Gear cutting from scratch

Moper361

Moper361

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Hi all hope you have had a good day

Im working on a new project and need a bit of help as i have never cut spure gears before and i want to get in the ball park for ordering involute cutters

Is this remotely correct ?

I have been racking my brain all day on working out involuted gear cutters with what I can find online

This is what I have come up with on my calculations please correct me if I an not correct

If I was to make a 40 tooth gear using following cutter
M 0.8 32 DP #2 cutter my outside diameter would be 1.312

If I was to make another gear using
M 0.8 32 DP # 3 cutter my outside diameter would be 2.562

From here how do I work out the diameter pitch so I can see centre lines we tweet the two shafts
I am looking for 45 to 50 mm between centers

Also how do you determine the depth if the cutter is not marked ?



If I'm totally wrong in my understanding of cutters please correct me

Any help appreciated
 
PD =N/DP That is the simplest way, there are a couple more that are more complicated. Find a book titled Gears and Gear Cutting by Ivan Law. Ity will simplify the mystery of gear cutting for you. The book is #17 in the workshop practice series. Good luck.

"Billy G"
 
Bill Gruby said:
PD =N/DP That is the simplest way, there are a couple more that are more complicated. Find a book titled Gears and Gear Cutting by Ivan Law. Ity will simplify the mystery of gear cutting for you. The book is #17 in the workshop practice series. Good luck.

"Billy G"
Click to expand...

I agree with Bill, Ivan Law's book is an excellent reference. I don't have it to hand, do I'll try remembering...

Module gear pitches are, however, like metric threads, calculated the other way around - pitch diameter is Mod x teeth (as you seem to have worked out!), but like imperial gears you need to apply 2x the addendum to get the OD - so your 32 tooth will be 34xMod OD, 34 x 0.8mm = 27.2mm.

The shaft centres will be half the sum of pitch diameters (NOT OD), so take e.g. 48mm between centres, 48/0.8 =60 so you need a total of 120 teeth on your pair of gears, e.g. a pair of 60 tooth or a 40 and an 80, 30 and 90 - depends on the desired ratio

The depth of cut I *think* will be twice the module so for 0.8Module it will be 1.6mm - putting the pitch circle (halfway down the cut) back at module x teeth.

I hope this helps rather than confuses!

Dave H. (the other one)
 
Thanks for the reply Dave ,I am confused as I thought to work out the diameter of what the blank should be the formula was ,If cutting a 40 tooth gear with a 0.8 module with equals a diametrical pitch of 32 as far as I can find on charts would be like this

D= number of teeth + 2 so this would be 42 then divide 42 by 32 this being the diametric pitch for a module 0.9
= 1.312 inches multiply that by 25.4 = 33.32mm outside diameter of blank to start with .

I may be reading your message were you use x may mean divide ?.

The info on depth is helpful and I'll keep trying to get my head around the rest

Thanks again
 
Moper361 said:
If I was to make a 40 tooth gear using following cutter
M 0.8 32 DP #2 cutter my outside diameter would be 1.312

If I was to make another gear using
M 0.8 32 DP # 3 cutter my outside diameter would be 2.562
Click to expand...

Your outside dia doesn't change with cutter change. A 40 tooth gear in .8m is only one size. If it is to be .8 M (31.75DP) then a #6 cutter is required.
A gear cutting program I have shows that gear 1.3228 O.D. and 1.1839 base dia so depth of cut .0694
 
Sorry that is my mistake that should read
Make another gear at 80 teeth

I'm wanting 2 to 1 ratio

It is for a small IC engine and I need a centre line between cam and crank of approx 45 to 50 mm to get cam to rod clearance

When I did the calculations I calculated on mod 0.8 as being 32 DP however this was from a chart I found on Internet and this is in fact not correct as it as you state 31.75 DP for a 0.8 m this may well be were my figures differ from yours also the number cutter I got from same chart as when I looked it seemed different for the cutter number for amount of teeth from Athors I had seen on various sights

I've never looked at the subject of gear cutting before so I'm new to it but was just doing some calculations to get a start point and see if I'm on correct path . After doing this I can see the teeth will be quite fine and quite possibly I would be better of with maybe a 0.9 or 1 m mod and reduce teeth numbers this would give a bigger tooth .

I also picked 40 and 80 tooth gears as they would be dead easy to do on indexing head .

I hope I'm heading in correct direction as I'd like to get a set of cutters close or usable for the job to practice with.
 
Last edited:
Why try converting the Module to DP? Do the measurements in mm and it all works out to nice simple measurements, whole numbers or tenths of mm! Module cutters should be cheaper than DP as well, as everywhere except the USA has standardised on the Metric system, some decades ago :)

Dave H. (the other one)
 
me being the beginner on gear cutting I have sourced info from the web in both metric and imperial so I've used bits and pieces to get my calculations as there are various bits of good info in both metric and imperial .
I see your point and will try stick with just metric ,I had never even thought about making gears until yesterday so still very new to it and sure to make a few blunders along the way but think I can get the hang of it
Thanks for the helpful input
 
I've only done a few gears and one issue that I have is knocking the sector arms on the dividing head. I now mark the hole for the pin with some soap stone. That way if the pin drags on the sector arm and moves it, I can still locate the correct hole. Take your time and you'll do fine
 
Hi Reeltor
Thats one of the reasons im picking tooth numbers that are eady to work with in indexing head to start with to get the hang of it a bit
 
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