What taps to purchase

[Don C Davis]

A lot of you might think this is not the place to ask this question, and I considered it, but honestly I have come to think of the folks on this forum as my shop-working friends, and are who I always think of when I have shop questions--which leads me to this possibly out of realm question--I was trying to re-tap one of my Easy Wood carbide tools-which came with a ridiculously small screw for the carbide blade on it--it is the so called Mid-Sized Easy Wood tool--and I heat treated the bar--annealed it to be soft, and I'm a knife-maker so I know what I'm doing with metal tools--but despite this I broke three 8/32 taps trying to tap the new hole I drilled in the bar--it drilled very easily btw, and I have broken quite a few taps, usually smaller taps like 4-40, 6-32, and 8-32. So that brings me to my question to you 'shop buddy's' which tap set should I buy? I am really frustrated, I tap slowly and use lube, but when tapping metal I flat out break a lot of taps--so I'm wondering if it's just that I haven't bought good taps or what? My last two sets of taps were Bosch, and the last set I bought was from Eastwood: https://www.eastwood.com/eastwood-110-pc-sae-and-metric-tap-and-die-set.html and I thought this wood be a good set, but apparently not--the second 2 taps I broke were both from that set-interesting that they put two 8-32 taps in there....

But any advice/recommendations appreciated

Thanks--Don

 

[Richard Coers]

What do you mean by "lube"? I use Tap Magic and nothing else, it makes a difference. Also what percentage of thread engagement have you tap drilled for? I also bought a bench mounted hand tapping machine. Now that makes a huge difference, well worth the money! Finally, American made HSS taps are the best. If I recall correctly, mine are a very old set by Irwin.

 

[RichColvin]

Don,

I buy the specific taps I need from McMaster-Carr. Better in the end than a set of badly made ones.

I also use a spring-loaded guide for tapping, like this one : https://www.amazon.com/Brown-Sharpe...=2025&creative=165953&creativeASIN=B005317ZMC.

Great help.

Kind regards,
Rich

 

[Mike Johnson]

I usually purchase the (3) tap sets which come in handy for tapping dead end holes. Drilling and tapping small holes in hard metal can definitely be a challenge, you need to use the correct drill size for the metal being threaded and take your time making a thread or two and cleaning the material from the threads.

 

[Bill Boehme]

Do you know the alloy of the bar and are you certain that you annealed it? EWT uses a non-magnetic alloy of stainless steel (NMSS) for the bars and some of the NMSS alloys will work harden at the drop of a hat making it nearly impossible to tap once that happens.

I only use Rapid Tap or Tap Magic. Make sure that you have used the correct drill size and use a cobalt drill. You might need to repeat the annealing process after drilling. When you start tapping you need to proceed at a moderately quick and smooth pace and complete it in one quick operation or else the risk of work hardening the bar again will increase.

There are special tap geometries for difficult materials like stainless steel as well as using a tap that has been nitrided or has a TiN coating. (TiN is titanium nitride not to be confused with "tin" the soft metal).

 

[john lucas]

As a former camera repairman I have used a lot of small.taps. sometimes you cant even make a 1/4 of a turn before backing up to clear the chips. If you feel the tap start to spring a little it's about to break. Take smaller bites. Hardened steel.is the worst. I have taken a small torch and annealed just the hole on rare occasions.

 

[Don C Davis]

Thanks a lot folks, 1st as to the percentage of thread I typically shoot for 85% and those are good points about the work piece possibly work hardening-I actually wondered about that.... I will admit I’ve been trying to take ‘bites’ of a half turn, so I’ll try to take less, I hadn’t thought about a tapping machine,I’ll look into this, it has been very frustrating!

 

[Larry Copas]

85% thread engagement is to tight for me in stainless or even steel. 50% is what I would use which for 8-32 is a #27 drill.

Aluminum and plastic I go to 75% which would be a #29.

I do have a tapping machine, but often just start the tap in the drill chuck, normally on a Bridgeport but sometimes on a drill press.

 

[john lucas]

For what ever reason that I don't understand I break more 10/32 taps than anything. I have taps down to 4/40 and some reallly tiny metric taps. Most of the time when I break one it's 8/32 or 10/32 however I was trying to tap a deep hole in a piece of 1" drill rod and snapped it off just as I was about to finish. I could feel the bit twisting or flexing and knew I should have stopped. The tapping machines would probably help a lot because it's probably the sideways pressure that causes them to snap as much as the twisting pressure. I keep looking at them but keep passing them up.

 

[Bill Boehme]

Thanks a lot folks, 1st as to the percentage of thread I typically shoot for 85% and those are good points about the work piece possibly work hardening-I actually wondered about that.... I will admit I’ve been trying to take ‘bites’ of a half turn, so I’ll try to take less, I hadn’t thought about a tapping machine,I’ll look into this, it has been very frustrating!

I consider 50% thread engagement in steel to be normal and I agree with Larry Copas that for stainless steel 85% sounds too tight. I could be mistaken, but I think that your plan to take smaller "bites" is a step in the wrong direction because it seems to me if you do that it will only make work hardening worse. See if you can find a tap with a bit of a relief angle behind the cutting edge to minimize the abrading that leads to work hardening. Also, a nitrided tap will remain sharp longer which also will reduce work hardening.

 

[Doug Rasmussen]

Come on you guys, you aren't supposed to back taps up to break chips. Use spiral point taps (also known as gun taps) for through holes. Tap right through, no backing up. The chips are pushed forward. Spiral flute for blind holes. Only buy HSS, name brand taps from tooling houses.

Don't ever use taps that come in assortments, they're junk. 99% are carbon steel, only good for cleaning dirty tapped holes. Buy quality taps individually as needed. Good taps do not come in assortments.

Find a copy of Greenfield Screw Thread Manual ($9 on eBay).. It specifies tap drill sizes based on class of thread and length of engagement. Percentage of thread is also shown. It's my bible for threading.

 

[Stan Semeniuk]

Hi Don,
I have done a fair bit of hand tapping over the years at my work including many exotic alloys. For me a tap handle is a must. I have seen more broken taps broken from not starting straight and running parallel to the hole than I can count. My choice of taps at work are Dormer, quality really makes a difference. On blind holes I always back up and blow the hole out. If you feel chips or hear that grinding noise I find I'm moments away from snapping the tap. Use a good quality lube like rapid tap, stinky but works.

 

[Don C Davis]

thanks for the leads and intel folks, Stan, I use a Starret tap handle, so I think it's fairly good--My taps are all from assorted tap kits....so maybe I do indeed have chepo taps. I will order some individual taps from McMaster Carr and see if they have some good ones--I will look at tapping machines, but as my admittedly weak mind remembers, they seemed to be more $ than I felt was reasonable for tapping 6-10 holes a year.

 

[Dean]

boelube is the best lube I have used on special metals. keeps the tap slick