Hi Nicholas

Where are you based, if you live not to far from someone who has the correct tools to set up your lathe I am sure they could help. I live Nr junction 28 M1 Nottinghamshire and have a machine level etc. Or maybe someone else.

David

No good using an 8.5mm piece of bar for a test piece. It flexes way too much under cutting load. Like said above, you need a piece of one-inch diameter bar about six inches long to do your tests on. It saves time if you rough turn the middle four inches or so down smaller to make a dumbell shape so you do your test machining on the two end pieces only, at the same setting.

Leveling the lathe is only a starting point, on a BRAND NEW lathe that had just come from the Myford factory where it was set up on a surface grinder and the top ways ground flat in relation to the four mounting feet on the bottom, which were sat on a dead flat surface grinder table. Leveling is merely a way to ensure that on your relatively wobbly and unflat home workshop bench, the bolted down bed is brought back to dead flat condition as it left the factory.

However, with a used lathe, you face two problems when leveling, both related to wear on the bed ways. First is that a used lathe will usually have a thou or three (or more) wear on the top surface of the ways at the chuck end where most of the work takes place. The front way will usually be worn more than the back way, by a good few thou. So when you set your level on this worn surface, you are not setting the bed back to the condition it left the factory in, you are pulling the worn surfaces back to level, and so quite possibly putting a twist in the bed. Second is that even if you miraculously manage to get the bed levelled to the same position it left the factory in, you still have wear on the bed ways which will cause the machine to cut tapered or otherwise out of spec.

The solution is outlined in the Myford manual, where you take test cuts over your one-inch diameter test bar, with no tailstock centre in place of course, and then further twist the bed until you get the lathe to cut dead parallel. This is done by jacking up the relevant mounting pad on the tailstock end of the bed, either by screw adjuster or shims.

But it sound like if you are getting as close as you are with an 8mm diameter test piece, when you use the one – inch diameter test piece and eliminate flex it should be pretty durn close to perfect, indicating that you have bought a lathe in very good condition. Well done!

Edited By Hopper on 10/05/2017 00:04:55

This may well open a can of worms, but have a look at Rollie's Dad's method of lathe alignment,

It's essentially the same method I used, before I was even aware of it, where, in my case, I employed a 2MT test bar and a dial gauge. Because you are only using a clock gauge, there are no cutting forces to consider.

In my case I couldn't afford a proper certified test bar, but found a brand new, beautifully machined and ground 2MT extension sleeve for £5 from a government surplus store.

I used that to set up the twist in the bed, though using the screw threads on the Myford raising block, rather than sheets of paper. Because it's 2MT, I didn't even need to use a chuck.

I then added a 2MT stub arbour to the 2MT extension, which allowed me to set it up between centres, and was thus able to set the tailstock offset correctly.

When I then used the "dogbone" testpiece mentioned above, with a very light cut, everything came out closer than I could measure with a micrometer, albeit not a 10,000" one.

"Levelling" the lathe is advantageous, but not vital. I've no personal experience of it, but from what I can gather, it's more important with large lathes in industry where the sheer size can allow the bed to distort under its own weight, if the cast in concrete floor mounts aren't perfectly level. I this case the precision level is used across the bed, at both ends in the same way that a wood worker would use "winding sticks" to check for a twist in the workpiece.

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Good attitude

MichaelG.

Nice one! 😀