The 'Fish Tail' 60 Degree Thread Gauge

[7HC]

I'll start with a simple tool. The 60 degree thread set up tool thats referred to as the fish tail. I've used the tool to set up my lathe bit to cut threads. I have successfully cut threads on the lathe & have compared my cut threads to some " professional" cut threads & could not see any difference in the two sets of threads, however the "professional" could tell what the three different size female 60 degree vees are for, why it has one 60 degree male vee, what the number chart on the tool means & how to use the tool properly to get the most bennefit out of the tool......... With this being said let "fish tail 101" begin. Any teachers available to start the class session ?
Phil

So, can anyone give definitive answers to those few questions, of provide a link to an article or video?

M

 

[David]

Picture to look at

David

 

[Benji]

The numbers are the "Double Depth" of of a sharp Vee thread, as stated on the tool.
Now I have a Starrett and a Brown an Sharp gage. They give the DD of an American National thread.
The two numbers are not the same. Sharp Vee threads result in a weaker thread.

The South Bend handbook " How to cut screw threads in the lathe" Bulletin #36A
Shows the tail of the gage being used grind the tool and the smaller vees on the side being used to set the tool normal to the work.
No mention of haw the point is used, but I use it to see if the bolt in hand is a BSF/BSW 55 degree thread or a USNC/F or Metric 60 degree thread.

 

[7HC]

This page from the Little Machine Shop, along with link it includes towards the bottom, probably covers a lot of the fishtail questions.

http://littlemachineshop.com/products/product_view.php?view=classic&ProductID=2743

 

[OldMachinist]

The 60 degree center gage has many uses. The female vee's can be used as a gage to grind a threading tool and to set up the tool to the work.





I prefer to use it with the Starrett #392 attachment for setting up on the O.D.



Can be used like this to set up a internal threading tool.



The male end can be used to verify a 60 degree thread or check a shaft center isn't damaged.



But it most likley started out as just being shaped that way because it saved material when it was stamped out.

The double depth numbers are a carry over from the old threading systems. The graduated sides are to help identify the pitch of a thread.

 

[OldMachinist]

I decided to go thru some old machine shop text books to see if there was anything add on using a center gage. Most of it was what I posted but I did find this.

 

[Tom Griffin]

A few of hints on using the center gauge:

Place a piece of white paper under the work and shine your machine light on it. That makes it a lot easier to see when the threading tool is properly aligned to the center gauge.

Jamming the center gauge between the threading tool and the work will damage the gauge. Instead, hold the center gauge against the work and align one side of the threading tool.

If your workpiece is difficult to use the center gauge on, line it up on the tailstock ram instead.

Tom