Chinese Vials

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ctwo
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Chinese Vials

Post by ctwo »

Someone has introduced me to these Chinese bubble level (inclinometer) vials. The accuracy spec is 4"/2mm.

I crudely measured the graduations to have 2mm separation, and the vial is 100mm long, so I presume each graduation is 4 seconds of a degree.

Some math says that is 20 millionths over 4 inches or 50 millionths over 10 inches.

And that is the same as the Shars levels.

I was thinking of a level, but did not like the look of the Shars levels.

I'm probably still a magnitude off of where I want though, this is a nice price ($12).

https://www.aliexpress.com/item/Size-14 ... 17931.html
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ctwo
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Re: Chinese Vials

Post by ctwo »

Oh, the guys on the electronical forums are going to use those vials and wrap them with foil layers to create a capacitvely coupled, digital inclinometer and increase resolution 4x via differential methods.
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SteveM
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Re: Chinese Vials

Post by SteveM »

I don't get what they mean by "Accuracy 4"/2mm"

Do they mean that it's 2mm over 4"?

I think that's carpenter level territory. The line on a carpenter's level is 1/8" per foot, which would be about 1mm over 4".

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ctwo
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Re: Chinese Vials

Post by ctwo »

Well, since they bill it as an inclinometer, I suspect that is 4 seconds of inclination for 2mm bubble movement. It has to be the same vial in the Shars levels.
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Re: Chinese Vials

Post by Harold_V »

ctwo wrote: Fri May 25, 2018 4:35 pm Some math says that is 20 millionths over 4 inches or 50 millionths over 10 inches.
I'm inclined to suggest that isn't true, as that degree of precision is ten times better than the levels that were and are offered by major instrument makers in the USA. For example, the Starrett 199 is reputed to yield a sensitivity of only .0005" over ten inches (that would be 500 millionths).

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ctwo
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Re: Chinese Vials

Post by ctwo »

ok, maybe they are more like 2 tenths in 10 inches
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pete
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Re: Chinese Vials

Post by pete »

I'll sure have to agree with Harold. Cheap carpenter grade levels are made by heat bending the vial if there actualy glass vials. Likely most are now injection molded plastic with the mold having the curvature. High accuracy vials are glass and precision ground to the proper curvature and that's why there expensive. The glass tubing is dirt cheap so it's the accurate grinding that raises the price so high. I honestly can't see that accuracy for 12 bucks from anyone.

Getting a usable and accurate vial is the easy part, my Mit 612 was damned expensive mostly because of all the work that went into the heat treated, stabilized, ground and lapped cast iron body. And it's only good to 3 tenths over 12". Tom Lipton and Robin Renzetti on Youtube have shown some amazing results with simple lapping or hand scraping methods so it's probably doable to make a high accuracy level in a home shop. But if it were me I think I'd start with a known and accurate vial. I'm pretty sure Starrett's most accurate vial is less than $100. There's some high end German made one's as well for about the same prices.

As Steve said there accuracy specs are a bit confusing for exactly what they mean.
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ctwo
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Re: Chinese Vials

Post by ctwo »

I received two vials that I ordered from ali. I set this on the kitchen counter and let it settle. It moves 5 divisions if I take one step left. It's a substantial wood home. I'll have to do some tests, but will likely accept its spec as-is. I'll be looking for some chassis ideas.
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John Hasler
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Re: Chinese Vials

Post by John Hasler »

Done right injection-molded plastic vials could be extremely sensitive and accurate.
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Re: Chinese Vials

Post by pete »

I'm sure you know the vial holder has to be screw adjustable. Some years ago most precision level makers seemed to bed there vials in the holders in what looks and feels like drywall mud cast around the vial and holder ends. My best guess is that's to semi protect the vial from any shock loads. I don't know if there's any silicone product available that would be stable enough. I know one guy who did rebed a new vial in his Starrett level using the mud and he said it worked well. If it were me I think I'd machine the main body from Durabar since it's supposed to be quite stable. Any good level I know of always has either a sheet metal piece loosely attached with a couple of socket head cap screws to use when moving and lifting the level (Mitutoyo) or a plastic piece used for the same reason to insulate the main body from the heat of your hands. Getting the bottom surface of the levels main body extremely flat is going to be the toughest part I'd think. Unhardened cast iron is also going to have a fairly fragile and delicate surface so you'd need to be pretty careful with it. There's at least a few decent Youtube videos around about precision levels that might be worth checking for design ideas.
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ctwo
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Re: Chinese Vials

Post by ctwo »

John Hasler wrote: Sat Jun 02, 2018 7:26 pm Done right injection-molded plastic vials could be extremely sensitive and accurate.
This is a glass ground vial. I will not assume it is very linear nor true in a rotational axis.
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John Hasler
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Re: Chinese Vials

Post by John Hasler »

ctwo wrote: Sat Jun 02, 2018 9:03 pm
John Hasler wrote: Sat Jun 02, 2018 7:26 pm Done right injection-molded plastic vials could be extremely sensitive and accurate.
This is a glass ground vial. I will not assume it is very linear nor true in a rotational axis.
Yes, I understand. I was making a tangential comment on the subject of injection-molded plastic vials.
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