# Themac J35 tool post grinder question



## Technical Ted (Sep 4, 2017)

Just picked up an excellent condition Themac J35 lathe tool post grinder from a Craigslist ad for $300 (MSC lists it for over $2000). Guy said he had only used it four times and it looks almost brand new. 

Anyways, checking everything over well when I got home I noticed that the internal arbor had a broken #4-40 screw in the end of it where the grinding wheel attaches. Got it out OK, but now I'm wondering what I might be missing. I can't find any good information on the web or even an operator's manual. Their website says :

#2021 - Extension Spindle for internal grinding with arbor and 2 wheel collars 3/8".
Does anyone have one of these? If so, can you please tell me what the broken screw/shaft actually looks like (maybe with some dimensions) and what the wheel collars dimensions are so I can make some up? Any information will be helpful! 

The internal arbor is shown here in a pic. 
	

		
			
		

		
	





Thanks!
Ted


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## kd4gij (Sep 4, 2017)

The white wheel with a shaft sticking out. Does it look like something is broke off the end?


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## Bob Korves (Sep 4, 2017)

Lacking someone with more information, I might add that grinding wheels generally need wheel flanges 1/3 the diameter of the wheel, and the outer diameter contact area should be within the factory wheel blotter diameter for that size wheel.  I hope someone can give you more definitive information than that...


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## Technical Ted (Sep 4, 2017)

kd4gij said:


> The white wheel with a shaft sticking out. Does it look like something is broke off the end?



No, nothing broken. It's just a standard 1" mounted grinding wheel. I know it's hard to tell from the picture I posted. 

Thanks anyways,
Ted


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## kd4gij (Sep 4, 2017)

Looks like shoulder bolt


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## Technical Ted (Sep 4, 2017)

Hahaha, we must have passed each other searching because I found those two pictures as well. A couple sites list that there should be two 3/8" collars and the one picture you posted clearly shows the two collars and the other pic does as well (if you zoom into the original) but they are drawn up tight to each other. So, they will be easy enough to make; I'll just copy the others I got, but downsize them to 3/8".

Now all I need to know are the dimensions of the screw/shaft that holds the collars. From the bore in the female end, it might suggest that there is a unthreaded section where the stone and collars would sit and slide into the non-threaded part of the bore. This would make sense since it would help in alignment. The thread is 4-40 and that little shaft won't be the easiest thing to single point because the screw will need to be fairly long. But, I'll come up with some dimensions and try my luck. I'll check but I don't think I have a dye. They want over $200 for that #2021 arbor so even if I end up buying a dye it will save me a lot of cash. 

Thanks for the help and effort,
Ted


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## kd4gij (Sep 4, 2017)

I would contact TheMac and see what they want for it.
https://themacgrinders.com/pages/contact


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## kd4gij (Sep 4, 2017)

Yes the shoulder dia. will depend on the bore size stones. McMasters  shows 4-40 threads come in 1/8,1/4,and 3/8" dia.


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## Technical Ted (Sep 4, 2017)

kd4gij said:


> I would contact TheMac and see what they want for it.
> https://themacgrinders.com/pages/contact



Is your username your callsign? If so, thanks Martin. AB2RY here.

Ted


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## kd4gij (Sep 4, 2017)

Yes it is my call sine. I am not active on air right now though.  Looks tike you have a small wheel for ID griding


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## Technical Ted (Sep 4, 2017)

Yes, I got a 3/4" wheel with it. From the listings I should have gotten a 3/8" wheel as well, but that's probably with the other end of the broken screw/shaft I took out of the arbor!  Traveling at that RPM, things really must go flying when TSHTF.

Ted


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## Technical Ted (Sep 6, 2017)

Called Themac. They want $52 for the screw and 2 collars and they have an $85 minimum! So, I think I'll try making something. After closer examination, I did find that it is a #5-40 screw, not a #4-40.

If anyone has one of these and can please give me some dimensions I would appreciate it!

Thanks,
Ted


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