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GeoffS
23-11-2009, 10:08 PM
Hello from the US. I have been machining for the last 12 years, mostly CNC, and have run into a problem that I'm hoping someone in the UK can help with. I am cutting a 1/2 G parallel pipe thread in titanium. I have found all sorts of info on the thread (od, pitch diameter, minor diameter) and have run the calculations in the machinist handbook to find best wire size and measurement over wires (.040). Could anyone tell me what the tolerances are for diameters?

Thanks,

GeoffS

Robin Hewitt
24-11-2009, 11:24 AM
Hi GeoffS

I am of no use to you at all but I suppose one of us has to pop his head up over the parapet and risk getting it shot off :heehee:

Welcome to the forum :wave:

I know National and British Standard pipe threads but never heard of 1/2 G.

What's this wire size thingy?

Perhaps tolerances are't specified, especially if the male and female thread forms differ.

Presume you are either only doing one side of the thread so you can't cut to fit, or, you cut to size and it didn't fit and you find yourself in a wrangle with the customer?

Either way, good luck

Robin

BillTodd
24-11-2009, 03:52 PM
Do you mean the tolerances for the wire gauges? if so then you need to measure them to at least three (or five) times better than the tolerances of the thing you're measuring. (it's important that the wires are exactly the same size - i.e. to within 0.00002")

As to the thread diameter tolerances for a given fit, is this of any help (they list A & B fit)?

http://mdmetric.com/tech/thddat7.htm



Hello from the US. I have been machining for the last 12 years, mostly CNC, and have run into a problem that I'm hoping someone in the UK can help with. I am cutting a 1/2 G parallel pipe thread in titanium. I have found all sorts of info on the thread (od, pitch diameter, minor diameter) and have run the calculations in the machinist handbook to find best wire size and measurement over wires (.040). Could anyone tell me what the tolerances are for diameters?

Thanks,

GeoffS

GeoffS
25-11-2009, 04:53 PM
Hi Guys,
I solved the problem. After further investigation I found what the thread tolerance was as far as minimum pitch diameter. I didn't want to just "make it fit" as that is not the correct way to turn a thread. For those of you who do not know...thread wires are a series of wires in sets of three of different diameters for measuring different thread pitches. Best wire size is calculated for a particular thread pitch. A micrometer reading is made over the thread wires and the pitch diameter (where the wires contact the thread) is calculated from that measurement. Of course this does not resolve the possibility of incorrect or variable feed rates over the length of the thread but is still the best way (other than thread ring gages) of measuring an od thread.

Thanks for your input..

Geoff:dance:

Peter Griffin
02-12-2009, 08:23 PM
Just a little tip. Don't try and hold the wires in place with one hand and measure with the other ( unless you have got more than the usual number of digits). Push the thread wires through a rubber band this will hold them in place.