Hi Dahui, if you are going to machine the base part of the tailstock assembly to drop the centreline of the spindle bore by .013", then you will have to mill the vee groove deeper and also the flat register further back, if that is how your tailstock is located.
There are two ways to achieve this, one is to mill it, if you have a mill big enough, and the other way is the tried and tested hand method, which I can assure you will give you 100% results, but requires carefull workmanship.
Make sure the tailstock upper half and lower half mating faces are clean with no paint or casting burrs.
Next ascertain the EXACT amount the tailstock is out, and that the tailstock BORE is parallel to the bed and not running uphill or down, done by checking from both ends in relation to the bed top face.
You should also check that the bore is in line with the centre of the bed and not running at an angle to it.
If you have this last fault it will play havoc when trying to turn parallel between centres or for drilling, all of which can be corrected by the application of a bit of common sense and carefull analysis.
To start off, mount a dial indicator on the 3 jaw chuck face and set the stylus to touch the OD of the barrel of the tailstock, just sticking out about 1/2", and rotate the chuck to swing the dial indicator stylus round the tailstock barrel, the tailstock being locked down onto the bed.
This will give you the amount the bore of the tailstock is out to the headstock centre line.
This method is also the most accurate way to reallign the tailstock for parallel turning.
Assuming you still have .013" high, remove the tailstock upper half.
The lower half of the tailstock must have metal removed from the Vee groove that the upper half locates into, and the flat face further back, NOT the bottom face that runs on the bed.
To achieve this metal removal, use an ANGLE GRINDER, (precision tool in the right hands), to lightly grind both the faces of the Vee groove and the flat
Don't dig the grinding wheel edge into the metal, but use the flat disc face at a shallow angle, and use a criss cross method, first making a number of light passes one way and then crossing the face in the opposite direction.
This will ensure that the metal is evenly removed.
Next lightly apply marking blue to the bottom of the tailstock body Vee and flat and then fit the two halves together and give a short back an forth rub to mark the fit between the two halves.
You will have a lot of high spots, shown by the blue being marked onto the bottom half.
Just lightly take off the bits marked with blue and keep repeating the process untill you get a more or less even marking pattern.
At this stage you will check the height again by the method outlined at the beginning, and also allignment in both horizontal and axial planes
If you carefully and lightly grind the faces, then the top half of the tailstock will progressively sink lower.
The important thing is to remove a SMALL amount of metal and CHECK your results. Then do it again, finally if you are capable a touch with a flat scraper is all you'll need to get the alignment 100%, which is better than the best machining methods.
The easiest way would have been to line bore the barrel bore, and have the tailstock barrel hard chromed and ground to the new diameter, takes less time and requires a lot less skill, and is standard practice in the machine tool rebuilding industry.
It also guarantees 100% horizontal and axial allignment in one operation.
I've been doing machine tool refitting for 40 years on and off as the occasion arises and this is just a breeze.
My biggest challenge was to refurbish a 10" swing lathe bed/saddle fit by hand, when the bed was worn from the middle of the bed to the chuck end by .013" and made any adjustment of the saddle impossible, but that's a long story and would bore most people.
Ian.  |