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tapping threads with a lathe

Discussion in 'The Hokey Ass Message Board' started by doctorZ, May 28, 2010.

  1. doctorZ
    Joined: Apr 10, 2006
    Posts: 1,243

    doctorZ
    Member

    i have heard of this being done, but am somewhat unfamiliar with it. i have a table lathe/ mill combo and need to tap about 50 steel bungs with 1/2" fine threads. do i just go real slow and let the metal pull the bit in? any tricks for not braking the teeth off the tap besides using a lot of oil?!
    thanks!
     
  2. use a tapholder that fits your tailstock and tap, MSC or other supply
    slow speed, belt loose enough to keep tap from breaking
    I usually used to leave the tailstock loose and push it in as you are taping
     
  3. dalesnyder
    Joined: Feb 6, 2008
    Posts: 483

    dalesnyder
    Member

    I am no machinist, but yeah that is how I do it. Chuck the work in the spinning jaws, the tap in the stationary collet. bring the tap up to the work and leave the lock loose so it can slide by itself. Run a low speed and push the tap in by hand til it grabs and self feeds. Lots of oil.. If it is a hard metal sometimes I turn the chuck by hand til I get the threads started then turn the power on...
     
  4. Rickybop
    Joined: May 23, 2008
    Posts: 7,427

    Rickybop
    Member
    from Michigan

    Some might tell me I'm wrong, but I don't that's such a good idea. The lathe has too much torque, and not enough control. Probably break some taps off, and make yourself more work. 50 holes is a lot though, and I understand wanting a little assist from a power-tool. How 'bout a reversible drill with a speed-control trigger? You could go slow and easy, and have the ability to reverse, so you can go in and out a little bit at a time as by hand, yet it'll minimize the labor. Maybe less set-up time too.
     

  5. doctorZ
    Joined: Apr 10, 2006
    Posts: 1,243

    doctorZ
    Member

    that's what i was thinking. my only problem is that it is geared rather than belt driven so i can't really loosen it. i figure i can use the tap t-handle on the tail stock since since it will slip when under too much pressure. i'll just have to keep it all aligned.
     
  6. randydupree
    Joined: May 19, 2005
    Posts: 665

    randydupree
    Member
    from archer fl

    i have tapped hundreds of holes on a lathe,my 13 year old daughter did lots of them too.
    I just jog the motor on the lathe,bump,bump,bump..works great,the holes will be straight too.
     
  7. thirty7slammed
    Joined: Sep 1, 2007
    Posts: 886

    thirty7slammed
    BANNED
    from earth

    You can definately power tap in a lathe, make sure you run at a slow speed, don't lock the tailstock while tapping (it will pull tap into tap drilled hole), use cutting oil, don't let your tap bottom out (threads or in blind hole), reverse lathe before this happens, and you'll be fine.
     
  8. Fat Fender Mike
    Joined: Nov 8, 2007
    Posts: 82

    Fat Fender Mike
    Member
    from Milwaukee

    Put the tap in a drill chuck in the tail stock. run your spindle at about 250Rpm and push the tail stock into your work piece by hand. Reverse the spindle after you tap through or before you bottom the tap and slightly pull the tail stock back so it will pull away from your work piece after the tap clears. Been a tool&die maker for over 25 years. This is a common practice. You should be able to tap that many pieces with one tap.
     
  9. owen thomas
    Joined: Jun 15, 2008
    Posts: 185

    owen thomas
    Member

    I do it all the time - tailstock loose as the other guys, but I start the tap in by hand, maybe keep going by hand too if I can.

    Do the same in a drill press sometimes - start the tap by turning the spindle by hand.
     
  10. 62rebel
    Joined: Sep 1, 2008
    Posts: 2,817

    62rebel
    Member

    i used a reversing spindle on the drill press i operated in the fab shop, can't remember the name of it. don't recall if it could take very large taps.
    it worked like a freaking charm every time i used it, hundreds of times, never broke a tap. i need to get back into that line of work.
     
  11. Johnalias
    Joined: Dec 8, 2008
    Posts: 56

    Johnalias
    Member
    from Cali

    if you have a light tail stock and reverse you should be ok. just go real slow and lots of oil . also invest in a high quality gun tap they can be a bit expensive but they are worth it
     
  12. thirty7slammed
    Joined: Sep 1, 2007
    Posts: 886

    thirty7slammed
    BANNED
    from earth

    If your using a hand tap you will have problems, use a good machine tap with a chip breaker.
     
