Best tap for aluminum

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Mr Ron
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Best tap for aluminum

Post by Mr Ron » Sun Jan 27, 2019 6:06 pm

Probably one of the most distressing things that can happen is having a small tap break in a piece you have spent hours machining. I've tried HSS thread cutting taps and thread forming taps in 2-56 to 6-32 thread sizes and get some breakage, so my question is: what is the best, long lasting tap, either cutting or forming? I work mainly with aluminum in 6061, 2024 and 7075 alloys. I'm hesitant to buy an expensive tap (vanadium or cobalt) and only have it snap as easily as a HSS one. I use a lubricant when threading, usually WD40, but also "tap magic". I've heard reports of people using a small tap for hundreds of threads, without tap failure. I would like to know the right way to tap, as I do a lot of small hole tapping in my model building as I'm sure the live steamers also do. Tap threading is probably my weakest skill.
Mr.Ron from South Mississippi

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Rick
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Re: Best tap for aluminum

Post by Rick » Sun Jan 27, 2019 6:49 pm

Mr Ron
We tap a lot of alum. With HSS taps. Small taps can take a fair amount torque but will not tolerate any bending.
What method are you using, hand, hand with a guide, or in a machine?
How much thread are you trying to get, 75% ....?

We use both water based coolant and a mixture of 50/50 Tapmagic mixed with marvel mystery oil. The Marvel oil gets rid of the smell of Tapmagic and just makes it more pleasant to use without any loss of effectiveness. I can equate the two times I got pinkeye with using Tapmagic at full strength. Needless I don't like to even get near it😬
Rick

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spro
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Re: Best tap for aluminum

Post by spro » Sun Jan 27, 2019 8:32 pm

Mr. Ron. What sort of a "tap head" are you using? Some would be great for those small holes. Downfeed pressure drives the tap CW and lift drives it CCW . The tap shouldn't exit the hole but it lifts out the strings, chips, to where the tap can proceed again.

Wolfgang
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Re: Best tap for aluminum

Post by Wolfgang » Sun Jan 27, 2019 8:36 pm

Mr Ron wrote:
Sun Jan 27, 2019 6:06 pm
Probably one of the most distressing things that can happen is having a small tap break in a piece you have spent hours machining. I've tried HSS thread cutting taps and thread forming taps in 2-56 to 6-32 thread sizes and get some breakage, so my question is: what is the best, long lasting tap, either cutting or forming? I work mainly with aluminum in 6061, 2024 and 7075 alloys. I'm hesitant to buy an expensive tap (vanadium or cobalt) and only have it snap as easily as a HSS one. I use a lubricant when threading, usually WD40, but also "tap magic". I've heard reports of people using a small tap for hundreds of threads, without tap failure. I would like to know the right way to tap, as I do a lot of small hole tapping in my model building as I'm sure the live steamers also do. Tap threading is probably my weakest skill.
h

6-32 and 1/4-20 are "ugly" threads inasmuch as they are very coarse for their size; consequently they require a higher torque for tapping and the smaller root dia. makes them weak in bending (proportionately to finer threads of equal dia,).

When building my turbo-generators (discussed elsewhere in this blog) I built a tapping stand from an old sensitive drill press and, since then, have never broken a 0-80 or 2-56 tap. I still avoid 1/4-20 as much as possible, using 12-28, 1/4-28, and 1/4-32 as appropriate.

As an apprentice oh so many moons ago I was doing a government job that required dozens of 1/4-20 tapped holes. It was on this job that I got to dislike 1/4-20 threads because I broke a fair number of taps threading all those stinkin' holess.:-))

For lubrication I use a can of cimtap I have had since my apprenticeship days. It is now running low and checking the stuff on the 'net it is still available at around $150 per pint can!. Hmmm, I better go easy on the usage of that jam. (it looks a bit like strawberry jam).

One can purchase taps specifically ground for aluminum but, unless you are doing serious production runs or tap a lot of aluminum, is probably not not worthwhile to buy them. w

spro
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Re: Best tap for aluminum

Post by spro » Sun Jan 27, 2019 8:53 pm

Mr. w, this is good info.

RSG
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Re: Best tap for aluminum

Post by RSG » Mon Jan 28, 2019 10:19 am

I assume you are mounting the tap handle some how to make it rigid so you can't bend them. Either in the tail-stock or a drill chuck in the mill. I use standard four flute HSS taps in 0-80, 1-72, 2-56, 3-56, 4-40 and so on and haven't broken one in years since I learned to mount them as above. I have found chip loading in aluminum to be more sticky than in say SS so backing up one turn to break the chip and backing out the tap periodically is a must. I use a tap lube specific to aluminum as well called A-9, whether it works any different than the others is questionable but they must make it for a reason I say, or unless someone convinces me otherwise.
Vision is not seeing things as they are, but as they will be.

Mr Ron
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Re: Best tap for aluminum

Post by Mr Ron » Mon Jan 28, 2019 11:44 am

Thank you all for the great info. I was taking the lazy way out by tapping freehand. I'm sure that is my problem. I will have to get away from 6-32 and 1/4-20 threads. I have used 5-40 threads, but there is not the same variety of screw lengths available in the fine thread series.

