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# Helical gear question

#### Mike Gre

##### Plastic
I have a K&T 3k machine. I bough a universal milling head but it did not have the drive gear and my current drive gear does not fit. I have the ability to cut new helical gears so I thought I would cut a new gear and mount it on a face mill holder for the correct distance from the mills face.

The gear on the back of the universal head has 33 teeth and an outer diameter of 5.525. This is the whole diameter not pitch or root. This gives me a DP of 6.335? I cant imagine that K&T would have used a completely proprietary DP for their gears. It also does not line up to module.

Is there something I am missing? I am very familiar with spur gears so I don't know if the OD does not work with my math on helical gears or what.

Also rotating the spindle on the universal head 360 goes two additional teeth past 360 on the gear on the backside of the head. I assume this would mean I need a 35 tooth gear to get my true speeds from my mill.

Any advice would be greatly appreciated. I am hoping to purchase the correct hob but I cant imagine getting this DP is possible.

#### Mike Gre

##### Plastic
Its a series 5812 universal head if anyone else has one and can measure the drive gear.

#### Dan from Oakland

##### Titanium
You have calculated the transverse pitch- the pitch in the plane of rotation. The cutter or hob must be based on the normal pitch of the gear.

#### David_M

##### Hot Rolled
How did you measure the outside diameter of an odd-toothed gear?

#### David_M

##### Hot Rolled
If KT used a 7 NDP hob and cut 33 and 35 tooth gears at 25.3582159 degrees,
it would have a center-to-center distance of 5.375". The OD of the 33-tooth gear would be 5.5027", though.

27.97962 degrees changes the c-to-c to 5.5", with the 33-tooth having an OD of 5.624"

26.7127175d c-to-c = 5.4375" 33t = 5.5633"od

Measure the center-to-center distance very accurately, and see if the 33 gear is 7 NDP with a gauge measuring perpendicular to the helix angle (you need to know the pressure angle, too).

Otherwise not enough information.

Nearest to opposite measurement converted to true od:

A 26.01146995-degree helix angle 7 normal diametral pitch 33 tooth gear has an outside diameter of 5.5313". The center-to-center distance for 33 and 35 tooth gears is 5.4046".

Last edited:

#### outlawspeeder

##### Plastic
Where did you pick up the head. Looking for myself.

### K&T 3K​

##### Aluminum
How did you measure the outside diameter of an odd-toothed gear?
Sir can you help me what isa the differential constant of seiwa iron works gear hobbing

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