  13. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208

    HemiRambler
    Member

    The only "tricks" I know when power tapping using a lathe are:

    1) Lots of cutting oil - usually "dark" oil (something with sulfur in it)

    2) Slow SLOW speed

    3) Clear the CHIPS - especially in a blind hole

    4) MARK the tap to how deep is enough or too much!!

    5) Chamfer your lead in edge before you tap

    6) Tap holders are nice, but not necessary. I also have a spring loaded gadget that fits into the end of a tap holder - you chuck it in the tail stock - put the tap handle against it and then you HOLD the tap handle from turning as it gets drawn in you can let go if the force feels too great - obviously a good thing for SMALL holes - not so much for the bigger stuff. ALso use a small enough handle that will clear the ways and other obstacles!! Makes a mess otherwise.
     
  14. Scott F.
    Joined: Aug 9, 2006
    Posts: 1,008

    Scott F.
    Member

    I'm not a machinist but can find my way around a lathe and bridgeport ok. i've done quite a few 1/2" tapped holes in 1" stock usually 1-1.5" deep and the best method i found as someone else stated is to 'bump' the power on and off. when doing a lot at once it is faster in the end to set up a stop of some sort for each piece, so the work is chucked with the same amount sticking out each time and then setting up some sort of stop for the tailstock so that the tap doesn't bottom out in the hole (blind hole). That assumes of course that you've used a similarly repeatable set up for drilling the holes all to the same depth.

    'bump, bump, bump' once you get a feel for it you will be able to leave the power on longer. use a lot of tap magic or similar.

    Scott
     
  15. ablebob
    Joined: Jul 29, 2009
    Posts: 76

    ablebob
    Member

    Hold the tap in a drill chuck & only tighten enough to cut threads. If it bottoms or grabs, the tap will spin in the chuck. I keep a old chuck around just for tapping - saves wear on my good one.
     
  16. dumprat
    Joined: Dec 27, 2006
    Posts: 3,184

    dumprat
    ALLIANCE MEMBER
    from b.c.

    I am a machinist. I do this all the time. It is easy. With a 1/2" tap it it likely that the tap will spin in the drill chuck before it breaks off. If it does break off, ya gotta build 51.
     
  17. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,661

    Ebbsspeed
    ALLIANCE MEMBER

    I won't say you're wrong, but I don't think your drill method is a good idea. Yer arms are gonna be sore after doing 50 half-inch taps. Not to mention that you're going to have a really hot drill motor running it slow enough to maintain control, yet generate enough torque to turn the half-inch tap.

    Use the lathe, it's easier, safer, and more accurate.
     
  18. budd
    Joined: Oct 31, 2006
    Posts: 3,478

    budd
    Member

    so the other day i was using the chuck and dragging the tailstock, just running the machine slow, a machinset friend came in and saw what i was doing, he went through my taps and found some with a center hole on the back end, he said i should be using a center along with a tap handle and have the tailstock locked and be feeding it in while holding the tap handle, anyone else tap holes this way?
     
    Last edited: May 28, 2010
  19. There is a center drill hole in the head of your tap handle for just such a purpose. The only problem with doing that is you have to lay the cross bar on the compound to hold rotationand feed the tailstock in as you tap. If you do it in a chuck, the tailstock will feed itself, as mentioned above.

    I've done hundreds of bungs this way, but I won't go under 1/2" threads. Use a good 1/2" air drill for anything smaller. You can adjust the torque easier. You can start the threads in the lathe to make sure they're straight...
     
  20. Zookeeper
    Joined: Aug 30, 2006
    Posts: 1,042

    Zookeeper
    Member

    As a machinist, if I have to do it in a lathe I always use a tap-sleeve, slow-ish RPM's (under 25 or so) and a new tap. For 1/2-13 tapping I also drill to 7/16 first. While that's not a true 75% thread, I've NEVER had one fail. BTW,if you think taps don't like RPM's you won't want to see it done on a CNC mill. If I do it, I use 400 rpm's on steel and twice that on aluminum. Scary? Sure, but you gotta live a little sometimes!
     
