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Unidentified gear cutters.

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Andrew Tinsley20/06/2018 18:13:52
827 forum posts

This must be a longshot, but!

Amongst some gear cutters that I have acquired, there are some with no identification on them. Is it possible to work out what DP they are if I can get a good shadow graph magnification of the profile?

They are definitely professionally made and have some coding on them, but nothing that remotely resembles a DP identification.



Brian Wood20/06/2018 19:25:29
1796 forum posts
36 photos

Hello Andrew,

I wonder if they have been slimmed down in width, taking off all the identification. As to reverse engineering what they were made for, maybe finding Unicorn hair might be an easier quest!

What a pity

Regards Brian

Andrew Tinsley21/06/2018 08:01:42
827 forum posts

Thanks Brian,

I thought that might be the case. It is a pity as they are pristine and very sharp! Now where did I see my last Unicorn!

Thanks again Brian,


Hopper21/06/2018 08:07:20
3144 forum posts
52 photos

Well, if you measure the radius on the cutters with a radius gauge and measure the tip width, you might be able to extrapolate back from Ivan Law's charts on making cutters by the two button method and get a close idea of the DP. Then you would have to check the cutter against a gear of that spec to confirm. Could be tricky though.

Ivan Law's book on Gearcutting would have details, but also quite a bit on the net about making gear cutters with the two button method.

If you don't have a set of radius gauges, you might use a set of drill bits to meausure the curves on the cutters.

Edited By Hopper on 21/06/2018 08:14:10

not done it yet21/06/2018 09:40:28
2566 forum posts
11 photos

Some extra clues, maybe?

Any aquisition history?

‘Professionally made’ - do you mean a one-offs or manufactured on a series production scale?

Are these a set (of eight?)?

Use each one to cut a tooth form to full depth and compare the fit with known cutters in your possession?

14 1/2 or 20 degree pressure angle? Might be discernible.

Arbor size? Keyway? More likely for someone to hazard a guess.

Might even be metric for all we know!

The others (less sharp ones) can, of course, be sharpened.

JasonB21/06/2018 09:51:40
14613 forum posts
1452 photos

Maybe a picture with the code that is on them would help others find that unicorn. Just because it does not resemble a DP identification the code could be for MOD or even bevel gears.

Andrew Tinsley21/06/2018 17:38:30
827 forum posts

Hello All,

Thanks for the help in the Unicorn hunt! I do have sets of radius gauges, so it is worth having a go as per Hopper (Thanks mate!).

I will dig out the cutters and sort out the codes on the ones I have. They seem to have been engraved freehand, but the quality does indicate they have been professionally made. A visit to the workshop will follow shortly!

Thanks everyone,


P.S. It just seems a pity to have what look like brand new cutters consigned to outer darkness..Even if they are no use to me. Someone else may be able to use them

Andrew Tinsley21/06/2018 18:47:49
827 forum posts


A little more information. One side has a K followed by a 4 figure number. The one I have picked up has K 3879 stamped on (or may be etched, difficult to tell). They all have K followed by the 4 figure number. This mark looks like a manufacturers mark.

The other side of this cutter has V 11-35/1. They all have V followed by varying numbers, but with the same hyphens. This number has been done freehand with an engraving pen.

I have 5 of the cutters , so maybe they are part of a series of 7 for simple gear cutting. Or perhaps this is a red herring!

It looks as though the cutters have been cut down on the side with the freehand engraving. So it looks as though Brian is correct in his surmise. They look to be 3/4" bore. I don't know what a close, in size, metric cutter would be

Any suggestions would be welcome. I have already given away those cutters that I am unlikely to need. If I can identify the cutter spec for these, I can probably gift them to a deserving cause.



Neil Wyatt21/06/2018 21:04:59
15454 forum posts
651 photos
72 articles

Quite a challenge as to know the correct radius for a cutter you need pressure angle, dp and the number of the cutter.

Knowing the radius you have to identify three different variables.

My advice would be to offer them up to a few gears of about the right size and see if they 'fit'.


Andrew Tinsley21/06/2018 22:08:25
827 forum posts

Hello Neil,

I have tried the cutters in the gears that I have to hand, with no luck. I shall be asking around friends to see if they have a better selection of gears that I could try.

Hello Hopper.

I have tried using the radius gauges and find that it isn't too easy to select the correct radius. Need to go to Specsavers! I shall dig out the Shadowgraph and see if I can get a better idea of the radius.

The cutters came from a gentleman who was a locksmith and clockmaker. There were also some cutters to produce ratchet teeth.



John Haine22/06/2018 07:11:50
2320 forum posts
130 photos
Posted by Andrew Tinsley on 21/06/2018 22:08:25:


The cutters came from a gentleman who was a locksmith and clockmaker. There were also some cutters to produce ratchet teeth.



So they may well be for clock gears, so DP & pressure angle won't be applicable. Maybe have a look at this?

JasonB22/06/2018 07:16:23
14613 forum posts
1452 photos

If he was a clock maker than they may not be involute form as that is not used on clocks, they have cycloidal form.

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