1/2-14 NPT

[Bullard]

We have been having problems with tapping 1/2-14 NPT in 1/2" colled roll plate. Now i know its not the best material to be trying to mill but its what the customer wants.

Anyhow, when they tap the plates they keep getting chatter in the threads and get rejected by our QC department. So they have been throwing money at the problem but i think they are just pissing in the wind. I asked them if they ever tried peck tapping and i got the blank look like WTF is that? So i got them to give it a try and it seems to be working but set it up to peck around 3/16" or so.

We were getting bad tap life on our 4 fluted taps and went with the higher priced 5 fluted taps and they last longer.

They are also using tapping paste like Jokitch(sp?) when doing these holes which i think the only thing it does is polute the coolant.

So i was wondering what you guys would suggest for peck depths, feed speeds, tap, and coolant.

Right now i think we are running these parts like a bunch of hillbillies. Any help would be appreciated.

 

Brent

[Don S at Barefoot CNC South]

Brent are you counter boring the taper before tapping, cold rolled should tap very easy.

 

Don S

[Threept82]

Taper reaming?

Staggard tooth/coated tap?

or

Do you have the time to thread mill (you may

think not but how long does it take to tap, check depth, check finish and reject.)

One pass with a solid carbide thread mill wont take long.

[J Coulston]

I am a converted thread milling maniac. I just finished a 316SS 1/4 npt with a solid carbide thread mill worked beautifully. Sorry I cant help you on you tapping problem.

I would recommend thread milling. Up front price is a little steep, but you get perfect threads. Search the forum on thread milling or NPT, there has been a lot of discussion in the last few months.

[Bullard]

It looks like we just use a spade drill for the pilot hole.

I have seen a lot about thread milling but i really dont know how to go about programming it. Also the programmer before me talked them into buying a thread mill for this job and got about 3 holes done before it broke. So it would take some convincing to try it again. Plus i would hate to get into to buy it and i do the same thing the other guy did.

I guess we have tried using a tappered reamer and they said we still ended up with chattered threads.

[Tim Johnson]

For a 1/2 NPT you can use an indexable thread mill. Thread mill inserts are about the same price as a tap and in what I'm guessing 1018 crs will last twice as long as you think it should. One day of thread milling and your shop will forget what a 1/2 NPT tap is. From the way your tapping problem sounds, $150.00 for a thread mill and about $20.00 each for inserts will pay for itself the first week.

[ROB]

anything over 1/4 npt threadmill it,

done it many times, programming is not hard,

most important is feeds and speeds and plenty of coolant.

[crazy^millman]

The is also that guy name Toolfab that makes some real kick arse ones. Might look him up also.

[RickG]

Thread mill all the way.

We converted to thread mills about a 2 years ago and now I have more problems looking for a tap in the cabinet then scrapping the parts as they come off the mills.

We even solid mill our 1/4 NPT parts. Mostly in cast steel so they should hold up good in just plain steel. And the finish will be great!

[Threept82]

Thread milling is a piece of cake.

If you go that route and need some help just ask

Note; When thread milling vary hard or gummy

material I found that if I conventional mill down

leaving .006 per side stk then climb mill back up

@ finish dia.

This saves tool life and also gives a much better

finish.

[jeff]

We always try to use a pipe reamer whenever we have to tap an npt hole.

Just the other day we were tapping in 6061 aluminum on our Okuma mill at 2000rpm.

And the threads could not have come out better!

[Bullard]

Thanks for the heads up on the thread milling. I am really curious about it.

I went and talked with purchasing about thread milling those cold roll parts and as it turns out, we arent using cold roll, its actually hot roll and thats the reason we were busting thread mills last time we tried it.

So after doing a little more researchs i have found that we are spending dollars to save dimes.

I love my job.

 

Brent

[robinfly]

I have to agree that thread milling is the way to go. Even single point thread milling, but you still may get chatter if your set up is not rigid enough, but I also haven't had any trouble with rigid tapping either. Try 30-60 sfm with a stager tooth tap and use moly-d. stagger tooth taps will prevent tearing of the thread and it should help with the chatter