collar was turned up in the 3 jaw and marked of the number 1 jaw. Run out at chuck was less than .001". The far end ran true to within the roundness of the bar...which wasn't real good. I spend some time lining it up with an indicator as best as I could.
Here is the bar bored out to fit the insert. I lightly knurled the insert in two locations ot center the insert in the bore of 0.800" with .002 clearanc at the knurl and .003 elsewhere...on diameter The insert is not pushed in flush yet.
I then cleaned, fluxed and soldered the insert into position and fed the solder until rejection.
I then mounted it back up in the lathe and faced and bored the end to final size. Notice the silver line all around showing good penetration.
Now for the thread. The thread is a 0.775 x 15.3 threads per inch 45/5 buttress thread.
To do this I set up a 37/47 metric transposition gear in the lathe thus
the lathe as is
moved the banjo
The gear pod
gear pod installed
Now with a 37/47 in the train and the box set to 12 threads per inch we get
12 x 47/37 = 15.243 threads per inch = .0656" pitch = 1.6663 mm pitch....off by .0004 mm
I won't tell if you don't....
Threading it was a pain, but doable single point. The compound was set to 45 degrees and backed out to put the cut on. This results in the cutter only cutting on one side...always a good thing.
Here it is finished with a "modern" W20 in place
Now when I went back to check the old collet for fit, it was clear that the thread on the collet was too big for the draw bar. So the sales brochure was correct.
Waltham thead 20mm x 1.6667 mm pitch
Schaublin thread 19.70 mm x 1.6667 pitch
A mystery solved....and my lathe one step closer to running again..
Dave
I posted this on the PM site, but I thought some of you might like to see it...so here it is
Some of you may know of my Waltham Lathe (http://www.lathes.co.uk/waltham/index.html)
The lathe takes a W20 collet. OK they predate Schaublin....so is it really
In reading the 1909 Brochure, it states that the thread is a "Ratchet Type" with a pitch of 1.6667 mm and a diameter "equal to the diameter of the body of the collet"
see page below
As I have 1 original collet, I can confirm that the body is 20 nm but the tips of the threads are worn and difficult to measure. It is made of cast iron...consistant with the brochure
Now I scored some W20 collets on the bay recently and they measure thus
You will notice the thread is 19.7 mm, not 20mm
Well, looking at the sorry threads in the draw bar, I came to the conclusion that the bar had to be repaired to make it functional again. 100 years and soft threads = alot of wear.
I Decided to be pragmatic and thread the bar for the "modern" W20, and see were this all ended up.
I decided to insert a piece into the bar via silver solder and then thread the original draw bar. I could have just made a new draw bar....well ..I didn't.
Making the insert, just prior to parting off. Material is 1144sp
Setting up the draw bar in the lathe with a steady rest. The handwheel end is pressed on and is too big to go into the spindle. Additionally, a shaft collar was made up to grip the bar in the 3 jaw. The collar was turned up in the 3 jaw and marked of the number 1 jaw. Run out at chuck was less than .001". The far end ran true to within the roundness of the bar...which wasn't real good. I spend some time lining it up with an indicator as best as I could.
Here is the bar bored out to fit the insert. I lightly knurled the insert in two locations ot center the insert in the bore of 0.800" with .002 clearanc at the knurl and .003 elsewhere...on diameter The insert is not pushed in flush yet.
I then cleaned, fluxed and soldered the insert into position and fed the solder until rejection.
I then mounted it back up in the lathe and faced and bored the end to final size. Notice the silver line all around showing good penetration.
Now for the thread. The thread is a 0.775 x 15.3 threads per inch 45/5 buttress thread.
To do this I set up a 37/47 metric transposition gear in the lathe thus
the lathe as is
moved the banjo
The gear pod
gear pod installed
Now with a 37/47 in the train and the box set to 12 threads per inch we get
12 x 47/37 = 15.243 threads per inch = .0656" pitch = 1.6663 mm pitch....off by .0004 mm
I won't tell if you don't....
Threading it was a pain, but doable single point. The compound was set to 45 degrees and backed out to put the cut on. This results in the cutter only cutting on one side...always a good thing.
Here it is finished with a "modern" W20 in place
Now when I went back to check the old collet for fit, it was clear that the thread on the collet was too big for the draw bar. So the sales brochure was correct.
Waltham thead 20mm x 1.6667 mm pitch
Schaublin thread 19.70 mm x 1.6667 pitch
A mystery solved....and my lathe one step closer to running again..
Dave
