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View Full Version : _ Any guidance for making a Tandem/Dual Style Acme Tap



iMisspell
09-20-2014, 11:04 PM
I need 12 (or more) 1018 cold-rolled slugs, roughly 1.5" long with a *left* handed ID 1-10 acme thread.

Could buy a bunch of nuts $125+ from McMaster
Buy a tap, close to $200
OR
I have stock to make the slugs here along with some 1" round O1 and A6 tool steel, so the thought of making a "tandem" tap came to mind.

Tap will be used in a 14x40 lathe with a 3HP motor and hopefully under power (tailstock), slowest spindle speed 70rpm - might beable to get some good (sorry for get the type) tapping compound from work, if not it will have to be Enco medium/heavy tapping oil.

Found these two links for this style tap:
http://www.taylortool.com/wp-content/uploads/Tandem-acme-tap-dimensions.pdf
http://www.newmantools.com/taps/special_taps.htm#311acme

Heres my game plan:
Lathe does NOT have tapper attachment.

Buy one nut and use it for a test fit while making the tap
Turning both (front/rough and back/finish) angles between centers off-setting the tailstock. Being this will be used on a smaller lathe, i was gonna make both tapers .200 longer then the links above list.
"re-center/align" the tailstock strait
thread the front/roughing threads with a 45deg
pick up the front thread with a 29deg then cut the back/finishing thread.
mill the flutes
back to the lathe to clean up threads of any burrs
hone
harden
hone


Single pointing the slugs is an options, but making a tap like this seams like it will be fun and the end result will be easier (i think), as long as the lathe can pull the tap under power.

Any input or alternative ideas ???

thanks.

ahidley
09-20-2014, 11:11 PM
Acme taps take such a big cut that they come in three steps to build up to the final depth.

iMisspell
09-20-2014, 11:32 PM
Thanks for the post.

Ive seen three step ones in catalogs, but can not find any dimensions for them online (and at work we single point (with CNC) OD .840 acme for one job) and have no multi step taps to use as a reference).

Maybe: the first step at 45deg, second at 35ish and the finial finish at 29deg ?

As noted in the first post, being this will be used on a smaller lathe was gonna make the tapper of each step alittle longer then said in the links (links show each step at roughly 2.625 long, i planed on 2.875 ).

Arthur.Marks
09-20-2014, 11:39 PM
I'm pretty sure that they retain the proper thread profile/angle for all in the series. What is sequentially different is the thread height. That's how I remember it anyway. I have a series of three trapezoidal (30deg.) thread taps in the shop. I'll try to remember and post a pic of them in the morning.

I support the making of the tap between centers. Why off-set the tailstock, though? Can't you turn the tapered nose (i.e. taper tap) angle with the compound?

Oh--also to add, when I used mine heat build-up during tapping became an issue. If you need a very precise thread, you might want to use flood coolant (if possible) or at least direct a misting unit on the OD of the slug. The taps remove enough material that the heat build-up can affect work dimension. When the work expands, the taps cut oversize.

iMisspell
09-20-2014, 11:48 PM
OK, thanks, that would be great.

Reading the info supplied in this pfd, 'these' taps have two different profiles, they say the first one is 45 for easier roughing, then the second is 29 to clean up and create the correct profile.
http://www.taylortool.com/wp-content/uploads/Tandem-acme-tap-dimensions.pdf


Tandem or Dual Style Acme Taps are designed to produce Acme threads in a
single pass. This style of tap is manufactured in 2 sections, the first
threaded section has a 45 included angle. This permits easier roughing
thread formation giving freer cutting action and greater stock removal. The last
few threads of the roughing section are a guide for the 29 finishing section,
this corrects the angles and finishes the thread formation to proper size.

These taps are designed for through hole applications only, they should never
be reversed from the hole.



This style of taps are new to me, so any info will help.

_

Rich Carlstedt
09-20-2014, 11:48 PM
I would sooner tackle the nuts single point, as once the set up is made, the repetition is easy.
how ever, if you do a tap, it does not have to be a two stage or three stage item.
the object is to keep tooth load low, so calculate the tooth load and make the tap long, like 8 inches tapered for example .
I would suggest a .001 " load per tooth , which means a three flute tap will remove .003" times the number of turns in the nut
That will be very hard (!) as your nuts are 1 1/2 " long

good luck

Rich

iMisspell
09-20-2014, 11:54 PM
I support the making of the tap between centers. Why off-set the tailstock, though? Can't you turn the tapered nose (i.e. taper tap) angle with the compound?

Yea... i guess i could... leave some extra material on left of the stock for the drive dog, thanks for the thought.

The steps in the taps link above have a 2-5/8 long tapper (id like to get 2-7/8)... not sure of the compound travel, will have to check tomarrow.

iMisspell
09-20-2014, 11:59 PM
how ever, if you do a tap, it does not have to be a two stage or three stage item.
the object is to keep tooth load low Humm... i like that.
The one thing which was a concern was the chips from the multi-step tap.
It seams that the chips from the first step would play havoc with the start of the next step.

ahidley
09-21-2014, 12:25 AM
You'll need a three foot long tap holder to turn it in. A huge amount.of torque will be required. I don't see how a tailstock can hold it.

Arthur.Marks
09-21-2014, 12:48 AM
Okay, you raised my curiosity enough to get me out of bed :) They're a little different than I remember. It's been quite a while since I've used them.

http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/Widgets/Tandem%20taps/4b786ae3-be1d-4653-9b4c-c7604f880775_zpsb14233cc.jpg (http://s771.photobucket.com/user/Arrak_Thumrs/media/Widgets/Tandem%20taps/4b786ae3-be1d-4653-9b4c-c7604f880775_zpsb14233cc.jpg.html)
Also for close up, larger resolution images click on this link (http://s771.photobucket.com/user/Arrak_Thumrs/library/Widgets/Tandem%20taps) and select from the images.

