Are thread foming taps practical for everyday use ?

[edwin dirnbeck]

It would be nice to do away with chips in a threaded hole. When I use a conventional tap ,say a 3/8-16 x 5/8 deep in a piece of 4140 steel ,I can drill the tap drill and not be to concerned about the geometry of the tap driled hole. If it is .005 or even .008 larger than I want or even .002 smaller or out of round A good sharp thread cutting tap works good.I know a few members love thread forming taps ,but how would they work in 1 off evey day real world conditions.Thank you Edwin Dirnbeck

 

[sch]

Prior thread in 2005: http://www.practicalmachinist.com/vb/general-archive/how-thread-forming-tap-used-86164/
and an MMS comment: When Cold Forming Threads Makes Sense : Modern Machine Shop

 

[F Spicker]

When using thread forming taps hole sise is critical. A thousandth of an inch makes a big difference in how the threads come out. The material makes a difference as to how the material flows when forming. On a one off job I would continue to use a cut thread tap. In our shop we usually used cut taps when threading thru holes and rolforming taps in small 1/4 and smaller blind holes. Our shop was a screw machine shop so we were tapping hundreds or thousands of holes.

 

[Conrad Hoffman]

For my one-off prototypes and hobby stuff in aluminum, I'll always use a former between #1 and #8. One caveat. If you're handing the part to somebody unskilled, they do have a better chance of cross-threading things. A slightly undersized or sharp screw can catch the fold of a formed thread and brute force users will then just jam it on it.

 

[Don Clement]

I have tapped 10s of thousands of blind 4-40 holes using a Balax form tap in 6061-T6 and Relton A9 tapping fluid with excellent results. The Procunier 1E tapping head works perfect with the Balax form tap for these blind holes as it stops within 1/3 revolution and the Procunier cushioned double-cone clutch really works well with these small taps. Programming also couldn't be simpler: infeed at 100%, no dwell, retract at 200%. Since I also assemble my product which has 128 black oxide SS button head screws holding down 18 pairs of SS flexures I am aware of any cross threading issues and frankly there are none. The thread appears to be very strong and almost never have a broken screw.

The key for me in making a useful tapped holes using the form tap is to spot drill a countersink before drilling and tapping so the extruded metal at the opening of the 4-40 threaded hole created during form tapping is not protruding out the top of the threaded hole. Having assembled many 10s of thousands of 4-40 screws there hasn't been any problems with slightly undersized screws or an issue of sharp threads catching using this method.

Don C.

 

[EPAIII]

I think you are going to have to keep some cutting style taps around for materials like cast iron if you use any of that.

 

[mjk]

always need a cutting tap for cleanup or retapping

I've switched to form taps on everything under 3/8...with a few exceptions

form tapping doesn't work well when done by hand

 

[Don Clement]

I use the same Balax form tap for cleanup sometimes after anodizing. Works for me. Also form taps work well for me in hand tapping using a Starrett 93 series T tap handle with a Fisher micro tap guide Tap Guide 1963 - LittleMachineShop.com

FYI form taps only work with some metals such as 6061-T6 aluminum.



Don C.

 

[18my]

I use the same Balax form tap for cleanup sometimes after anodizing. Works for me. Also form taps work well for me in hand tapping using a Starrett 93 series T tap handle with a Fisher micro tap guide Tap Guide 1963 - LittleMachineShop.com

FYI form taps only work with some metals such as 6061-T6 aluminum.



Don C.

I have used them on 303, 304, 316 ss, general carbon steels 1045 etc, aluminium and 4140. As you mentioned you cant use them on all materials. Long story short for a one off I wouldn't bother with form taps

 

[sean9c]

This thread got me thinking. Can you form tap by hand? I've used form taps for lots of machine tapping but have never thought about using one for hand tapping.

 

[ewlsey]

This thread got me thinking. Can you form tap by hand? I've used form taps for lots of machine tapping but have never thought about using one for hand tapping.

Not really. A form tap has to go in absolutely straight. If they don't go in perfectly straight, the end will break off due to the side pressure.

