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Changing tailstock quill taper

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dtsh

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#1
My old 1903 Seneca Falls 10" lathe happens to have a #5 Jarno taper in the tailstock. It's not in terrible condition, but tooling to fit it is hard to find and when it can be found, it is invariably expensive. I've modified a few bits of tooling to fit the Jarno taper, but it's a hassle setting it up to cut a taper everytime I want to add a new tool. I've been thinking for some time that reaming the Jarno to MT2 would be the most expedient solution, but before I destroy an otherwise working lathe it seems prudent to get some advice. I'm not at all concerned about keeping it original, it's a tool and anything that makes it a more useful tool for longer is great in my opinion.

Jarno #5
large end: 0.6250
small end: 0.5000
length: 2.50
Morse #2
large end: 0.7000
small end: 0.5720
length: 2.56

I'd appreciate advice and warnings from those of you who have been down this path before.

Thanks in advance.
 

bfd

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#5
my lathe (old one ) came with a # 2 mt and I wanted a #3mt so I measured the od of my spindle and on vacation went to grizzly tools and measured theirs found one .001 larger than mine and ordered one from grizzly. then I changed the whole spindle. maybe you can do this. worked for me bill
 

Bob Korves

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#6
My old 1903 Seneca Falls 10" lathe happens to have a #5 Jarno taper in the tailstock. It's not in terrible condition, but tooling to fit it is hard to find and when it can be found, it is invariably expensive. I've modified a few bits of tooling to fit the Jarno taper, but it's a hassle setting it up to cut a taper everytime I want to add a new tool. I've been thinking for some time that reaming the Jarno to MT2 would be the most expedient solution, but before I destroy an otherwise working lathe it seems prudent to get some advice. I'm not at all concerned about keeping it original, it's a tool and anything that makes it a more useful tool for longer is great in my opinion.

Jarno #5
large end: 0.6250
small end: 0.5000
length: 2.50
Morse #2
large end: 0.7000
small end: 0.5720
length: 2.56

I'd appreciate advice and warnings from those of you who have been down this path before.

Thanks in advance.
The differences in diameters between the sizes is really too much to ream, so it will have to be bored, which is possible. It is not particularly easy to get great results in producing a machine taper that is to the correct size, the correct taper, and concentric to the lathe axis, with a nice surface finish, all at the same time. Make sure you are up to the challenge.
 

derf

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#7
This seems to be a common problem with Seneca Falls lathes. I recently ran into the same problem with a 12" Seneca Falls, but it had a taper closer to a #2 Morse. A #2 stuck out quite a bit and didn't quite seat right. I first bored it, then finished up with a #3 Morse reamer.
I might add, that I did this on another lathe... not the one I was correcting.
I first put a #3 Morse sleeve between centers and swept it with an indicator and adjusted the compound to follow the taper. I did have to bore the depth slightly deeper (cylindrically) for the tang area. Once I bored the taper, I had it very close and was just going to lap out for a final fit, but that's about the time my buddy showed up with a new MT reamer ( it was his lathe) so about a dozen turns and we were golden.
 

benmychree

John York
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#8
Yes, either make a new one, or bore out and ream the old one; I'd do the latter if the old one was still a snug fit in its bore. The Jarno made a lot of sense on its dimensional calculations, but came to late in history to be adopted as a standard for anything except cylindrical grinders.
 
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