Attaching a sprocket to a round shaft

Pooh_Bear · Nov 27, 2006

I have a round shaft (3/4 inch) about 2 feet long and smooth.
One end has a 6x6 inch plate welded on it
The shaft gets 2 pillow block bearings on it with a sprocket in between them.
There is no keyway for the sprocket. The shaft is smooth.
I can't weld the sprocket to the shaft or I won't be able to change the inside bearing.
I'm not sure the set screws will have enough holding force to keep from slipping.

I'm wondering if I can take an angle grinder with a cut-off wheel
and very carefully cut a slot for a square key.

Or if anyone has any better ideas I sure would like to hear them.

Thanks.

Pooh Bear

jarokoro · Nov 28, 2006

I would use the set screw with Loctight, then tac weld two spots one front one back. If you have to remove use a cutoff or grinder it would be nothing to grind off the weld.

Another sugestion would be to set the sprocket and mark the rod, drill a hole in the rod and use at least a grade 5 bolt same size as the set screw and grind to a semi-round to a point, use a nut on the bolt so when you tighten the bolt down and seats into the rod, you have an adjustment to ensure that it is tight.

Youare · Nov 28, 2006

Anothe option is once the sprocket is in the place you want it drill a hole through the hub of the sprocket and the shaft and insert a roll pin. Roll pins can take quite a bit of torque and can be removed when necessary with a pin punch. On a 3/4 dia. shaft I would use a 3/16 dia. roll pin.

Should you not want to drill and pin the shaft the next best thing would be to dimple the shaft where the set screw of the sprocket tightens. Using a drill of the same dia. as the set screw drill into the shaft 1 1/2 times the dia. of the screw. This will create a pocket for the set screw to fit into. A little thread locker like Lock-tite should keep things tight. Or, if there is room use two set screws in the same hole one to lock the other in.

Randy

ovrszd · Nov 28, 2006

Not sure anyone's ideas are worth much without knowing what this sprocket is powering???? How big of load is on it, etc.

Farmwithjunk · Nov 28, 2006

Youare said:
Anothe option is once the sprocket is in the place you want it drill a hole through the hub of the sprocket and the shaft and insert a roll pin. Roll pins can take quite a bit of torque and can be removed when necessary with a pin punch. On a 3/4 dia. shaft I would use a 3/16 dia. roll pin.

Should you not want to drill and pin the shaft the next best thing would be to dimple the shaft where the set screw of the sprocket tightens. Using a drill of the same dia. as the set screw drill into the shaft 1 1/2 times the dia. of the screw. This will create a pocket for the set screw to fit into. A little thread locker like Lock-tite should keep things tight. Or, if there is room use two set screws in the same hole one to lock the other in.

Randy

What he said!

scott_vt · Nov 28, 2006

Mornin Pooh Bear,
Well you didnt say how thick the sprocket is ? If it has some beef to it you could get away with drilling through it and putting a roll pin through it and thye shaft. With that said I am not a fan of doing this especially if you have any kind of an appreciable load on the shaft and sprocket !

My suggestion would be to mount a small hub on the sprocket providing there is room to do this. Through holes through the sprocket and tapped holes in the hub. Drill and tap 1/4 x 20 through the hub OD and slightly drill into the shaft so your set screw will penetrate the shaft OD.

The keyway idea is good also but needs to be done properly to be effective.IMHO

Pooh_Bear · Nov 28, 2006

I like the ideas to drill a small shallow hole and use a small pointed bolt.

The shaft will turn at about 23 RPM.
The square plate welded onto the end of the shaft
is bolted to bottom of a 55 gallon polyethelyne drum.
I am making the drum into a concrete mixer.

All that is left of this project is to power this shaft from the gear box.
1725rpm motor to a 50:1 gear box to a 2 inch sprocket to a 3 inch sprocket.
1725 divided by 50 = 34.5 and 34.5 divided by 1.5 = 23
The 3 inch sprocket is the one that goes on the main shaft for the mixer.
The gearbox already has a keyway.

A few days ago I had to find the balance point
of the drum/motor-gearbox assembly.
So I filled the drum (half) full of dirt like it would be mixing concrete.
Took seven 4 gallon buckets to fill it up and it wasn't easy to turn by hand
but it wasn't too hard either. Wet concrete should mix a lot easier.
And I won't ever have that much concrete in it while mixing.

Is 23 RPM too fast for a big concrete mixer.
I need to know before I order the sprockets.
Will #60 chain suffice for this project.

Soon as I'm done I'll get pictures.

Pooh Bear

Soundguy · Nov 28, 2006

I'd use an angle grinder and cut a slot for a halfmoon key.. or a square key.. your choice.

soundguy

Pooh_Bear said:
I have a round shaft (3/4 inch) about 2 feet long and smooth.
One end has a 6x6 inch plate welded on it
The shaft gets 2 pillow block bearings on it with a sprocket in between them.
There is no keyway for the sprocket. The shaft is smooth.
I can't weld the sprocket to the shaft or I won't be able to change the inside bearing.
I'm not sure the set screws will have enough holding force to keep from slipping.

I'm wondering if I can take an angle grinder with a cut-off wheel
and very carefully cut a slot for a square key.

Or if anyone has any better ideas I sure would like to hear them.

Thanks.

Pooh Bear

KYErik · Nov 28, 2006

After drilling the set screw holes and seeing them get ovalled out on a go cart axle years ago, I ground a slot and then used a square key on a 3/4" shaft. Its next to impossible to make the slot perfectly sqare so you will need to take a little off the edges of the keystock with the bench grinder until you get a close fit.

If you use a longer piece of keystock that sticks out a half inch or so from the pulley hub, you can tack weld the key to the shaft on one end so you don't lose this "custom key" should your sproket get a little loose and slide sideways on the shaft.