[woodzrider]

Here's a thread milling question I haven't been able to find an answer to:

I'm thread milling a 1/4-18 pipe thread into 316 S.S. using a 7/16 predrilled hole. The thread mill i'm using is a tapered hss mill (for pipe). My question is:
Do I need to taper ream the hole first or can I just thread mill the straight hole letting the mill cut the taper? I have programmed the lead in arc to the
small end of the the thread mill and am starting from the top of the hole and arcing downward so I know there is clearance but am concerned about side loading the mill as it arcs downward and breaking it. Spindle speed is 725rpm with feedrate of 2.5. I have been taper reaming but want to take out the extra tool if possible.
Thanks,
Robert

P.S. I did a quick search but could not find a way to post in appropriate
catagory.

[poster]

This may be a dumb question, but why are you thread milling something so small? Would a tap not be faster?

[txcncman]

Most taper pipe thread mills can handle not having a taper hole. The reality is, try it, it will either work or it won't.

Oh, the reasons for thread milling are: zero tap breakage/scrapped part and less horsepower required.

[Shane1234]

when doing 1/4-18 npts in pipe, 316 & 304, i like to use a interrupted pipe tap like this....... Deprecated Browser Error i dont use that brand specifically, nor that supplier either, just a quick find of a picture to show you. I just did some on thursday and found a nice sweet spot for em. I used a keo #4 center drill to poke centers so my carbide drill wouldnt wanna walk from pipes not being exact, a mitsubishi carbide 7/16 mws coolant thru drill, and one of those interrupted pipe taps, feed of 11ipm, speed of 198 on the tap. i went double speed/rpm but she started squealing, and i only had the one tap to finish the job. 11 holes per pipe were only taking about 2 minutes.......

[Shane1234]

and for the depth of the tap, i think i was going .6" deep to get my tolerance for the spraybar tips.

as for threadmilling the pipe, you might be ok since there isnt much wall thickness there, unless your going schedule 120 or mechanical tubing.......

[woodzrider]

and for the depth of the tap, i think i was going .6" deep to get my tolerance for the spraybar tips.

as for threadmilling the pipe, you might be ok since there isnt much wall thickness there, unless your going schedule 120 or mechanical tubing.......

Thanks for the info. BTW i'm going thru the sidewall of 1-3/8 hex bar w/ 3/4 hole thru.

[woodzrider]

I was tapping the hole at first but have to use a tapered ream and not having good life span.Iwas was using an OSG "exotap" hence i'm trying the thread milling.

[Delw]

I usually use a tapered reamer then the pipe tap. as we run them in quanities of 50-100 and I dont like changing tools, it might take an extra min but saves time in the long run.