# Gear cutting from scratch



## Moper361 (Oct 27, 2017)

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


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## Bill Gruby (Oct 27, 2017)

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"


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## British Steel (Oct 27, 2017)

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"



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)


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## Moper361 (Oct 27, 2017)

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


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## rgray (Oct 27, 2017)

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



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


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## Moper361 (Oct 27, 2017)

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.


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## British Steel (Oct 27, 2017)

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)


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## Moper361 (Oct 27, 2017)

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


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## Reeltor (Oct 27, 2017)

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


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## Moper361 (Oct 27, 2017)

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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## Reeltor (Oct 28, 2017)

YouTube is your friend, in addition to checking out Mr Pete 222 aka tubalcain, look for gear cutting on Keith Rucker's vintage machinery site

https://www.youtube.com/results?search_query=keith+rucker

https://www.youtube.com/results?search_query=mr+pete+222


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## rgray (Oct 28, 2017)

Checking my gear cutting program a few ways and a 1.75m cutter with a 20 and 40 tooth gears would be center to center 2.0669 (52.4993mm) not sure if that is close enough to 50mm.
1.75m is close to 14DP which is a popular one. at 14dp the center distance is 2.1429 (54.43mm)
My 14dp cutters are stamped .154 tooth depth. My program shows a .152 tooth depth for 1.75m.
Here's a cutter set on ebay 1.75m:
https://www.ebay.com/itm/Involute-G...179157?hash=item3f8957e795:g:KWAAAOSwMmBVuQS5

There are probably lots of tooth counts that would get closer to the 50mm center distance but uneven counts would need better indexing.


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## savarin (Oct 28, 2017)

There is another way of cutting gears.
I made a 40 tooth spur for my tumbler reverse thats still in use today.
http://www.hobby-machinist.com/threads/tumbler-reverse.10122/  from post 27
I got the idea from here
http://users.tpg.com.au/agnet/cq9325rev7.html


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## rgray (Oct 28, 2017)

savarin said:


> There is another way of cutting gears.
> I made a 40 tooth spur for my tumbler reverse thats still in use today.



Nice! 
My first gear was cut somewhat in that style, and in 2012. HSS bit ground to tooth profile, but I did it in a mill. It was a approx 6" gear for the drive on a snowblower. It's still going strong.


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## NortonDommi (Oct 29, 2017)

Hello Moper361, here's a little program from W.M.Berg Engineering that I have found very useful. Not only good for blank dimensions but also when reverse engineering to find out what a mystery gear is. Hope it helps.


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## NortonDommi (Oct 29, 2017)

Here's another one that may also be of use and my take on setting backlash.
  Cheers,
  Barry.


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## Moper361 (Oct 31, 2017)

Hi everyone just a brief question will the chinese 22mm involute cutters fit on a 7/8 arbor or will i need new arbor to suit specific 22mm cutters


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## Moper361 (Oct 31, 2017)

Just like to thank all who replied with information to my origanal post  it has helped a lot and i have gained lots from it hopefully ill be busy knocking out gears next time im home 
Regards Nat


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## NortonDommi (Oct 31, 2017)

7/8" X 25.4 = 22.225mm
-22 = 0.225mm
0.225/2 = 0.1125mm or 0.00443" to small.

  In the real world your arbour may be slightly over or under,(usually on or just under nominal size), and the cutters are usually a fraction oversize so most likely they wil fit. If slightley tight that's good but a quick hone with a bit of fine emery cloth in a slotted dowel held in a drill,(work from both sides or reverse drill), will clean up the inside to make them fit. Can polish the arbor as well.
  The drive is through the key and the clamped faces so as long as they go on no worries aye.


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## NortonDommi (Oct 31, 2017)

Hey Moper361,
                          I just had a thought, you well may know this but it sometimes is easy to overlook. Imperial cutters,(DP), of the Brown & Sharpe pattern start cutting low tooth numbers,(12 & 13), at cutter No.8 working to high tooth numbers,(135 to rack),at cutter No.1.
  Metric cutters,(Module), are the reverse. Pick Imperial or Metrickery depending on the application. They ARE NOT interchangable.
  Have a play and you will be fine and heed Bill Gruby's advise, Ivan Law's book is an extremly valuable bedside reader.
  P.S. Go to page 37 in the downloads section.


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## Moper361 (Jan 6, 2018)

I would just like to say thanks for the input some people provided to get me started with gear cutting ,The information was very helpful ,I've managed to make a couple of gears for practice just with number 1 modules but I can see now I'd be better of with modules maybe number 1.5 or up for what I want to do but at least I'm on track now ,I was furtunate enough also to be given some great books on gear cutting by a generous old gentleman ,books being
P.S Houghton gears
Ivan Laws gears and gear cutting
Calvin and Stanely gear cutting practice
Tha Caxton engineers hand book
Marshall gear wheels and gear cutting
Model engineers hand book volume 100 1949 .

The depth I'm still in doubt a bit but using a module 1 cutting I made the depth of cut at 2.157 mm I'm not convinced this is correct formula being known module x2.157    = 1x 2.157. This came from a web chart I found before I received the books  the chart was from maryland metrics spur gear calculations .


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## NortonDommi (Jan 6, 2018)

Have a look at the W.M.Berg program I posted above. What is the tooth count 46? Bergs program gives total depth of 2.251 mm.
  Nice looking gear you have made.


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## Moper361 (Jan 6, 2018)

NortonDommi said:


> Have a look at the W.M.Berg program I posted above. What is the tooth count 46? Bergs program gives total depth of 2.251 mm.
> Nice looking gear you have made.


I'll need to wait to get to a Computor that can open the program as I'm limited to iPad most of the time even tho I have PDFs write on here I'm having issues opening the program . The gear tooth count its 48 tooth gear for the larger one and 24 the smaller one .

The gears seem okay and came out pretty good for a first go it's just the depth I'm still in a small amount of doubt about .These were for practice only however I may use them as a reduction for a power feed I plan to build for my mill at some stage .
Regards Nat


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## NortonDommi (Jan 7, 2018)

Hi Nat,
           Ran through Shop Calc and it came up with 2.157 mm however Bergs program says 2.251 whole depth,(2.000 mm working depth), and as gears are their business I go with their recommendations.
  I saved using the print function and files saved as .xps, unfortunately these cannot be uploaded to this site with this file extension, sorry.
  Amend that, I have put them in a zip folder and that has uploaded O.K. Hope you can open it .
 Cheers,
  Barry.


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## Moper361 (Jan 7, 2018)

NortonDommi said:


> Hi Nat,
> Ran through Shop Calc and it came up with 2.157 mm however Bergs program says 2.251 whole depth,(2.000 mm working depth), and as gears are their business I go with their recommendations.
> I saved using the print function and files saved as .xps, unfortunately these cannot be uploaded to this site with this file extension, sorry.
> Amend that, I have put them in a zip folder and that has uploaded O.K. Hope you can open it .
> ...


Thanks for that Barry ,appreciated  seems the calculation I used was about correct then ,it's a learning curve but good results which is encouraging for future gear cutting ,I have also fitted a 3 axis DRO on my mill since I made these gears so it's a bit easier and more accurate to set the depth in future .i will take a look at the attachments when I get chance thanks 

Regards Nat


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