38 Tpi thread

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38 Tpi thread

This topic has 18 replies, 8 voices, and was last updated 17 February 2014 at 15:23 by Michael Gilligan.

Viewing 19 posts - 1 through 19 (of 19 total)

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15 February 2014 at 20:09 #144037
Clive Hartland
Participant
@clivehartland94829
Can someone help me please, I have a Metric ML10 and a full set of change wheels for metric and Imperial threads.

I need to cut a 38Tpi thread for an eyepiece fit so can someone please calculate a gear cluster for me.

Clive
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15 February 2014 at 20:09 #7041
Clive Hartland
Participant
@clivehartland94829
15 February 2014 at 20:23 #144039
Les Jones 1
Participant
@lesjones1
Hi Clive,
I do not know what the full set of change wheels for an ML10 consists of. If you can list the number of teeth on the change wheels, the number of teeth on the fixed gear on the spindle and the TPI of the leadscrew I will have a go at working out a working out a way to do it. I also have a program I found on the web some time ago but I can't remember where. If you PM me with an email address I will send you a copy of the program.

Les.
15 February 2014 at 21:55 #144053
Bazyle
Participant
@bazyle
On Duncans metal pages he has programs for gear calculating.
15 February 2014 at 22:01 #144054
Roderick Jenkins
Participant
@roderickjenkins93242
Clive,

Assuming a basic set of wheels from 25 to 65 in 5s plus a 63 I get:

Drivers 25, 35, 50 and drivens 55, 60, 63 on an 8tpi leadscrew giving 38.016 tpi

Does the the metric ML10 have an 8tpi leadscrew like the metric 7 series?

I've written an EXCEL spreadsheet for calculating threads. PM me if you'd like a copy

cheers,

Rod
15 February 2014 at 22:52 #144064
MICHAEL WILLIAMS
Participant
@michaelwilliams41215
Hi Clive ,

38 tpi is o,668 mm pitch or very nearly o,667 mm .

Think of it as 2/3 of 1 mm pitch and do all gear calcs directly in mm .

Regards ,

Michael Williams .
16 February 2014 at 08:36 #144079
Les Jones 1
Participant
@lesjones1
Hi Clive,
I've found the website for the screwcutting calculator I mentioned in my last post. The program I was referring to was "nthreadp.exe" and there is another one that looks very similar "boxfthreadp.exe"
They are on this website.

Les.
16 February 2014 at 10:23 #144089
Clive Hartland
Participant
@clivehartland94829
I have been unable to get into the workshop at the moment so will come back in a couple of hours and let you know how I get on. Thank you for the details so far.

A point here is that the optical inst. makers always seem to use odd pitches and threads, we have boxes of them but not this 38tpi one.

Clive
16 February 2014 at 13:30 #144104
Michael Gilligan
Participant
@michaelgilligan61133
Clive,

Just a thought … 4 BA has a pitch of 38.46 tpi, which is pretty close.

Maybe the threads were originally chased ?

MichaelG.

.

Edit: Sorry … pitch is the wrong word there

Here is nother useful reference

Edited By Michael Gilligan on 16/02/2014 13:36:39
16 February 2014 at 16:59 #144113
Michael Gilligan
Participant
@michaelgilligan61133
As a rather pleasing digression, I just found this description of a Karger "Sliding Spindle" lathe.

… I don't think my father ever had that luxury, but I do remember him hand-chasing threads on brass tube in the early 1960's.

MichaelG.

Edited By Michael Gilligan on 16/02/2014 17:00:17
16 February 2014 at 18:46 #144122
pierre ehly 2
Participant
@pierreehly2
Cleeve,

Harold hall site

http://homews.co.uk/page30.html

brgds

pierre
16 February 2014 at 19:17 #144126
MICHAEL WILLIAMS
Participant
@michaelwilliams41215
Optical threads might have origin in the Lowenherz thread system .

This delightfully oddball thread system was used for a lot of early scientific equipment .

Originally a seemingly quite random collection of sizes and pitches but later got tidied up a bit .

Michael Williams .
16 February 2014 at 20:44 #144146
Clive Hartland
Participant
@clivehartland94829
Michael, My bro. has a Schaublin(old) with the sliding spindle and the brass thread quadrants. I have used it and chase the threads very slowly. It does have a tendency to 'jump' threads occasionally.

All OK now with the 38tpi, cut and done with a chaser from a friend. All I have to do now is take it into work and see if it fits.

Clive
16 February 2014 at 20:53 #144148
Michael Gilligan
Participant
@michaelgilligan61133
Well done, Clive

As a matter of curiosity … whose manufacture is the eyepiece?

MichaelG.
16 February 2014 at 21:16 #144153
Clive Hartland
Participant
@clivehartland94829
Hello Michael, The telescope is of Hilger and Watts name so is very old but is perfect for our target system as it has a Pentag prism on the OG.

Clive
16 February 2014 at 21:32 #144157
Michael Gilligan
Participant
@michaelgilligan61133
Thanks Clive

Beautifully made equipment …

My wife recently treated me to an old Watts Theodolite [pre Hilger] … The reticules are a bit grubby, but the build quality is awesome.

MichaelG.
17 February 2014 at 09:38 #144186
Brian Wood
Participant
@brianwood45127
Hello Michael,

Having made a recent study of obscure threads, including Lowenherz, 38 tpi at 0.668 mm pitch falls between the two Lowenherz sizes of 0.60 mm and 0.70 mm; 4BA at 0.660 mm pitch was actually the best match being only a few microns out.

The thread angle for the series was 53 degrees 8 minutes.

Regards

Brian
17 February 2014 at 15:02 #144230
Clive Hartland
Participant
@clivehartland94829
I went through the box of chasers and taps and dies from the old stuff, I found chasers of 31 and 41 tpi. Also lots of odd tpi, even a 23 tpi. I have no idea where or what they were used for. Some of the taps have no markings but seem well used so maybe production tools. I think I may well take the box of chasers and any that I can identify from the taps and dies. I have no idea what I will use them on! Also found a box of taps and dies of whit. form down to 1/16", it seemed very coarse for the dia. It seems this stuff was stored many years back and as workers retired the knowledge is lost so they become useless, that is until I uncover them !

Clive
17 February 2014 at 15:23 #144234
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Clive Hartland on 17/02/2014 15:02:42:

… It seems this stuff was stored many years back and as workers retired the knowledge is lost so they become useless, that is until I uncover them !

.

Keep up the Good Work, Clive

You might find this listing useful for quick reference.

MichaelG.
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