Form taps can be used in a tapping machine when power tapping. They can't really be used with just a tap handle unless you start them straight on a machine. Cut taps should also be started straight, but if they are a little off, they will just cut their own clearance. A form tap can't do that.

I love for taps. I use them from 2-56 through 3/8-16. 1/2 and above are not as advantageous since the drill sizes are odd and the torque needed is very high. Form taps are great because they are not material specific (I use them on Al, steel, stainless, even 4140HT). Also, you can use the same tap for blind and through holes. Although, they do push up a burr on the back side of the through holes.

That said, you can't just chuck out your cut taps. For little piddly jobs, thread repairs, and tons of other things, a cut tap is more practical. Also, you can't form tap cast iron or most kinds of plastic.

 

[edwin dirnbeck]

Thanks for all the replies

I have used them on 303, 304, 316 ss, general carbon steels 1045 etc, aluminium and 4140. As you mentioned you cant use them on all materials. Long story short for a one off I wouldn't bother with form taps

Please share your experiece with these taps. THANK YOU. Edwin Dirnbeck

 

[6061Mike]

Not really. A form tap has to go in absolutely straight. If they don't go in perfectly straight, the end will break off due to the side pressure.

Form taps can be used in a tapping machine when power tapping. They can't really be used with just a tap handle unless you start them straight on a machine. Cut taps should also be started straight, but if they are a little off, they will just cut their own clearance. A form tap can't do that.

I love for taps. I use them from 2-56 through 3/8-16. 1/2 and above are not as advantageous since the drill sizes are odd and the torque needed is very high. Form taps are great because they are not material specific (I use them on Al, steel, stainless, even 4140HT). Also, you can use the same tap for blind and through holes. Although, they do push up a burr on the back side of the through holes.

That said, you can't just chuck out your cut taps. For little piddly jobs, thread repairs, and tons of other things, a cut tap is more practical. Also, you can't form tap cast iron or most kinds of plastic.

Call me an asshole, but you just contradicted yourself... Not sure what you were trying to get across? coatings? ... They are material specific in the fact that some mat's just don't 'form' as well as others...

 

[Conrad Hoffman]

Trust me, I'm not that good, but I do all my form tapping by hand with no problems at all. Most of my stuff is very small and I don't like standard tap wrenches much. I use a Starrett thing that looks like a pin vise but holds taps.

 

[ewlsey]

Call me an asshole, but you just contradicted yourself... Not sure what you were trying to get across? coatings? ... They are material specific in the fact that some mat's just don't 'form' as well as others...

OK. I stock one form tap in every size. It's good for everything but cast iron and plastic.

You need a different cut tap for cast iron too. Regular spiral flute or point are not ideal for cast.

 

[Steveo]

You will always need cut taps for thin wall applications. Forming threads is not recommended in applications where the wall thickness is less then 70% (or something like that) of the nominal tap diameter. It distorts the wall.

 

[Don Clement]

Long story short for a one off I wouldn't bother with form taps

Why not?

Don C.

 

[Don Clement]

Not really. A form tap has to go in absolutely straight. If they don't go in perfectly straight, the end will break off due to the side pressure.

I hand tap with forming taps all the time and rarely break a tap. Why I like Starrett series 93 Tap handles http://www.starrett.com/metrology/product-detail/93A is because the 93 series tap handles have a countersunk hole in the rear that can be used with the Fischer micro tap guide Fisher Machine Shop Pee Dee Wires and Tap Guide so when hand tapping taps go in straight. I use the Fischer micro tap guide in the tailstock of the lathe and in the spindle of the mill.
Don C.

Hand tapping in the mill using the micro tap guide. This example is a cutting tap, however form taps work just as well hand tapping using the micro tap guide

 

[Big B]

I have yet to use a form tap but a friend of mine who owns a fair sized shop uses them a lot. He also told me that you can form tap steel up to Rc60, which I found kind of surprising.

Big B

 

[ewlsey]

I'm not sure you can really tap anything over 40Rc. I have tapped 4140HT which is 35-40Rc.

Per above, yes you can tap by hand if you keep the tap straight. That's all I was trying to say.