# Cutting Spur Gears



## xo18thfa (Jan 23, 2012)

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 Harold Hall 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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## cfellows (Jan 23, 2012)

Nice thread, Bob. I'm sure this will be very useful to a number of readers.

Chuck


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## xo18thfa (Jan 24, 2012)

Thank you Chuck.


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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## tel (Jan 25, 2012)

Nice gear train there Bob - love it! :bow:


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## Maryak (Jan 25, 2012)

tel  said:
			
		

> Nice gear train there Bob - love it! :bow:



Me too :bow:

The other Bob


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## fcheslop (Jan 25, 2012)

HI Bob,nice gear train :bow:what size is the Cracker i have a soft spot for them as well.
best wishes Frazer


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## xo18thfa (Jan 25, 2012)

Thanks fellows. This was a fun project to do. 

This "Cracker" is in Gauge 1, so it is scaled up 1.4 times. The bore works out to 7/16" and 5/8" stroke. It is not as easy as you would think scaling up from Gauge 0 to Gauge 1. It would have been easier I think to use a scale of 1mm = 1/16" and bring the wheels in.


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## fcheslop (Jan 25, 2012)

Hello Bob,many thanks for the info and good luck with the build
best wishes Frazer


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## shred (Jan 25, 2012)

xo18thfa  said:
			
		

> Thanks fellows. This was a fun project to do.
> 
> This "Cracker" is in Gauge 1, so it is scaled up 1.4 times. The bore works out to 7/16" and 5/8" stroke. It is not as easy as you would think scaling up from Gauge 0 to Gauge 1. It would have been easier I think to use a scale of 1mm = 1/16" and bring the wheels in.


I think the ultra-cheap scale-up is to move the wheels to the outside of the frame, but that's not quite the same thing


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## hobby (Jan 27, 2012)

Thankyou for taking the time to explain in greater detail.

I have that book, and I can comprehend only about the first couple chapters of it, the basics of gear geometry, but start getting lost when he explains how to actually make a gear cutter tool..

That's whjy I reread it and still don't get what he's trying to explain about making a gear, your explanations are helping to make more clearer the actual production of a gear.

Thanks for a very imformative thread.


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## xo18thfa (Jan 28, 2012)

hobby  said:
			
		

> Thankyou for taking the time to explain in greater detail.
> 
> I have that book, and I can comprehend only about the first couple chapters of it, the basics of gear geometry, but start getting lost when he explains how to actually make a gear cutter tool..
> 
> ...



Law explains in Chapter 12 how to make the cutters, but not explain what those tables mean. Back in the Appendix he explains how to use the tables to come up with the cutter dimensions (at least in my edition). You divide the values in the tables by the DP (48 in my case) to get the required dimensions. 

For example, the 52 tooth gear, 20 degree pressure angle. Use cutter #3. Dimension "D" is 15.07/48 = 0.314 Dimension "C" is 15.52/48 = .323 Dimension "E" is 5.87/48 = .122 Dimension "W" is not really critical, I used 3/32" 

In Chapter 7, the only 2 formulas you really need are OD (stock diameter) and D+f (cutter depth). For the 52 tooth gear OD = (52+2)/48 = 1.125 D+f = 2.157/48 = .045

Have your wife or girlfriend double check the math. Other then that, I still have not read the book.


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## hobby (Jan 29, 2012)

Bob, 
Thankyou, for that additional examples.

Using your information, is helping me look into that book with more interest again.

Thanks for posting this thread.


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## mostbahgat (Oct 3, 2014)

Hi there ,
thank you for sharing this, the thing is ... the attached pictures does not open. i have tried every thing but it did not work.
what am i suppose to do to view these pics?
thanks again and good job. ( i did not see it yet but i know it is good )


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## Cogsy (Oct 3, 2014)

mostbahgat said:


> the attached pictures does not open. i have tried every thing but it did not work.
> what am i suppose to do to view these pics?


 
Unfortunately those pics appear to have been moved or deleted on their hosting site. Either way, they're long gone. Sorry.


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