Any tips to centering a MT3 dead center in a lathe?

Rather than using an existing taper to set the taper, I would turn two collars on a bar. The first collar would have a diameter of 1.0000" and the second collar would be located 3" further along the bar. The MT3 taper is .60235"/ft or .1506" in 3" so the second collar diameter. would be 1" - .1506" or. 8494". Make the collars about 1/2" wide for convenience.

The angle between the taper and the spindle axis is 1.4368º so for 3" along the spindle axis, the compound will have to move 3"/cos(1.4368º) or 3.0009". Zero the indicator on one collar and move compound exactly 3.0009" to the second collar and you should have a zero reading if the compound is set correctly. Adjust the compound angle as required. It will help to turn the section between the two collars so the dial indicator doesn't have to be moved to clear.

The advantage of this method is that it doesn't rely on the accuracy of machine alignment.
 
Chuck up a 3MT extension sleeve. Indicate the taper to run true then set your compound to that. Indicating the ID of te tailstock taper also works so does indicating the id of a center sleeve in the headstock.
 
bill stupak said:
chuck up a piece of scrap, center drill it, mount another center in the tail stock, put the first center in between. Accuracy is dependent on the tail stock being aligned.
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I got it done using this method. I lined up my compound with the dead center, but I couldn't get under .002 with the indicator running up and down the MT3 dead center, but I figure it's good enough for me.
 
Glad you got her done. Did you have enough travel in the compound to do it all in one shot?
PS If you have an MT5 to MT3 adapter you can use it to check your new taper using some blue.
 
I don't have enough travel on the compound slide to do the whole thing. Had to move the carriage, touch off, then keep turning the compound handle. Kinda confused me, but I got it done.

Still disappointed there's .002 difference between both ends, though.
 
Pcmaker said:
Still disappointed there's .002 difference between both ends, though.
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Even if a center is not going to torque the MT3 taper much, you do need a good fit in the MT3 socket so the center does not move at all during turning. I would not rely solely on measurements and find a way to check the fit of your new center in an MT3 socket using some machinist blue.
 
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