lathe design

I've been looking at lathe design - you can probably guess why, but I shan't tell you, that would be too (un-?) fairbrotherish.
However, I have some questions, and I hope you can help.
Does anyone know of any good sources on lathe design, preferably online, but I can try the library if that's warranted. I'm especially interested in smallish lathes, about 70mm above bed and 200mm between centres, but capable of very high accuracy (~0.001mm).
Is belt drive better, or is a fully geared head a reasonable choice? Remembering also that I am probably going to have to cut any unbuyable gears...
In the headstock of a small lathe with some kind of belt drive, the pulleys are usually arranged so the largest is nearest the chuck. Any special reason?
Is myford type backgearing better than the traditional type with two cog sets at either end of the pulleys? Why?
I have a zillion more, but that's enough for one post. :)
Thanks,
-- Peter
"Sweet dreams are made of Anything that gets you in the seam And I feel like I'm Seventeen again." Eurythmics
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Peter Fairbrother wrote:

You'll need more than sweet dreams to attain ~0.001mm, you'll need fantasies and the attendant treasure trove...
Tom
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

And a touch like a bloody midwife -- Regards,
John Stevenson Nottingham, England.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 02 Dec 2004 05:04:12 +0000, Peter Fairbrother

You could also try asking on rec.crafts.metalworking A lot of their members 'claim' to have hand scrapped old clapped out WWII South Bends to hold better than this over 24", not taking the curvature of the earth into account.
I often wonder why we went to the trouble of inventing cylindrical grinders when people with these skills are so abundant -- Regards,
John Stevenson Nottingham, England.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 02 Dec 2004 08:32:00 +0000, John Stevenson

Remarkably, they also seem to manage these feats (or should that read "these feets"?) while recumbant in their armchairs, with a glass of beer in one hand & the TV remote in the other.
Regards, Tony
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

"scrapped" is probably nearer the truth than you intended!
From this thread, the project book by Harold Hall I'm working to which says I should aim for better than 0.005mm over the length of the cylindrical squares to be made is rather a challenge for a novice then? I began to worry about this tolerance given that my clock gauge only indicates down to 0.02mm, so I doubt I can even measure to 0.04mm with any certainty - (as a novice in a shed)?
Steve
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Production automatic lathes can produce work to a 3 micron tolerance, so what the man is asking for is not impossible. It is nice to have an interesting aim; even if very difficult.
wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 2 Dec 2004 16:25:40 -0000, "Richard Bennett"

Bollocks <g>
What the man is aiming for is ONE micron tolerance on a home built lathe. Designed by someone with no knowledge of machine tools and built in a garden shed with a machine mart bench drill, a set of measuring instruments that can't read to one micron and a slice of cold toast [ metric slice that is ]
Let's take a good look at this micron or 0.001 of a millimeter.
Coefficient of thermal expansion of say Aluminium is approx 0.0255 microns per millimeter, per degree C rise.
So lets take it you are machining a 50mm bar, that's1.275 microns per deg C
So unless you can prevent the work from rising less than one degree C you have blown your tolerance.
If you have a draughty shed then forget it.
I do agree with the word interesting though <g>
Also at this point we won't discuss the tolerances of the tool marks.

-- Regards,
John Stevenson Nottingham, England.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Richard Bennett wrote:

Well I'm glad that question has been answered, we can now move on to building the optical comparator required...
Tom
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Which could easily be made from a set of NHS bi-focals and a catapult frame for the gimbals -- Regards,
John Stevenson Nottingham, England.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
John Stevenson wrote:

Do the NHS specs come certified to a ~.001mm specification or would one need to make a lens grinding machine to improve the optical magnification and then build a collimating jig? Then of course, there would be the problem of parallax..
Tom
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 03 Dec 2004 06:41:35 +1300, Tom wrote:

this -001mm seems rather vague, is it the radius or focal length of the lens? It must of course be operated with both eyes open or closed - or could it be in varying sequence. The problem of paralax could be solved by using one lens above the other.........
Anyone got a tongue bandage?
--
Linux counter number 335851
Neil
Delete delete to email
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
John Stevenson wrote:

Aiming for about that. Two would be okay. Even five would be better than nothing.

Got some - and I'm a fast learner.

Oh dear me no. I don't have a shed. I'm a math geek, not a shedi.
The lathe will be built initially in the workshops at Trowbridge College, where they have Harrison lathes and Bridgeport mills and such (including a Super7), fine for roughing work to 0.1 or even 0.01 mm, depending on size etc.
I'm a part-time student of model engineering there. Incidentally I recommend it if anyone local is interested, the tutor is good (though busy), and you get to play with all kinds of machines.
Then I can use the modern cnc lathes and mills and the very accurate measuring equipment at [..] University to do the finishing work (as it's a bit unofficial I'm not naming anybody).
It will be used in a proper workshop, on the first floor of a modern brick building, with a concrete underfloor and climate control (well, with central heating at least).
BTW, an optical comparator? didn't they use them in the war, for gun parts and suchlike? - video measuring technology, and now 3D laser, is the "in" technique.
--
Peter Fairbrother


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 02 Dec 2004 21:06:55 +0000, Peter Fairbrother

In which case ignore everything I have said as it was all practical and not theory. -- Regards,
John Stevenson Nottingham, England.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Tony Jeffree writes................

I don't think they 'do' feet, only the metric stuff!
Mike
--
Mike Whittome

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
John Stevenson wrote:

If you don't mind too much, I won't - you usually talk practial sense, and I'm usually much better at the theory than the practice anyway.
--
Peter Fairbrother


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'm a physics geek. Which is several orders of magnitude closer to actual reality than a maths geek. However, I have discovered that physics geeks are several orders of magnitude from engineers, who are themselves often a couple of orders of magnitude from machinists in actually knowing how to shape bits of metal. Forget everything you know. It's fun to try to work it back to first-principles once you know it, but learn from those who do know first.
If you remember you know nothing you'll learn a lot.
Tim
--
Foo.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hand "scrapped"? I think you have misintentionally spelt that correctly John.
Regards,Mark.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
John Stevenson wrote:

What's a midwife's touch supposed to be like? I'm guessing that's a common metaphor, but I haven't heard it.
The only midwife I know (who happens to be a guy) is a rather rough-n'-ready type. He is said to be very good, but I have never needed his services. He does get bloody sometimes though, maybe his touch changes then.
Come to think of it, you wouldn't want a midwife who dropped the baby because her hands were slippery with blood, would you? I guess that's what it's about.
On a somewhat battered college Harrison 300 I can machine a short round section to size to considerably better than one 0.01 mm division on my micrometer (say to 0.003 mm), that just takes patience (and a good feed helps). On a small purpose built lathe I'd expect to do better than that without great difficulty.
I don't know about doing it over any length though.
Thanks for the rcm suggestion, I think?
-- Peter Fairbrother
Who would skip and who would plod Or who would lie quite still-ly And who would ride backwards on a giraffe Stopping every so often to laugh by Mike Heron
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You could check out single point diamond turning for inspiration. This achieves even greater tolerance and good surface finish for optics. eg: http://www.leioptics.com/diamond_turning.htm
Scrim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.