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Lathe Spindle MT5 Taper Trouble - Help Please

Circus Bear

Plastic
Joined
Oct 17, 2018
Problem
I have a Cadillac 14x28 with A5 Short Taper mount. The spindle runout measured on the outside of the spindle face is 2 tenths and I'm thrilled at that given the age of the lathe. The MT5 taper in the spindle has lots of shallow but visible nicks and dings from years of parts roughly inserted into the bore of the chuck. I have stoned the surface as carefully as I can and have improved the runout of a dead center but only to 0.001". When I mark the high point on the spindle face, it is repeatable when I remove and rotate the dead center so the issue is in the bore of the spindle, not the dead center.

Set the Compound Rest Help
Asking for experienced advice on setting the compound rest to the correct angle of the MT5 spindle bore. My approach is to chuck a piece of stock, face off and center drill. Suspend the MT5 dead center between the checked center drilled hole and the tailstock center (point towards the chuck). Adjust the angle of the compound rest to parallel the operator side of the dead center using a test indicator. This should set the compound rest to the angle of the non operator side of the spindle taper.

Cut or Grind?
Flip my boring bar face down and skim the nick high points from the the back side of the taper using the compound rest. or...I have a tool post grinder just not sure if I have the reach needed to hit the length of the taper.

Is my approach sound or am I missing something? Constructive feedback requested.
 

TGTool

Titanium
Joined
Sep 22, 2006
Location
Stillwater, Oklahoma
Sounds like a perfectly good plan. The spindle isn't hardened if it's nicked and dented so doesn't have to be ground. Nice surface finish, but you can stone and emery the turned surface. And using and existing MT taper you trust is also valid Just to keep that hones you might try rotating the MT5 after setting the compound to be sure there isn't another factor throwing it off.
 
Joined
Apr 19, 2006
Location
Manchester, England
I wouldn’t worry too much about a minimal run out of the spindle bore. It wouldn’t have been perfect even when new, everything in engineering has a tolerance. I can’t recall what “ Schlesinger “ has to say about spindle bore run out but there will be an accepted error. How often will it be relevant to an actual turning operation ? How many times will you be turning between centres ? I certainly wouldn’t be attempting to correct the error by machining the spindle bore with your tool post. If you’re really bothered I’d persist with the light stoning of the bore and then get yourself a cheap test bar off the internet. That will give you a better idea of the error.

Edit - “ Schlesinger “ gives the tolerance for spindle nose run out as an acceptable error of 0.01mm to 0.03 mm. In English money that is 0.0003” to 0.0011”.
So as I understand it your lathe is just within tolerance.

Regards Tyrone.
 
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Joe Henderson

Aluminum
Joined
May 21, 2006
Location
Blooming Grove, Texas
If it has dings in it still lightly using a mT5 reamer might help it but truth tell I've never used the ones on any of my lathes. when I need a center I just chuck a short piece of round rod and turn a 60* taper on it. That's as good as it's going to get for any lathe.
 
Joined
Apr 19, 2006
Location
Manchester, England
Lathes are there to be used. They aren’t really ornaments or showpieces.
I have seen photos of lathes on here that look to be in ” show room “ condition. They are immaculate. I’ve installed brand new lathes and inside an hour of hard turning the paint near the gap piece is all chipped and scorched by the hot chips. We used to call the colours “ bonus blue “ and “ piecework purple “ ! That’s how hot they were.

It all reminds me of the guy who bought a really expensive hi fi system with a separate valve amp etc. He just turned the amp on and cranked it up to 10. He said “ Listen to that, you can’t hear the faintest noise, buzz or hum and I’ve got it turned up to the max”. No music playing but he was thrilled.

Regards Tyrone.
 

Circus Bear

Plastic
Joined
Oct 17, 2018
Sincere thanks for the quick replies and guidance. I tried a MT5 finishing reamer but it was too " grabby" so I stopped before removing material. My 5C collet holder seats on this MT5 taper and am just trying to tighten the runout to closer match what I measure on the outside face of the spindle. I'll try to find the high points by inking the bore and dead center, then spend a little more time with the stone before I make any cuts. I do appreciate the feedback and reality check. Thanks guys!
 

jscpm

Stainless
Joined
May 4, 2010
Location
Cambridge, MA
You could ream it and lap it, but it will be set deeper into the spindle than before, so it will be non-standard. Lapping tapers is quite tricky. I would advise practicing on something you don't care about first before trying to recondition a spindle in a working machine.

You cannot fix a taper bore by fiddling.
 

Circus Bear

Plastic
Joined
Oct 17, 2018
Follow up - Thanks again for the reality check. I spent an hour carefully hitting any dings with a Norton tapered round stone. Validated my progress with checking the contact of the taper with dye and checking run out. I'm within 0.0004 on my Interapid indicator. The 5C collet holder and the dead center are seating 100 times better than when I started. Moving on to the next project. Thanks again for the input.
 








 
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