# Idea for "lapping" plastic gears



## smalltime

Lately I've been building cars based on the A.W. T-jet chassis. These cars are fun and easy to build, as well as being cheap. Less than $35.00 for a Fray style car that can beat a full up Fray car.

The problem is the geartrains.
I need to go thru so many gears to get the combo that works, I've been racking my brain trying to find a way to get these geartrains smooth.

Well tonight I'm going to back to old school.

One of the first articles I read on T-jet hop ups was a tip on getting the brushes run in. This was the one where you drop the whole chassis into water while it's running.

Well I'm goin' one better. I think if I use boiling water, it will get the geartrain smoothed out.

I'll keep you posted.........


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## clydeomite

Howdy: I have had good luck with the Jl/AW gear trains by using Brasso it is liquid and really smoothes them out. After you lap them try using a bit of "Armor-All" for a lubricant . You might be surprised how well this works. Just dont get it inside the motor or you will need to clean everything out and dry it off.
Clyde-0-Mite


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## noddaz

*I toss the plastic gears*

right into the parts box. (For later use. Right...)

And I install brass gears from the parts box.

Of course RTHO has Delrin gears but that would almost double the money involved in the chassis... And I think that is the whole point here.
To keep it cheap.

Hey, instead of boiling the whole chassis, how about a heat gun strategically aimed at the gear plate while the chassis was running?
Scott


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## smalltime

I treid the heat gun thing, it's way too hard to controll the placement of the heat. You end up with a warped plate.

The brasso thing sounds good, but I've never gotten ANY lapping compound to do anything to plastic.


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## clydeomite

Howdy: The trick with the Armor all is not to saturate the gear plate with it. I warped a plate trying to saok it in but had good results applying a little after lapping with brasso. You could use tooth paste also or Semi chrome- massa etc. cremes the work well also.
Clyde-0-Mite


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## smalltime

I have tried everything to lap plastic. No joy.

I have lubricated with silicone based lubes for years. They do work very well on plastic.


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## Illinislotfan

Have you ever tried the polishes like Bill uses to restore the shine to the tjets he restores? I never have myself, just wondering if it might do the trick.


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## Bill Hall

The polishes work great on brass gears...

...but I use toothpaste on plastic gears with GREAT results.


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## neorules

Put the whole car into a solution of water and simichrome--- dont keep it in longer than 30-40 seconds because you could wear the brushes more than you'd like. I do this with some boxstocks to smooth them out.


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## Pete McKay

I've boiled both AW and NOS cars, you don't want to boil them without them being on a jig like the one RT-HO offers or they will warp. I warped two good cars figuring that out. Second, while lapping stock gears is a great idea get yourself a set of the delrin gears and they're already lapped, camfered and about .2 of a gram lighter than the stock gears with the new cluster shaft. Yeah, as Noddaz said it's more expensive but IMHO worth it. And I also agree with the silicone based lube, can't beat it with a stick.


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## bearsox

*Soak plastic gears in lighter fluid then light em up as you take laps ! Let the wind blow out the flames and voila ! Ok so if it don't work ..... it looks cool as hell !!! 

Bear :freak::wave:*


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## rodstrguy

I use a little Comet Cleanser mixed with water to a paste. works better than gritty tooth paste and is easy to rinse off. I am going to try the Armor all trick though, sounds easy and like a good idea...


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## smalltime

bearsox said:


> *Soak plastic gears in lighter fluid then light em up as you take laps ! Let the wind blow out the flames and voila ! Ok so if it don't work ..... it looks cool as hell !!!
> 
> Bear :freak::wave:*


THATS what I was lookin' for!
Thanks Dennis


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## noddaz

*please...*



bearsox said:


> *Soak plastic gears in lighter fluid then light em up as you take laps ! Let the wind blow out the flames and voila ! Ok so if it don't work ..... it looks cool as hell !!! *
> 
> *Bear :freak::wave:*


Please post pictures when you do this!


