Lathe realignment

[Robfo]

So how do you realign a lathe?

I use a Cobra lathe that i've had for over 7 years and i think its about time that i made sure it's cutting straight, i think it might be slightly coning my comms.

Any help would be much appreciated.

[Mark Christopher]

I quess you would measure it!! :D
try an engineering firm or lathe shop, they will set it up

[PDW]

It seems to me unlikely that the lathe needs re-aligning, the cutting forces are so low. To check taper...

Using a micrometer, measure the comm diameter at the tip, middle and end. All three diameters should be very close, but are unlikely to be identical. Anything up to .003" taper/difference won't be noticed in use.

I suggest you check the play on the slides that move the toolpost in/out and back/forwards. If there is excessive play, then this must be removed. Some lathes have adjustable strips (gib strips) for this purpose. If you have a couple of grub screws to move each gib strip, make sure you adjust each one the same, otherwise you may create a taper in the comm you haven't got now!!

Re-check tool height. Although ideally, you should run the tip on the centre line of the comm, I run mine slightly (.005") above centre to ensure that there is no rub on the back of the tool. Incorrect tool height can cause the comm to move about.

Lastly, if you have rolling element (ball) bearings, take them out, clean them, re-pack them with grease (not oil) and replace. When they are clean, check them for play - too much and, again, the comm is moving around during cutting potentially giving you a taper. Change for new ones, but make sure you get the right grade, otherwise too much play will put you back where you started!

Do one of these at a time, cut the comm, and re-measure the taper - or, hopefully, lack of it!! HTH :)