I have just purchased a Boxford Lathe

[123hotchef]

If you work in mm but your lathe is inches just use a digital caliper and use the MM/inch button to swap between them. Lets say you want to turn something down to 8mm. Set your caliper to 8mm then zero it and push the mm/inch button. Now measure the part and it'll give you a reading (in inches) of how much you need to take off.

Hey that's simples I like that

 

[brightspark]

digital callipers are a must for working metric and imperial and can be zeroed. dial callipers cant but I still use and have both

 

[zx9]

Hey that's simples I like that

But remember that is how much you need to take off the diameter not the radius, easy to forget with everything else to think about when you are a beginner lathist, not that I have ever done that

 

[northwest]

it does when it needs to be accurate

No, I think you misunderstood Seadogs comment. What he meant was, it doesn't matter whether he is working in metric or Imperial, he is comfortable with both.

At the end of the day, both systems are units of measurement and as long as you understand the concept it doesn't matter what the measurements are in. I can "visualise" both so I too work in metric or Imperial though I do try not to mix them both together on the same job, it can have unintended consequences.

 

[123hotchef]

Ah I understand now.
I guess I will get use to it I find it more difficult when tenths and thous are used but the gauges on the lathe are in 100's if I read them correctly

 

[Brad93]

Ah I understand now.
I guess I will get use to it I find it more difficult when tenths and thous are used but the gauges on the lathe are in 100's if I read them correctly

With inches, if we say tenths, we are actually talking 0.0001”, so a tenth of a thou which is 0.001.

You won’t need to worry about tenths, unless you buy a cnc lathe.
To turn anything within 1-2 thou is pretty damn accurate.

 

[123hotchef]

a tenth of a thou that is small! so the gauge on my slides are marked in 100s

 

[addjunkie]

A DRO fixes most of these measuring miss understandings, they have a mm/inch button.

And if measuring with digital callipers buy a decent set for good repeatability.

 

[Brad93]

Yeah you’ve got 100 thou graduations in one revolution of the handle.

So one full rotation is 0.100”

 

[northwest]

You won’t need to worry about tenths, unless you buy a cnc lathe.
To turn anything within 1-2 thou is pretty damn accurate.

I am usually working in tenths, it can be challenging :-(

and slow.

Setting up my new CNC mill over the coming weeks so that will hopefully move things on.

 

[123hotchef]

Yeah you’ve got 100 thou graduations in one revolution of the handle.

So one full rotation is 0.100”

so one full turn will take off 2.54mm

 

[northwest]

so one full turn will take off 2.54mm

Perzackly!

 

[123hotchef]

Perzackly!

when set at 30 degrees though! and that is 2.54mm of of the diameter where as the cross slide will take 2.54mm of of the radius?

 

[addjunkie]

Your best bet is to stick some stock in the chuck, and have a play, measure play, try a spring cut see how it goes, keep winding the handle in over if you wind out, you will then have back lash to contend with.

Sometimes I ignore the dial make the cut, mark the dial with a piece of chalk, wind it out, return to the start after measuring, and then wind back in to the chalk mark, to account for back lash, then take the next cut. I use a dro, but find the chalk easier to see than keeping a close eye on the dials. I usually do this screw cutting too, just something I was shown 35 years ago by a Korean fitter when I was at sea.

Every machine is different you need to become familiar with yours.

 

[northwest]

Every machine is different you need to become familiar with yours.

This. In a nutshell. Make something, doesn't matter what, a piston to fit a bore, a nut and bolt, a scribe handle. Anything, this will give you a greater insight to the machine than anything else. Constantly testing and checking will drive you nuts and teach you little.

 

[123hotchef]

I am making bits, thanks guys

 

[Brad93]

when set at 30 degrees though! and that is 2.54mm of of the diameter where as the cross slide will take 2.54mm of of the radius?

Radius. Never diameter. Whatever cut you put on, it is cutting that off the radius.

The cross slide will take 2.54mm for one full turn.

The compound would take 1.27mm if set at 30°

 

[123hotchef]

ah so inreality

Radius. Never diameter. Whatever cut you put on, it is cutting that off the radius.

The cross slide will take 2.54mm for one full turn.

The compound would take 1.27mm if set at 30°

but the cut is off of the whole radius both sides does that not mean the diameter is reduced by twice the cut

 

[Seadog]

The cut obviously reduces the diameter. Some dials are calibrated in diameter rather than radius, you just nned to know wgic type you have (yours is radius, btw). The techique of off-setting the compound is used to allow finer control over finished dimension.

 

[123hotchef]

thanks that saves me taking cuts and measuring although I will at some stage, I need to move the compound to 30 deg and the tool post back to compensate then