Mystery thread

This topic has 6 replies, 4 voices, and was last updated 23 October 2015 at 12:43 by John Rudd.

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22 October 2015 at 13:07 #208842
John Rudd
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@johnrudd16576
I have a machine with a threaded leadscrew, my thread gauges tell me it is 20 tpi, with a 55 degree angle based on what my tired eyes tell me….

The outside diameter of the thread is approx a shade under 0.5 inches. Research leads me to think it is either a BSC or UNF threadform but they are both 60 degrees, else my rhinking it is a specially machined lead screw…..

As I want to replicate this lead screw, what are my options? Anyone come across this before?
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22 October 2015 at 13:07 #24177
John Rudd
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@johnrudd16576
22 October 2015 at 13:15 #208845
Neil Wyatt
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@neilwyatt
I'd grind up a single point cutter to match the thread and not worry about exactly what form it is.

Neil
22 October 2015 at 13:22 #208846
JasonB
Moderator
@jasonb
1/2" ADM is 55deg and 20tpi here

An idea of what machine its off would help

But quite possibel they just went for 20tpi to give an easy 0.050" per turn of the handwheel and 1/2" as it was the right proportion and a bit more substantial than 1/4whit in which case do as Neil suggests
22 October 2015 at 14:03 #208851
John Rudd
Participant
@johnrudd16576
Neil,

I'd be inclined to use a 55 degree threading tool….this what you had in mind?

Jason,

The leadscrew is from my Ajax AJ8 milling machine….being an old machine, I'm inclined to think it is a special 1/2" x 20 tpi with a 55 degree angle…hah, misssed the ADM link….cheers for that…

Thing is the machine has ben butchered and I'm trying to restore it….the leadscrew I dont think is original as its longer than the table….the l/s nut has been formed from a lump of phos-b.

Info on this machine is sparse…..

Edited By John Rudd on 22/10/2015 14:11:29
23 October 2015 at 11:34 #208971
Bazyle
Participant
@bazyle
20 tpi is going to give you some arm ache. I'd consider something coarser bearing in mind that the essence of a horizontal is a lot of long sweeps rather than trying to set a co-ordinate and some small machines had a rack feed on the x-axis. Also 55 degree V is not presenting a brilliant thrust face and wear expectation.
23 October 2015 at 12:43 #208980
John Rudd
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@johnrudd16576
Bazyle,

Thanks for your comments….I believe the mill did at one time have a rack feed/return mechanism but have been unable to find any info in this….The machine came my way without it….

Agreed a 55 or 60 degree anle face isnt going to have much opposition, maybe a different thread form? Acme?

Changing the thread form presents me then with sourcing taps/dies and another block of material for the leadscrew nut….changing for a different diameter presents me with even more issues to resolve…( shaft support bushes etc..)

I'm trying to keep this as simple as possible….if thats possible…

Edited By John Rudd on 23/10/2015 12:44:42
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