What about thread cutting vs thread forming taps?

Spro: I don't use a tapping head, although I own 2 of them. They are too big for the small threads I use like 1/4" and larger.

Will cobalt or vanadium taps give me longer life or should I stick with HSS?
Mr.Ron from South Mississippi

John Hasler
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Re: Best tap for aluminum

Post by John Hasler » Mon Jan 28, 2019 12:51 pm

I replace the drill bit that I used to drill the hole with a center and press it gently into the hole in the back end of the tap, stabilizing it while I turn the tap holder.

spro
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Re: Best tap for aluminum

Post by spro » Mon Jan 28, 2019 4:18 pm

There are so many designs of small tapping heads, I don't know where to start. Frank Ford's fret site has at least 3 different ones which will inspire. Mark Klotz and many others have shown how to make these tools. The main problem is alignment, the second is speed and the third is retracting the chips. Aluminum tends to form before being cut, so it clogs the thread clearance putting stress upon the whole tap. So it is either a certain tap (spiral flute for aluminum )? certain speed or the other way. The other way, in larger form, is a sensitive drill press with an opposing drive unit. It does the same as hand tapping only quicker with accuracy. It is downfeed pressure increasing the speed and letting up, reducing it, to where the tap is turning CCW and retracting the chips. It becomes a pecking as long as the tap hasn't existed the thread. That is why they are sensitive.
This is reproduced inside an actual tapping head attachment. They are big honkers but look at the plate and see what they can cover. It may be a question of tap collets or the grease has seized up. I've seen a few likely candidates go past on ebay. They are fair intricate inside so dormancy is not good.

ChipMaker4130
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Re: Best tap for aluminum

Post by ChipMaker4130 » Mon Jan 28, 2019 10:39 pm

If you can use a spiral-point tap it makes life a lot easier since the chip precedes the tap instead of getting bound up in the hole. I use them for all through-holes and on blind holes whenever I have enough material thickness to overdrill the depth sufficient to catch the chip. It can be a nuisance to remove packed chips after the fact, but with picks and practice it isn't too bad. Spiral flute taps are supposedly as good in the other direction, but I find them weaker in general and not very effective in some materials. Spiral flute taps are also often more expensive.

Harold_V
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Re: Best tap for aluminum

Post by Harold_V » Tue Jan 29, 2019 2:55 am

ChipMaker4130 wrote:
Mon Jan 28, 2019 10:39 pm
Spiral flute taps are supposedly as good in the other direction, but I find them weaker in general and not very effective in some materials. Spiral flute taps are also often more expensive.
I share your position with spiral flute taps. My experience in using them leaves a little to be desired. I also agree with your assessment of spiral point (gun)taps, which are my first choice, discounting thread forming taps. For holes where the chip gets packed, I use a needle nozzle with an air gun, plus a pick. Removing even compacted chips isn't all that difficult, and certainly worth what little time it takes as opposed to risking tap breakage by using a spiral flute tap. I just flat don't like 'em!

Personally, I do not consider the ¼"-20 tap a problem. I've used them in pretty much any way one can think of and have achieved favorable results, rarely breaking a tap, even when power tapping by gripping the tap in a drill chuck (common practice when building tools). For me, they work just fine, but I also ensure that I use a tapping fluid. Doing so makes all the difference in the world.

That said, Wish I could say the same for the 6-32, which is, without a doubt, troublesome, especially in tough materials.

I should note that tapping with a drill chuck is asking for oversized threads. If the work at hand is to be inspected, I don't recommend the practice. It's too easy to get bell mouthed starts.

H
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whateg0
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Re: Best tap for aluminum

Post by whateg0 » Tue Jan 29, 2019 6:29 pm

spro wrote:
Mon Jan 28, 2019 4:18 pm
There are so many designs of small tapping heads, I don't know where to start. Frank Ford's fret site has at least 3 different ones which will inspire. Mark Klotz and many others have shown how to make these tools. The main problem is alignment, the second is speed and the third is retracting the chips. Aluminum tends to form before being cut, so it clogs the thread clearance putting stress upon the whole tap. So it is either a certain tap (spiral flute for aluminum )? certain speed or the other way. The other way, in larger form, is a sensitive drill press with an opposing drive unit. It does the same as hand tapping only quicker with accuracy. It is downfeed pressure increasing the speed and letting up, reducing it, to where the tap is turning CCW and retracting the chips. It becomes a pecking as long as the tap hasn't existed the thread. That is why they are sensitive.
This is reproduced inside an actual tapping head attachment. They are big honkers but look at the plate and see what they can cover. It may be a question of tap collets or the grease has seized up. I've seen a few likely candidates go past on ebay. They are fair intricate inside so dormancy is not good.
Where are these tapping heads you speak of? I looked at Frets.com and I see tapping guides and the like, but no tapping heads, such as would be put in a drill press, mill, or lathe. I would think that designing and building a tapping head that reverses would be quite the feat. Obviously it can be done, but I have never run across a DIY one.

I have two SPV tapping heads but haven't used either so far as I need to make collets or holders for the taps.

Dave

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