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

[Naio]

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

[Naio]

opnspaces wrote:
Another thought while the machine is down. Consider taking the hard to replace sprocket to a machine shop to be replicated. It may not be cheap figure $200 - $800. But if it's your business income it might be worthwhile to have a replacement made.

When I say it's basically impossible to replace, what I mean is that in order to get the one, I called every place I could find in the US on Google, and every place I could find through word of mouth.

I finally found a place that makes custom sprockets and they made me one. But it took them about six months to get it done, and only then did they've mention that normally, although they make custom sprockets, they make runs of a few hundred or a thousand, and it was really a big hassle for them to make just one. It was a kindness.

I have told them how grateful I am, but I can't ask them to do it again.

Of course if I'd known, I would have asked them to make me several, but by the time I found out the difficulty, they had already taken the machinery apart again, and reset it for the next job.

When I say that the drive sprocket is easier to replace, I mean that I could probably buy one somewhere....maybe.

[Naio]

Dusty R wrote:

schlep1967 wrote:

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?

X-2

Dusty

Well, when I got it it didn't have a fuse at all. I've tried various fuses and circuit breakers over time.

I've also replaced the cables multiple times. I don't remember what size was on it when I got it. I certainly haven't gone to smaller cables, but I might have gone to larger.

My goal is that the circuit breaker be for unexpected things like a person dropping a wrench over the battery terminals. Not something that blows during normal use. Is this wrong of me?

[Dusty_R]

schlep1967 wrote:

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?

X-2

Dusty

[MrWizard]

All very good advice
But I wonder , why is the custom sprocket made out of Alu
Is it some custom harder than steel alloy ?
In would have that thing copied, I would also get a drive sprocket for the spare motor
Sprockets are gears, but they drive a chain connected to another gear/sprocket instead of being inner meshed gears

[opnspaces]

Another thought while the machine is down. Consider taking the hard to replace sprocket to a machine shop to be replicated. It may not be cheap figure $200 - $800. But if it's your business income it might be worthwhile to have a replacement made.

[time2roll]

Naio wrote:
This is for my shave ice machine.

LOL

I would wait for the right stuff but if you must use the available parts I would look at running at reduced power if you can.

I doubt there would be any damage except to the mismatched sprocket and shaft. Unless that chain comes off and there is continued momentum in the secondary sprocket causing the chain to jamb or tangle on something.

If this is all temporary consider just having it welded on.

[fj12ryder]

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.

[opnspaces]

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.

[pigman1]

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.

[schlep1967]

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?

[ksg5000]

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.

[RLS7201]

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

[Acampingwewillg]

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.????

[K_Charles]

"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.

[pianotuna]

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.