Tapping Pipe Thread On Mill

[BAYWATCH-TIM]

For anybody that can help me. I just recently made a part that had six holes that had to be tapped @ 1/4-18 NPT. I did it in the mill, and they looked great. But when I put the fittings in, they seemed to go in a little bit to far for my comfort. When I am tapping pipe thread like that on the mill, is there a rule that says you should not run the tap down to %100 percent of the threads? Maybe I should be only be tapping down to about %75 of the tap. These are not being tapped for pipe nipples, but brass straight fittings, and 90 degree fittings. Any help would be appreciated.

Tim Barry
www.baywatchtowers.com

[Geof]

You can probably find a rule in The Machinery Handbook and you can probably buy gauges for tapping threads. Generally with 1/4" NPT I have the part available that will fit in the thread and tap deep enough to get around 5 thread engaged before it is too tight to turn by hand. Often this is less than 75% of full depth on the tap.

If you are doing these parts for a customer and they are expected to be interchangeable with parts from other sources I think it is a case of you must get the gauges and do things according to standards.

[BAYWATCH-TIM]

Geof,

Thanks for the input. I did have the parts on hand. Just didn't think about it until after they were tapped. I think I will search for a tap gauge. That would probably be best.

Thanks,

TB
www.baywatchtowers.com

[mhtom]

I worked for a company that does a lot of pipe tapping and a lot of thier customer's reqiured a special projection. So a standard tap would not do, and yes a thread gage is allways needed.