1/8" NTP Threads: Tap or mill?


Results 1 to 14 of 14

Thread: 1/8" NTP Threads: Tap or mill?

  1. #1
    Registered
    Join Date
    Feb 2009
    Location
    US
    Posts
    38
    Downloads
    0
    Uploads
    0

    Default 1/8" NTP Threads: Tap or mill?

    Hi all, I am trying to make a small aluminum manifold for a flood coolant system for my Taig 2019 CNC mill. I need to drill and tap 3 1/8" NPT holes into 6061 aluminum. I am pretty new to metalworking in general, so yesterday I picked up a cheap tap set at Harbor Freight that included a 1/8" tap. I drilled the hole properly and then set to tapping it. I got about 3/8" in before I felt like I would break the tap if I pushed any harder.

    The problem, of course, is that NPT is tapered and I drilled a straight hole. Reading more about the subject, it seems I need a NPT reamer and to ream out the hole before tapping it. The cheapest reamer I can find is about $20 before shipping.

    This got me thinking about the perfectly functional CNC mill I have sitting on my bench. Could I make this job easier with it?

    I thought I'd ask and see if anyone has any suggestions for me. Consider me a total newbie but willing to learn and work

    I want to drill and tap 3 1/8" NPT holes about 3/4" deep in 6061 aluminum. I have:
    Taig 2019 CNC mill
    1/6", 1/8" and 1/4" endmills
    A 1/8" NPT hand tap

    I've been thinking that I could probably at least use the mill to "ream" the hole out without spending another $20 on a specialized tool. But what about thread milling? Can I buy a small thread mill and just throw my hand taps away forever?

    I've also been thinking about making a tooling plate with a bunch of 10-32 holes in it and it would sure be easier to have my mil cut all those threads for me than to hand tap them all.

    Thanks,
    Jason

    Similar Threads:


  2. #2
    Member hoss2006's Avatar
    Join Date
    Apr 2006
    Location
    United States
    Posts
    8159
    Downloads
    0
    Uploads
    0

    Default

    A "Q" drill bit (.332) is just fine for a 1/8-27 NPT tap.
    You made it in 3/8, did you check the hole with the mating part, that's probably deep enough.
    5-7 threads worth of engagement is enough.
    Hoss

    Gosh, you've... really got some nice toys here. - Roy Batty -- [URL]http://www.g0704.com[/URL]


  3. #3
    Registered jstiltner's Avatar
    Join Date
    Feb 2008
    Location
    USA
    Posts
    37
    Downloads
    0
    Uploads
    0

    Default

    The problem may also be in the tap you are using. I have a set of HF taps that are complete junk! it almost looks like they were cast into shape!



  4. #4
    Registered
    Join Date
    Feb 2009
    Location
    US
    Posts
    38
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by hoss2006 View Post
    A "Q" drill bit (.332) is just fine for a 1/8-27 NPT tap.
    You made it in 3/8, did you check the hole with the mating part, that's probably deep enough.
    5-7 threads worth of engagement is enough.
    Hoss
    Thanks for the response Hoss. I used a "R" to drill the hole. The 3/8" depth is enough to get a solid seal, but I wanted to go the full 3/4" purely for aesthetics. This is for the plug side of a Loc-Line hose and I just wanted it to be flush.



  5. #5
    Registered
    Join Date
    Feb 2009
    Location
    US
    Posts
    38
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by jstiltner View Post
    The problem may also be in the tap you are using. I have a set of HF taps that are complete junk! it almost looks like they were cast into shape!
    That could definitely be. The tap seems pretty junky but I figured I could at least get 3 holes out of it

    Would it be reasonable to expect that a good tap could cut NPT threads without first reaming the hole to a taper?



  6. #6
    Registered vlmarshall's Avatar
    Join Date
    Mar 2006
    Location
    usa
    Posts
    474
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by vonnieda View Post
    Would it be reasonable to expect that a good tap could cut NPT threads without first reaming the hole to a taper?

    Yes! Especially in Aluminum. Use a Q, like Hoss mentioned, and get another tap.



