Completed (almost) Pendulum Level

[Graziano]

Apart from a typo Nicks figures are correct. If that were me, I'd use a level with a 0,05mm per metre resolution, exactly as he said. If you had that level sitting on a 1 metre long straight edge, and shovelled a 0.05mm shim under one end of the 1 metre long straight edge, it will change by 1 division.

Phil.

So Phil, for that resolution of spirit level you'd see an angular resolution of TAN^-1(0.05/1000)=0.00286 degrees?. Kind of renders mucking about lasers and reflectors almost obsolete without a long folded path to resolve 1000ths of a degree .

Edit, actually it would be sin^-1(0.05/1000)=0.028647 degrees, sine=opposite/hypotenuse not tan=opposite/adjacent.

[tongleh]

I don't know anything about lasers, but surely the point would be too large to measure in the increments being talked about here?

[Graziano]

I don't know anything about lasers, but surely the point would be too large to measure in the increments being talked about here?

Not if you are measuring it against a large diameter circle, iow a long beam path: that's why I picked a distance of 5.729 metres, at that distance, one degree of angle is equivalent to 10 centimetres of the circle's circumference, i.e. 1/360th of a 36 metre circumference circle.

That's just if you have the laser mounted to the moving pendulum, if you have the laser shining on a moving mirror on the pendulum, then the movement of the beam doubles compared to a laser just mounted on the pendulum. Mirrors reflect so the angle of incidence equals the angle of reflection, this means if the mirror rotates one degree then the laser beam shining on it will bend two degrees. If you ran the beam between to mirror strips one fixed and one on the pendulum pivot say three times, then one degree mirror rotation would reflect the beam 2 degrees on the first bounce, 4 degrees on the second, 8 degrees on the third bounce.

That means with a beam length of 5.729 metres bouncing three times over two mirrors 143cm apart would move the laser dot 80cm for a one degree rotation. so if your dot is 2mm diameter you could resolve 1/400th of a degree with a millimetre ruler.

[scottyd]

Has anyone considered the use of diffraction around a sharp edge to amplify the motion of the laser? The diffraction pattern moves much faster than the laser does. One could set the "centre" of the level for when the diffraction pattern matches a predetermined set of marks. You could also bounce the light between a pair of mirrors a number of times before meeting your diffractive edge. Two mirrors placed 572.9mm apart with the laser arranged to bounce ten times will give you your 5.7 meter length. You could make a slightly cumbersome but pretty cost effective level.

[Bryan]

I got all excited when the talk about laser pointers came up. But your right about the target. I can't think of a way to make it reference back to the lathe.

Ben I'm way behind some of these guys with their smoke & mirrors, but the thing that dawned on me is that the pendulum always points down, so a laser attached to that will always point to the same plane, and so provide a reference (target). If you then stick another laser on the base - which sits on the ways - and measure the distance between the two points on the wall, you're set like a jelly. I know Mark Graziano alluded to that in post 45, I just thought I'd expand a little in case it helps the slow learners - like me!

[MuellerNick]

But when anyone makes an 'absolute' statement to an Aussie that we are wrong... Well it just gets my back up! there is a 'gentle art of conversation' too often lost these days.

I didn't say that Aussies are wrong. Nor that they are always wrong, not even for genetic reasons. I said that this specific math is wrong.

When I once was in OZ, I didn't have the impression that Aussies are pussies like the Americans that immediately start crying whenever you critic something. I had the impression that they are robust, direct and open minded people. And VERY kind!


Nick

[simonl]

I didn't say that Aussies are wrong. Nor that they are always wrong, not even for genetic reasons. I said that this specific math is wrong.

When I once was in OZ, I didn't have the impression that Aussies are pussies like the Americans that immediately start crying whenever you critic something. I had the impression that they are robust, direct and open minded people. And VERY kind!

Nick

Hi Grumpy Nick. I'm robust. Stay with us buddy!

........ even if we do do your head in and we're #### at maths!

Cheers mate!

Going to have a BEX and a lie down. Happy father's day to me and eveyone else!

Simon

[MuellerNick]

Hi Grumpy Nick. I'm robust.

The Aussies must be robust. From what I have seen and learned in OZ. The way they drink!
And from what I have seen at the Oktoberfest Munich. OMG! But I don't think they are all combat drinkers.

It's OK to call me "grumpy". From time to time.

OK, back to topic ...


Nick

[Ben Dono]

The Aussies must be robust. From what I have seen and learned in OZ. The way they drink!
And from what I have seen at the Oktoberfest Munich. OMG! But I don't think they are all combat drinkers.

It's OK to call me "grumpy". From time to time.

OK, back to topic ...


Nick

Sorry Nicko! I got a little hot headed. Nothing worse than a poorly behaved Aussie!
I I'm getting the feeling a pendulum style level if kept simple in halfway between a good carpenters level and forking out for an engineers level.

I think when I get around to it, will just make a jig that sits on the ways with a laser line (not a point style) projected on the ceiling. No pendulum or any moving parts. Mark that line and reposition it at the other end and check the difference. I'm lucky as I have about 3m above the lathe bed. Will let everyone know how it goes.

[QC Inspector]

There is another way to measure using a laser and that would be one of the Faro Laser Trackers. It sends a laser beam to a reflector which sends the beam back to the sending unit and measures the distance. In this application you would attach the reflector to the pendulum and measure the distance the pendulum moves to .0001" or .00254mm.

The thing is that if you do have access to a Faro Tracker you could just take your readings directly off the bed of the lathe for level, twist, etc., and skip the pendulum altogether.

FARO Laser Tracker - Home

[ame=http://www.youtube.com/watch?v=6hLTKw-GizA&feature=related]The Worlds Most Accurate Large Volume Laser Tracker: FARO® Laser Tracker ION - YouTube[/ame]

Note: I don't work for Faro so don't get a kickback if you get one for your shed. I get to use one at work on occasion though.

Pete

[tongleh]

"I'm getting the feeling a pendulum style level if kept simple is halfway between a good carpenters level and forking out for an engineers level."

The idea in the first place!

[Ben Dono]

"I'm getting the feeling a pendulum style level if kept simple is halfway between a good carpenters level and forking out for an engineers level."

The idea in the first place!

Did you try out the shim test after you zeroed the scales yet? I just went through the posts in did not see a report on it.

[tongleh]

Yes I did, but the results I posted recieved quite a bit of negativity: Don't think I'll bother with posting anymore!