Tap use limits

starr256

starr256

H-M Supporter - Gold Member
H-M Supporter Gold Member
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Apr 7, 2018
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Background: I am building 9 cylinder radial engine (The Ageless design). I am currently working on the crankcase for this beast and it requires me to tap 109 4-40 holes. The instructions warn me that the crankcase at this point if far more valuable that the price of a couple of taps and that I should use "fresh" ones. This 6061 aluminum, by the way. Some are through holes and some blind holes. I am planning on using coated spiral fluted tap, both pointed and bottoming. I really, really, really don't want to break a tap at this point. My question is for those with manufacturing experience. How many holes can a tap tap if a tap could tap? (Sorry, couldn't help my self.) The number is obviously somewhere between 1 and 110 for my project. Lots of TapMagic is expected to be used. I will acquire what is needed, but the taps do range between $15 and $25. Any recommendations tap brand and number would be helpful.
With machining metal, I am always learning new things, usually that involve more money.
Thanks in advance.
 
I'd say 2 of each will do you and then some. You're far, far more likely to break one through mishandling than you are to wear even a single one out appreciably on that job.

Get branded HSS taps, not carbon steel.
Make a small tap handle of appropriate size like Joe Pie does and uses.
Tap with support of a good quality spring loaded follower right after you've drilled in the same setup. This can be tedious, but it's well worth it. Set up your workflows around getting the taps dead square in the holes, whether that's a tool change to tap before moving on or accurately returning later.
Be super careful with spiral flutes. They're great to use but don't always like breaking the chips off when backing out of blind holes. This is one of the most likely moments of breakage. Easy does it!

Do post some pics or a write up as it progresses please!!
 
Never heard of thread forming taps until I saw it here. Are they harder to use?
 
I have tapped hundreds of 4-40 hole in aluminum. If at all possible, I prefer to use a spring loaded tap guide in the mill. It ensures that the tap is going straight and it helps to prevent applying a side torque which is the main cause of tap breakage. Barring that, a guide that rests on the work will help. When tapping, pay close attention to the tap, If it begins to twist,back off or a broken tap is soon to follow.
 
RJSakowski said:
prefer to use a spring loaded tap guide in the mill. It ensures that the tap is going straight and it helps to prevent applying a side torque which is the main cause of tap breakage
Click to expand...
I also have put a lot of 4-40 and 6-32 threads in 6061 and (almost) never break a tap. Good quality taps but like RJ says, use something to eliminate any side torque !
 
Drill hole with mill then place in neutral or high speed and put tap in chuck and turn by hand.

There are floating pin vise tools that slide on a support and turn by hand.

Aluminum can be nasty gummy stuff, get cnc rated taps and use ATF or other good stuff.

Finger tips ONLY touch the chuck to thread in.

If and binding it slips.

Back out and clean often.

Verify correct drill with a mic.

Verify correct, smaller drill is tighter thread but maybe not so much strenggth

Sent from my SM-G781V using Tapatalk
 
Comparing a 4-40 thread rolling or forming tap with a cutting tap... note: needs a different tap drill!!!
They are kinda triangular and squish the metal into shape.
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Sent from my SM-G892A using Tapatalk
 
with that many holes, and tapping probably a key technology in your future, I think a smaller size tapping head, like a Procunier, would be a good purchase. It turned tapping fron a scary chore to an almost pleasant task, for me.
 
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