# Cutting custom brass gears



## xo18thfa (Jan 2, 2008)

The task is to cut some custom spur gears in the home shop. If the gears work out they will go into a little live steam project. The gears are 48 diameteral pitch. Diameteral Pitch or DP is the relation between the number of teeth on the gear and its pitch diameter. For 48 DP, a 1 inch pitch diameter gear will have 48 teeth. We will cut 2 sizes of 48 DP gears, one with 16 teeth and three with 52 teeth.

The reference for this job is the “Workshop Practice Series” book #17, “Gears and Gear Cutting” by Ivan Law:










The book is available from Amazon.com or you can download it. Do a Google search for “Workshop Practice Series PDF Gears”. There will be a number of sites that have the PDF download. I followed Mr. Law’s procedures without deviation. 

First step is to make the cutter tools. The first cutter is a forming tool, used to make the actual gear cutter. The tables in Chapter 12 show all the dimensions. I used that table for 20-degree pressure angle. I also used the single button form tool, Fig 94 on page 117. The final gear cutters are 3/4" diameter. Here are cutters I made:










The steel for the cutters is alloy “O1”. O1 is the most widely used tool steel and is available from McMaster Carr and other suppliers. O1 is very easy to work with and harden. Shape and form the tool to the desired size. Heat with a torch to 1400 degrees F, which is cherry red heat in room light. Plunge in oil to quench. I used some leftover salad oil from the kitchen. Leave in the oil quench about 30 seconds, it cools down slowly. Quenched tool steel is too brittle at this point and needs tempering. To temper, suspend the tool in a small pot of salad oil on the kitchen stove. Heat to 350 degrees F using a candy thermometer to check the temperature. Leave it in about 10 minutes, pull out and let air dry. The O1 steel comes out very hard and will cut just about anything.

Let’s cut the 52-tooth gear first. These are from 1/8” thick flat brass bar. Chuck a length of 1/2" diameter steel in the lathe cut and turn a 5/16” diameter boss. Thread the end to accept a nut.










Make sure the 1/2" is centered perfectly in the lathe to turn the boss. If your 3 jaw is not accurate enough, dial it in on the 4 jaw.

Gang up three pieces of brass stock on the shank and turn them to the final stock diameter for the gear.










Time to cut some gears. You will need a dividing head or rotary table mounted vertically. This is my little homemade dividing head.










It is a “direct indexing” head that uses the change gears from the Atlas 6” lathe for indexing.

The spindle hole is tapered with #2 Morse Taper (2MT). A 2MT collet holds cinches stock tightly in the dividing head be means of a draw bar.










Secure the 52-tooth lathe change gear to the spindle of the dividing head. Mount the dividing head to the mill table. Use a 1/2" 2MT collet to chuck the gear blanks










Bolt the gear cutter on the shank and chuck up in the mill spindle. Use a height measure device to set the gear cutter height.










Adjust the depth of cut and start cutting. 48DP gears are shallow tooth, so one pass per cut. Advance the dividing head spindle one notch on the indexing gear. Repeat 52 times.










Turned out just right.










Next time we will cut the 16 tooth gear and do something with the results.


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## bnsfconductor (Jan 3, 2008)

Bob, 
Wow that looks like fun! It's nice to know that people can still learn out to manually mill things. Not that CNC is unworthy, but it seems like it takes a bit more skill in writing the programing etc. One of these days I hope to own a mill and lathe and take some introduction classes in milling/machining. But tell then I've learned quite a bit from reading threads like these! 

Craig


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## HMeinhold (Jan 2, 2008)

Bob,
thanks for another great how-to. However, as we are lazy guys, we came up with a scheme, which uses only one cutter for all gear sizes/pitches of a certain pressure angle. The idea is to simulate the action of a hob on the CNC mill. It takes close to one hour for one gear (or a gang of gears), but who cares. The gears mesh pretty well. 

Regards


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## xo18thfa (Jan 2, 2008)

Thanks guys. Henner: Hold on buddy, I found a one cutter technique already.


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## xo18thfa (Jan 2, 2008)

For Henner: Check out how this guy cuts gears using a single cutter: http://helicron.net/workshop/gearcutting/




Finish the 52 tooth gears by soft soldering an appropriate hub and tapping for set screws. They are done.

The 16-tooth pinion cuts in the same general manner as the 52’s. The notable difference is we will machine an integral hub with the 16 tooth, rather then hub less.

Change out the 52 tooth indexing gear on the dividing head and replace it with a 48 tooth. During machining, skip every third tooth to get 18 divisions.

A 16 tooth, 48DP gear has a rough stock diameter of exactly 3/8”. How convenient. Use a 3/8” collet to chuck some 3/8” stock and get to work.










Change the gear cutter and reset the height.










Cut as before










Chuck the 16 tooth gear in the lathe and turn a hub. Tap for some set screws. It’s done too.










These gears are going into a scaled up Ernest Glaser “Cracker”










They mesh perfectly. The chassis rolls smooth as silk.










Observations:

- Mr. Law’s book is the way to go for cutting gears. Simple to follow, no tricky steps.

- The single button forming tool works better then the 2 button. My lathe is not rigid enough to cut both sides at the same time without horrible chatter. The single button tool allows you to take several cuts to get the final profile.

- Although the round gear cutter tools did the job, I think fly cutters would work better. The round cutters bottom out a little bit. Fly cutters won’t do that.

- Mr Law’s book shows how to cut bevel gears. That’s the next experiment.

- Overall grade: A-


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## HMeinhold (Jan 2, 2008)

Hi Bob,
thanks for the tutorial and the link. I think we looked at this hob method and decided, we could simplify it even more. We made one V-shaped flycutter and had the CNC mill simulate the hob. So basically the flycutter cuts at different heights given by the pitch of the simulated hob, then indexes to the next tooth and repeats the sequence. This reproduces the round shape of the teeth pretty well. We had to empirically find the correct depth of cutting (because of the rounded tip), but the gears meshed well. May be Mark can give more comments.
I am curious how you will do bevel gears and eventually even skew bevel gears (Do I hear Climax)? We were not yet able to design a flycutter/find a tool path for the CNC mill to cut this type of gears. Thanks again for your tutorial!
Regards


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## xo18thfa (Jan 2, 2008)

Henner: The method you described is the best. That is essentially how a real gear hobbing machine would work.

The depth of the cutter is 2.157 divided by the Diametral Pitch. My gears are 48 Diametral Pitch so the cutter dept was 0.045". If you are doing metric gears it would be 2.157 divided by 25.4 divided by Module (to get it in inch). 


Some day I am going to try offset bevel using Kozo's method. Kozo uses a lot of Ivan Law's methods. Kozo does that math, where Ivan draws pictures and measures graphically. Ivan has a nice trick to determine which standard industrial cutter to use rather than making costume cutters as Kozo does.


These bevel gears are "do-able" Henner. We can do this job.

vr Bob


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