So, first off, these are quite a bit smaller than your thread, being 9/16"-5. That said, all four in the series use the same thread profile of 30 degrees. I remembered them as being more like a normal tap with a majority straight section with a taper in the front. Instead, they are as Rich mentioned---tapered for nearly their full length. I also remember now that the shank is small on these because they are not intended to be reversed. The tap is threaded entirely through the nut and slid off the shank.

I wouldn't be surprised if there are more progressive changes in the thread form for larger sizes. If so, I would be curious to learn. Machinery's Handbook 28 ed. has Table 27 in the Machining chapter listing "Dimensions of Acme Threads Taps in Sets of Three Taps." Do you have a copy to reference? Some of the accompanying text is copied below.


The first tap in a set of Acme taps... should be turned to a taper at the bottom of the thread for a distance of about one-quarter of the length of the threaded part. The taper should be so selected that the root diameter is about 1/32 inch smaller at the point than the proper root diameter of the tap. The first tap should preferably be provided with a short pilot at the point... Acme and square-threaded taps should be relieved or backed off on the top of the thread of the chamfered portion on all the taps in the set. When the taps are used as machine taps, rather than as hand taps, they should be relieved in the angle of the thread, as well as on the top, for the whole length of the chamfered portion. Acme taps should also always be relieved on the front side of the thread to within 1/32 inch of the cutting edge. p920

The table shows a tapered section and a straight section for each of the three taps. The ratio between them changes. The first, roughing tap for 1" threads has a taper length of 3-13/16" with a straight section of 13/16" length. The second, semi-roughing tap has a taper length of 3-3/8" with the parallel portion 1-1/4" long. The third, finishing tap has the shortest taper length of 3" and a parallel length of 1-5/8".

[EDIT:] It just occurred to me that my terminology hasn't been accurate. The thread title brought to my mind a multiple set of taps to form one thread progressively. Those are "serial taps" and not a "tandem tap." I very much apologize. I have personally never used a tandem tap, which is probably why I confused the term.

RussZHC
09-21-2014, 01:19 AM
Not that it matters but that thread size, 1" x 10tpi is tough to find generally (find listed in catalogs or for that matter charts, I mean).

With that size I am not so sure tandem is the way to go, see ahindley remarks about amount of torque. I would consider a series of taps like Arthur talks about, in fact, given the size, I might even consider more and almost ridiculously long tapers/overall cutting length with the same torque issue being the root. Though I certainly don't know, it may not be nearly as great as I suspect.

By the by, there is a Regal 1" x 10 tpi, left hand Acme rougher on ebay for $32.50

On the plus side there are several other good threads on making your own Acme taps on this bbs as well as in other early hits of a search.

JCHannum
09-21-2014, 08:18 AM
A 1" bore is a good size for single pointing as it will permit use of a fairly stout boring bar. My suggestion would to single point a rough thread and clean it up with a finishing tap.

davidwdyer
09-21-2014, 12:35 PM
Maybe I'm not understanding what you need, but how 'bout an "Evan nut?"

iMisspell
09-21-2014, 09:56 PM
Okay, you raised my curiosity enough to get me out of bed :)
Sorry about that :) and thanks for the images... it jarred my memory, ive seen taps like that long ago... forgot all about them.
And also thanks alot for the page number from the book. Took alittle peek at it before, very useful, thanks.



By the by, there is a Regal 1" x 10 tpi, left hand Acme rougher on ebay for $32.50Cool... thanks for the heads up.



Maybe I'm not understanding what you need, but how 'bout an "Evan nut?"
Thats another idea which i forgot about.
These nuts will be used for a table on a "basement made" horizontal drum-sander.
Some of the nuts will only be used to lock the "lead screws" (four acme rods which will raise and lower the table), other nuts will be tack welded and have to hold the weight of the planks being sanded, but for the lock nuts some 'Evan nuts' might be quick and easy... gonna have to give this more thought, thanks for bring it up.

LKeithR
09-22-2014, 12:13 AM
If you look in the right place you can find nuts for a pretty reasonable price...like these...

http://www.roton.com/mating_components.aspx?family=7159495

iMisspell
09-22-2014, 12:49 AM
If you look in the right place you can find nuts for a pretty reasonable price...like these...

http://www.roton.com/mating_components.aspx?family=7159495

I appreciate your effort and thanks for the link, but it looks like mcmaster carr are alittle cheaper:
$8.67 compared to $9.04
http://www.mcmaster.com/#91808a121/=tttjy0

Just realized i also have at least two (maybe four depending on how i use them) sprockets which will need ID threads also.
If i do buy the nuts, single pointing two sprockets will be no big deal, but the seed is planted on making some taps sooo :)

The ID bore for a 1-10 acme should be .910
Thinking of making two Tandem taps, the first with a major of .960 then the second 1"

Maybe because its new to me, but the idea of the Tandem taps with the rough 45 threads first then 29 to create the correct profile is kind of cool and seams like it would be fun to make.

Forestgnome
09-22-2014, 10:28 AM
It's going to take a huge amount of force to thread a 1"-10 nut, even with a store-bought 3-tap set. Do yourself a favor and buy the nuts. Finishing the project will be satisfying enough. Otherwise single-point them with a nice store-bought cutting tool.