Lapping TJet Gears - HobbyTalk
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post #1 of 22 (permalink) Old 09-06-2013, 05:06 PM Thread Starter
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Lapping TJet Gears

What does everone use to lapp the gear train on a Tjet? I use permatex lapping compound. I have seen some people use tooth paste etc.
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post #2 of 22 (permalink) Old 09-06-2013, 05:19 PM
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I have tried Novus #2 and a 50/50 mix of Brasso and Break Free gun oil. Both work pretty well.

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post #3 of 22 (permalink) Old 09-06-2013, 05:32 PM
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someone gave me valve lapping abrasive once (I'm not gonna mention Sgrig's name) without any advice.
I smoothed out a complete set of gears quickly. yes, no teeth left on any of them. so, you want something a tad LESS abrasive than THAT
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post #4 of 22 (permalink) Old 09-06-2013, 05:39 PM
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post #5 of 22 (permalink) Old 09-06-2013, 06:51 PM
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SemiChrome & Transmission fluid, less of the 1st, more of the 2nd

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post #6 of 22 (permalink) Old 09-06-2013, 07:34 PM
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They're really just an inefficient lil vacuum cleaner

Something around 400 and 800 grit and a lubricant that trips your trigger...give er take.

Everyones got their own voodoo formula. I prefer the the squeezens from a ripe banana and some comet; but the banana must be picked in Havana during the full moon or your results may vary.

400 to 800 is roughly around the size of all the crud and corruption the gear train normally eats over time. The idea is to simulate in short fashion, a gear set that has been well broken in over time. Under magnification, my observation has always been that T-jets are dirty nasting tar burning beasties. You can polish it to perfection but everything returns to it's naturally scuffed state after some use. I'm not trying to make light of a top five in the fundamental build process, but the idea is to hone in the optimum running clearance with a minimum amount of fan fare and call it good. Most especially after you've scrambled up gear sets. Extra drama time is better spent on selecting good gears in the first place or better yet, pick up shoe voodoo. Lapping should be a one and done process.

LOL @ Al...I'm sure Jim is just expiditing the process in his own way by using ashtray sand, obviously some stuff cuts quicker than others and for the inexperienced is best to sneak up on the process and learn the intricasys . It's been proven time and time again that there is more than one path. I just snip up some small squares of 600 wet and dry carefully polish the top and bottom gear sides on a running gear set with synthetic motor oil. The freed abrasive mixes with the oil and creates the exact slurry we require. I just use an old Aurora tranny and press the contacts against the screws with the chassis front tilted downwards so the spent slurry drools out neatly to the front of the gear plate. Once I hear that the "no go" point is achieved, I spritz the chassis with electrical parts cleaner, then blow it off, and re-lube.

In most cases there's no need for the insanity lappings. No sloppy prolonged immersions in tubs of secret potions, or slathering the contents tubes of high dollar goo and flinging it on yer shirt. Papering the gear set properly cures a multitude of ills. For the special builds, your chosen rouge goes any where 600 paper cant by applying it with the model murdering specialty application tool part # 0001 (aka der toothpick).

Enough lapping is just right, and too much is called excessive wear. Simply put it's and ear thing and the process itself must be developed to suit yourself and your own bench/needs.

Last edited by Bill Hall; 09-06-2013 at 10:17 PM.
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post #7 of 22 (permalink) Old 09-06-2013, 09:17 PM
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While we're on the subject of reducing friction, has anybody tried filing down the gears? See idler gear in photo below. I saw this idea in an old issue of Model Car Science, the theory being the less gear there is to mesh, the less the friction produced, so I tried it. All I did was lay a file on the workbench, and slide the gear back and forth until it was about half the thickness. I wish I could say it allowed me to run amazingly faster, or the motor ran way cooler, but I don't have any way to objectively test, and didn't see any obvious differences. Has anyone else tried this?

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post #8 of 22 (permalink) Old 09-06-2013, 09:45 PM
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From the standpoint of less tooth contact friction, your idea is sound. It will, however, make the idler gear less stable due to reducing the contact area at the post. The net effect will at best cancel out. A wobbling or loose idler is a huge power drain. Most rules (if you race under them) do not allow that kind of treatment anyway.

+1 on Simichrome
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post #9 of 22 (permalink) Old 09-06-2013, 09:49 PM
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I have not tried that, but I did try beveling the teeth of the gear to reduce the friction against the other two gears. I would love to say that it worked great, but in the process I opened up the center hole so badly that now all I have is sloppy beveled gears! Live and learn.

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post #10 of 22 (permalink) Old 09-06-2013, 10:02 PM
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I do it the easy way RT-HO gears, just put them in. No lapping needed.

Slow Ed
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post #11 of 22 (permalink) Old 09-06-2013, 10:16 PM
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I started off using crest tarter control toothpaste
hook a dremel to the axle and spin backwards.

I then decided to make my own cutting oil.
I ground polishing compound (polishing sticks from lowes) into marvel mystery oil. I have a chassis that i put the gear plate on flip it upside down into the mix and lap the gears in.

works very well

what surprise me was the 1st time i did it, the mix was to high and it came shooting up though the brush holes and did not miss a beat
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post #12 of 22 (permalink) Old 09-06-2013, 10:23 PM Thread Starter
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Laping T-jet gears

I use an ameter in series and measure the current, that way you can see when the load meaning the amps decrease you are reducing the friction.
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post #13 of 22 (permalink) Old 09-07-2013, 02:04 PM
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I have to agree with Ed,rtho and go!
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post #14 of 22 (permalink) Old 09-07-2013, 02:28 PM
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I like those too, but for those on a budget lapping may be worth a shot.
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post #15 of 22 (permalink) Old 09-07-2013, 10:00 PM
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the rtho gears are great.

but knowing how to lap gears can not hurt
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