In search of accurate measurements

given how slow the Z axis is, I would also reduce the ‘safe height’ in the
g-code file.

I have the length of pin adjustable so that it can match the hole, I had assumed
they were 1/4" deep, but now that I see they are 5mm, I’ll shrink the pin by
default

I found a new option for the configuration options, so I changed the variables
from being something that you have to clone the page to use to something that
you can change without being logged in and then export the result.

even without the square support peg on the end and with an over-long pin it
works pretty well for a one-person measurement (as long as your arms are long
enough to reach both holes).

you either want the dovetail a little snug, or you want to put a rubber band
around it to keep it from falling off the tape measure. When measuring, it’s
easy to have the end of the tape get a little loose and not get a fully accurate
measurement at the end.

David Lang

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I posted this to thingiverse so you can order them printed.

I’ve ordered versions in resin, PLA, and ABS and will report how they come out
when I get them.

David Lang

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A friend of mine is printing the 0.05 version with resin. Should have it next week sometime. Will report back!

Also, he said his resin printer build volume is 115 x 65 x 155mm but it has an accuracy of 25um!

EDIT: final product is very nice! Haven’t used it yet, still making other frame mods.



I’m not sure why the peg didn’t come out round but the resin print is very nice.

Would you have a recommendation for a tape measure to go with that? I suspect I will have to order the tape measure too, here in imperial-tape-measure-land.

any tape measure with metric. Here in the US you can easily find ones that have
both Imerial and Metric. you want one with metric on the bottom and 0 on your
left (otherwise I need to make a mirror version)

I like wider tape measures, but this is designed to handle any width.

If you print one of these out, take it in when you buy a tape measure and see if
you can find one that is exactly correct (the 0 on the vernier scale is exactly
at a cm mark), that way you don’t have to account for error on the 0 end as you
measure (this is just a nice-to-have, but it’s a very nice, nice-to-have)

David Lang

Guys! I apologise for stirring this discussion but we should abandon idea of tape with vernier. I think that we are barking wrong tree.
Read this:

and my respond

and my response:

When I was a teen I wrote a short paper for science class regarding how any measurement is an approximation.
I guess the only way to decide how close to accurate a tape measure is, is to use an object with a known length and check the variance between that object and your tape.

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Wait a minute!!! If all parts of my project are re-scaled to measure tape with 2mm ABSOLUTE error that’s OK! I need resolution - I do not care if my boat IS 5000mm long measured with one tape or 4998mm using another tape. When assembling parts made by my Maslow all what I care is how precise they fit to each other - and this is RESOLUTION.
I AM CALLING OFF MY PREVIOUS POST! TAPE WITH VERNIER IS NOT STUPID IDEA!

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After this discussion about tape accuracy, and seeing how far off some common tapes are, I’m starting to think that we should start thinking about including a class 2 tape (and possibly a couple of these vernier aids, and possibly a level) in the kits, increasing the cost of the kit just a little bit.

I have a couple of these that I’m happy with ($10 each) https://www.rockler.com/fastcap-procarpenter-standard-metric-tape-measure

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Stanley tape measures are class 2 as well.

all of them?

we need a tape that has metric on it, and for folks in the US, I think we should
also have imperial (the tape I linked to has both)

David Lang

@dlang I recall reading about a stick or dowel to use for making manual calibration marks. That gave me an idea.
For measuring Holey Calibration, what if we could fabricate two laser cut, concentric, stainless tubes (tube within a tube like a curtain rod but much better!) that have laser etched mm scales at each end. Each end would have a slightly tapered 1/4" nipple to snug fit into the drilled holes. I realize this could be expensive but if (when :smiley:) Holey becomes stock, maybe a supplier (cough, cough, ehm @Metalmaslow) could find a place, or an alternate design that is reasonable at relatively large quantities.

you still have the problem of how to go sub-mm

the result will be fairly long (remember you are measuring from ~700mm and
1300mm on a stock machine, smaller on smaller machines, larger on larger
machines)

I don’t see this as being any cheaper or more accurate than a class 1 or class 2
tape measure (especially when combined with something like the 3d printed
vernier adapters)

David Lang

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Most likely not.

I disagree here and the reason is that it is very hard to measure hole to hole with a tape. There is inconsistency in how and where you might “hook” the tape, tape sag between holes and what angle you look at the tape.

