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Thread forming taps

12/24/2009 10:48 AM

I have to tap about (60) holes in aluminum 6061 for 4-40 machine screws. I'm trying a thread forming tap for the first time, hoping it will go faster than with thread cutting taps and with less chance of breakage. Can you tell me what procedures to follow, as to lubricant, power vs hand tapping?

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#1

Re: Thread forming taps

12/24/2009 11:21 AM

We called them roll taps in my day.

This site gives some good advice.

Don't Cut Threads -- Form 'Em - Society of Manufacturing Engineers

Note this:

Emuge offers a computer model service that compares expected performance of forming taps versus thread cutting. By inputting the work material, thread parameters such as size and tolerances, the type of machine being used, and hole type, users can get a direct economic comparison between thread forming and cutting.Emuge offers a computer model service that compares expected performance of forming taps versus thread cutting. By inputting the work material, thread parameters such as size and tolerances, the type of machine being used, and hole type, users can get a direct economic comparison between thread forming and cutting

And, do you have a Tap-o-Matic? If you do much repetitive tapping they are great!

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#8
In reply to #1

Re: Thread forming taps

12/25/2009 1:19 PM

Thanks for the good info. I have a tapping head, but it is too large for a 4-40 tap. I was going to try using a cordless drill for controllable drive power. Holes thru 1/4" thick 6061 alum are to be tapped. Some 5052H32 might also get used. For a lubricant, I was going to try a heavy (SAE 50) wt oil or something like Marvel mystery oil or Slick 50. What do you think. My biggest concern is tap breakage which could mess up my project. I have considered other fastening methods, like epoxies and roll pins, reinforced with epoxy. The area involved is between two 1/2" sq surfaces as in 1/4 x 1/2 bar crossing another 1/4 x 1/2 bar at 90°.

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#2

Re: Thread forming taps

12/24/2009 12:16 PM

4-40 in 6061? Can I recommend a good prayer site? You certainly have my sympathy. Really, really, really push the tap drill size. Maybe even 90% if you can stand that. I'd use a chucked tap, turned by hand. I use Tap Magic especially marked for aluminum, but I just looked on McMaster and I don't see that - just one type of Tap Magic. Maybe they've quit making it?

As an aside, have you considered something like z-drive screws that cut their own threads as you pound them into the hole?

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#3
In reply to #2

Re: Thread forming taps

12/24/2009 2:25 PM

Yes, you will need to remove the material that would have been cut away by the tapping operation with a larger drill.

Is this thin stock or solid, with blind holes?

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#4

Re: Thread forming taps

12/24/2009 4:42 PM

Use an oversize drill & lubricant to reduce the tapping torque or drill a plain hole & use a Taptite screw. These will leave a 4-40 hole if you need to replace the screw at any time.

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#5

Re: Thread forming taps

12/25/2009 2:55 AM

It may seem hokey but Kerosene with some lard mixed in is the best cutting/forming fluid for aluminium I've ever known

About one pint of Kerosene to a tablespoon of lard...

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#6
In reply to #5

Re: Thread forming taps

12/25/2009 7:20 AM

I worked for an aerospace company & one of the things they made was a missile nose cone machined from a forged magnesium billet. The best cutting fluid was paraffin so the had a lathe in it's own enclosure with 1 machinist & another man with a fire extinguisher although I'm not sure how useful the extinguisher would have been. Luckily we never had to find out.

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#7

Re: Thread forming taps

12/25/2009 9:38 AM

A roll tap will really need to go in under continuous power to work properly. The last place I worked at that did a lot of aluminum used wire inserts (helicoils) which were even stronger than a rolled thread due to the larger grip area of the insert.

I don't remember the name of the lube that they used, but it was available as both a dilutable concentrate and a rub on solid. A very little went a very long way.

www.monroefluid.com/products/tapping-fluids/cool-tool-ii This Cool-Tool fluid has been used by people I know with good success too.

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#9

Re: Thread forming taps

12/26/2009 2:13 AM

Hi ronseto,

I'm not sure a thread former will be that good in 6061 if it is in the high "T" range. I.e. T-4 up. It's not that malleable. I'd recommend spiral flute taps. For a lubricant TapMajic or WD40 or the kero/lard. The 'caution' with spiral flute is they wont 'pull straight' like a straight flute hand tap, so a square start is important.

http://www.victornet.com/subdepartments/Spiral-Flute-and-STI-Taps/1338.html

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#13
In reply to #9

Re: Thread forming taps

12/26/2009 2:16 PM

In my experience T-6 6061 Aluminium is free machining and less problematic of forming/tapping than T-4.

Be-careful as Tapmatic can dissolve Aluminium and contribute to embrittlement.

Use of WD40 in the presence of heat and water may cause a release of Phosgene gas

The Kero/Lard mix enables smooth working of the material and leaves a fine finish.

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#14
In reply to #13

Re: Thread forming taps

12/26/2009 7:59 PM

Tap Magic -

Tapmatic

Spiral flute taps will change your opinion on tapping in any material

I agree with kero-lard, despite flammability, as it is tapping, not a carbide speeds situation.

