Where can I buy a parallel bar ( I need to true my lathe tailstock)

Chronos do them. See

Click on Lathe accessories, and they're the last two items in that section. For an M250, if it's like my older Harrison 140, the headstock will have a bush to enable fitting of 3 morse items, so you'll need an MX185, =A337 inc VAT.

I'm sure other people like Warco, Rotagrip et al. do them as well.

Cheers

Alastair

imagedude wrote:

Hi, I don't know what the taper is in a Harrison tailstock but

list parallel test bars up to 5mt. I suspect J&L would have something similar. I think the Chronos price is about =A335.

I'm no expert in this game but I am intrigued as to why you need a test bar for the tailstock setup. If you want to check that it is parallel to the bed can't you test on the extended barrel? If you want to check the height or offset, I've used the trick with two new centres and a flat shim between the points to get exact centre and then a dial gauge to set the offset if required, it has always worked for me.=20

Best regards

Keith

If that's all you want to do, then save your money and use the following method... Put an accurate dead-centre in the tailstock and a largish (1/2" is big enough) ball bearing in the chuck with as much of it protruding as possible. The chuck must hold the ball accurately, so use the 4-jaw independent if the self-centring is not good enough. Place the flat side of a 12" rule against the ball and bring up the tailstock to sandwich the rule between the ball and the tip of the centre. If, and only if, the rule remains perpendicular to the lathe centre-line, the tailstock is correctly aligned. If the rule is not parallel to the chuck face, one end will be closer than the other. Let's assume that the difference between the ends is

1/16" (which is pretty easy to see). A 1/16" difference in 12" gives a slant of 1/(12x16), or around .005 and is because the point where the rule is pressed against the ball is not on the centre-line of the ball. The 1/16" then, is a magnification of the distance that the centre-point deviates from the lathe centre-line, and is approx. the slant (.005) times the radius of the ball. With a 1/2" ball the radius is 1/4", and the distance between the tailstock and headstock centres is around .25" x .005, or about .001". Accurate enough?