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28th Apr 2020, 10:13 PM #1Most Valued Member
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Maths help re levels and calibration
Gday All
Calling all the better mathematicians than myself.
I've always been a bit of a dunce when it comes to some maths and this one is doing my head in.
So, I have a bubble level that I removed from a busted theodolite that was going in the bin at work some time ago.
Its marked 30"/2mm (lines are 2mm apart)
I'd like to try and find out how that relates or compares to a machinists level as far as accuracy.
Eg from the Starrett site for a 98-6 level
Main level vials have graduations that are approximately 80-90 seconds or .005" per foot (0.42mm per meter)
Ive had a bit of a look on the net but I cant get my head around how to compare the two.
I'm thinking if they are anywhere near close (they might be way off though) it would be a nice little project to make a level incorporating this bubble.
From what I have been able to pick up, you need to know the radius of the arc of the level which I think the calcs below show for my bubble
1 deg of arc has 60 minutes and 1 minute has 60"
If I'm doing this right for my bubble
30" = 2mm so 60" or 1' = 4mm. 4mm X 60 = 240 (1 deg)
240 X 360 = 86400mm circumference.
86400 / pie = 27501.97416628mm or close enough to 27.5metre dia or 13.75 metre rad
Is that correct?
Even if it is I still can't relate it back to the Starret.
.42mm /metre = .00084mm/2mm
but I still cant figure out how to convert that into " of arc.
So I'm stumped at this point.
Can anyone offer insight?
thanks
Peter
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29th Apr 2020, 01:42 AM #2Senior Member
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The easiest would be to send it to a calibration lab to tell you what it is. All they will do is set up a sine bar and gauge blocks to get the numbers. You can do the same if you have gauge blocks etc. Good excuse to buy an inexpensive set from the bad place. They are more than good enough for hobby use and inexpensive. If you don't but do have a Starrett or equivalent you could just do a side by side comparison.
Always looking for a no think method these days.
Pete
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29th Apr 2020, 09:04 AM #3Most Valued Member
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Pete - Here in Aus it would probably cost more to have a calibration lab look at it than to just buy a new Starrett unfortunately.
I dont have sine bars, gauge blocks or a good Starrett either. I'll probably make a machinists type level with this at some point anyway as if I'm just trying to level something, eg my lathe, this level has got to be more accurate than a builders level.
I'd still like to find out how to compare them though.
peter
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29th Apr 2020, 09:31 AM #4Golden Member
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I assume that they mean that each division equals 2mm per 30 inches ,if so it is approximately .0315"/ft, so not much good for precision work.
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29th Apr 2020, 11:04 AM #5
I have 2 levels here, and a gauge block set.
Bring it with you next time and we will put it on top off one of my levels.Using Tapatalk
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29th Apr 2020, 11:41 AM #6Intermediate Member
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Hi Peter
By my calcs,
30" (arc secs) = 0.00833deg
therefore at 1m = 1000 tan(0.00833) = 0.145mm
Seems to correlate to Starretts conversion (80-90" = 0.42mm at 1m, so roughly 3 times less sensitive than your vial).
Cheers
Si
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29th Apr 2020, 01:47 PM #7Golden Member
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Ah yes, 30 seconds of arc makes more sense, I thought it was strange that they mixed imperial units with metric.
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29th Apr 2020, 06:54 PM #8Most Valued Member
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29th Apr 2020, 07:41 PM #9
Just watch making a super high precision level, it will drive you nuts trying to level a lathe etc.
Using Tapatalk
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29th Apr 2020, 07:56 PM #10Most Valued Member
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Agree with Dave,
I recently levelled my lathe, finishing with a 0.02mm/m level which is by no means a super precision master level but good enough for what I needed. However, I bet you if I go out to the shed right now and test it again it will be out by a few divisions.
It changes depending on the temp AND the moisture in the ground! Unfortunately it's the price I pay for a standard 100mm slab.
Still, a fun and interesting project. Please post the project on this forum.
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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29th Apr 2020, 07:58 PM #11Most Valued Member
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29th Apr 2020, 08:06 PM #12Most Valued Member
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Simon. I will, but dont hold your breath waiting for it. If I do it, it wont be because I want to level my lathe super precisely. I reckon mine would be pretty much like yours, probably worse actually.
Its just I've got this bubble/level and its seems a shame not to use it for something. It came from what would have been a vey expensive electronic theodolite in its day (probably 30+ years ago) Unfortunately once the unobtainium electronic boards failed all that was left was this level and a nice little telescope.
peter
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29th Apr 2020, 08:19 PM #13Most Valued Member
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Yea I get it. I love re-purposing stuff too rather than sending to landfill. It's fun and a challenge.
Simon
Sent from my SM-G970F using TapatalkGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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29th Apr 2020, 08:50 PM #14
Admit it, you love it lately, lol. But you do a good job at fixing problems.
After all isn't that what hobby machining is about, fixing our machines to make them better to make tools for that machine, lol
Having the mybusters wharehouse in your backyard and under the house is a great start, I always think your place is just that.
Honestly I never know what your going to say you have on hand from years ago that you pulled off something out of somewhere that works out perfect for your project, just like the wheels you gave me. And I think I'm a horder, lolUsing Tapatalk
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29th Apr 2020, 09:22 PM #15Most Valued Member
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Hahahah. Ive been on the wagon for a few years now though I must admit I have fallen off a few times.
I'm a lot more selective now, plus I dont climb into the bins anymore. Too scared of not being able to get out again. lol
PIcked up a gas lift stool a couple of weeks ago. It had a steel frame for the casters and one of them had busted off. The frame required welding. The rest is in really good condition. So I was just about to dig the welder out when I remembered I had a caster base for an office chair in the roof if the shed. Dragged it out and knocked the base off the stool and the leg fitted into the plastic one perfectly.
peter
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