It is my modification of ordinary calliper. As long as tape and calliper are in the same units vernier still works but I can measure long distances with vernier accuracy. Well almost - keep in mind that tape is not as tight as slider and it is easy to miss-align and screw the measurement.
I do not know what rolling calliper is - I just bought cheap Chinese typical one; unscrewed slider and replaced it with tape.
Tape calliper would have been a better translation, in dutch we say “rolmeter” rolling measurer.
Keep in mine that the accuracy of a tape measure is quite low, a class II has almost 2 mm possible fault per meter, so while that calliper gives you good resolution, it doesn’t give you reliable accuracy. 0.05mm resolution with 2mm accuracy doesn’t make sense http://www.pewa.de/DATENBLATT/DBL_CT_BANDMASSERSATZ_DBL_DEUTSCH.pdf if you want to know about precision ask a german
Aaaa… Thank you @Dag83!
But it also mean that my calliper modification was a stupid idea. It gives you false sense of acuracy. It reminds me a Kepler Space Telescope blunder - they polished mirror with super accuracy but wrong curvature.
This idea is dangerous and should be scrapped asap!
Not necessarily. If you use a tape measure that has good accuracy, then your caliper modification is a good idea. If you use a bad one, then yes, will have a false sense of accuracy. The key question is, “how do we tell the difference?”
At first look you are right, but we are working within the same machine and being off by systematic error is not a disaster. I need relative error small - I need resolution. As long as I am using the same tape all the time I am fine. I do not care if part cut on Maslow and measured by one tape reads different length that using another tape.
USING TAPE WITH VERNIER IS NOT STUPID IDEA
I agree that using not accurate tape to calibrate your Maslow will result in inaccurate translation of your drawings to cut parts, but all parts will be re-scaled and they will fit to each other.
actually, you will have problems, the calibration will be off and what should be
stright cuts will be curves
but 2mm in 1000mm is an error of 1 part in 500, so trying to measure to 1 in 50
or so is not insane.
I also think that current tape measures are going to be more accurate than 2mm
per meter, routine accuracy of even cheap manufacturing machines is FAR more
accurate today than it was 20 years ago, so even the ‘cheap stuff’ is as
accurate as the ‘good stuff’ was a couple of decades ago. I recently saw a
yourtube video something like ‘the source of accuracy’ that tracked the history
of accuracy and the development of gage blocks, and it talked about how the ones
make in WWII cost ~$5K/set (in 1940s dollars, several months pay for an
machinist) while today you can get similar sets for a couple hundred.
But as someone else said, how can you tell which tape measure is accurate?
can someone try several tape measures from different brands and see how much
they disagree at say 15 ft? I wouldn’t be surprised to learn that they all
match (or that they mostly agree with a few outliers that are obviously wrong)
The file i posted earlier are todays norms, most tape measures you buy are class ii, for a class i, i had to look online.
Those are european norms i believe, possibly there are other norms in the us.
Gauge blocks need very, very accurate measurements, tape measures not so much, so the norms are a bit more loose.
After took those photo’s a while back, i went and bought me a class i tape measure, and if i’m ever in need of a new one i go trough the shelve in the store with the cheaper ones till i find the one that is closest to my good one, the guy in the store had some wierd questions for me when he saw me do it
Seems like i misinterpreted the data, I said almost 2mm difference, that’s the ± 0,9mm most tape measures are class 2, and the most common tape measure is 3m (at least in my house, that’s the longest one that still fits easily in my pocket ) i must have misread and thought it was per meter, but appearantly its along the whole length. Tha problem i had was mostly with wooden folding rulers
Wow, you never stop learning in life do you? I never thought of this before. Very interesting! Looks like the temperature variation is the biggest killer with accuracy. I feel so betrayed by my trusty tape measure now - I’ve been lied to all these years thinking it was 100% accurate.
I was recently in the large local tool supplier KMSTools (kmstools.com) and they have great woodworking and metal working areas and of course lots of tapes. I was talking to an older gentleman who was re-stocking the tapes and I was trying to decide between a Starrett and something else so I asked him about accuracy. He wasn’t familiar with the idea of class I or class II and here in Canada I can’t find any markings suggesting that standard is respected. I didn’t do much better online.
The employee suggested that if measurements were key that a digital measure like the Bosch can get you to 1/16th accuracy, of course it’s use is limited but I do have one and it did give me the idea of cross referencing tapes to the laser to weed out any bad ones in my tool box…
Looking at this design again since my garage is clearing up. Is there a reason you didn’t use a trolley rail with hanger (think barn door track) instead of the ball bearings riding on the metal tubes? I’m thinking it may be a better alternative as dust will be less likely to gather on it. Just not sure if the wheels will cause issues with friction.
Barn door hangs vertically on the beam and there is only one - vertical - force component acting on the beam. Yes it works perfectly for barn door, but Maslow is inclined about 15deg from vertical and gantry rolls on two set of bearings - parallel and perpendicular to workspace components. The weight of gantry and sled is split into these components and bearings taking that load.
You cannot win with dust - you have to clean machine from time to time ;-))