How to lap gears - HobbyTalk
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post #1 of 34 (permalink) Old 01-05-2008, 12:24 AM Thread Starter
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Question How to lap gears

Hi there, I'm new to the forum and starting to get into the hobby with my 9 and 11 year old sons, I've noticed it being metioned about lapping the gears in the T-Jet with toothpaste. What exactly is involved in doing this. I honestly looked in the search part but couldn't find anything on how to do it. Thank you very much. Dave
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post #2 of 34 (permalink) Old 01-05-2008, 03:06 AM
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Dave, Everyone has their own method. Using various compounds in conjunction with some form of lubricant.

Brasso/other polishes, Comet/other cleansers, Toothpaste.... whatever.

The jist of which is to make a lubricate slurry of lubricant and mild abrasive, then drizzle it onto the gears, shafts, axles while running at moderate speed. Clean it out and start over if it heats up or binds. Some guys even just dunk the running chassis upside down in a tupperware of slurry so the plate is submerged but the comm doesnt foul. I do both the drizzle and the dunk; as well as the quickee toothpaste trick, just depends on the individual car/setup and what I think I'm trying to prove.

The idea is to allow the abrasive to cut gently and gradually without ruining the motor by either excessive friction or riduculous RPMs. Really the whole deal hinges on decent setup to start with. Proper clearances on shafts and gears are the true starting point. Bound or boogered gears, and warped chassis and tweaked gearplates cant be lapped straight.

THE most important thing is to go easy on your motor so you dont do irreversable winding damage; AND be absolutely scrupulous when cleaning up afterwords.

HO World has a comprehensive tutorial.

Go easy! Be Clean!
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post #3 of 34 (permalink) Old 01-05-2008, 01:08 PM
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Simichrome chrome polish is a favorite of many. mj
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post #4 of 34 (permalink) Old 01-05-2008, 03:50 PM
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I chuck the rear axle into a dremel (make sure it is spinning the gears in the correct direction), pack in the simichrome and fire it up at a low rpm. Make sure to remove the motor brushes, and you don't really need the magnets in either as the dremel does all of the work. I'll repack the gears with simichrome a few times and then when it sounds like it has quieted down, I will finish it up with brasso.

Doing this on top of following Bill's advice on gear clearance will get you a much faster car.
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post #5 of 34 (permalink) Old 01-05-2008, 04:09 PM
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Watch for the "gears" section of Fray car tuning.

The simi-chrome thing is going in the right direction.

Tim
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post #6 of 34 (permalink) Old 01-07-2008, 12:28 PM
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Interesting thread. Shouldn't you run it *backwards* if powering from a dremel on the axle to get the gear tooth faces lapped right?
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post #7 of 34 (permalink) Old 01-07-2008, 01:23 PM
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Like I said in my post....
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Originally Posted by martybauer31
I chuck the rear axle into a dremel (make sure it is spinning the gears in the correct direction)
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post #8 of 34 (permalink) Old 01-07-2008, 02:58 PM
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Quote:
Originally Posted by Franko
Interesting thread. Shouldn't you run it *backwards* if powering from a dremel on the axle to get the gear tooth faces lapped right?
Both directions!...but finish in the forward direction. A smooth backlash makes for a smooth car when your off the juice.
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post #9 of 34 (permalink) Old 01-07-2008, 03:14 PM
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Originally Posted by Bill Hall
Both directions!
Bill do you think that that is true of all HO cars including G3 type cars. thx mj
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post #10 of 34 (permalink) Old 01-07-2008, 03:44 PM
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I run them both ways. For standard TJETS I have a Junk chassis with an extra lon axel. I chuck it up in my reversible drill add the semi chrome or mothers mag polish and let her rip in both directions.. I have a bowl with denatured alcohol that I place the top plate in and run the drill to clean everything up then hit it with some compressed air and I'm ready to go. For slim lines they are a different animal. I have a TJET plastc box lid with to posts epoxied to it so I can place the slim-line chassis in the box upside down and screw it in place. The posts are set to jusl lift the the gear plate off the bottom a hair. I then pour Brasso in the box even with the gear plate the hook up two alligator clips and let the slim-line run fro 10 mins in one direction the 10 mins in the other. When I am in a hurry with a slim-line I will put it on my break-in box and take a plastic cup with Brasso and a paint brush and add a little Brasso at a time to the gear plate.

