On 19/08/2020 13:23, T i m wrote:
On Wed, 19 Aug 2020 12:33:35 +0100, John Rumm
wrote:
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.
No, true, assuming you can then hold said eccentric object rigidly
enough to bring the OD into concentricity.
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.
Sure, anything 'can' be done but still requires quite a few tools and
'jigs'.
A lathe makes the whole process that much better / quicker. ;-)
Probably not allot in it TBH
Eh? It's *the* tool for that job, if not injection molding, especially
if you have to also make / setup jigs etc?
I was referring to the speed aspect - and for the level of accuracy
required. If you can tolerate a couple of thou, then you can sand to that.
Jigs can be *really* basic if only doing a one off job. I made posher
versions because I need to true up a number of bandsaw cut cogs.
I just stick the stock in the 3jaw, face up the end, centre drill,
drill ID, slide out to live centre, do OD, part off the lengths ...
done and very true / concentric?
Indeed, I am familiar with a lathe :-)
[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).
'Disk sanders table ...' ... ;-)
Then I routed a rebate perpendicular to the disc,
Router ... ;-)
and ripped a strip of
wood
Saw table ... ;-)
that fits snugly into the rebate, flush with the top.
Peasy.
As I said, scrap of wood, and a clamp will do it for a one off.
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.
And you accurately control the od how?
You are rotating the work on an accurate spindle (i.e. the drill bit
that made the clearance hole though it) at a fixed distance from the
sander. Once spun through 360 degrees, you will have a very accurate
circle concentric with the pivot.
(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
Neat. I can see how it could work but question how good it might be
for even nylon, compared with a lathe ... and especially for anything
longer (tube V washer etc)?
ISTR it was only 10mm required - should not be a problem.
Not that Pete's guide rollers necessitated any super high tolerance
but if you have that to hand ...
I can't remember the exact setup but I was wondering if you couldn't
find some suitable ID/OD bearings to fill the gap and let it run on
them?
Yup that was my first suggestion - its actually what my bandsaw uses
anyway.
--
Cheers,
John.
/================================================== ===============\
| Internode Ltd -
http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/