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## bearsox

noddaz said:


> Please post pictures when you do this!


*Got to close with the 1st pic and camera melted ! So..... hope it's ok if i draw pics instead .

Bear :wave:*


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## slotcarman12078

Why would you want to lap plastic gears anyway??? They taste awful!!! The brass ones are sooooo much tastier!! :tongue:


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## joegri

today i tried rodstrguys cocktail of brasso and comet. i did just fine on brass thanx for that. as for the plastic well they taste awful with comet. yuck !


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## noddaz

*Hmmm*



smalltime said:


> I treid the heat gun thing, it's way too hard to controll the placement of the heat. You end up with a warped plate.
> 
> The brasso thing sounds good, but I've never gotten ANY lapping compound to do anything to plastic.


make a metal mock up plate to heat the gears to lap them... :freak:


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## bearsox

*Chassis set at mild idle on breakin box. Take soldering iron approx 1/16th in above idler gear teeth. Look for appearance change in gear and noise change . Once either or both occur remove heat and let chassis continue to run . After another minute or so chassis and gear should be cool enough and lapped in. One may also go so far as to think this could work on the crown too . Sounds good ? Ahh but then i could be just over medicated again and this is all just my gears not meshing in my head LOL . 

Bear :wave:*


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## smalltime

Back in the day, the hot trick was to use a cigarette next to a running crown gear.


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## bearsox

smalltime said:


> Back in the day, the hot trick was to use a cigarette next to a running crown gear.


I tried the butane mini torch as well but it's hit or miss as it's less focused on the crown and too hot too quick even when run parallel just under crown. You can however do some interesting things to axles holes IF you remove tires and run chassis on box then heat up axles momentarily then remove heat and run in.

Bear :wave:


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## Bill Hall

*Flavor of the month for normal Joes*



rodstrguy said:


> I use a little Comet Cleanser mixed with water to a paste. works better than gritty tooth paste and is easy to rinse off. I am going to try the Armor all trick though, sounds easy and like a good idea...


I cant wait to try the Armorall...what a no brainer!!!! I've used cleanser with reasonably good success. Lets keep in mind that not all toothpaste is gritty...AND that the right grit is really what we are after no matter what it is suspended or carried in. It is a ROUGE.

First thing you have to determine is where you are at. Are we just tight? Do we have damage? Out of round? Axis problems?

Just because the gear set is factory doesnt mean it's good...or bad...it may be somewhere in between. The worst scenario is the parts box hodge podge where a random selection can bind you up worse than processed cheese.

Also keep in mind that much like commutator plates the type of crud that spins through during normal operation eventually averages out to about 600 to 800 grit anyway. Ridiculously retentive polishing is generally a waste of time and materials; AND at the extreme can be detrimental... AKA premature wearing out of tolerances. Regardless of a see yourself shine on the tooth surface after a few hours of run time the finish will be fuzzed back to it's blurry old self 

The point is that at some point you dont get no more no matter how much you lap, lather, rinse or repeat.

Choose yer flavor of the month, hog it on and buzz the chassis up carefully. When it starts to bog or grunt add some lubricant and let it eat until the R's pick up or you need more lubricant and rouge. THEN while it's all nice and soupy; change your direction and do the backlash side of things...because?...gear teeth have two sides!...and you want yer decelleration to be as smooth as yer acceration. At the point that the R's no longer climb and yer gear set has quieted down yer done. Hose it down, scrub it out, blow it off and re-lube it. 

Also noteable, worn out brass sets will clatter like a scrap truck, and no amount of lapping will put yer tolerances back.


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## slotnewbie69

quoting dr hall.

When it starts to bog or grunt add some lubricant and let it eat until the R's pick up or you need more lubricant and rouge. THEN while it's all nice and soupy; change your direction and do the backlash side of things...because?...gear teeth have two sides!...and you want yer decelleration to be as smooth as yer acceration. At the point that the R's no longer climb and yer gear set has quieted down yer done. Hose it down, scrub it out, blow it off and re-lube it. 

