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Trying to identify

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Alan Crawley18/04/2021 12:08:44
22 forum posts

I have a damaged gear that I need to reproduce. It is .750" or 19 mm diameter and has 14 teeth. This does not fit any Mod or DP formulae as far as I can see.

The closest is 1.25Mod but that gives 20 mm diameter, it runs on a rack on my Hardinge clone, and I seem to recall from way back they tended to use weird gears. I seem to think I have two options, make a single point fly cutter and cut 14 teeth or make the blank 19mm diameter and cut 14 teeth 1.25 Mod.on it. The pattern is cut onto the shaft and has an unworn section so the diameter is as I stated.

I'm sure there are people on here who will be able to point me in the right direction.Thanks in anticipation.

Pete Rimmer18/04/2021 12:25:04
979 forum posts
57 photos

Sounds like a 22DP long-addendum gear Alan.

DOH!, I should read all of your post before replying. Hardinge love 22DP gears.  I can reproduce it for you if you like.



Edited By Pete Rimmer on 18/04/2021 12:26:49

Alan Crawley18/04/2021 12:29:13
22 forum posts

There's a clue in " it runs on a rack on my Hardinge clone" Sorry. I couldn't resist it!

Howard Lewis18/04/2021 12:47:54
4866 forum posts
12 photos

14T, 22 DP would be 0.727" OD,, so Pete is right, in my book, given my limited knowledge.

Sounds like a very generous offer.



Bazyle18/04/2021 13:42:55
5896 forum posts
218 photos

If it is running with a rack it is the rack you need to measure as it is likely to be a cyclic pitch, though that might by chance be near a regualr DP. Hardinge would have used the correct pitch but a clone might use something near for cheapness.

Pete Rimmer18/04/2021 17:09:47
979 forum posts
57 photos

The HLV rack is 42 pitches over 6" which is exactly the circular pitch for 22DP.

old mart18/04/2021 18:43:37
3067 forum posts
194 photos

I have this gear size calculator in my favourites:



You should be able to get close to a standard size, although small variations in the OD can be difficult to work out.

Edited By old mart on 18/04/2021 18:46:09

Mark Rand18/04/2021 21:42:03
1013 forum posts
11 photos

The reason that Hardinge (and some others, like Beaver) liked 22DP, at least for rack gears, is that the pitch is within .04% of 7tpi, Thus is quite useful for linear calibrations.

The other thing is that Hardinge didn't use a plain 22DP gear, they used 22/29 stub form gears (pitch 22DP, but with the height and depth of 29DP gears), so the diameter is less than one might suppose.

PS:- Pete. I really must get back to you about gearbox cover castings. I've been a bit distracted over the last several months and have kept putting it off. crying

Pete Rimmer18/04/2021 22:53:42
979 forum posts
57 photos

No problem Mark, whenever you can.

BTW even though the Hardinge stub gears are famous, Hardinge UK certainly used full 22DP gears I have a factory drawing for them.

Alan Crawley26/04/2021 14:02:54
22 forum posts

Sorry I've not got back for a while. Second vaccination laid me low!

I have made a gear which drives the carriage satisfactorily. I cast my mind back to the days when I was a design draughtsman and searched out some information which said that theoretically the perfect pinion for running on a rack could have round pins. I made a cutter as close as I could to the unworn part,and cut the little gear. This part is actually a compound, with the other bigger gear running on the clutch gear.I turned down the worn gear to 8mm and pressed on the new gear. I then drilled half-and-half holes and tapped M3 and put in grub screws. It winds by hand and with the power feed smoothly. The pitch circle is a little small when checked on the hand wheel, but this is of no consequence as it has DRO fitted. Incidentally this machine is a Feeler Mk.2 and when it was at British Aerospace we found that parts from a Hardinge HLV-H were all interchangeable I seem to recall though that the Feeler used metric screws. One slight difference I came upon is that it has useful jacking screws to get the apron off easily.

old mart26/04/2021 16:58:10
3067 forum posts
194 photos

The teeth of a rack, being of infinite diameter have straight sides, so the round pin idea is sound.

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