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Koford crown gear question


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#1 Tex

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Posted 19 October 2017 - 09:43 AM

I ws looking at the Koford gears on the PCH website. There are two different 28-tooth crown gears for 3/32 axles, KOF-M668-28 and KOF-M671-28. Are there truly two different gears or is there a typo? If there ARE truly two different gears, what's the difference between the two? Thanks in advance.


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#2 Gator Bob

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Posted 19 October 2017 - 09:50 AM

IIRC, the 671 is a cut-down/lightened version of 668.


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#3 MSwiss

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Posted 19 October 2017 - 10:00 AM

Yes.

M668-28 came out and it was pointed out the back side, with its sharp 90 degree corner, created a clearance issue with some chassis with a brace/weight between the uprights.

Stu came up with a lightened version, notching out that back side, for plenty of clearance.


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#4 Tex

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Posted 19 October 2017 - 11:47 AM

Since there was no mention of it, I assume there was no similar clearance issue with the 27-tooth(?)...


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#5 MSwiss

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Posted 19 October 2017 - 11:52 AM

He never bothered to make a "heavier" version of the 27t.

 

I'm also pretty sure he will discontinue M668-28 once he uses up his stock.


Mike Swiss
 
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#6 MSwiss

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Posted 19 October 2017 - 12:30 PM

Tex,

 

If you haven't run the Koford gears before, unless you run a flatted axle, don't even consider using the set screw that comes with it.


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Mike Swiss
 
IRRA® Components Committee Chairman
Five-time USRA National Champion (two G7, one G27, two G7 Senior)
Two-time G7 World Champion (1988, 1990)
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Note: Send all USPS packages and mail to: 5858 Chase Ave., Downers Grove, IL 60516
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#7 JoB

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Posted 23 October 2017 - 02:30 AM

So what’s the problem with the original set screw?
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#8 MSwiss

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Posted 23 October 2017 - 06:28 AM

They don't grab well on a rounded surface.
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Mike Swiss
 
IRRA® Components Committee Chairman
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Two-time G7 World Champion (1988, 1990)
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mikeswiss86@hotmail.com (also my PayPal address) 
Note: Send all USPS packages and mail to: 5858 Chase Ave., Downers Grove, IL 60516
Make checks out to Chicagoland Woodworking, Inc.


#9 gotboostedvr6

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Posted 23 October 2017 - 07:22 AM

Mike,

Over the years I've found that removing the machining on the bottom of every set screw does wonders for both increasing thread engagement and improving the gears grip on the axle.

I use a Dremel and a diamond cut-off disk spinning at low speed. Mount the set screw on my wrench and on a slight angle grind the bottom of the set screw off leaving a very small taper.

Try it.


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#10 Cheater

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Posted 23 October 2017 - 08:04 AM

Ray Gardner used to rage about hollow set screws, claiming he'd lost an untold number of races because of them. He'd always switch them out for solid bottom set screws and I followed his example in my racing, with a noticeable lack of problems with them slipping or loosening if I had tightened them sufficiently to start with.

 

And Ralph Thorne Racing sell a quality set screw with a knurled tip, although I have never used them.


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#11 boxerdog

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Posted 23 October 2017 - 09:55 AM

I never had many set screw issues until the last few years, then I had several. So I dug around in previous threads and elsewhere and learned that there are important differences in thread shape and quality ( a magnifying glass confirms this), there are many styles af cup and knurled tips available, and there are still some USA manufacturers. So, here is a resource:
 
Set Screws
 
So you have options. Personally I like the knurled type.
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#12 kvanpelt

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Posted 23 October 2017 - 11:17 AM

Ralph's screws are the best!



#13 Gator Bob

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Posted 23 October 2017 - 11:58 AM

There is another style not seen too often. **

 

Oh no...

 

 

In the early 70s I worked for a cutting edge medical electronics start-up.

The company name was IREX and we got bought up by Johnson & Johnson in 1976. The product was the first thermal printed EKG/EEG chart recorder to come to market. 

It used Globe motors and in-house designed right angle bevel gear drive units. I started work there doing the chassis assembly and harnesses.

The guy building the motor drives was a seasoned aeronautical/aerospace assembler retired from Curtis-Wright. I watched him build those up and put them on the break-in rack thinking 'I can build those'. One of the other young guys (20 yr old) gave him the nick name 'old man'. I remember he drove a 1964 Fury.

