Sander Disc Problem - kind of urgent

[nicer20]

Hello Gurus,

As some of you remember and helped, I have this Craftsman Disc/Belt sander which I restored. It is turning out to be a super useful tool. Need to attend this kind of urgent repair because when you get used to having a tool and it is down, you feel more helpless than when you didn't have the tool in the first place

The Disc is fixed on the round shaft with the help of a set screw. Please see pictures below. One problem with it (and has gotten worse) is that the disc is coming loose now more often. I am able to tighten the set screw but after it starts rotating it comes loose soon. I have a feeling the threads in the Disc collar are stripped somewhat.

I am thinking of using a slightly oversize tap and cut new threads.

Now while I am at it I am thinking of making two mods -
a. replacing the set screw with a regular screw because reaching the set screw through the dust shield/shroud is a PITA.
b. filing the shaft and create a flat surface for the screw to hold. Currently the shaft is just round.

Do you guys see any problems with these mods? I am wondering if it is OK to use a regular screw. Is there a reason why set screw is preferred? Am I going to cause a slight off-center load due to bit of screw & its head hanging out? I doubt it but don't know if at high speed it matters? May be that is why they use a set screw in such situations?

Also, is there a same issue of creating some kind of imbalance if I filed the shaft to have a flat surface for screw?

Thanks a million in advance.

- Nicer

[Jim Frye]

If it's urgent, my first thought would be some blue Thredlock on the set screw. When money was tight, I used to use SWMBO's cast off nail polish as a thread lock. The next fix would be the next size up tap and set screw with blue Thredlock. Don't think filing a small flat on the shaft where the screw contacts the shaft is an issue.

[nicer20]

Well urgent in the sense that a tool down = less productivity.

I think I already tried the Red Threadlock. So next size tap may be needed.

Thanks for your inputs

[LCHIEN]

My comments FWIW
instead of enlarging the hole, consider a new hole and tap it 90 or 120 degrees off. But considering how close to the disk the hole is and the depth of the disk its going to be tricky to drill. For some reason I am thinking a larger hole is trouble.
Since the mass of the screw or a flat is so close to the center the moment of inertia is a lot smaller than the same mass at a large radius so it won't be too bad. (vibration wise).
And a ordinary bolt will be blunt. whereas I bet the set screw either has a point or a flat end.

Maybe look into what the real issue is.

Is the threaded hole worn? in which case a new hole might help
or is the set screw on the shaft slipping? Maybe a new set screw with a sharp point that digs in might be a better solution But most I have seen have a dished point that makes a circular contact., not ideal for a round shaft.

Or maybe the flat on the shaft will work but its going to be hard work, usually motor shafts are pretty hard material. Grinder rather than file. But that means pulling the motor shaft out of the motor.
My last thought is a cotter pin or roll pin though both parts. Again a drilling issue and its going to be hard to put the pin in since its the back side of the disk against the sander.

[nicer20]

All good points to look into. And your inputs, ideas and tips are always worth a lot. You have been such a great mentor. Thank you ...

[dbhost]

I see the design, and it both makes sense, and stinks. Probably pretty common. It sounds like the thread hole that exists is worn. You have options, not all are great, but slightly upsizing, and going with a slightly larger set screw would be a good plan. It looks like maybe an allen key is supposed to slip behind that shroud. Probably set that up before you slip the plate on the shaft. And yes threadlocker might help.

In all honesty I don't see how that is supposed to work. It wouldn't take much to overcome the resistance of the set screw against the round shaft. I guess they did that as a safety thing?

You *could* cut a flat spot into the shaft end, and yes a file would work, but be painfully slow and likely end up ugly. If you have a rotary tool A.K.A. a Dremel, and a flex shaft, you might consider using one of the grinding stone bits to make short work of it. It doesn't have to be a large spot, just flat enough to give the set screw something to grab onto and resist rotational forces. Mind you I am uncertain if this is a good idea or not, do so at your own risk...

[capncarl]

I believe the problem is more than threads. These sanders aren’t know for their precision machining. The bore of the disk probably not even bored, it’s just a cast hole. I’ve gone through a number of these sanders and have never had much luck with the disk component. On my last sander, a 6”x48” belt sander with a 9” disk, it vibrated all over the floor. I finally got smart and removed the disk and the problem went away…. As much as you could expect from a large belt sander running 900 miles an hour.

My suggestion. Since the disk isn’t something that has to come off I’d pack in a generous amount of JB Weld and coat the side of the disk bore and the shaft and push it on, pack the set screw threads full of JB and tighten everything up and let it set for a while.

[LCHIEN]

I've never had my disk off the 6" disk/4" belt sander so epoxying it or gluing it might not be the worst strategy.
As tools go the are relatively inexpensive.