Working out which gear cutter

[jg_jake]

Hello all,

Ill be cutting my first gears soon and I've just been looking into how to work out what module gear cutter ill need.

The gear OD is 65mm, Root is 59mm and its 40 teeth. Using OD/(2+T) I get 1.547, is it correct to assume this is a 1.5 module #6 gear cutter?

Next question, the plan states using a cutter with a PA of 14.5. Due to costs and not being easily able to source this, would there be any issue changing to a PA of 20?

Thankyou in advance.

 

[Jasonb]

Sounds more like a DP gear, measure it in inches and do the maths

14.5 pressure angle is also more common on DP gears so that also points to imperial.

What is the plan? Also what is the mating gear and the ctr distance of the two as these can be used to confirm PCD.

 

[jg_jake]

I get 16.4 for imperial.

The plan is a hit and miss originally by David Kerzel, but redone by Julius De Waal in metric. The gears in question are on page 4.

https://www.modelesavapeur.com/telechargements9/kerzel-hit-and-miss-jdw.pdf

 

[Jasonb]

That is where your problem is . He draws all these engines at different sizes and just does a mathmatical conversion but never actually builds them to see if they work or can actually be made.

He has basically doubled it up and then just picked the nearest whole mm. The original engine had 32DP so an exact double up would give 16DP.

However given your location it will be easier to get MOD cutters, so go with 1.5MOD & 20pa if you cut both with 20pa they will be fine. What you must do is adjust the PCD of the two gears to mesh correctly which will mean moving the stud that the larger cam gear rotates on so that it is 17mm in from the edge which will give a PCD of 45mm and adjust the push rod length to suit.

PCD of 40 + 20 = 60
60x 1.5MOD = 90
90/2 = 45PCD

 

[jg_jake]

That clears things up as to why the numbers on the plan were not adding up.

Thankyou Jason for your help, I appreciate it.

 

[HMEL]

Hello all,

Ill be cutting my first gears soon and I've just been looking into how to work out what module gear cutter ill need.

The gear OD is 65mm, Root is 59mm and its 40 teeth. Using OD/(2+T) I get 1.547, is it correct to assume this is a 1.5 module #6 gear cutter?

Next question, the plan states using a cutter with a PA of 14.5. Due to costs and not being easily able to source this, would there be any issue changing to a PA of 20?

Thankyou in advance.

You can change pressure angle of all the gears are made to the same pressure angle. But you cannot mix and match. But if these gears are used for timing purposes then switching from imperial gear to a metric gear could cause issues.

 

[peterl95124]

"I make everything from scratch, except for screws, gears, and ball bearings, those I buy" !!!

the only thing thats important for timing gears is the 2-to-1 ratio, actual module/DP doesn't matter, and actual size isn't all that critical either just location of the second shaft relative to the crankshaft.