Machinist's Level help

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liveaboard
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Re: Machinist's Level help

Post by liveaboard » Tue Sep 08, 2020 2:08 am

ctwo wrote:
Mon Sep 07, 2020 11:03 pm
the bench moving throughout the day - the bubble will go full tilt one way then the other.
That's interesting!
Only on sunny days?

My lathe is in a 20' sea container sitting on little concrete squares in sand.
I have no hope.

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ctwo
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Re: Machinist's Level help

Post by ctwo » Tue Sep 08, 2020 9:31 am

liveaboard wrote:
Tue Sep 08, 2020 2:08 am
ctwo wrote:
Mon Sep 07, 2020 11:03 pm
the bench moving throughout the day - the bubble will go full tilt one way then the other.
That's interesting!
Only on sunny days?

My lathe is in a 20' sea container sitting on little concrete squares in sand.
I have no hope.
It could be my level configuration, the stuff it's stacked on or the bench, or a combination of things. I've only been looking at it for the past week or so and we're having a heat wave - 106F the other day and 62F now. The house only moves about 25F at most.
The bench is steel box tube framing with thick laminate top and a lot of stuff stacked on it. The back two legs are on concrete and the front two on carpet. The level is sitting on the middle front on a 6"x6" granite plate and overhangs a bit. I should really put it out in the shop on my big plate but it's been getting too hot out there.

Now this reminds me of another discussion elsewhere where the engineers had wrapped the vial with three pieces of separated foil (bottom and L/R top half's) to make a differential probe. They claimed they could detect the presence of their car out in the driveway with the level sitting inside the garage floor, as well as when they walked near the setup, amongst other things like trucks driving by or other anomalies. Of course now you can just get an inclinometer in a single chip with a range up to ±30º and resolution to 0.001º
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BadDog
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Re: Machinist's Level help

Post by BadDog » Tue Sep 08, 2020 11:48 am

I'm a bit confused with some of the commentary on using various reference planes. For calibrating a very sensitive level, you are going to have to use a very rigid surface that is close to level within the range of the vial. Otherwise, even if the bubble is reading on the scale, once you turn it, it's always going to be off the scale. If I were calibrating my 199 I would probably use the my lathe, and first as close to level as possible with my 98 (verifying it in turn).

But then again, it's not actually critical that a lathe be level. So you don't have to use a calibrated level, just don't flip it (or change it's orientation at all) as you check the reference points, and make sure they all read as close as possible the same.
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John Hasler
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Re: Machinist's Level help

Post by John Hasler » Tue Sep 08, 2020 3:54 pm

Assume that the level is out of adjustment such that when placed on the mythical truly, totally level surface it would read one division off. That means that the actual zero position of that level in its out of adjustment state is one division away from the point on the scale marked "0". Thus when it is placed on a tilted surface and rotated until it reads "0" it is actually one divsion away from level. Rotating it 180 degrees will cause the bubble to move to a position on division on the other side of the point where the bubble would be on that truly level surface, which means that the bubble will be two divisions away from the point labeled "0".

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Re: Machinist's Level help

Post by Bill Shields » Tue Sep 08, 2020 8:38 pm

Liveaboard

It is only hopeless if your lathe is in a sea container on board of a ship floating in a body of water.
Too many things going on to bother listing them.

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Re: Machinist's Level help

Post by pete » Wed Sep 09, 2020 12:24 pm

Maybe something worth mentioning, adjusting a machinist's level so it shows the same vial reading each time it's turned 180 degrees is the last step. Ideally you'd have at least a decent surface plate to first check if the base is flat by pressing on each corner of the level and see if it rocks at all. If that proves to be ok then checking where it hinges on that surface plate would be the next step. It's a very common trick used by most who do hand scraping. Gently pulling and pushing on one end of the level an inch or so in each direction while it's on that surface plate is all you need to do. If the levels base is flat it should pivot around a point at about 1/3rd the distance away from the end. Do the same check on the other end of the level. Having a concave base it will only pivot at the ends, convex and it will pivot around wherever the high point is.But it's a sensitive enough test to show even a 10th deviation.Those would be the rough first tests only. Better would be to lightly blue up the surface plate and then test the level's bottom bearing face against that. A good but known to be non flat level can still work, but it has to be supported in the same way during each reading. If it can rock at all the readings are worthless since there not repeatable. So those basic checks should be done first before calibrating it to read the same in both directions. It depends on your expectations of accuracy, but that thermal stabilization is still a good idea. My Mit. level is good to 6/10ths over 12". It does show very small but still measurable changes if it isn't equalized to the part it's checking because it's base is either slowly contracting or expanding. Leveling a lathe it's probably not enough to matter, but it's still worth knowing it can happen.

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Re: Machinist's Level help

Post by liveaboard » Wed Sep 09, 2020 1:49 pm

Bill Shields wrote:
Tue Sep 08, 2020 8:38 pm
Liveaboard
It is only hopeless if your lathe is in a sea container on board of a ship floating in a body of water.

ctwo said his level is showing his workbench shifting during the day...
The container floor is plywood over steel beams. It will probably deflect significantly as I step from one side to the other, not to mention different work and materials being moved around.
I think the degree of accuracy you guys are talking about could only be achieved with a solid and massive concrete foundation.

A friend of mine has a lathe in a boat. Big lathe, small boat, I think he built the cabin around the machine.
I stayed in the tiny front cabin once; he told me not to worry, he wouldn't start the lathe early.
I said please do, it's like music to me!

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seal killer
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Re: Machinist's Level help

Post by seal killer » Wed Sep 09, 2020 6:17 pm

Pete--

Thank you for that expert advice! The surface plate is in a box and I know where it is!

--Bill
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Re: Machinist's Level help

Post by John Hasler » Wed Sep 09, 2020 7:34 pm

Some precision levels have a foot at each end rather than a continuous flat bottom. This eliminates the possibility of teetering. You can get the same effect by placing a gauge block under each end though of course that adds uncertainty.

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Re: Machinist's Level help

Post by pete » Wed Sep 09, 2020 10:42 pm

Thanks Bill, but I'm sure no expert at anything and least of all machining. After enough time you just naturally pick up bits and pieces of information here and there and sometimes it's even useful. Maybe if I pack enough in there Dementia won't have any room to get started? :-)

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ctwo
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Re: Machinist's Level help

Post by ctwo » Thu Sep 10, 2020 9:46 pm

John Hasler wrote:
Wed Sep 09, 2020 7:34 pm
Some precision levels have a foot at each end rather than a continuous flat bottom. This eliminates the possibility of teetering. You can get the same effect by placing a gauge block under each end though of course that adds uncertainty.
I am imagining adding modular feet to the bottom of mine now... or maybe I will just mill out the center 1/4 of the span.
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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Re: Machinist's Level help

Post by Harold_V » Fri Sep 11, 2020 1:19 am

ctwo wrote:
Thu Sep 10, 2020 9:46 pm
John Hasler wrote:
Wed Sep 09, 2020 7:34 pm
Some precision levels have a foot at each end rather than a continuous flat bottom. This eliminates the possibility of teetering. You can get the same effect by placing a gauge block under each end though of course that adds uncertainty.
I am imagining adding modular feet to the bottom of mine now... or maybe I will just mill out the center 1/4 of the span.
That's not a good idea. Any metal removed from the base will most likely result in the base moving (bowing). The amount may not be much, but a level must be stable to be able to do the work intended. It would be in your best interest to scrape the base, or to lap it. Both of those methods, done properly, will be self correcting.

H
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