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New Thompson 2f Issues

Blazemaster

Hot Rolled
Joined
Oct 13, 2009
Location
Olympia, Wa
I was given this grinder from a working shop, and told it had 2 issues. Yes it's a project but I have the space and had the capacity to move it pretty easily so I bought it home. I have a 6x18 Norton but this is a 8x24 so it would give me a little more capacity. The first issue is the motor quit working in the middle of a job. They started taking the motor apart and then had a 2nd problem. On the spindle end there is a threaded stub on the end to hold the hub on, and this was busted off as they were trying to remove the spindle/armature. After looking at the broken parts, it had a crack that was old and bumping it with a hammer finished the job. Good thing it didn't fly off when it was running, this grinder takes a 12" wheel. I will mess with the motor at another time, for now I would like to focus on the broken spindle thread.

I would like to get some input on how you would tackle the job to get some ideas. My first thought was to remove the spindle, face it off then bore and single point a thread in the end and make a stud to thread in. A file skates over the broken area but I am not sure if it is through hardened.

Anybody done something similar? What would you do?

Also I got a manual with the machine but there is no diagram showing the spindle breakdown. Has anyone ever removed the spindle on a Thompson?


Thanks for your replies!
 

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Yikes. That's either a new spindle or a serious spindle-out repair. I would bet that it's not case hardened. You can probably repair it even if it's fully hardened if you use all carbide tooling, including single point threading it.

For a repair, I would take the diameter up closer to the small end of the taper and make a threaded end on the plug with a straight fit section toward the outside that is a slight interference fit. Then I would warm up the spindle to 250° - 300° and screw that bitch in quick. Double nut on the spindle end and use an impact quick. Kind of like the attached hasty sketch. You'll almost certainly need to regrind the taper afterwards.

20210125_090042.jpg
 
Yea I know its not great, but I'm a glutton for punishment and I only have gas money into it. The thread doesn't do any precision locating, it just holds the wheel hub on the taper.

I know I will have to remove the spindle for sure, and most likely replace the spindle bearings. I like the idea of a plug, but not sure I want to heat the spindle up and drive the plug in with an impact. We will see, I am going to think on it for a few days while I clean the machine up.
 
If the spindle nose center area is soft enough to put in a screw thread, that (a screw) would do as well as a nut.

File test should tell.

If so it might be repaired with not a teardown...just a drill and tap.


From here it looks like the nut's thread was right hand..that would be odd.
but with having a key would be OK .. I have run Thompsons and think they are great machines, always thought the long-travel ways were some of the best scraping I have ever seen. the cross travel can wear out but can be scraped in.
Any machine having something Odd should have a notice painted in view. On TC grinder often the spindle would be put back with the wrong end out and the next guy would tighten when he thought it should come lose.

I always thought left-hand spindle nuts should be painted red.
 
Slightly crazy idea, how about repair in place? Fixture a drill to table, use spindle motor for rotation to drill to size, then hand tap hole, or shrink fit a plug as shown above?

Maybe drill to 3/8" then swap out drill for a boring bar. Might need a vfd to control spindle rpm?
 
I would be surprised if I could hand tap something this hard, I think I am stuck in carbide territory. I also thought about how I could drill it in place, threading is the problem. It doesn't look too bad to remove the spindle, I didn't measure the thread but it looks to be around 3/4". Thanks for your replies!
 
Yeah probably not going to be able to tap it, but you never know. The female thread and a socket head cap screw would work to hold the wheel hub on but you'd probably lose the ability to easily use the hub puller, if you swap wheels much.
 
If you drill/bore it in place, you might get a better idea of how hard the core is. If too hard to tap, do a shrink fit as in post #2. The question I can't answer is would that affect the external taper, if so maybe mount a tool post grinder to correct?
 
I got to cleaning the machine a bit today and looked closer at the broken spindle. It is a right hand thread. My first thought was to try and put a left hand thread into the spindle, mcmaster has left hand b7 all thread. Do Thompson grinders spin in reverse? Bad idea? I haven't done any repairs to a grinder before.

I also got out some small die files and tried the center of the shaft, the file cut it easily.
 
I think I would steer clear of the drilling and tapping in place. If you don't bore the hole and single point thread it, you will never get it perfectly centered... that means runout. That means vibration.
 
Good. I think that's the only way to go. The left hand thread is probably unnecessary since the spindle is keyed, but certainly won't hurt you any. I'm sure the Thompson spins the same as every other grinder - that is to say, clockwise when viewed from the front.
 
And one more thing... The reason I suggested the fit between the bored diameter on the spindle and the turned diameter on the stub is just so that you know they are concentric. There's usually a lot of slop in a threaded fit... and it doesn't take hardly anything to throw the spindle out of balance.
 








 
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