Omnimill 00 feed gear

[Wade BeattyParticipant @wadebeatty78296]

Good morning from Norway,

 

My Omnimill 00 is missing the 16T feed gear and I would like to make a new one. I have never made a gear before but have spent considerable time reading up on it and searching various sites and forums.

The second gear, that the 16T should mesh with has 48T. With the standard Diametral or Module formulas I do not get close to a “standard” pitch or module.

The measured OD of the 48T gear is 2.718″ or 69.037mm. I have used gauge blocks to calibrate 2 different micrometers to be sure of this dimension.

By the Diametral Pitch formula (2 + T)/OD(in), the result is 18.39, not a standard pitch

By the Module formula OD(mm) /(2 +T), the result is 1.38, again not a standard module

Any constructive criticism or help appreciated

Thanks,

Wade

[JasonBModerator @jasonb]

Can you measure the distance between the two gear centres? Then the PCD can be used rather than OD which could have been adjusted.

[DC31kParticipant @dc31k]

Can you measure the centre-to-centre distance of the shafts on which the two gears rotate?

Do you have any of the other gears (20, 44, 39, 25, 35, 29) that you can measure?

It is easy to find pictures of the gearbox setup plate and every combination they give adds up to 64 teeth total.

Please check the logic of this but the centre-to-centre distance should be the same as the pitch circle diameter of a 32t gear of the appropriate specs.

The 48t gear only ever meshes with the 16t one. The 48t one is close to 18 DP. It is possible that because the 16t one has a low number of teeth, they did a pitch shift on the gears – the 16t one made larger and the 48t one made smaller.

A pitch shift might also be used if the dedendum on the standard pitch circle made the amount of metal between the tooth root and the gear’s bore too little.

[bernard towersParticipant @bernardtowers37738]

Sounds very much like 18DP

[Wade BeattyParticipant @wadebeatty78296]

First I want to thank everyone for their replies, I learned quite a bit from them.

 

18DP indeed seems to be the correct pitch, I measured the diameter of the other pairs:

35T  2.05″   18P         /  29T  1.72″  18.02P

25T  1.5″    18P         /   39T  2.28″  17.98P

44T  2.56″   17.56P   /    20T  1.22″  18.03

48T  2.72″  18.38P    /    16T  1″       18P

 

Shaft center distance is 1.785″

 

Thanks for your help

 

Wade

 

 

 

[Pete RimmerParticipant @peterimmer30576]

The size for the 48T is correct. Long-addendum rules require the 16T to be increased in diameter by 55 thou for a 18DP gear (0.997/18) and the 48T would have to be decreased by the same amount. Take 0.055″ from the diameter and it works out to 18DP.

 

[Pete Rimmer]

On Pete Rimmer Said:

Long-addendum rules…

And notice that the tooth count of all the pinion plus minimum-to-avoid-undercut gears in the table add up to 64, the same as the total tooth count used on the mill (16/48; 20/44; 25/39; 29/35). Coincidence or clever design by Elliott?

[Wade BeattyParticipant @wadebeatty78296]

Thanks again for the replies. Pete Rimmer, that table is very good, what text did it come from?

 

Wade

[Pete RimmerParticipant @peterimmer30576]

It’s from Machinery’s Handbook.

[Wade BeattyParticipant @wadebeatty78296]

I sometimes get so hooked on looking something up on the net that I forget that Machinery’s Handbook is right next to me.

[Wish I was retired Barry!Participant @wishiwasretiredbarry]

Hello Wade in Norway.

The 16 tooth gear off my OO is 1.058″ od and 0.801″ across the root diameter.

Annoying not to have the gear but I tend to use the next one at 1.3″ a min still slow. However the vertical head is not very rigid. Have the swivel head as well but only a morse 2. Was trying to think how to easily make a copy for you. Tracey tools, do gear cutters but probably expensive for a one off, worth a call.

Regards Barry

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