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View Full Version : 4MT collet so i can adjust the headstock on my lathe - do they exist?



Elninio
01-06-2010, 09:29 PM
I need a 4MT collet to hold a 1/2" precision ground rod in order to adjust the headstock on my 10x22" KING lathe, do these things exist? I'm in ontario canada - maybe KBCtools has it but I haven't been able to load the pages on their website ...

oldtiffie
01-06-2010, 09:56 PM
First of all, there are two kinds of "run-out" on any cylinder or taper in a mill or lathe that will show up as "Total Indicated Run-out" (TIR) on the test piece/cylinder :

1. Cylindrical: where the run-out is the same from end-to-end

2. Conical: where the run-out varies from end to end.

Both can exist together.

All tapers and cylinders have these "defects" which can all add up or cancel each other out - or mostly somewhere in between.

You head-stock taper will have a limited degree of run-out as will the tapers on the outside and the cylinder inside that MT collet.

Knowing where and what they are is the problem.

You can save yourself the worry and expense of the collet by mounting the test piece in your 4-jaw chuck with a bit of thin copper wire wound around the cylinder (1 or 2 turns should be enough) and with the copper gripped near the front of the chuck jaws.

Now, using a good (0.0005"/0.01mm) indicator adjust the two ends of the test piece until you have a minimum of run-out at either end of the test piece. "Tapping" the end with a brass or bronze "dolly" (scrap stuff is OK) is quite in order.

Your test piece is now very accurately axially aligned to and concentric with your lathe spindle axis.

All errors in the machine tapers and the collet - and the 4-jaw chuck have been by-passed and are of no concern (at this stage).

Now, with the lathe spindle (still) stopped, run your indicator along the test piece (front and top) by using the lathe saddle/carriage and any movement in the indicator will be the amount that the spindle axis is out of axial alignment with your lathe bed axis. Work out the "error per inch" to give yourself something to work with.

Now would be a good time to put your indicator on both ends and the middle of your lathe spindle MT taper and see what if any deflection there is there as well and then work out the error per inch.

At this stage - with no cost and little time and effort you will have a very good idea of your lathe spindle and its MT alignment.

derekm
01-07-2010, 08:17 AM
With a bit of thinking and arithematic you can set it up with any piece of bar stock thats only very approximately lined up in the chuck. the bar can even be tapered and oval. if fact it only needs to be round bar for convienience and ease of use with dial gauges.

put your bar stock in to the chuck. with a scribe or felt tip attached to the tool post draw a line down the length of bar. rotate the bar 180 degrees and repeat. now draw two circumferal lines about 75mm (3") apart. Where the lines around the bar and along the bar meet are the measuring points.
the ones nearest the headstock lets name them A0 and B0 and those furthest away A1 and B1. make sure A0 and A1 are on the same side of the bar.
measure the diameters across A0 to B0 and A1 to B1. Call those measurements d0 and d1.

with a dial gauge attached to tool post with cross slide locked, measure
A0,A1,B0,B1 by sliding the saddle and rotating the chuck. call those measurements a0,a1,b0 & b1.

if the headstock is aligned parallel to the bed a0+b0+d0 = a1+b1+d1

the axis of rotation is at (a0+b0+d0)/2 and (a1+b1+d1)/2