Also noteable, worn out brass sets will clatter like a scrap truck, and no amount of lapping will put yer tolerances back.[/QUOTE]

great point Bill about two sided teeth!and the smooth decelleration thing!i will go one step further and lap em in properly,as i only go so far as to wire brush em with my dremel!never thought about reversing direction,but i probably did unwittingly due to the no finesse factor of dremels...food for thought


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## shocker36

Try this stuff called Plastic Polish most lhs should have it also try they stuff they are using to polish the haze out of headlights on cars.


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## T-Jet Racer

I have used dupont polishing compound with a few drips of water works great!


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## bkreaume

I going to try my hand at lapping my cars for the first time. I have a few questions.

1. how long do you Lap them for?
2. do you place the chassis upside down in the solution?
3. do you do a break in period before or after the lapping?

thanks guys.


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## Bill Hall

Yes, 

Ideally you'll want the basics done before you begin lapping. First I like to take the magnets, brushes, and idler out and "feel" my way through the drive train. By also omitting the idler gear you can check the rear end for excessive friction or weirdities; then quickly drop it back in to check if the addition of the remaining components upsets the apple cart. Magnet whacking, armature binding and brush snagging are other obvious problems to be corrected first.

I have different approaches for different build scenarios. 

Stage one: If the chassis is just a stocker and the gear plate is not to be disassembled: Using plenty of oil, and re-oiling as I go, I slip a piece of 600 CAREFULLY under the edge of the driven and armature gears and let it eat until the rpms come up. Then fold the paper up to stiffen it a bit and do the top of the idler as well. Then do the topside of the driven and armature gear and flip the idler over and do it as well. 

When you have the idler in hand I like to pull a piece of 1200 through the center bore. A snip of 1200 is trimmed and rolled in yer palms to make a small roll. I pull it carefully throught the center bore just so's to clean the bore, but not ream it out excessively. It doesnt take much to make a HUGE difference.

I find it best to do this on an old Aurora set transformer with the back wheels up and the pick ups mashed directly against the transformer power screws....this allows all the "gooz" to run out from underneath towards the front edge of the gearplate. I keep a q-tip on hand to mop the excess slop that you WILL have... if your doing it right! Once you get this trick down it barely takes two minutes to get the kinks out. Of course a thorough cleaning afterwords is a must.

Stage two: Pretty much the same as above EXCEPT that the plate is dis-assembled and the gears are in hand first. All the gears are carefully faced on a flat glass and 600 paper then carefully burnished using a wire wheel in the dremel. DONT forget yer eye protection. Once you've brushed your teeth, everything is carefully pressed together. I try to take up any excessive play at that time...if possible. Once it's assembled, I use the sandpaper trick to quickly take any other snaggles out. At this point you can choose your grit/rouge of choice and lap away. I like to go in both directions.

I also like to do the crown and pinion mesh, the rear axle holes. They are the often FORGOTTEN areas! You can buzz the crown gear ever so gently with the wire wheel before lapping...but it takes a very light touch.

While it can be done using stone knives and bearskins, stage two kinda requires the use of gear pullers and presses. Beating stuff back together sorta defeats the purpose of the precision assembly process. 

I've used the exotic immersion slurry baths as well... which is absolutely great and has some advatages; but if your looking for quick down and dirty and back on the track...stage one is the ticket.


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## bkreaume

Bill,

Thanks for the detailed explanation. 

Are you saying you use the wire wheel on the plastic gears? I can see me eating those away in a hurry.


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## Bill Hall

After you've done a few brass sets....you'll acquire a feel for doing a plastic one. Helps if you push an axle partially into it ...as this will give you improved control and confidence. 

Just the slightest touch will do it....ever so lightly...with the teeth ....through the root...not across the tooth.

...no reason you couldnt pratice on a fubar one to get yer feet wet!


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