Themac Tool Post Grinder DIY Spindle

I have found the Tail Stock getting in the way to be a common problem when cutting lite tapers with the compound. I made a #2 size pulley wheel for the drive side of the Tool Post Grinder and to give the pulley a crown in the middle I put the compound at 1.5 degrees off parallel with the lathe bed. I had to extend the tailstock quill almost the full 4" travel to get enough room to clear the compound crank just enough to advance the cutter. I was turning between centers with the work on a mandrel. One way it would seem to help when it comes to the TPG would be to use a larger grinding wheel so you can put more distance between the compound and the work. Just curious what Lathe you have? Size?
I was aware of the good practice of covering the lathe ways when doing anything in the grinding realm.
So back to the THEMAC arbors, I guess the only surprise I have from your info is the difference in what you have as the Arbor Taper of 0.0391" per inch as opposed to my 0.0354" per inch. I didn't have the ability to put a factory arbor on the lathe to measure since I don't have one, but I really thought I did a good job of setting up to measure the bore of the spindle. Seems to me that on a very small taper like this that almost 0.004" is a large difference.

Thank you for the PDF drawings with dimensions. You have made it very easy to understand compared to my hand written diagrams and notes that I didn't really remove all the bad measurements before putting this on the back burner.
 
You've raised a good point about the taper. I have 2 ID arbors plus 1 collet chuck arbor all with same taper shank. The ID arbors I was able to (kinda) hold between centers using the center drill pip on the thread end and the screw hole on the wheel end between centers. The collet chuck I held a 0.250 ground pin in my collet chuck but I can almost guarantee that was iffy.

Anyways I first rotated the ID arbors with DTI on the OD. It was pretty concentric runout but I did see variations, likely due to the thread hole not really being a center hole. Then I put my DTI on the compound, found vertical center of the arbor, advanced in until DTI registered zero on one end of taper, traversed the carriage to other end of taper, advanced in again to same DTI zero & read off my DRO X displaced value. I'll have to dig my notes because I did see some variation in arbors and different rotate positions, but like I mentioned I took an average of those & that's what I made my drawing & taper test slugs from. Could well be some measurement variations though. Also my compound turning is not as good as with a taper attachment so some hand finishing was required - more room for variation!

Then when I made my arbor I decided to set my compound in the more classic way - DTI-ing along the taper of the arbor itself. My plan was to make a few more arbors but I need a specific tool for a job & got busy with other things so I only have the one.

One thing occurs to me, when I blue check a Themac arbor, its always being engaged by the threaded section before the tapers come in contact with each other & that might have some influence over the rub off. When I made my test slugs it was only the taper section, no threads. I blued with felt pen & gave a half turn.

I wish they would just publish the taper & we could just get on with life, LOL. So I wouldn't throw out your number quite yet. It sounds like it might be a logical nominal taper ratio but who really knows.
 
Regarding tailstock 'in the way' I suspect that's why these machines were invented, probably 100 years ago. I would love to have one.

 
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