A Few Quick Threading Questions...

[kustomkb]

Oh again! When advancing the compound at an angle, I can do the trigonometry to figure how far to advance it, but is there a simple formula or a chart with this info.

If you want to use the 29.5 deg. method and know the DOT, trig and charts are unnecesary;

1. Zero the compound
2. Move cutter to touch work with cross slide
3. Zero cross slide.
4. Back cross slide out DOT (taking backlash into consideration) a DRO really speeds things up.
5. move compound in to touch the work.
6. read compound dial. This is your depth to travel with the compound.
7. Have fun! ;D

 

[steamer]

KustomK is right. :bow:

For a sharp thread, you advance the compound ( total depth of cut) by an amount equal to the pitch of the thread your cutting. Remember that what you dealing with is an equilateral triangle. Now unified threads are a little differant as the sharp point is replaced by a flat equal in width to 1/8 x Pitch. Best bet is the Machinery Handbook........you all have one right? : ;D


Dave

 

[formula156]

So I start with a .500 diameter on the internal and external and cut the threads from there?

Thanks for all the other tips guys. I planned to try a few scrap pieces first, and I hadn't thought of using the cross slide to measure the depth first. Awesome idea. The kind that makes me think 'why didn't I think of that?"

 

[kustomkb]

1/2-20 external

.6495/20=DOT (per side)

1/2-20 internal

nominal(1/2)-1 pitch(.05)=bore Dia.

.51427/20= DOT (per side)

Just remember 2 #'s and no charts needed!

what i have done in the past is use your thing you want to fit as a gage for it's mate. and cut the mate till you get a fit that your happy with.

2nd that.

;D

 

[steamer]

" Awesome idea. The kind that makes me think 'why didn't I think of that?"
[/quote]

Trust me.......everyone here has said that to themselves more than once.....welcome to the club! ;D

 

[formula156]

1/2-20 external

.6495/20=DOT (per side)

1/2-20 internal

nominal(1/2)-1 pitch(.05)=bore Dia.

.51427/20= DOT (per side)

Where did you get those numbers? Where did the .6495 come from if it's a 1/2" diameter, and how is 1/2 - .05 = .51427?

 

[formula156]

So, for external I start at .500 and thread to a minor diameter of .454.

For the internal I start at a bore size of .500-.038 = .462.

Is this correct?

 

[DickDastardly40]

Right...but what about the major diameters of both the internal and external. If they are both .500, there would be no clearance. That's the part I am unsure about. Unless cutting to the correct minor depth brings the major depth down a little from where it started.

If you look at the picture on the UTS wiki link and read the text you can see that although .500 is the 'notional' major diameter, it can be rounded out beyond that in the nut. In real terms if you cut your thread a little deeper than the numbers state you will have a little more clearance at the thread crest (tip)

Hope this is clear.

http://en.wikipedia.org/wiki/Unified_Thread_Standard
http://en.wikipedia.org/wiki/Screw_thread

Where did you get those numbers? Where did the .6495 come from if it's a 1/2" diameter, and how is 1/2 - .05 = .51427?

I believe the the numbers are constants rather than diameters, I don't have any reference material handy so can't look where kustom got them from.

So, for external I start at .500 and thread to a minor diameter of .454.

For the internal I start at a bore size of .500-.038 = .462.

Is this correct?

Looks about right to me ;D , did we say the external minor dia was 0.456 earlier in the thread? 0.002" extra clearance (0.001" per side) won't hurt.

Try it on some scrap and make pair of mating threads to ensure you're happy with the outcome, technique and fit. Let us know how you get on

 

[formula156]

Looks about right to me ;D , did we say the external minor dia was 0.456 earlier in the thread? 0.002" extra clearance (0.001" per side) won't hurt.

Try it on some scrap and make pair of mating threads to ensure you're happy with the outcome, technique and fit. Let us know how you get on

Cool, but I just don't see how this will be a resonable fit with both majors at exactly the same diameter. Would basically be an interference fit right?

This is with a 60° pointed tool right? Not one with a flat?

EDIT: Perhaps I am retarded, as I seem to still be missing something. Could that be the problem?