"Phosgene gas" - in tapping? I thought you needed a chlorinated hydrocarbon and welding temperatures. Nor did I know WD40 had such. (But neither do we use WD40 for carbide speed operations.) More info please.

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#16
In reply to #14

Re: Thread forming taps

12/27/2009 1:44 AM

The label reads as "Proprietary ingrediants", I can't rule out they include CCI4 and only enough heat to fume is needed w/water.

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#17
In reply to #16

Re: Thread forming taps

12/27/2009 2:02 AM

Thanks bwire, I shall have it looked into as the product development people seem to use WD40 by the gallon.

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#10

Re: Thread forming taps

12/26/2009 11:26 AM

Tap lube with lard is really good as mentioned before Ron don't waste time with fancy lubes for 60 holes. Drill your hole oversize to reduce thread engagement a 4X40 in 1/4" aluminum will still have full strength due to depth of thread engagement.Use a taper thread cutting tap with a reduced shank and run it right through the plate with your battery drill do not reverse drop the tap out of your square drive and reengage for the next hole, there is less chance of chip clogging and thread damage this way.

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#19
In reply to #10

Re: Thread forming taps

12/27/2009 1:06 PM

Reduced shank in 4-40 size? Do such exist?

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#20
In reply to #19

Re: Thread forming taps

12/27/2009 9:41 PM

Hi dk, possibly they are available , I was thinking more along the line of grinding your own, I do this. Must admit shank dia will be fragile but if the hole is sized correctly it should be ok.

A tapping machine would have the advantage of keeping the tap perfectly straight so backing out the tap would not be such a problem, it all depends on the set up and accessibility, positioning holes under a tapping head has to be precise, it is possibly less trouble to do 60 holes by hand.

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#21
In reply to #10

Re: Thread forming taps

12/28/2009 3:22 AM

Possibly a drill guide and or a tap extension would help...one can make a fixture...

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#11

Re: Thread forming taps

12/26/2009 11:42 AM

First very sorry for May English

Second - this is welding material, Alu 6061 is very gummy. You must stray low speed (small RPM). Better is milling thread on CNC milling machine. If you are using taping tool you will weld in holes due to temperature on sharp. You can tray low speed. Sometime machinist using paraffin like cooling. Best Regards Libor Pírko

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#12

Re: Thread forming taps

12/26/2009 1:05 PM

Ronseto,

Sounds like a one time operation to me and that you will be using a cordless drill for sizing clearance and tap drill holes. Top member would have a clearance hole size with bottom member having a threaded hole size. #4-40 form taps are small and break somewhat easily unless hole is sized properly and proper speeds/feeds are employed for drilling and reversals. You can use higher speeds for form tapping (as compared to cut tapping) and form taps don't break as easily as cutting taps since chip loading has been eliminated. Form taps generally work well for "stringy chip" materials. Parts should be mounted square to the rigid drill axis, which might complicate matters for you and the cordless drill. Tap drill hole sizes are different for form taps than they are for cut taps, in case you didn't know. In your case, tap drill hole size for #4-40 formed threads is about .098/.100 in. for 70% thread. Slightly larger hole sizes needed for reduced thread percentages. Countersink holes that you will tap beforehand as form taps will create raised burrs at surfaces. Lubricants mentioned are fine for aluminum. I'd also recommend hand tapping, for this small size, if this is critical to you where you can't afford any mistakes.

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#22
In reply to #12

Re: Thread forming taps

12/28/2009 4:26 PM

It's a one time operation at the moment, but will be doing a lot more tapping in the future, mostly in 4-40, but also some 5-40. In some instances, I might just get away with through bolting, but not much. BTW, I'm using socket head cap screws, not machine screws. I would like to use hex head screws, but in that small size, they are very expensive.

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#24
In reply to #22

Re: Thread forming taps

01/04/2010 4:49 AM

Ref. my comment in post #4, Taptites are available in hex head 4-40, just drill the holes and fit with a cordless screwdriver. No tapping required & you still get a 4-40 thread in the part.

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#25
In reply to #24

Re: Thread forming taps

01/04/2010 9:57 AM

Thats a good idea, they are tough little devils, I find they hold better than regular screws especially in thinner sheet metal.

A GA for that

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#26
In reply to #25

Re: Thread forming taps

01/04/2010 11:20 AM

They perform marvelously on sheet metals not so thin too

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#15

Re: Thread forming taps

12/26/2009 9:41 PM

i spec out #4-40 unc-2b taps into 6061 all the time. i have never had a vendor complain about tapping it. ????

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#18

Re: Thread forming taps

12/27/2009 11:57 AM

Be careful with Alu 6061. We have Creno routing machine with stack. We was cutting stack Alu 6061. Tools dealer told us „you can use high speed cutting. On this time we welded all parts together.

Best Regards Libor Pírko

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#23

Re: Thread forming taps

12/28/2009 9:22 PM

would it be possible to use Pemserts instead of tapping.

http://www.pemnet.com/fastening_products/pdf/fdata.pdf

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