Cutting or Rolling

Getting ready to build a frame for my newest project. I am looking at building a set of Hairpins and curious, should I use a Cutting or Rolling tap while threading the ends? I have both and I am under the ***umption that the rolling tap is better since you are not removing material. What do you think?

Jim

 

a rolled thread is stronger than a cut thread,right?
maybe you could find a machinist's message board and ask them.
where do you get rolling taps from?

 

I asked my machinist friend about this, he confirmed my ***umption that this most likely could not be done in the home garage.

 

building the hair pins or rolling threads versus cutting...I only ask because I have done all three in my garage,with little effort, and I'm no rocket scientist...

what choo talkin 'bout willis?

 

I will be getting mine compliments of the tool room at work, the rest of you can get them from McMaster, they are otherwise known as "thread forming taps". They are designed to roll the threads instead of cutting them.

 

I've got some 3/4"-16 roll forming taps in the garage. They work very, very well. So, yes, you can "roll" 1/2"+ threads at home.

I bought mine off ebay, brand name is OSG. There are usually quite a few up for auction, and usually in the fine thread variety.

HTH,
Tim D.

 

how many of you folks are actually rolling threads?

I know they are stronger and all but i've used standard taps on just about everything i've done hotrod and even industrial related....

overkill?

 

No such thing as OVERKILL when it comes to safe designs especially when we are talking about front suspensions and steering.

 

The claims are that rolled threads are stronger - the questions is how much ??


We used to use lots of rolled threads at work - the problem we encountered was an unusual amount of cross threaded ***emblies. The "problem" with rolled threads is that when you form them there is a sort of "mini thread" 1/2 way inbetween the REAL threads - a result of the process. If you're careful this is of no consequence, but on our production floor they prooved far more h***le than they were worth.

I personally prefer "cut" threads - they worked for a zillion years without trouble and they'll continue to work just fine.

I'd tend to think if your fastener was sized such that you NEEDED the additional strength a rolled thread provides then I 'd say you undersized your fastener from the get go.

OTOH - I can also see why a machine shop would prefer rolled threads - no cleanup for one thing.


YMMV

 

Pretty impressive, learn something new every day.

 

Metallurgically speaking, a rolled thread is better for fatigue. It is not necessarily stronger in a tension pull-out strength test. Almost all bolts (external threads) are rolled threads, it is faster and provides a better thread for fatigue. A rolled thread also does have a bit of cold working so the metal is in fact a little bit stronger.

As to your application, I think either would work, you do not really have an application that is fatigue problem.

 

As 38Chevy454 said, the primary advantage to rolled threads is in fatigue. The handbook I have here has a table of fatigue stress concentration factors for bolts, which lists a stress concentration factor of 3 for rolled threads and 3.8 for cut threads. (Stress concentration factor is basically the amount the applied stress is amplified by geometric factors such as notches - i.e. thread roots). So effectively rolled threads are 21% stronger than cut threads in fatigue. This only accounts for the geometric advantage due to the radiused thread root (vs. the v root on cut threads). The cold worked material at the surface will give an additional boost in fatigue resistance, my rough guess is another 20% or so. The bulk of the material is the same whether you roll or cut, so the static strength doesn't change much

 

I have been rolling external threads for over 30 years and can vouch for the fact that the fatigue resistance is the main advantage to the rolled threads over cut threads. Almost all fastener manufactures roll their threads although there are a few requirements for cut threads.
Speed and consistent quality and dimensional accuracy are the real advantages not to mention reduced material cost, you are not removing any material thus no s****. Speed, we have a customers roll threading machine in my shop we are building a parts feeder for and we were threading 3/8-16 all thread studs today at over 120 FEET per minute.
As for the internal threads, use a cut thread tap and you will have no problems, almost all failures are in the male thread.