Thread: Keyway in shaft

I've repaired the belt cover with perspex - should be a useful surveillance window!
IMG_9746.jpg

Hi Chris, any chance of several pics of the pulley please? To see if there is enough room to machine a bit of the pulley away where the nut sits. Is there enough thread there for a full nut?
Kryn

Kryn,
Here's some pics of another machine that has had a similar failure.
The pulley is already deeply machined

And you can see that there is no more thread for a full nut to use.

Thanks Chris, the idea was there, but wouldn't work.
Kryn

Looking at those pics, I'd be tempted to make a new pulley from solid material with the appropriate thread in one end and a keyway* in the other (will have to be in two parts to actually make it and fit it). Looking at it, the load on the pulley is going to be applying a force to the hollow part of the pulley which in turn applies a moment to the portion on the shaft, tending to stretch the bore. Once the bore is over size it will shake around and allow the key to slop around.

* Cunning plan - If the pulley/ nut is one piece you might be able to get away with using a dog point grub screw to locate in the shaft groove. The dog point will stop the pulley rotating with respect to the shaft, the thread will stop the pulley sliding off and because the pulley is effectively mounted on the OD of the nut, there should be no moment on the shaft to make it sloppy.

Pulley and nut.jpg
Chris, have you the gear to accurately measure the shaft?
Almost tempting enough to try...

Michael

Standard rule of thumb I've always used is 2 dog point screws 90 deg apart, one bearing on top of the key. This takes out all play from pulley to shaft and positively restrains the key. Assumes there is enough thickness over the hub keyway to effectively tap for the threads.

That shaft keyway is wallowed out beyond salvage for the original key. Got to be re-machined on the other side or machined out for the next size key that will clean up in the shaft, then a stepped key or enlarge the pulley keyway.

I wouldn't trust that nut on the end to do anything useful at all. Loctite on its threads would be mandatory.

PDW

Originally Posted by Chrism3

Yes, I guess that would provide support to the whole pulley, not just the side with the key. Do you know of instances where this technique has been manufactured in?

Yes, I've seen it many times. For example, that's how car ignition distributors usually had the driving parts at the bottom attached.
Also, many parts on machine tools, like handwheels, are fitted with pins this way.

Jordan

Wow, you guys are really getting into this! This is turning into a national competition, which wasn't my intention.
My current plan is to get a new key cut in the shaft, courtesy of a kind forum member, and I have ordered a new pulley and key. I intend to use some "permanent" Loctite on both the key and the pulley/shaft.
But I like the idea of a solid one piece pulley with grub screws, and will think about it some more. I might also run it past Delta, who have known about this problem for some time, but haven't come up with anything other than the Loctite solution.
Thanks for all the suggestions!
Chris

When i have the parts in front of me i will look at what we may be able to do to make it a permanent fix.
Cheers,
Ew

Originally Posted by KBs PensNmore

Anyone with a milling machine or shaper should be able to do it, not a hard job, takes longer to set up than to do it though. I had a similar thing happen on my car engine, the machinist re machined the crankshaft and cut a new key. Yesterday my metal lathe stripped a plastic gear, pulled it apart and the shaft needs the key way re cut. To make matters worse, my mill, stripped one of the cast metal gears inside the head.
Kryn

I feel your pain with the stripped gears. I ended up putting steel ones in my mill to replace the rubbish plastic ones. I would think that the cast ones are not much better.

Originally Posted by Ueee

When i have the parts in front of me i will look at what we may be able to do to make it a permanent fix.

You could weld it on

Originally Posted by Chrism3

Kryn,
Here's some pics of another machine that has had a similar failure.
The pulley is already deeply machined

And you can see that there is no more thread for a full nut to use.

What a arrangement ! When you get the new keyway cut, drill and thread a hole for a retaining bolt in the end of the shaft.

1 or 2 grub screws thru the side of nut to lock the nut to the shaft

Originally Posted by PDW

I wouldn't trust that nut on the end to do anything useful at all. Loctite on its threads would be mandatory.

PDW

It's still a puzzle to me as to why a left hand thread would come undone.