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Open Roads Forum  >  Tech Issues

 > Can I put a sprocket made for a keyed shaft on a D bore?

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Naio

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Posted: 12/19/19 11:02pm Link  |  Quote  |  Print  |  Notify Moderator

This is for my shave ice machine.

I overheated my motor and need to send it to a shop for rebuilding. I have available a possible temporary replacement motor. But my main motor has a keyed shaft, and the replacement has a D shaped shaft.

I talked to the people at the local sprocket shop where I am, and they said they thought I could use my keyed sprocket on the D shaped shaft. They suggested just tightening the set screw real well on the flat part of the D, and maybe even using a drill to make a dimple there.

The machine requires quite a bit of power and torque. When I used a 100 amp fuse I sometimes blew it. I now have a 200 amp circuit breaker which I have never blown.

I guess the worst case scenario is that the set screw would score the shaft of the temporary motor? Could anything else go wrong?

The drive sprocket is small and off the shelf. But the larger sprocket that the chain turns is new, aluminum, custom-made, and there's no way I'm ever going to get another one. Would I be endangering it in any way?

Here are some pictures, not of my equipment specifically, but of a sprocket that goes on a keyed shaft, and a one that goes on a D-shaped shaft, in case people are wondering what the heck I am talking about :-)

https://www.amazon.com/Yerf-Dog-Jackshaft-Sprocket-Tooth/dp/B01MSYOY2G

http://tncscooters.com/index.php?route=product/product&product_id=461


3/4 timing in a DIY van conversion. Backroads, mountains, boondocking, sometimes big cities for a change of pace.


pianotuna

Regina, SK, Canada

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Posted: 12/20/19 05:18am Link  |  Quote  |  Print  |  Notify Moderator

Hi Naio,

I'd consider having a 3 d scan made of that sprocket so that if it ever fails, it could be 3 d printed.

As to the D shaft I can not offer advice.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

K Charles

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Posted: 12/20/19 06:27am Link  |  Quote  |  Print  |  Notify Moderator

"I guess the worst case scenario is that the set screw would score the shaft of the temporary motor?" I think that is your answer. Drill a small hole for the setscrew, but not on the flat spot on the shaft.

* This post was edited 12/20/19 06:34am by K Charles *





Acampingwewillgo

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Posted: 12/20/19 09:01am Link  |  Quote  |  Print  |  Notify Moderator

I'd check with "Spacely" to see if the proper sprocket is available. Say Hi to George,Jane, Judy, Elroy and Astro while waiting for your sprocket!!!

Sorry, I couldn't help myself when I read "sprocket".

Merry Christmas all!!! OK, Happy Holidays too.????


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RLS7201

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Posted: 12/20/19 09:02am Link  |  Quote  |  Print  |  Notify Moderator

I cringe when I see only one set screw on a sprocket. Drill and tap for a second set screw and you'll be fine. The dimple is a great idea.

Richard


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ksg5000

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Posted: 12/20/19 09:37am Link  |  Quote  |  Print  |  Notify Moderator

Naio wrote:



I talked to the people at the local sprocket shop where I am, and they said they thought I could use my keyed sprocket on the D shaped shaft. They suggested just tightening the set screw real well on the flat part of the D, and maybe even using a drill to make a dimple there.



I did something similar on my tractor - like you I figured that there wasn't much downside. Worked for a month or so which was long enough for the correct parts to arrive.


Kevin

schlep1967

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Posted: 12/20/19 10:11am Link  |  Quote  |  Print  |  Notify Moderator

Naio wrote:


The machine requires quite a bit of power and torque. When I used a 100 amp fuse I sometimes blew it. I now have a 200 amp circuit breaker which I have never blown.

For some reason this bothers me more than anything you might do to make your sprocket work.

Did you happen to upgrade the wire when you "upgraded" the fuse?


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pigman1

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Posted: 12/20/19 10:29am Link  |  Quote  |  Print  |  Notify Moderator

Are you trying to keep the D shaft on the temporary motor untouched? If NOT, I'd have a machine shop cut a keyway in that temporary motor shaft opposite the D flat. Then have them make a piece that would fill the open D area where the temporary shaft and the sprocket come together. Finally, a dimple on the insert piece that your set screw would mate into.

If you don't want to cut a keyway in the temporary motor shaft, a keyway could be cut into the piece you have made to fill the D area. Depending on how thick that piece is, the D piece may split at the keyway when high motor torque is supplied, but even if it cracked, it should stay in place if you make the fill piece to tight tolerances. If you use this solution I'd make it so tight I had to drive the key and the D shaped fill in piece on to the shaft. A snug interference fit.

My choice would be the first case. If you had to use the temp motor shaft for a matching sprocket, an open keyway opposite the D flat wouldn't cause any problems.


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opnspaces

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Posted: 12/20/19 10:30am Link  |  Quote  |  Print  |  Notify Moderator

Well it depends. Which sprocket has the set screw and key? Is it the easily replaceable one or the one that's hard to come by? Next question is how tightly does the sprocket fit on the shaft?

If the sprocket in question is the easily replaceable one. And the fit of the shaft is SNUG. I would go with just a set screw to the flat of the shaft.

If the sprocket in question is the easily replaceable one. And the fit of the shaft is loose but less than 4 thousandths of an inch loose(.004 is about the thickness of standard 20 lb printer paper). I would just set screw to the flat side of the shaft.

If the sprocket in question is the easily replaceable one. And the fit of the shaft is loose like MORE than 4 thousandths of an inch loose(.004 is about the thickness of standard 20 lb printer paper. Then I would drill a small dimple opposite the flat part of the shaft. If no drill, you could even just file the shaft a bit flat, but not anywhere near as flat as the other side, just a little flat. Then carefully and tightly wrap the shaft very smoothly with aluminum foil until it's about .004 loose, and scotch tape to hold it from unraveling until you can gently slide the sprocket on.

If the sprocket in question is NOT the easily replaceable one. I would only do the set screw to the flat of the shaft. And only of the fit is snug as in you can feel it dragging the sides of the hole when you press it on the shaft. Anything else and I would probably not mess with it until you get the motor repaired.


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fj12ryder

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Posted: 12/20/19 10:45am Link  |  Quote  |  Print  |  Notify Moderator

Depending on long the "temporary" motor has to be in operation, a set screw into the flat on the shaft will work fine. Be sure to use a pointed setscrew, not a flat one, and use a drill bit to put a divot in the shaft where the setscrew will hit the shaft. Lastly use some blue Locktite on the setscrew, or use a double setscrew if there's enough room. Check frequently until replaced.


Howard and Peggy

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