May seem a daft question, but how much discrepancy in levelling the bed is
too much?

I'm aware it's bed twist that really matters, rather than end-to-end or
exact side-to-side levelling, but how much twist?

I've found that my grandad's WW1 clinometer (used for setting up the sights
on Vickers .303 machine guns - he was the final inspector in one of the
factories!) is accurate to 1 minute of angle , which I think is an inch in
about 95 yards, and can be set +/- 15 degrees consistently- accurate enough,
too accurate?

Thanks all,

Dave H.
--
(The engineer formerly known as Homeless)

"Rules are for the obedience of fools, and the guidance of wise men" -
Douglas Bader

On Nov 5, 12:49*pm, "Dave H."
wrote:
May seem a daft question, but how much discrepancy in levelling the bed is
too much?

I'm aware it's bed twist that really matters, rather than end-to-end or
exact side-to-side levelling, but how much twist?

I've found that my grandad's WW1 clinometer (used for setting up the sights
on Vickers .303 machine guns - he was the final inspector in one of the
factories!) is accurate to 1 minute of angle , which I think is an inch in
about 95 yards, and can be set +/- 15 degrees consistently- accurate enough,
too accurate?

Thanks all,

Dave H.


Try it. The real test is if it can turn a cylinder parallel to the
accuracy you need (or can measure). Uneven wear and misadjustment may
cause more error than the twist.

The bubble on my 12" South Bend Lathe level moves about 1/32" per
thousandth.

jsw

On 11/05/2010 11:49 AM, Dave H. wrote:
May seem a daft question, but how much discrepancy in levelling the bed is
too much?

I'm aware it's bed twist that really matters, rather than end-to-end or
exact side-to-side levelling, but how much twist?

I've found that my grandad's WW1 clinometer (used for setting up the sights
on Vickers .303 machine guns - he was the final inspector in one of the
factories!) is accurate to 1 minute of angle , which I think is an inch in
about 95 yards, and can be set +/- 15 degrees consistently- accurate enough,
too accurate?
A master precision level is accurate to about .0001" per foot, not
exactly sure what that converts to in arc seconds. I use an electronic
level that is good to a couple arc seconds, and it is more sensitive
than I actually need.

Jon

"Jon Elson" wrote...
A master precision level is accurate to about .0001" per foot, not exactly
sure what that converts to in arc seconds. I use an electronic level that
is good to a couple arc seconds, and it is more sensitive than I actually
need.

Jon


I make that master level accurate to about 1.7 arc seconds... and a minute
of angle is about 3 thou"/foot so a couple of orders of magnitude away

Dunno if anyone can give a *quantative* answer though? Currently the Big Toy
isn't in working order (still have to hook up the VFD and interface to the
original switchgear and 3-speed motor) so I can't do a parallel-turning
test, but it appears to be level to less than 20 m.o.a. across the boring
table, about 1+1/4 degrees head-down due to a sloping shed floor, and
(possibly thanks to the 2 tons of Old Iron) less than 10 m.o.a. of twist?

Cheers, thanks for the info,

Dave H.
--
(The engineer formerly known as Homeless)

"Rules are for the obedience of fools, and the guidance of wise men" -
Douglas Bader