Dimple that shaft!

Urban Fatbiker

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There's a hole in my Buzzbike 100 mile thread, where I said I'd be back tomorrow, came back over a week later?

I didn't want the continuity of that thread wrecked by my dumbassedry.
Ok I've built ONE mb....not counting the etrikes.
But I've dimpled hundreds of shafts, sent back dozens to machinists over a LONG career, so yes, I Am A Dumbass.

Let's make that worse won't we? Yeah I've built ONE m/b...but I assembled, installed, programmed, ADVISED, reviewed, at least 10 robotic workcells...huge industrial tube forming machines...making everything from handlebars to exhaust to frames of almost every m/b, atv, golf cart, bicycle, thats made here...or brazil...or mx.
Never owned a Honda or a Yamaha. But I've been in their facilities from Marysville to Manaus to Hammamatsu.

Someone might think I'm a real dumbass, I should have a Goldwing and a Razor as my rides, but I was into cars. I did get employee discounts on Holley carb, and threw a set of headers into their chroming process when I was in Aberdeen for a week.
I preferred Manaus. Jus saying.
But I ramble.
Back to the point, that should have veen seated in a dimple.

I did ride that day, after putting the 21T gear on my jackshaft. I used thread lock. But no dimples.
After 10 miles, R side chain came off. When I looked, I saw 9T sprocket and bearing almost out of bracket, entire shaft slid right.
20220301_210128.jpg

At least I was a dumbass with tools.

When I got my new shaft and bearings a few days later, I mounted and aligned everything, marked, took apart.

A 5mm punch fits great in the 1/4" set screw hole. Punch using sprocket as guide, remove. Use small bit to start dimple, just enough to seat next bit 1/4".
Drill ONLY to countersink, less than bit diameter, but slightly larger than cup point of set screw.

Reassemble.
Using non-dumbass tech, please.
I added a shim and lock collar to LH side too.

Get longer set screws for the larger sprocket, and put a few in your tool bag.

Note on shaft:
I saw many grumbles about SBP shaft under tolerance, and this one seemed also.
But shaft I got from McMaster-Carr was identical and both seemed 0.0025 undersize.
I used some punch strikes in bearing area. Lots of threadlocker, and I clamped sprocket to bracket when tightening set screws.

As Murphy stalks me, I'm already considering a hi-tolerance shaft, but I have to buy a long length, and it ain't cheap.
I won't dare rag on SBP. Pricing some of this stuff, yeah they could make a hi-tolerance kit, better bearings, etc...and it'd be way too expensive.

Damn if only I'd got into m/b years ago. Back when I spent all my working time inside places that made Yamahas and Hondas...somewhere in Brazil peeps are riding pretty yamahas with chrome handlebars bent on a robotic workcell I programmed and installed with many many cups of what they call coffee, we call kick ass double expresso kind of shizz.
And those nuts at Pro Circuit, just listening to their motocross stories at lunch, I coulda used more than shirts as sovieniers.
😇
 

Urban Fatbiker

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Have I ever seen a situation where set screws in a sprocket weren’t seated properly, and caused a problem with a motorbike?
Kinda.

Sprocket set screw on feed axis of 45mm forming workcell wiggled loose, making it bounce and hammer key under load. Enough play to introduce 2mm forming error in bottom rails of Bronco ATV, and wouldn’t fit the welding fixture.
Lots of scrap.
They called of course.
Spent a day rebuilding shaft.
With dimples.
Dammit I’ve done this before.
 

Chainlube

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You're pretty good at messing up a jack shaft. When you know where the set screw is going to land, file a flat spot on the shaft just for that purpose. Dimples work, but if you ever need to take apart again it's difficult. With a little flat spot the sprockets slide right off.
 

Karl Snarl

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You're pretty good at messing up a jack shaft. When you know where the set screw is going to land, file a flat spot on the shaft just for that purpose. Dimples work, but if you ever need to take apart again it's difficult. With a little flat spot the sprockets slide right off.
If you weld the sprockets on, you never have to worry about taking them off.
 

Karl Snarl

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If I use that kind of setup, it's because I plan on driving it real hard. If it blows up, then I can quickly change it over.
I figure if you have to cut the shaft, it's because you are changing the sprockets. A piece of 5/8th smooth rod isn't very much. An at the same time, swap the bearings out, and you're good to go for another long spell.
 

Urban Fatbiker

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Double set screws too, usually there's enough room for 2.
Yes.
I can’t on the 9T, but definitely on the 21T, it gets two.
That’s something else I was radical about when paid for it...but a slacker on enforcing on my shed build. Rotating shafts with collets got deep dimples, bronze inserts, compressed with double set screws.
Several machines shipped w/o doubles. That was a disaster for months.

I did disassemble shaft a week later when I blew the wrist pin circlip. Drilled concave dimples do not impede sprocket removal, as long as cup point of set screw is seating inside dimple.

However....it was bearings locking up that forced shaft loose, not just a loose screw.
100 miles, crapped out.
Hoping new PGN bearings last longer.
 

Karl Snarl

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Yes.
I can’t on the 9T, but definitely on the 21T, it gets two.
That’s something else I was radical about when paid for it...but a slacker on enforcing on my shed build. Rotating shafts with collets got deep dimples, bronze inserts, compressed with double set screws.
Several machines shipped w/o doubles. That was a disaster for months.

I did disassemble shaft a week later when I blew the wrist pin circlip. Drilled concave dimples do not impede sprocket removal, as long as cup point of set screw is seating inside dimple.

However....it was bearings locking up that forced shaft loose, not just a loose screw.
100 miles, crapped out.
Hoping new PGN bearings last longer.
I use the PGN bearings, they lasted long time so far. An for a good price. I'm actually impressed with the 3-4 years they been going. I'm pretty hard on my bikes. I do clean them out if I go boggin, and then relube. No crunchy yet, no play. Few thousand miles on 'em. I haven't even had to get into the 12 I bought as back ups. I don't even know where I put them it's been so long. lol
 
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