  21. diggers4life
    Joined: Jun 26, 2006
    Posts: 202

    diggers4life
    Member

    I am a machinist. We tap holes using tailstocks every day. Leave the tail stock loose and let the tap pull it in.

    The type of tap, and the type of hole you have will make all the difference. If it's a thru hole, use a sprial pointed (gun) plug tap. It will curl the chips to the leading edge of the tap and out the end of the hole. 1/2-20's will be a breeze.

    If all you have is a hand tap, it won't work as well. You will have to stop and break chips every so often, otherwise the chips will clog the flutes up and ruin your threads.

    If it's a blind hole and you are using a spiral pointed tap, make sure you stop before the end of the hole because the chips will all go to the bottom of the hole. You will have to clear them before you tap it to depth.

    Use a quality tap and good cutting fluid, and you won't have any troubles at all.

    Good luck!
     
  22. thirty7slammed
    Joined: Sep 1, 2007
    Posts: 886

    thirty7slammed
    BANNED
    from earth

    Iv'e done this a lot also, sometimes its not worth taking a chance breaking a tap in harder material ( tool steel, stainless, ect,) or tapping large or very small holes. Most larger taps have a center drilled hole in the square end, you can use a center in you chuck in the tailstock of your lathe, or in the chuck in the quill of your mill, to hold the tap perpendicular to material to be tapped. Most tap handles are also center drilled and can be used this way for smaller taps.
     
  23. Homemade44
    Joined: Feb 7, 2007
    Posts: 534

    Homemade44
    Member

    From your description of your lathe it sounds like it is single phase. With a single phase motor you do not have instant reverse. If you have a 3 phase motor you will have instant reverse. On a single phase motor if you don't let the motor stop before trying to reverse the motor it will keep running in the same direction.
     
  24. Rickybop
    Joined: May 23, 2008
    Posts: 7,427

    Rickybop
    Member
    from Michigan

    Thanks for not saying I'm wrong, Ebbsspeed, but fact is...I was wrong.
    I don't know why, but I failed to see that he was doing 1/2" taps. I was thinking something like 1/4"-5/16"-3/8". Then again, you guys probably know how to do those on a lathe fine too! That's what I get for posting on something I know little about. I'll shut up now.
     
  25. CoolHand
    Joined: Aug 31, 2007
    Posts: 1,928

    CoolHand
    Alliance Vendor

    If he's doing blind holes, he needs to be using a "spiral flute" tap. They pull the chips out in continuous ribbons that will shoot out towards the tailstock. No stopping to clear chips, and no problem running all the way to bottom in a single operation.

    I've done the tails stock dragging bit with taps all the way down to 1/4"-28, though I did "assist" the tail stock manually while it was cutting to lessen the load on the threads.

    Anything smaller than 1/4", I use thread forming taps instead of the traditional thread cutting ones. They don't make chips, they cold form the threads. Be careful when drilling the hole for thread formers though, the tap drill is larger than you would use for a cutting tap.

    And to the OP, be careful overall as well. When a good 1/2" tap breaks, it's not a gentle occurrence. They don't so much break as explode, so mind your appendages, and wear your glasses. If it happens, it'll happen faster than you can curse. And like the guy before said, then you'll need to make 51. ;)
     
  26. doctorZ
    Joined: Apr 10, 2006
    Posts: 1,243

    doctorZ
    Member

    good advice! i should have mentioned that they are not blind holes. does anybody have pics of the two different types of taps? i was planning on using a standard Snap-On tap. with this work?
     
  27. oldskool30
    Joined: Jan 4, 2009
    Posts: 121

    oldskool30
    Member

    What is more important than the brand is the type of tap. 4 flute taps with long leads are usually hand taps. Gun taps have a smaller lead and are usually in the 2 - 3 flute range . By lead I mean not full threads. Long lead means there is a lot of incomplete threads at end of tap so you can start it by hand.
     
  28. oldskool30
    Joined: Jan 4, 2009
    Posts: 121

    oldskool30
    Member

  29. agreed, power tapped buttloads of holes
     
  30. frizi
    Joined: Aug 15, 2008
    Posts: 181

    frizi
    Member

    1/2-20 fine thread tap will tap fine in your lathe, the tap that you have is a hand tap from snapon. You will want to go as fast as you are comfortable with, you could tap it at 2500 rpm and not break the tap, but it will pull your chuck out of the tailstock:)
     

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