Starrett has some weird threads.

[woodchucker]

I need to make a new set of stops for my vise. The original is for very small parts, but I keep running into my parallels.
My second stop is my mitutoyo magnetic stand since I don't use it that much.

I have rods for a Starrett stand without the mag base. My holes in the vise are 1/4-20 and 5/16-18...
The Starrett rod is 5/16-20, not even on the chart.. WTH.

The rod size is 15/32 (0.466) I guess because they needed to take 1/2 rod and turn it down,

Gotta make a new one if I am going to use this rod and snug.

 

[mmcmdl]

Pics , pics , pics !

 

[woodchucker]

Pics , pics , pics !

of what the starrett bar?

 

[woodchucker]

don't know what you are looking for.
the last one is what I want to re - purpose. Going to make a new rod. I just started making one, with 1/4-20 on one end and 5/16-18 on the other.
but the last 5 thou wound up being 10 thou over the length... not sure how it happened... wierd.. so much for using that piece of scrap.

 

[benmychree]

Sometime look a listing of special taps in a tool catalog --- there are literally hundreds; all for that one special application.

 

[woodchucker]

Sometime look a listing of special taps in a tool catalog --- there are literally hundreds; all for that one special application.

what makes them do that? So that no one can easily fit to their threads?

 

[benmychree]

what makes them do that? So that no one can easily fit to their threads?

There are many good reasons for special threads, for instance threads in thin wall tubing, using a coarse thread would thin the wall thickness unduly. Brown & Sharpe were somewhat famous for odd threads on their older machines, they set their standards before there were standards; and example is their 1/2" thread at 14 TPI when others in the early days adopted 12 TPI, later changed to 13 TPI that we use today., their milling arbors use odd threads also, and changing the subject, their machines used 55 deg. dovetails instead of 60 deg. up to WW-2.

 

[Chewy]

5/16 X 20 is a standard thread. Tap and die are available from KBC among others. $9 & $11 in catalog. Spec's are in Machinery Handbook. You can single point it. On the 15/32 , is that the rod diameter where the holder/stop goes and then is turned downed to 5/16-20? That is what it looks like in the pictures. Gotta remember that Starrett has been around since Freddy Flintstone was machining granite wheels. So a thread that was common in 1900 may be obsolete today. But if the company has already tooled up and was using it, they would continue.
Have run into this before and had other people point out what it was from their collection of notes.

 

[mmcmdl]

I think Starrett started out with a meat chopper if I remember correctly . Late 1800s or so .

 

[Chewy]

Probably for cutting up Dinosaurs.