Need help with Bspt thread

[smithy1851]

Hi ,
Im looking for the starting size and finishing size for 1/2 bspt threads external...
we are running a rlx protrak 1630, trying to get the thread sizes correct in custom threads but its not working..
does anyone have the correct sizing for the starting point..
major dia is 20.955, minor dia is 18.633, pitch 1.814, were cutting the correct pitch but the thread isnt correct in height etc, trying on a new fittings and not working..
cutting en3b bar...but we have pb bronze to machine shortly...
any help on sizing would be most appricated
thanks
Chris

 

[Mtndew]

Hi ,
Im looking for the starting size and finishing size for 1/2 bspt threads external...
we are running a rlx protrak 1630, trying to get the thread sizes correct in custom threads but its not working..
does anyone have the correct sizing for the starting point..
major dia is 20.955, minor dia is 18.633, pitch 1.814, were cutting the correct pitch but the thread isnt correct in height etc, trying on a new fittings and not working..
cutting en3b bar...but we have pb bronze to machine shortly...
any help on sizing would be most appricated
thanks
Chris

Your numbers are spot on.What insert are you using? Is it sharp enough?
Are you cutting a right hand thread?

 

[pcasanova]

also using 55deg cutter?

 

[smithy1851]

Hi
Yes cutting righthand thread, new 14tpi insert, vardex, brand new only cut these threads, nice and sharp point...
55' angle, coming in at 27 degrees to make sure insert is cutting on leading edge...
its just not working and cant see why not...!!

 

[wmpy]

Are you figuring your taper correctly? It should be 3/4" taper per foot, if I'm not mistaken.

 

[sinha]

May help BSPT Thread Chart Calculator

 

[Mark Rand]

Is it a full form insert?

 

[smithy1851]

Hi
sorry for delayed reply.....

its a Vardex size 3, single point insert ...ive re calculated everything and its still far too tight,
whats strange too is that the pitch is correct when checked with a thread gauge...
im now wondering if the insert if wrong..
having to dig out the coventry die box with chasers to get the job sorted..

 

[sinha]

Starting with a slightly lower OD may help.