Tips/Techniques Threading Basics from April 6 Toronto Meet

Here is a PDF of my notes from the little tutorial I presented at our April 6 meet-up. Hopefully it's not too convoluted.

If anyone has any questions, I will try to answer them as best that I can.

There is more information that I need to post regarding this in the next couple days.

 

[LenVW]

When are you posting the Accusize details ?

Have you approached KBC for a CHMWs discount ?

Attention @Susquatch .

 

[Susquatch]

Attention @Susquatch .

As soon as we can figure out how to keep them secure.

If you want the Accusize details early, send me a PM. I do have a 10% discount code and they are all setup to go. Just no free shipping yet. They are working on that.

KBC, Princess Auto, KMS, etc, etc are all on the radar screen. We just need to make sure we have our ducks in a row first.

 

[thestelster]

I've been quite remiss about finishing up this thread (pun intended).

I want to show how I make a Unified thread using a non-topping (partial profile) insert. Remember, a non-topping insert can do a variety of thread pitches. A HSS tool can also be used.

I will make a 1/2"-13 UNC thread. According to the UN standard basic specifications, the following dimensions for this thread are required:

OD= 0.500"
Depth of thread: 0.042"
Root width: 0.019"
Pitch diameter: 0.450"
(The above information is on the chart that I posted earlier)

The insert that I will use is a non-topping (partial profile) and it has a sharp point with only 0.002" - 0.004".

 

[thestelster]

I rotate my compound so it's direction of travel is parallel to the ways. I set it to 0.

I turn my stock to 0.500" in diameter, and start cutting my thread with repeated plunge cuts until I get to our required depth of thread of 0.042". Remove burrs.

 

[thestelster]

Lets try our nut. Hmm....it won't screw on. Oh yeah, we don't have the proper root width. It's too tight.

 

[thestelster]

We need a root width of 0.019", but our insert only has a 0.002" tip width. We have to widen the root section of our thread by app. 0.017".
We now advance our compound several thousandths, and we will make another pass while the cross-slide is at our 0.042" depth of cut. Doing this only removes metal from the leading edge of the thread.

I continue advancing the compound several thousandths at a time with every pass until our nut screws on nicely.

Oh, look at that... we widened our original root, (0.002"), by the amount we moved the compound (0.017"), that equals 0.019" and low and behold, our nut threads on nice.

 

[thestelster]

So, our OD is correct, our root width is correct; lets check our pitch diameter. Sure enough its 0.450", and that's correct.

In fact we have just made a UNC 1/2"-13 screw thread, and it's a class 3A tolerance!!

 

[thestelster]

I would like to reiterate that the fit of the screw/nut interface is based on how well the flanks of the thread fit, and not on the height of the thread.

What I'm trying to say, if you're going to make a screw, and you accidentally turned it a little smaller than the OD required, don't think you need to scap your part.

For example, on the screw thread I just made, which has class 3A fit, the nut threads on smoothly with virtually zero wooble. I then turned that screw to 0.485" OD, 0.015" smaller, and the nut still threads on the with the same tightness.

As you can see on the thread below, the root with is proper at 0.019", but the crest width is much wider than the UN basic crest width of 0.010", and the nut still fits perfectly well.

 

[thestelster]

Everbody has a thread pitch gauge similar to the top, but who has one like the bottom?

That's what we need!! It shows you what the root width should be when you go to grind your own HSS threading tool.

We have them for acme threads, why can't we find it for 60° v-threads? Maybe you guys with 3D printers can pump them out. (Of course hardened steel would be better.)

 

[combustable herbage]

We need a root width of 0.019", but our insert only has a 0.002" tip width. We have to widen the root section of our thread by app. 0.017".
We now advance our compound several thousandths, and we will make another pass while the cross-slide is at our 0.042" depth of cut. Doing this only removes metal from the leading edge of the thread.

I continue advancing the compound several thousandths at a time with every pass until our nut screws on nicely.

Oh, look at that... we widened our original root, (0.002"), by the amount we moved the compound (0.017"), that equals 0.019" and low and behold, our nut threads on nice.

One question is is there anything different doing internal threads? as the crest and the root are opposite to an external thread?

Another question I have tried to figure out to no avail is what is the importance/significance to the last column Pitch Diameter-OD(06495P) in your chart from what I think I understand its the imaginary dimension of a certain part of the thread but I just don't see the the advantage or use for it??
Thanks, I haven't had much shop time where my mind was into it but hoping soon to do some more experimenting with this.

 

[thestelster]

One question is is there anything different doing internal threads? as the crest and the root are opposite to an external thread?

Yes. Internal dimensions is the mirror image of the external, so the threading tip nose is 1/2 of the external.

importance/significance to the last column Pitch Diameter-OD(06495P)

Knowing what the pitch diameter is supposed to be, and being able to measure it (either by thread micrometers, 3-wire method, or go-nogo thread gauges), you can determine whether your thead will fit into a given "nut" if you don't have that "nut" on hand. So for instance, you have to make a special part that has a male thread that has to be attached to another part in Guatemala. And the blue prints calls for that thread to be 1/2"-20 UNF-3A, you can make that part knowing that if you get the proper pitch diameter specified in the drawings, it will fit that part in Guatemala.

 

[PeterT]

Another question I have tried to figure out to no avail is what is the importance/significance to the last column Pitch Diameter-OD(06495P) in your chart from what I think I understand its the imaginary dimension of a certain part of the thread but I just don't see the the advantage or use for it??

PD (pitch diameter) is very important because it has to fall within a certain range which defines how it fits to a established standards. If PD is loose, it will have excessive axial play or lash & the opposite if too tight to the extent threads may not engage. PD is what a thread micrometer or wire method is measuring. Not to say we can disregard OD or thread depth as unimportant because they have min & max & profiles too, but those are broadly speaking 'clearances' not really fit. You can have 2 identical PD fasteners with different major/minor diameters.

I like this online calculator because it provides a lot of information about a thread. Standard threads are important when you are trying to match some established size. But the calculator also allows you to override & input a user defined OD. Like if you have a 0.800" shaft that requires 20 TPI, there is no standard fastener to look up, but its a perfectly legitimate part as long as its machined to the specs.

UN imperial screw thread calculator

theoreticalmachinist.com