Calculated Thread Depths for Metric fine threads

[madman]

Hello Every One.
Many thanx for the Help. My Parts came out nearly perfect, The male and Female threads were very nice . Thankyou Mike

[PixMan]

I got an M12x1.25 6HX tap made specifically for blind holes in stainless steels. If you're a neighbor you can borrow it and be done, no gauge needed.

[willmac]

M12 x 1.25 is a standard Metric Fine thread so you should be able to find all the information you require in the normal thread tables.

[madman]

Thank you Thankyou Invaluable Help. Its appreciated .The mention of making a accurate gauge has merit, For a standard m12 x 1.25 pitch thread whats the best way to make a accurate gauge for the male to fit into my machined female Part? Thanx Mike

[dp]

OK, the calculation again, with the correct thread pitch.

Based on M12 x 1.25 and Sharp Vee tool:

Depth of thread = 0.614 * pitch. Even for wrong pitches.

[dp]

Oh lordy it raised a big ruckus the last time needles were brought up. I remember because it was me who said that, then. It turned out to be a good way to identify angry machinists

[boslab]

Sewing needles make good thread wires for small sizes, they are quite accurate too
Mark

[Paul Alciatore]

OK, the calculation again, with the correct thread pitch.

Based on M12 x 1.25 and Sharp Vee tool:

Bore Size = Diameter - Pitch.

12mm - 1.25mm = 10.75mm

That's an easier drill to find. If you have access to inch size drills, that translates to 0.423". That's almost exactly 27/64" (27/64" = 0.422"). Again, you can go with a smaller hole than this. Anything between 10.6 and 10.8 mm will probably be OK. I don't know what drills are available where you are so I will go with 10.75mm or the 27/64". Since it is important to start at a known ID, I would suggest drilling a bit smaller and boring it out to exactly 10.75mm.

With a 10.75mm bore, you will need to move your SHARP VEE tool out far enough IN A RADIAL DIRECTION to bring the flat of the thread (which does not exist on that sharp vee tool) to the 12mm nominal OD size of the thread. Thus the tip of that sharp vee tool will be at a greater diameter than 12 mm. The metric standard thread has a 1/8 h flat on the tip of the threads where h is the height of a sharp vee thread. (same paragraph as before)

Height of a sharp, 1.25mm pitch thread, h = 1.25mm x cosine(30) = 1.083mm.

And 1/8 of that is 0.135mm.

So we are going to need to move the tip of our sharp vee tool out to a diameter of

12mm + (2 x 0.135mm) = 12.271mm

We are starting (touching off) at 10.75mm and going to 12.271mm

12.271mm - 10.75mm = 1.521mm

But that is on the diameter and we are moving on the radius so we need only half that amount:

1.521mm / 2 = 0.761mm (0.030")

You can use that if you are moving out using the cross slide.

If you are using the compound set to 29.5 degrees then that amount would be increased to

0.761mm / cos(30) = 0.879mm or 0.034".

That would be a theoretical thread size. Since you have no way of testing it, I would recommend that you cut just a bit further to ensure a fit. Perhaps another 0.025 or 0.050mm or one or two thousandths more.

Again,I would greatly appreciate it if someone else here would check my math on this.

Also, as I and others have stated above, it would be best to have a gauge to check these internal threads. Even a shop made gauge is of great value here. Cut the gauge a thousandth or two larger than the maximum size allow for a male thread, then cut the internal thread using that gauge for proper fit.

[PixMan]

The OP is a classic example of why we all want to see your location in your profile. You need to make a simple, standard, relatively small internal thread. I have several styles of M8 taps and would loan one to you if I knew you were close to me.

But I have no f'n idea.

BTW, an M8x1.25 is not a fine thread, it's the standard pitch (coarse.)

[oldtiffie]

Mathematically it s quite feasible to measure thread pitch diameters with "wires" three wasy:

using three wires;

using two wires; and

using one wire.

I will cover it at my leisure at some time in the future.

It should be said in this context that the "3-wires" are only used on ISO and UNC/UNF ("Vee") threads that have a helix angle not exceeding 5 degrees.

(Check Machinery's Hand Book).

[oldtiffie]

There are tolerance limits on: OD of a bolt (male); the pitch cylinder required as well as the point radius on the threading/screwing tool.

So in that lot there is no one set "in" feed on the screwing tool that will give everyone /anyone the pitch cylinder diameter.

Check Machinery's Hand Book.

The maths required for using the "3-wire" method will stop some people cold if they do not have the maths for it.

The logical answer is to use a good thread micrometer where the pitch cylinder diameters can be read off directly without any maths and without the frustration of keeping control of the three wires - and Using machinery's hand Book for the sizes required.

https://www.google.com.au/search?q=t...2&ved=0CCUQsAQ

https://www.google.com.au/?gws_rd=ss...ead+micrometer

[oldtiffie]

First of all the"3-wires" can be any diameter so long as they are all quite accurately the same diameter and all will engage the thread on its "flat faces".

The diameter sought does not need to be the Pitch diameter but within the pitch diameters at the limits of the sizes as specified in Machinery's Hand Book.

Here are the workings for a 1/2"- 13 - UNC - 2A male thread.

http://i200.photobucket.com/albums/a...wirecomps1.jpg

Here are the 3-wire sets:

http://i200.photobucket.com/albums/a...ds/3-wire2.jpg

http://i200.photobucket.com/albums/a...ds/3-wire3.jpg

And here are the thread details and limits:

http://i200.photobucket.com/albums/a...n_P72-73_1.jpg

[elf]

How hard would it be to make or find some thread wires the correct size? https://www.youtube.com/watch?v=QGBRwXwxnuU

[Carld]

I agree with Forrest, you will have to make a male thread to the diameter and pitch you want and use it for a test part to make the internal thread. I have never found a measuring tool to measure an internal thread. Making an internal thread without a mating male test part is like taking a shot in the dark with a blindfold on and expecting to hit a target.

To make the male thread you will have to use measuring wires or measuring triangles for it to be accurate.

[Carld]

removed post