Need Help!- Harrison m300 lathe problem

[garrygun]

Hi guys, as i am very new to machining, i have come across a problem with my lathe, when i make a cut it runs out by .25mm over 75mm cut length, the cuts were taken from tail stock towards the headstock i tried auto feed and manual feed with and without tailstock live centre, i still get same run out, so if there is someone that could help me put this right or if there is a video of how to set up, i would greatfully apreciate it, be gentle with me as im a beginner and do not understand all the jargon. Thanks, Garry.

[handlewanker]

Hi Garry, you might need to reallign the headstock to the bed ways.

To do this simply, first get a piece of 20mm diam Silver steel about 800mm long, and use this as a test piece when checking headstock/tailstock allignment.

Next, use the fixed steady to centre the two ends, and check the bar between centres for rotational accuracy with a dial indicator.

The silver steel is in the annealed state and with a ground finish, but still hard enough to withstand wear and tear.

Then place the silver steel in the three jaw chuck and LIGHTLY nip up the chuck jaws.

Assuming your chuck is in good nick you can now test the accuracy of your chuck holding capability, by rotating against a dial indicator.

A .02mm (,001") runout over 100mm (4"), is acceptable for most purposes, and with a fairly used lathe this is quite good.

If you have any degree of bellmouthing in the chuck jaws you'll be all over the place if you try to hold work accurately, so a jaw regrind is required if the scroll on the chuck is in good shape, (hardly likely if you have bellmouthing).

The second method, and one advocated by most lathe users, is to mount a piece of 30mm diam mild steel bar in the tree jaw and sticking about 160mm out from the chuck jaws.

Mark a line round the bar, with a pointy tool, about 25mm from the jaw end and another at the end of the bar.

Undercut the bar BETWEEN the two lines about 4mm deep, (rough turning will do as the surface finish is irrelevent here) and this will give you two collars 25mm wide at each end of the bar.

Do NOT use the tailstock for the next operation.

Now take a LIGHT cut on the bar end about .1mm deep, to clean up, and continue to the chuck end WITHOUT, repeat WITHOUT moving the crosslide, and repeat the cut there.

Measure the diam of each collar, and any variation in diam will tell you if the headstock needs to be realligned.

If the two collars are of equal diam then it is most probable that the chuck is bellmouthed and allowing the material to push away from the tool while cutting.

Mount the dial indicator on a mag base on the saddle and test across the top of the two collars.

Any variation here indicates the headstock is pointing up or down, and seriously needs adjusting.

If the silversteel test bar is made with two accurate centres, you can now test the tailstock allignment by first cutting a centre on a piece of mild steell in the three jaw chuck, and placing the silver steel test bar between centres (a dead centre NOT a revolving centre in the tailstock end) and using a dial indicator along the bar on top and side.

The side test will give you an indication of side allignment, easily adjusted, but if you get any variation in the top test, this will indicate tailstock to bed wear, (assuming the headstock tested OK), and that is serious.

The silver steel test bar, once made is an invaluable tool to check tailstock allignment quickly, and should be wrapped in oiled cloth to maintain it rust free.
Ian.

[garrygun]

I thank you for your info, im working on this now, i think ive made a cock up some where, i will let you know when ive done all those tests.
Thanks, Garry.