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Parallel Turning

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Alan Worland06/02/2010 23:29:50
247 forum posts
21 photos
I have recently moved my Myford to paint the cabinet and remove all the swarf that had collected 'down the back' - couldn't believe it!
I found this very awkward and top heavy.
I have made  small 'skates' for each foot. Each foot now has 2 wide nylon wheels to enable the lathe to be 'rolled' out - when in position bolts are screwed down through the new skates onto the concrete floor for staabilisation and leveling - seems to work well
Anyway after all this I checked for twist in the bed and managed to do the lathe feet up with about .00025 twist, measured over a 18 inch bar. The lathe bed feet are in fact pieces of 10mm studding nutted into the top of the cabinet so the lathe bed is 'elevated' above the cabinet by a couple of inches, this enables the bed fixing positions to have a nut/washer top and bottom and makes for simple setting.
Turning a 9 inch length of bar between centres I found the tailstock end to be 3 or 4 thou larger than the headstock end. After about an hour of adjustment and taking a few thou off I have now got this down to about .0005 over a 7 1/2 turned length - is this a typical figure?
The lathe is an ML7 bought in the early 50's but well looked after.
Jens Eirik Skogstad07/02/2010 05:57:01
394 forum posts
22 photos
To make true parallel turning are not so easy at a long bar with lathe only..
To make true parallel bar: use emerypaper and micrometer. Important to keep dust away from bed and clean up all dust from bar before measuring the parallelism of bar.
Wait to the bar has cooled down to room temperature (20 C degree before use micrometer).
Jens Eirik Skogstad07/02/2010 07:21:26
394 forum posts
22 photos
Forgotten to write in addition, we have a rule about tolerance to set up and get an acceptable measure when we are making a machine part to example since not all machine tools are accurate to make exact measure every time.
mgj07/02/2010 09:30:09
1008 forum posts
14 photos
I'd have thought half a thou over 6", or 1 thou per foot is quite acceptable. You can do better, but whether you need to depends on the nature of the work you are doing. And, as Jens says, there is always emery and oil.

Edited By meyrick griffith-jones on 07/02/2010 09:30:28

Brian Emerson15/02/2010 22:30:38
1 forum posts
If my old ml7 were only .0005 in  out of paralel i would jump for joy, (break out the whisky bottle).   i have been at this game man and boy for over 60 yrs   , and not yet found a lathe
that is PERFECT every time,even a thou or two in tool hight variation can make a lot of difference.  go along to an engineering firms workshop and see how many of their lathes are as accurate as yours.
camper16/02/2010 10:57:46
11 forum posts
twist etc is best checked with a test bar in the headstock taper any lathe can be coaxed into turning parallel between centres with tailstock adjustment and fag papers sadly this newfound precision is not reflected in chuck held work or when trying to bore parallel

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