# Meshing of spur gears



## Brian Rupnow (Jun 1, 2013)

Last year, or possibly two years ago, I read a post where someone had machined a set of mating spur gears, and the meshing of the gears left a lot to be desired..---Sticky, binding spots as they were rotated. He solved the problem by putting some carborundum paste on them and letting them run that way for a bit. He claimed that it fixed things right up. I thought at the time that it sounded a bit crude, but I filed it away for future reference if I ever needed it. Today I needed it. The gears on my "something old Something older" project were very nasty---some spots turned freely, other spots were very "tight" during the rotation. The gears are pretty lousy as gears go---they were reclaimed from an old TV antenna rotor. I happen to have a full jar of automotive valve grinding paste that I purchased when I built my first I.C. engine. I found out that it was far to coarse for grinding small engine valves, but I kept it anyways. Since I didn't want to invest a lot of time in this project, I thought, "What have I got to lose?"--I coated the gear teeth with some of this compound and ran the crankshaft for about 5 minutes with my variable speed drill. WOW---What amazing results. Those gears now mate like as smooth as can be. The method may be a bit crude, but Hey!!!-Who am I to argue with success? I thought I would post about it.---Might help somebody out of a BIND!  (Groan.)


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## cfellows (Jun 1, 2013)

My kind of metal work!  It worked and it reclaimed two otherwise less than useful gears.

Chuck


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## wild350x (May 24, 2014)

It is still a common practice for gears cut on older style , not to mention worn out, gear cutting machines such as sykes, sunderland, etc. That in their hayday could only cut an agma 6 quality gear to "lap in" a set of gears by using a gearbox with abrasive in the lube system to make a matched set. Only way to make them run quietly. Not saying its the best way at all, but still used.


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## Hopper (May 24, 2014)

Not necessarily  crude. Standard practice when fitting new camshaft gears in old Harley engines. Just be sure to clean all the abrasive off  afterwards or things could get a bit nasty.


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## dnalot (May 24, 2014)

I used a 400 grit lapping compound to mate the gears on a differential recently. Mounted the two piece axle in a lathe, pasted the gears with compound and spun one end at 28 RPM with the other end clamped in a chuck at the tailstock. After 5 minutes the gears were turning silky smooth. 

Mark T


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## gus (May 25, 2014)

Brian Rupnow said:


> Last year, or possibly two years ago, I read a post where someone had machined a set of mating spur gears, and the meshing of the gears left a lot to be desired..---Sticky, binding spots as they were rotated. He solved the problem by putting some carborundum paste on them and letting them run that way for a bit. He claimed that it fixed things right up. I thought at the time that it sounded a bit crude, but I filed it away for future reference if I ever needed it. Today I needed it. The gears on my "something old Something older" project were very nasty---some spots turned freely, other spots were very "tight" during the rotation. The gears are pretty lousy as gears go---they were reclaimed from an old TV antenna rotor. I happen to have a full jar of automotive valve grinding paste that I purchased when I built my first I.C. engine. I found out that it was far to coarse for grinding small engine valves, but I kept it anyways. Since I didn't want to invest a lot of time in this project, I thought, "What have I got to lose?"--I coated the gear teeth with some of this compound and ran the crankshaft for about 5 minutes with my variable speed drill. WOW---What amazing results. Those gears now mate like as smooth as can be. The method may be a bit crude, but Hey!!!-Who am I to argue with success? I thought I would post about it.---Might help somebody out of a BIND!  (Groan.)




WW-1 technology but it worked. Will take note. KG Gears , Japan stocks hardened lapping gears. As a young lad,I did wondered how on earth they grind every gear tooth so smoothly.


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## GailInNM (May 25, 2014)

Although I can not  vouch for how true it is, the story on Shay locomotive side gears goes something like this. For those not familiar with Shay locomotives, they had a side mounted engine that ran a drive shaft on the side of the locomotive to open bevel gears that drove each set of wheels.

On some of them the gears were cast iron with just the really rough spots on the cast teeth filed off to make them useable. The engineer on a new locomotive would pick up a handful of fine sand and pour onto the gears every few runs until the gear teeth had a smooth mesh.

Gail in NM


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## MachineTom (May 26, 2014)

This past winter I built a friction car for a fellow. He wanted Four Wheel Drive rather than 2wd. I purchase cut spur gears and mocked them up on an AL plate laid out by the calculated  spacing, The string of 14 gears would barely turn, not good for a car that uses a flywheel alone for power. The end result of a half dozen lay out tests was an average of .005" added to the calculated center distance. 

It was a bit noisier than I would have liked but low friction was the goal.


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## gus (May 27, 2014)

When I was a young lad living in an industrial area where wood pattern for very C.I. Gears were made by pattern makers.
These C.I. Gears were used as casted by the foundry. They were for low speed machines such as Steam Rubber Rollers for Calender Presses. The cast gear teeth were not even file smooth. After a week or so in service they ran dead quiet.

Watched the maestros cutting gears on the slotting machine and even shapers. Their manipulation of main/cross slides were so good and gear teeth need minimum filing. 

All these happened in the 1940s and 1950s .By the 60s and 70s they were all gone. Entire machineshop was driven by one 20hp motor and overhead flat belt pulleys.


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## spurgear (Aug 8, 2015)

R/C Cars Steel,Plastic, Nylon 80%-90% engagement


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