Taper Mandrels and accuracy

I have dusted off the Stuart 10V castings, dug out the building book and found Issue 51 of MEW. Time to get started after only four years.
In MEW 51, there is an article about jigs and fixtures by Harold Hall. He uses the 10V as an example. In it he suggests machining the flywheel and bearings on a taper mandrel once the bores have been reamed. This, he says, allows for good accuracy and will permit both sides of the flywheel to be machined by simply removing it from the taper mandrel and turning it over.
I can't see how this works. I don't doubt that it does, I just don't understand and can't find any reference in my meagre library to the technique. It seem to me that any taper will, by definition, leave the flywheel tight at one end and loose at the other. I even did some sums. Over the 3/4" of the flywheel length, if I had a taper of 0.5 deg (1 degree included), the casting would have one end tight and the other 0.013" oversize. That would wobble about all day and any machining forces would throw it out of true.
What have I missed? Can someone explain (or point me to an explanation) of the business of turning accuately on a taper mandrel?
Thanks
Pete Harrison
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http://wess.freeshell.org/Boring_new_hub.jpg
http://wess.freeshell.org/mandrill.jpg
http://wess.freeshell.org/clausing/clausingdriven640.jpg
http://wess.freeshell.org/clausing/clausingdriven2_640.JPG
http://wess.freeshell.org/clausing/Clausing.html if you want text.
First, there isn't much of a taper. Set your tail stock over so you get a nice press fit in that reamed bore. Check out tables of press fits to figure just what you want to use. 0.001" per inch of diameter is my rule of thumb.
In my case, I needed to make a new hub, had to get it concentric with the old sheave, and then needed to hold and machine the hub's od.
HTH,
Wes
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Peter, The answer is it's not 0.5 degrees but far less, a tapered mandrel usually has about 10 thou per foot so on your flywheel it's about three licks off a gnats cock.
John S.
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John S wrote:

That sounds more like it. Probably more true than my topslide normally turns then :)
Pete
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Some lathes, with wear on the ways, automatically make tapered mandrels ;) .
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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John S wrote:

Note : This is a consenting gnat, obviously.
--
Boo

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Boo wrote:

I think he said "off" not "of" :)
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wrote:

If you are not too confident of turning the taper, just turn the end of the bar to fit in the reamed hole and then bring the rest down to a thou over and reach for the file and emery cloth to finish off, we'll forgive you. Peter
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wrote:

If you are not too confident of turning the taper, just turn the end of the bar to fit in the reamed hole and then bring the rest down to a thou over and reach for the file and emery cloth to finish off, we'll forgive you. Peter
I'm building a 10V at the moment. I've not done the flywheel yet but I finished off the ends of the bearings and the top of the column using taper mounting. Just created the taper with a few seconds with a file on a parallel mandrel turned a thou or so over and it worked fine.
For the flywheel I'm more inclined to use a threaded mandrel.
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snipped-for-privacy@hotmail.com wrote:

OK. I get it now. This evening turned a couple of inches of stock down to about 0.004 over size. Then turned the last inch to a snug fit in the flywheel. Next, with the topslide set to about 0.5 deg. I left the crosslide alone and used the topslide to turn the inner inch of the mandren to get the taper.
The flywheel is a good tight fir with no wobble and it can be reversed to machine both sides. I now have it machined on all (relevant) surfaces and it runs beautifully true. Mounting the flywheel like this does allow it to 'ring' a bit giving some fine chatter patterns. However, theu look quite pretty so I will leave them there for a bit.
Thanks for all your help.
I'l be back.
Pete Harrison
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Peter Harrison wrote:

Pete, Were you using the tailstock to support the mandrel? Should reduce/remove the chatter if everything else on the lathe is in fair shape.
Bob
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Bob Minchin wrote:

Hah!
Only thought of that after I finished! Then again, reading my post, I was actually machining a small christmas tree.
Pete
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