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29th April 2014, 10:42 PM #1SENIOR MEMBER
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Using an internal tap with a lathe
The few times I use an internal tap to thread work in the chuck, I generally mount the tap in the tailstock and let the tap pull itself (and the loose tailstock) into the work.
It works OK for me, and I'd never considered any other way.
Then recently I saw a video where a guy had the tap mounted in the toolpost and appeared to be driving it into the work - ie. set the change gears for the thread pitch to match the tap entry speed.
Anyone else do this?
RobThe worst that can happen is you will fail.
But at least you tried.
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29th April 2014, 11:16 PM #2Senior Member
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No, but I've done the reverse, using a jaw from an old threading machine head as a chaser to cut a 1 5/16 x10 TPI Whitworth form thread to make a dummy spindle nose for the old Brackenbury and Austin lathe. The lathe gearing was set to cut 10 TPI. The photo shows the partly cut thread. The finished thread is a beautiful fully formed thread with the correctly shaped Whitworth rounded crests and valleys, just like the original spindle nose thread.
Frank.
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29th April 2014, 11:35 PM #3Distracted Member
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No but I'm intrigued by the idea. Can you link the video Rob?
What would the advantage be over letting the tap feed itself? More accurate pitch? (Prolly not on my lathe.)
Besides that, when you backed out, would backlash in the gear train/leadscrew bite you?
Seems like the tap would no longer be in sync with the thread.
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29th April 2014, 11:58 PM #4SENIOR MEMBER
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I might have to give that a try with a tap. On my AL960b that is the only practical way to do metric threads (that I know of) as it has an imperial leadscrew and thread dial. Power it in half nuts engaged, feed out and power reverse that puppy with half nuts still engaged. Rinse and repeat.. I have not had any issue with backlash messing up the threads. I have cut threads with no discernible play in them. I think the leadscrew backlash issue seems to be overstated. I was initially concerned until I cut some threads this way, and they turned out great. That said my machine is new.. An old worn out lathe and it is probably an entirely different story.
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30th April 2014, 12:32 AM #5
Backlash could be a big problem with a tap. Single point threading is a little different because the tool is not touching the work whilst you are reversing. With the tap though the spindle may rotate somewhat before the leadscrew does, with all the clearances in the gears. If the half nuts are a good fit the tap will not be able to push the saddle back and something will have to give
Power it in maybe, though i don't see why you really need to or what advantage you get over using the T/S like i imagine most of us do. But i would disengage the half nuts and let the tap push the saddle back.
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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30th April 2014, 12:43 AM #6
I just had a thought.....
He wasn't using it like an internal thread chaser? Cutting say a 20x2mm thread with an M16 tap?
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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30th April 2014, 12:53 AM #7GOLD MEMBER
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The only other reason I can think of for doing this is if the finished product had a very short thread in a blind hole, so you dont want to risk a little "drilling" with a bottom tap before it started. Though I think if I was that worried and I had more than a couple to make, I'd make a tap holder connected to the tailstock with a bolt of the thread the same pitch as I was cutting.
Stuart
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30th April 2014, 06:13 AM #8SENIOR MEMBER
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30th April 2014, 09:30 AM #9SENIOR MEMBER
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I actually contated this guy and asked him how he was doing it. His English is a bit poor and it appears he sometimes drives the carriage, and sometimes lets it just pull itself in.
It got me thinking about using the change gears, and also even about feeding into the job (and out) by hand with the carriage.
I am going to make up an adapter for this and give it a go.
The site is Romanian (I think) and he's an interesting rough and ready sort of guy.
http://www.youtube.com/watch?v=jdqMR...1nJBgHdxPdvkjQ
RobThe worst that can happen is you will fail.
But at least you tried.
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30th April 2014, 11:29 PM #10SENIOR MEMBER
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G'Day all, I vaguely recall seeing an article about this technique, and if I were to guess, it would have been a tip sent out from Village Press, home to "Machinists Workshop" and "The Home Shop Machinist". It was some time ago, and I thought that I had bought it to the attention of this forum in a response to a question someone had about threading using a lathe. I have not been able to find the thread here, and neither have I found the original article, but from memory the author claimed that it improved thread quality in difficult materials. He was using a tap of the size he wanted the thread, not doing internal thread chasing as Uee was wondering. When I have the time I will check the magazines from V.P. to see if there was an article in one of them on this subject.
Rob.
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1st May 2014, 12:49 AM #11
I have only just looked at the video. An M45 tap may be a bit of a different story to what most of us use and certainly what i was thinking of, plus he is using either an intermediate or plug tap.
Interesting job, all the drill rig rods i have seen have a tapered thread for fast fitting and removal.
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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1st May 2014, 01:17 AM #12SENIOR MEMBER
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1st May 2014, 10:17 AM #13SENIOR MEMBER
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I had a look on Google and can't find any pictures or links to a tool post tap holder, such as we are discussing.
Interesting concept.
I can see it could be a big help starting threads using the carriage.
The tap mount would either have to be self centering, or very accurate to prevent tap beakage from mislignment.
In the video it appears to be fairly lightly made in comparison to the tap diameter.
RobThe worst that can happen is you will fail.
But at least you tried.
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1st May 2014, 11:58 AM #14
POWER
It would require a decent amount of power to do that ? My little Sheraton would have a hernia if I tried that Mike
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