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Sizing an M2 thread during screwcutting

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Graham Meek24/02/2019 12:32:46
95 forum posts
92 photos

I thought I would post a little poser to exercise the little grey cells. I recently made the above arbor to permit me to cut quite a few small 64 DP gears. The M2 thread needed to be screwcut to ensure absolute concentricity with the location diameter. It will be seen from the assembly drawing that the "Nut" portion of the arbor locates on the 2.00 mm diameter as well. Any run-out in the thread will cause the Nut to bend such a slender shaft. The Nut is also coned at the rear to take a centre for much needed support. This would mean the whole arbor would be running out.

The problem, or poser is how to size the thread such that the Nut is a good fit. A sloppy thread will not be of any use as regards maintaining concentricity.

The 3 Wires dimension required wires of 0.23 mm diameter. None were to hand and besides balancing 3 wires of this size on the thread did not appeal to me, even with grease. It is however one solution. It will be appreciated the centre support which would later be cut off, was needed during the screwcutting operation.

The solution was simple in its execution and it is the main reason for this post, ie to pass on the method. As it could be used on larger threads., but before that I offer this conundrum to the forum to make suggestions.

Regards

Gray,

duncan webster24/02/2019 16:46:25
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2111 forum posts
27 photos

I'll jump in with my size 12s.

Sweat 2 pieces of brass together to make a square, say 6mm AF. Set up in 4 jaw so joint is on centre, drill and tap M2 and turn the OD to a known size, concentric with the thread. Part off a piece just shorter than the required thread and heat to get apart. Clean off the solder and you have some loose jaws for your micrometer. Be careful not to lose them as they will be quite small. Then you can screwcut the male using the loose bits to measure.

JasonB24/02/2019 17:04:40
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15535 forum posts
1594 photos
1 articles

That's too easy, I would have thought Gray screw cut the female thread to suite the male one using that as the plug gauge once the end had been cut off wink 2

A very small female ctr may have been another option and would allow test fitting of the male thread.

Edited By JasonB on 24/02/2019 17:07:01

blowlamp24/02/2019 18:08:52
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1195 forum posts
82 photos

Turn a rod to a certain O/D (say 5mm). Drill & tap to M2. Slit this across its diameter & 'part' the two halves off the rod. Thoroughly deburr the threaded section.

I think it should then be possible to then use both halves of this nut - when fitted over the area being threaded - to measure its diameter, until an acceptable fit is achieved, i.e 4.99mm. smiley

 

 

Martin.

Edited By blowlamp on 24/02/2019 18:09:56

duncan webster24/02/2019 18:42:05
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2111 forum posts
27 photos
Posted by blowlamp on 24/02/2019 18:08:52:

Turn a rod to a certain O/D (say 5mm). Drill & tap to M2. Slit this across its diameter & 'part' the two halves off the rod. Thoroughly deburr the threaded section.

I think it should then be possible to then use both halves of this nut - when fitted over the area being threaded - to measure its diameter, until an acceptable fit is achieved, i.e 4.99mm. smiley

Martin.

Edited By blowlamp on 24/02/2019 18:09:56

BLATANT PLAGIARISM!

blowlamp24/02/2019 19:35:53
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1195 forum posts
82 photos
Posted by duncan webster on 24/02/2019 18:42:05:
Posted by blowlamp on 24/02/2019 18:08:52:

Turn a rod to a certain O/D (say 5mm). Drill & tap to M2. Slit this across its diameter & 'part' the two halves off the rod. Thoroughly deburr the threaded section.

I think it should then be possible to then use both halves of this nut - when fitted over the area being threaded - to measure its diameter, until an acceptable fit is achieved, i.e 4.99mm. smiley

Martin.

Edited By blowlamp on 24/02/2019 18:09:56

BLATANT PLAGIARISM!

Lol. I read your post straight after I submitted mine.

I was just making allowance for people with no solder. devil

Martin.

Graham Meek25/02/2019 10:21:17
95 forum posts
92 photos

I was beginning to think no-one was going to rise to the challenge. The two half nuts are a very good solution, but my solution was for a change much simpler.

I found some copper wire 0.24 mm diameter, from a multi-stranded cable. Winding the wire into the thread and taking a measurement could not have been easier. The wire was discarded after each use to minimise loss of diameter from stretching and the possibility of small flats from the micrometer anvils.

I was well satisfied with the fit of the two parts once the end was cut off. Checking the mandrel between centres with the components in situ showed no detectable run-out.

This method and it's ease of use is one I shall keep in mind for larger threads, provided I can find a suitable diameter wire.

Regards

Gray,

Brian Wood25/02/2019 13:39:57
1909 forum posts
37 photos

Gray,

That's an inspired idea and so simple; there will surely be many other ways to exploit it.

Congratulations

Brian

Jeff Dayman25/02/2019 16:57:54
1526 forum posts
37 photos

If doing over-wires thread measurement with copper wire, one caution - check that the wire is actually round. I have seen lots of copper wire bought for coil winding and sensor making that is seriously deformed off-round. Some oval, some triangular, some almost square. I became aware of these deformations when trying to troubleshoot wire feed issues in high speed coil and sensor winding.

If the wire is round it is a clever and simple method and will work well, same as measuring over wires with ground steel wires on larger threads.

Neil Lickfold25/02/2019 18:29:17
551 forum posts
102 photos

The copper works well as does the split nut method. On very small stuff like the M2 thread I have found that a thread mic with the anvils, not the points to be the best. The biggest problem I find with small threads is the variation in the taps themselves and the thread that is in the nut. As for fine wire, music shops sell the wire in 1 thou diameter increments. I buy sets of wires in a selection. Its what I make my circlips from for the model engines .When I used to make up wire for thread measuring , I left it very long, and looped it around and had tow on top and two on the bottom. As it was hinged it sort of stayed together. Another guy I worked with made his like a coil spring. It was just 2 loops. These he put tooth picks for handles on and would unwind the spring to fit over the thread form. This was for M3 and M4 LH threads for inserts. Both worked well, but the thread mic is quite fast. Down side to a thread mic is the purchase cost of the anvil sets. What I do like about the thread mic, is that you can make different anvils to suite differing applications , IE ball anvils etc.

Trying to get concentric threads I had always found difficult. So one way was to modify some taps, and on the lead in area, make it very close to the drilled size hole. This make it into a piloted tap, and that has solved a lot of issues for me. I use it to get the start of the thread form concentric, and then follow through with the regular tap. 

Neil L

Edited By Neil Lickfold on 25/02/2019 18:32:51

JohnF26/02/2019 10:57:52
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824 forum posts
92 photos

An excellent and simple solution Gray !

Neil -- I agree with the thread Mic and your comments, I have one purchased from Shars tools in the USA several years ago and its invaluable for some of the work I do. Much less expensive than you can purchase here.

My original problem came when I had to cut accurate metric threads on my imperial lathes, they have to be produced to a correct standard and wires are difficult/time consuming to use [unless you have the Horstman clip on type sets] so purchased an thread imperial mic. with 60deg anvils then made a table for conversion of metric thread measurements to imperial and it works well.

Anyone interested in the Shars mics here is a link **LINK** After some negotiations with them regarding freight, and they were very helpful sending the unit by insured post rather than a courier saving ££££'s

John

Nick Hulme27/02/2019 08:33:57
690 forum posts
37 photos

I'd go with a set of M2 chasers for one of my die heads.

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