Anyway I said to him one day "hey old man, I could build those motor drives". He laughed ' no way" and probably called me a long hair punk or some such. By then ...I wasn't kidding. 

 

The other kid (can't remember his name right now) would take a random hand full of screws or nuts (only the best SS hardware) and throw them and yell "look out old man, incoming!" He was a character, had a birth defect and always walked with a cane. He could actually run pretty fast when the old man would chase him around.

 

So... after a few months 2 out of 5 motor drives were creating 'jitter' on the chart paper as it was feed through the printer and over the heater plate.  I saw the opening and was Mopar buddies with the head of QC who was taking all the heat for machines not going out the door. John Tostio, car guy, I helped him get his 383 Cuda back on the road. I told him to 'chunk' that motor, he put a sleeve in it.... with regrets

"Hey 'Tosi-spoumonte' (a nick name I gave him) why don't you go tell Serchio (COO) that I can fix those 'jitter boxes'. He did and I did. Machines went out the back door and big money came in the front.  Me .. the second lowest man on the company 'totem pole' saved the little start-up company from a serious cash flow problem.

I get called to 'The Front Office' by my direct boss to go see Serchio and on the way get directed to the Owner's office. Wow, he only was seen about once or twice a month.

 

Picture this, a long haired 19 year old stoned punk in jeans, boots and a T shirt sits down with the two biggest 'suits' in the place to get 'praised'. Then walked me through the whole building to meet every one of the 40 or so employees. "This is our motor new drive guy".

Serchio said he would take me up in his P51 which he loved more than anything. That never happened.... they hit it big and J&J bought them out for millions. He left the company and so did I.

That is where and when My Career truly began. It helped give me confidence to go kick some...on the way up. 

 

OK !  What does this have to do with this thread. Why did you waste all that time writing that stuff?

 

The answer is - Locking set screws.

And ..

I could never have done those motor drives if I did not (try to) build slot cars as a kid.

 

BTW: the company was right across Rt.17 from where Grand Prix Raceway/Hi-Way Hobby was in Upper Saddle River NJ. The first place I ever saw a commercial slot track.

------

** on the motor drives we used set screws with nylon locking inserts that were in the threaded side.


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#14 Mike Patterson

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Posted 23 October 2017 - 09:41 PM

Great story, Bob! Thanks for sharing.


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#15 Gator Bob

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Posted 23 October 2017 - 11:39 PM

Thanks Mike, It was fun to recall, write and share.

 

So here is the secret I used to get those drive units broken in and run smooooooth as ...

Guess where I learned it... yup. Slot cars, 1/32nd Atlas cars to be exact, you know the ones with 'beveled' gears.

 

It was all 1/4" shaft stuff, beveled gears, oilite bushings,thrust washers and precision shims in a custom billet alum square right angle drive box that mounted to the motor. Geared 1:1.  

One of the chassis mounted 1/4" idler platens used the same bushings and thrust washers but instead of shims it had a spring steel Wave Washer between two thrust washers.

So... when I 'get the call' I proudly wheel the worst of the problem completed units to my new workstation next to 'the old man' and promptly disassemble it and remove the drive.  

Gear box comes apart, wash out the lube, check the bushing alignment. Go to the stock room to see Charley, sign out a new gear set, roll pins,shims, thrust bushings and some of those Wave Washers. 

I reassembled the unit using a wave washer on both shafts which kept the beveled gears in a constant slight pressure setting. Slapped some of the old mans gear lapping compound on the gear faces, spun it in my hand thinking... I sure hope this works. Closed it up, mounted it to the motor and locked down the set screw. Here we go... power on. Mhmmm, sounds 'rough' but it stays on anyway. The old man comes over, hears it ... I here it too, him bustin' on me about the all racket.  LOL

I go to lunch, tune up and return ... I picked it up and "Wow, It's HOT" ... I thought it was wasted...no that was me. Disassemble, flush, flush again, reassemble with care, new thrust washers less the wave washers and the mesh shimmed to as perfect as I could get it. Run in again, check play, reinstall in chassis and send it off to inspection for retesting. A small number gathered for the initial test. Runs perfect but the real results are after they do another 'burn in' and let it run overnight. Never another jitter line and out the door it went... it was weeks late to the hospital.


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#16 NSwanberg

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Posted 24 October 2017 - 02:58 AM

See above for what our youth are missing. :(


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