On 18/08/2020 23:07, T i m wrote:
On Tue, 18 Aug 2020 22:32:17 +0100 (BST), "Dave Liquorice"
wrote:

Why do you need a lathe?

Get hold of a suitable short length of rod (eBay?) of say 15 mm dia,
cut a 10 mm length, carefully drill a 5 mm hole in the centre,

That's the first reason ... ;-)

If you start with something larger in OD than you require, and drill the
right sized hole in it, then it does not matter if you are a bit off.

Yes, if you were in the back of India or on a desert island I'm sure
with enough material to work with you could eventually get a pair of
rollers that are concentric and worked.

I find its easy to get a very accurate and concentric ring of stuff
using nothing more than a fixed disc sander, and a circle truing jig[1]
- which is basically a small bit of ply or MDF that you can fix your
work to such that it can spin round a pivot, and can be offered to the
sander.

A lathe makes the whole process that much better / quicker. ;-)

Probably not allot in it TBH

[1] I made a "posh" version - a 8" square (ish) bit of 3/4" MDF with a
bar fixed to the underside, that fits snugly into the slot on the disc
sander's table so it will stay a fixed distance from the disc (the
simpler version - just use a clamp).

Then I routed a rebate perpendicular to the disc, and ripped a strip of
wood that fits snugly into the rebate, flush with the top.

To use it, drill your blank, and then partly drill the strip of wood at
the end with the same drill. Remove the drill, invert it and push it
through the work and into the strip. Set it up on the sander and tap the
strip toward the disc such that the corners of the work will touch the
spinning disc. Turn the work through a full circle round the drill bit
pinion, and then advance the strip. You will end up with a concentric part.

(the non posh version - bit of wood and a clamp or two)

Here using a Forstner bit as a pinion:

http://wiki.diyfaq.org.uk/index.php/...andingRing.jpg

--
Cheers,

John.

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