Levels of precision

[Tin Falcon]

The thread free lathe reminded me of the fact that all levels are not created equal.
I did some research and was surprised at the published data.

A good carpenters level is good to .0005 in per inch this translates to .006 in/foot. max accuracy I was surprised at this claim as the starret 98 series is only rated to .005 in per foot.
a master precision level reads in .0005 in per foot.

Use the best you can and remember a good level will always give the same reading when you turn the level 180 degrees.
Tin

 

[enfieldbullet]

you can actually calibrate it with that 180 turn.

if the bubble is in the exact same spot after reversal that means it is calibrated. if it does not match you must tilt the vial or the base to adjust. on precision levels there are screws or something to allow adjustment.

you can use feeler gages to determine which side is lower and by how much. the aim here is to make the bubble stay on the same spot. remember to use the feeler gage on the same side of the level during adjustment.

 

[///]

Precision levels also have less curvature in the vial, making them more sensitive.
They also often have better scale markings making it easier to judge the bubbles position.
I have seen some cheap levels with at least 1/16" gap between the bubble and the markings at each end, useless.

 

[dnalot]

OK I want a precision level but the price has put me off. Even the used ones on e-bay are pricey. So I bought the glass vial for a Starrett 12" ~ 15" level for $22 and I plan to make my own. I'm thinking I will make the body out of brass unless someone here thinks that's not a good idea.

Mark T

 

[enfieldbullet]

what is the vial's precision?

common practice for precision level is cast iron body, pin point scraped flat on the bottom.

 

[Tin Falcon]

Not a lot of point in a precision vial if the bottom of the body is not near dead flat.
Tin

 

[dnalot]

The vial is Starrett part number PT10524. It measures a little over 3.5" long. Perhaps steel or cast iron would be a better material. The surface would need to be honed to mate it perfectly to a surface table.

Mark T

 

[enfieldbullet]

you should if possible scrape it, best possible way of guaranteeing flatness.

cast iron scrapes well, steel not so much, and brass i believe is hard to scrape also although i have never scraped it, only engraved.

 

[aarggh]

Would the glass vial itself be symmetrical enough? I recall Jans Ridders when making his engines found glass tubes didn't have enough tolerance to be used with graphite pistons, and had to get "precision" test tubes. If your tube is even slightly out at any point, the level will be out. Last year when I wanted to replace a couple of 1200mm levels, I quickly tested about 20 in store before I picked out the best that was there, I was stunned at the amount some were out.

cheers, Ian

 

[enfieldbullet]

they're supposed to be supported at two points in both ends.

they're about cylindrical in the outside but barrel shaped on the inside, there's also that.

also, spreading those two points apart by making a base for the level increases it's ability to detect error. somewhat of an amplification effect.

 

[aarggh]

What I meant was, the very minutest deviation from manufacturing will render it useless as a precision level, regardless of length. From the ones I've seen, the small individual glass vial levels are more for determining if things are more or less straight or plumb over a length or height. Any imperfections in the glass greater than 0.001" mean it's not a precision level? Have you run a micrometer over it, as if the outside isn't spot on, you can be sure the inside won't be. There's also the issue of machining a body for it, again, unless you can do it to 0.001" or less precision, the level will not be able to be turned around if there's any deviation to one side, as it will never read the same level when flipped. You'd need to build in some sort of very fine adjusting mechanism, and a lot of effort to get it to read right in the end.

cheers, Ian

 

[enfieldbullet]

Ian,

i will have to disagree slightly.

the glass vial may be out of shape on the outside, because that part is not 'precision'. usually only the interior is ground to a slight barrel shape. and that grinding only ensures smooth dislocation of the bubble, otherwise it would dance around to much or jump from graduations to another.

the glass vial itself can't be used as a precision level because of the surface deviations you pointed out. however what i think he bought is the vial for a precision level, which now can be fitted on a base.

the precision needed for machining the base consists only of achieving a flat bottom surface. the vial is put on top and with adjusting screws you can make sure it shows true level.

what i meant to say, i guess, is that i think it can be done, and i don't think it would be too hard either. it would take some almost forgotten techniques but it won't take very expensive equipment.

 

[Tin Falcon]

Options a good usa made master precision level new can cost several hundred dollars . Almost as much as many have in there budget to buy a late in the first place.
so options a import one can be had for less than $100 .

master precision level on e -bay


There is another option buy a precision vial pre mounted in a tube made in USA and make your own base . a little more money and work but made in USA quality.
For $ 90 you can get one that reads .0005 in/foot for a little more$102 you can get one that reads by.0003 per foot .
Tin

View attachment 4-6010_drawing.pdf

 

[Davo J]

You can get a 8 inch level posted for $85 from CTC tools.
http://www.ctctools.biz/servlet/the-403/PRECISION-LEVELLING-OF-MACHINE/Detail

Dave

 

[aarggh]

Ian,

i will have to disagree slightly.

the glass vial may be out of shape on the outside, because that part is not 'precision'. usually only the interior is ground to a slight barrel shape. and that grinding only ensures smooth dislocation of the bubble, otherwise it would dance around to much or jump from graduations to another.

the glass vial itself can't be used as a precision level because of the surface deviations you pointed out. however what i think he bought is the vial for a precision level, which now can be fitted on a base.

the precision needed for machining the base consists only of achieving a flat bottom surface. the vial is put on top and with adjusting screws you can make sure it shows true level.

what i meant to say, i guess, is that i think it can be done, and i don't think it would be too hard either. it would take some almost forgotten techniques but it won't take very expensive equipment.

I'm fine with that but my point was that unless the vial purchased was a high precision one already, which i'm fairly sure it wasn't, the inside as well as the outside are going to have imperfections whether you like it or not. And given the stated purpose was to make a precision level, no amount of adjusting the vial or the base it's fitted to, will completely remove any errors introduced by the variations of the imperfections. At best you'll get "close" or be able to use it in one direction, but as soon as you swing it around, any imperfections will magnify the error won't they?

My point is, you'll easily get it level, but given the OP wanted a precision level, how are you going to get a "precise" level, when the measuring implement isn't precision itself?

cheers, Ian

 

[Tin Falcon]

There plastic vials made for run of the mill carpenter levels.
curved glass tubes and precision ground glass vials.
And lets not forget bulls eye levels of various material and precision . The bulls eyes are used on balances and transits so we will not discuss those.

do not be fooled by the words machinist level or precision. without a Minute of angle or ten thousands per foot marking specs you really are guessing at what you get.
take a look at the Geier & Bluhm precision tuble level page many sizes and precision points to choose from. located in Troy NY USA.

sorry I thought i included this link in the last post.
tin

 

[Tin Falcon]

CDCO tools has an 8" 10 second of arc master level for $58. the 12 in is $78

The level is marked .0003 per 10 inches.
http://www.cdcotools.com/index.php
Tin falcon

 

[jack620]

Mark,
What are you going to use the level for?

 

[Tin Falcon]

This PDF explains level sensitivity. The question is how much angle moves the bubble on division. The other difference between a precision level and a a carpenters level is markings. some levels have a pair of center marks only.

Tin

View attachment Sensitivity%20-%20Tubular%20Levels.pdf

 

[dnalot]

Mark,
What are you going to use the level for?

Its off subject, but you asked.

Another hobby of mine is building telescopes. Once built they need a very level surface to sit on to minimize the time it takes to setup the software for pointing, and to relieve the load on the tiny steppers that move the heavy device.

This is my 12" dobson wide angle.

The only machine used to built this was my homemade CNC router

Mark T