 

[DickDastardly40]

Cool, but I just don't see how this will be a resonable fit with both majors at exactly the same diameter. Would basically be an interference fit right?

This is with a 60° pointed tool right? Not one with a flat?

EDIT: Perhaps I am retarded, as I seem to still be missing something. Could that be the problem?

Not an interferance fit, but similar to a close clearance fit H7h6 which can be shaft and hole at the same diameter.

If you use whichever tool you are most happy with grinding either a point or flat and cut to the dimensions specified all should work. If you use a tool with a flat, no further work should be required. If a point then you will need to open out a flank to make a flat and fit the nut to the bolt; this method may also give you a fit with less backlash, which is the axial clearance so far not mentioned.

The only silly question is the one not asked!

 

[formula156]

Awesome, I think I'm ready to give it a shot now. If only I hadn't ordered the wrong 5" 4-jaw chuck adapter for my new 4-jaw chuck. Now I've got to wait until Friday to start

 

[Kermit]

I've been following all this and now I have a question too.

:-X

If you cut the screw thread, say 1/4-28, and you use change gear "xx" on the lathe for the correct carriage travel speed.
When you cut the internal thread on the corresponding nut 1/4-28 is the same gear "xx" used, the same lead screw speed? I would think it was, but the tool is in a different place for internal and external cuts and I'm often wrong with my assumptions.

Also for 360 Brass did I read correctly here(somewhere on this website), a smallish thread can be cut in one pass? I could see that working on large diameters but my mind gives me a ? when I try to picture that on small diameters.

Please input your information,
then press'ENTER'
Kermit

Now I've got to wait until Friday to start

Did someone say wait? I'm hurrying, I'm hurrying already. Glad to have some company in this waiting room Formula156 even if its only for a day or two. ;D Thanks for starting this thread so I don't have to do it next month when I get going finally.

Peace to my peeps

 

[formula156]

The gears stay the same, as you want the same speed for both. Whether you are doing internal or external threads, you want the tool to cut 28 rotations every inch, so you would want the same gear ratio.

 

[DickDastardly40]

If you cut the screw thread, say 1/4-28, and you use change gear "xx" on the lathe for the correct carriage travel speed.
When you cut the internal thread on the corresponding nut 1/4-28 is the same gear "xx" used, the same lead screw speed? I would think it was, but the tool is in a different place for internal and external cuts and I'm often wrong with my assumptions.

Also for 360 Brass did I read correctly here(somewhere on this website), a smallish thread can be cut in one pass? I could see that working on large diameters but my mind gives me a ? when I try to picture that on small diameters.

The lead screw speed (gear set up) is the same for both the internal and external threads, the spindle speed doesn't have to be the same but slower is better, you can even turn the chuck by hand. The position of the tool has no effect on how fast the carriage needs to move, it just needs to move 1/28" for every rotation of the chuck.

A small thread (shallow thread depth) can be cut in one pass however your results may be dependant on the sharpness and rigidity of the tool. Internally the tool will flex away from the job on deeper cuts perhaps causing chatter or incorrect dimensions.

 

[Noitoen]

The lead screw speed and the spindle speed is synchronized. When you set up the lathe to cut a certain pitch you actually adapt relation between the spindle and lead screw so that the tool advances in accordance to the thread (pardon my English) so when you slow the speed of the spindle to cut slower, automatically you reduce the lead screw speed.

Helder

 

[Bernd]

Interesting thread. I just went through three pages of thread cutting and didn't once see mention of the tool pictured below in setting up your threading tool.

If you don't use this tool how will you know you are setting it up square to the lathe axis? If the tool is out of square it will not cut a 60 degree thread, right?

Here's another pic showing two more tools used for Acme threading. They are in the upper righthand of the pic.

These tools are used in grinding and setting up a thread tool.

You can read all about how to use them in "The Shop Wisdom of Frank McLean" on page 52.

Bernd

 

[kvom]

Here's a pic I took when first using the fishtail gauge:

 

[Bernd]

kvom,

You get a gold star. Thm:

But as I said, it didn't seem like anybody mentioned using a thread gage to set their tooling properly.

Bernd