Mini Lathe and Accessory Advice Please.

[Stub Mandrel]

That's a better finish than I imagined, thanks for sharing the pic, is it a solar blocking filter? 

It's a 0.965" 40mm eyepiece (two coated binocular objectives back to back) I made for a 'toy' scope in the hope it would work as a finder, but the field of view through the RACI prism is tiny :-(

That was with hand feed too - I have the lathe set up for gear cutting and couldn't be bothered to swap the change gears as I need to make another thread at the same setting. With more care a mirror-like finish is possible.

[Chris]

Hi John, so what are reasonable/workable tollerances for out of round and taper on workpieces when using a hobby lathe? I'm guessing this is subjective and job dependant, but it would be nice to turn down a bar, measure it and have an idea if the bearings are good or not.

I guees it's like astro, the more observing you do the more you notice aberrations  

[Ajohn]

 Not to be out done by Stub here is a bit of brass work done with the tip shown and hss in places such as screw cutting the inside of the larger tube and the parts that screw into it.. No polishing of any sort just straight turning. It is as good as it looks  but brass goes dull over time.

It's a centring telescope for setting up a microscope and had to be made up from several parts.

This is a macro shot of poor quality silver steel thats been turned using the tip shown. Marks are at the micron level and it feels as smooth as glass. Patterns are down to bearing noise and vibrations even as hefty as a boxford is.

I did this to try the tips out on a quick and dirty tap I had knocked up and finished with. 0.5mm pitch. The thread that can be seen was cut with HSS. Cut dry. Cutting oil would improve both but I don't think it's a good idea to use that and run so fast that things smoke. It wont work so well and lots would be needed rather than a thin smear on the work. It's better to use black bar really for this sort of thing. Silver steel equivalents are available in it.

Any lathe with decent bearings and reasonably tight slides should produce work like this.  Loose slides spoil the finish on many lathes. Actually from the rings I can see that the bearings were a tiny bit loose in some way. Probably just slight miss alignment front to rear. Believe it or not I have used better but no chance what so ever of having that sort of machine at home or being able to afford a really good example.

John

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[Stub Mandrel]

You can download the 'bible' on testing machine tools HERE

The 'finish turning lathe' limits around page 54 are the ones to aim for, but not all hobby lathes will meet them all.

[RLWP]

You can download the 'bible' on testing machine tools HERE

The 'finish turning lathe' limits around page 54 are the ones to aim for, but not all hobby lathes will meet them all.

This document? http://totallyscrewedmachineshop.com/documents/Testing%20Machine%20Tools%20(Dr.Schlesinger).pdf

Your link only has two pages

Richard

MORE: Incidentally, those are all lathe measurement tests based on having good equipment to quantify the deviations

[Chris]

Thanks guys, definately looks like quiet time reading, i.e when the kids are in bed

[Chris]

John, 

I hope the brass dew shield cap and focuser dust plug I plan on turning for my Skylight 60mm looks half as good!

Very nice

[RLWP]

I think this is the Schlesinger tests as a one page summary: http://osp.mans.edu.eg/s-hazem/Mtdr/MTD04-4.html. The Working Accuracy bit at the bottom is the relevant part - I think. John?

Richard

MORE: The test piece sizes are here: http://osp.mans.edu.eg/s-hazem/Mtdr/MTD04-33.html. In the interests of science and harmony, I'm going to have a go at these on my lathe to see what I get

[Bizibilder]

This thread seems to have run its course.  It has, after answering the original question, now drifted so far off topic that it is time it was closed.