  7. #7
    Registered
    Join Date
    Feb 2009
    Location
    US
    Posts
    38
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by vlmarshall View Post
    Yes! Especially in Aluminum. Use a Q, like Hoss mentioned, and get another tap.
    Can someone explain to me why to use a Q instead of an R? I'm not questioning the recommendation, I just want to understand it. I've been looking at tap/drill charts and the Internet seems to be split on whether to use a Q or an R for NPT 1/8". A Q is smaller then an R so it seems like I would have even more trouble getting the tap through the work.

    Thanks all for the helpful info!



  8. #8
    Registered vlmarshall's Avatar
    Join Date
    Mar 2006
    Location
    usa
    Posts
    474
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by vonnieda View Post
    Can someone explain to me why to use a Q instead of an R?
    Good question...
    I've almost always used a 'Q', mainly for a better seal. Taper pipe threads (in my opinion, at least) should be a slight interference fit, and not a "100% thread". I'd rather have a pipe fitting sit a little high, than have it thread all the way in and still not seal because of a drill cutting oversize or a tap too deep.



  9. #9
    Registered Hirudin's Avatar
    Join Date
    Jun 2008
    Location
    Albuquerque, New Mexico, USA
    Posts
    1082
    Downloads
    0
    Uploads
    0

    Default

    I'm just beginning with CNC-ing / metalworking so I might be completely wrong, but since I was reading this thread and I have a drill/tap chart sitting right in front of me I figured I'd share what it says...

    This chart says use an "R" for NPT and use a "Q" for NPTF for tapping without reaming.

    Attached Thumbnails Attached Thumbnails 1/8" NTP Threads: Tap or mill?-03162009138-jpg  


  10. #10
    Registered vlmarshall's Avatar
    Join Date
    Mar 2006
    Location
    usa
    Posts
    474
    Downloads
    0
    Uploads
    0

    Default

    Yeah, I've got a quick-ref from Morse tools here that says the same thing. Listen to them, not me.



  11. #11
    Registered
    Join Date
    Feb 2009
    Location
    US
    Posts
    38
    Downloads
    0
    Uploads
    0

    Default

    Sounds good to me. Thanks for the responses all. I'll give it a try with a Q (non-reaming) and my HF tap and if that busts off I'll go shopping



  12. #12
    Registered Regnar's Avatar
    Join Date
    Mar 2006
    Location
    USA
    Posts
    427
    Downloads
    0
    Uploads
    0

    Default

    It sounds like you have the same crappy HF tap set that I have. I tried the 1/8 NPT that came with both kits Metric and Standard. Gave up on both and bought a Irwin one from Ace Harware. Well worth every 599 pennies. Cuts a lot easier and the finish was nicer.

    Also to help you out you will want to pick up one of these. Drill a hole, Throw this in and lining up the tap is idiot proof. http://littlemachineshop.com/product...963&category=2



  13. #13
    Registered
    Join Date
    May 2008
    Location
    USA
    Posts
    26
    Downloads
    0
    Uploads
    0

    Default

    Let's beat this to death.

    We live almost exclusively in the 1/8 NPT world...everything I've ever designed has at least one. NPT is tricky. You do not want the thread so deep that your fitting is bottomed out, if it does you'll need a mile of teflon tape to seal it up. In aluminum you should not need a reamer, but you will need a quality tap for any kind of NPT threading...and ones from HF may or may not be so, but ones from a true tool vendor; McMaster-Carr, MSC, J&L, etc would be.

    On the other hand, a cnc mill could make you a sweet tapered pilot hole......



  14. #14
    Registered
    Join Date
    Feb 2009
    Location
    US
    Posts
    38
    Downloads
    0
    Uploads
    0

    Default

    Just to close this out: I picked up an Irwin tap, used a Q drill and everything went great. Thanks everyone for all the excellent advice and information. My coolant manifold works perfectly!



Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

1/8" NTP Threads: Tap or mill?

1/8" NTP Threads: Tap or mill?