Roger Corrie
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post #11 of 34 (permalink) Old 01-07-2008, 05:51 PM
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Quote:
Originally Posted by citylights17@ho
Bill do you think that that is true of all HO cars including G3 type cars. thx mj
All things being somewhat relative IMHO; Smooth gear mesh in both load and unload conditions seems like the ticket to me whether its a modern inline or the venerable T-jet monkey motion.

It's just like the ring and pinion in a big car where toothloading patterns are critical. Certainly the forces are smaller in slot cars but no less important. Nowadays in competition the highend guys are fighting for small fractions in lap times. It is truly a marvel from whence we've come.

That being said the common theme seems to be that a smooth car with good throttle input manners trumps a twitchy rocket that is a chore to drive.

The variables car setup are many. Comm pressure, motor magnet strength, down force relative to magnet strength and tire profile, pickup geometry and spring strength. All factors of friction to a simpleton like me. A fine line that can never be drawn in black and white. In other words some stuff works in certain combinations and some stuff just doesnt.

I feel gear mesh is more of a yes or no proposition. It's either right or wrong. As we do spend a certain amount of time off throttle the backlash should be addressed. The total smoothness of a car is a factor of how the geartrain responds in both load and unload condtions providing all the other setup variables are reasonably correct.

Conversly, at some point, too much lap creates a scenario where the tooth contact points actualy slap or hammer against their mate. The tooth geometry is worn to the point that they are clubbing and not meshing smoothly. The clue here is visual to the naked eye, one gear moves excessively before the other engages. A trained ear can hear this on the test pack when other noises are not present.

Some folks consider gear selection tedious but is just a fact of life unless mated sets are purchased. I just keep trying till I get something that feels right and lap from there. No guarantees. I've got a few hundred gears for this and that, both used and new. As I go through the process they are sorted into simple piles - those that are fat/tight - those that are thin/loose - and of course the trash which is tossed immediatly. Ya just never know what's gonna work til ya get there. Cuz I'm old and blind it helps me to use the ole magnifiying glass to spot "tooth decay or irregularities so I dont waste time on a turd gear.

A complete lap provides one less thing to wonder about.
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post #12 of 34 (permalink) Old 01-07-2008, 10:22 PM
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City watch the pitch count on your mag car gears,some are 64 and some are 48,and they don't interchange.
Wizz's are usually 64 and BSRT's are usually 48,not sure what Slottech's are.
You can visually check whether the pinion and crown are going to match up,by meshing the pinions and crowns in your fingers,and looking very closely at the bottom of the teeth,if you can see daylight through the bottom of the teeth,they won't work together,but if you can't see any daylight through the teeth,then it's a worthwhile test.
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post #13 of 34 (permalink) Old 01-07-2008, 11:09 PM
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Quote:
Originally Posted by Hornet
City watch the pitch count
Thanks for that Hornet. One more nugget, so much to learn. I'm having better success with my gearing. As Bill said sometimes i have to try a few to find the two that mesh the best. Then lap them. mj
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post #14 of 34 (permalink) Old 01-08-2008, 12:42 AM
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Quote:
Originally Posted by vaBcHRog
...snip... When I am in a hurry with a slim-line I will put it on my break-in box and take a plastic cup with Brasso and a paint brush and add a little Brasso at a time to the gear plate.

Roger Corrie
Hey Roger, How about a pic of this contraption...something ya made?
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post #15 of 34 (permalink) Old 01-08-2008, 01:08 AM
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Tom Bowman's article has some great pics of a gear lapping rig.

http://www.bat-jet.com/webspot/fraycar06.html

By the way, Tom's article is an excellent How-To reference for building up a competitive Fray ready racer. Great advice from a great source. His Fray compatible resin bodies are second to none too. Highly recommended.
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