I have one, which I think I forgot to update this thread about my experiences. I like the idea for measuring sub-millimeter at the end of the tape, but the other issues I mentioned above are still a problem.

If we laser etch a submillimeter scale at the ends, where it is needed, I think we can have something that is easy to do by yourself, rigid, thereby (practically, compared to tape) eliminating flex in the measuring device, and a consistent “anchor” method to the drill holes.

I’m currently making a model in fusion… :smiley:

I disagree here and the reason is that it is very hard to measure hole to hole with a tape. There is inconsistency in how and where you might “hook” the tape, tape sag between holes and what angle you look at the tape.

I have one, which I think I forgot to update this thread about my experiences. I like the idea for measuring sub-millimeter at the end of the tape, but the other issues I mentioned above are still a problem.

what were your experiences?

If we laser etch a submillimeter scale at the ends, where it is needed

unless you intend to do a vernier type scale at one end, you need the sub-mm
scale across quite a bit of length to cover the different size machines.

without a vernier scale, how accurate are you going to be able to make the
marks?

David Lang

Well, I wish I would have asked my co-oworker to make two; it would have made anchoring the tip of the tape easier and more accurate. The resin print turned out beautiful but there needs to be a more robust way to clamp the scale to the tape. I see benefit to gaining measurement resolution but not necessarily accuracy due to the inherent issues with a tape measure, which I listed above.

Well, I wish I would have asked my co-oworker to make two; it would have made
anchoring the tip of the tape easier and more accurate. The resin print turned
out beautiful but there needs to be a more robust way to clamp the scale to
the tape.

yes, they are intended to be used in pairs.

first off, the one on the end has a round pin to put in the hole, second it’s
vernier lets you figure out how far off the end of the tape is.

the ones I’ve 3d printed have a fairly stiff fit between the holder and the main
part, but a rubber band across it would help. I thought about including a screw
hold to provide a clamp, but thought it would cause more grief than it solved.

I see benefit to gaining measurement resolution but not necessarily accuracy
due to the inherent issues with a tape measure, which I listed above.

That is a valid point. I think using a pair does improve accuracy, if only in
that you are better measuring hole-to-hole than trying to figure the center of
the hole against the tape.

David Lang

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Yes, I don’t see why not.

I don’t think so. Just as your 3D print scale is at each end, so should the laser etching. If the steel is laser cut on a professional machine, I think we will have an accurate measuring stick.

I said stainless because, well, who doesn’t like stainless but, no reason it couldn’t be made out of cheap carbon steel. Just keep it oiled (reminds me of my younger years cleaning out the shotgun after hunting)…or not…a little rust never hurt anybody :wink:

@dlang. I still like the idea of concentric, telescoping steel tubes with vernier scales but it isn’t financially practical (pushing >$60 just for 1/2" cut steel, not including “nubs” to press into the holes, and before laser etching scales). I think I’ve got it out of my system now :slight_smile:

Thinking cheaper…Use a wood dowel. A 1/4" (or slightly smaller depending on actual bit diameter) bolt fastened to one end of the dowel will act as the “nub” that is pressed into the first drill hole. To measure the distance between holes, a 3D printed sleeve, with a nub for the drill hole, can slide up and down the dowel to measure the hole spacing. The sleeve would need to have ~3/16" of material removed down the length of the sleeve so it can be clamped with a Trigger Clamp. This would allow the dowel to be removed and placed on a table where a tape measure and 3D printed vernier scales can be used to reliably measure the full length (bolt OD to sleeve edge). Calipers can be used to deduce the actual dimension from the edge of the 3D printed sleeve to the center of its nub (which is the center of the drill hole).
But alas, I don’t have a 3D printer :wink:

EDIT:
Another thought is to have three separate dowels; one for the short distance measurements, medium distance measurements and long measurements. Standard closet rod dowels are 48"/1219.2 mm (also 96") and can be used for all three.
The “long dimensions” for Holey are between 1198 and 1197.5 mm. Fasten bolts at both ends, without the sliding sleeve, so the distance is exactly 1198 mm, center to center. Insert one bolt into the drill hole and measure the error from the second drill hole to the second bolt with a pair of calipers.

A second dowel for the “medium dimensions”, which are between 963.5 mm and 959.5 mm with bolts installed so that their center to center dimension is 960 mm. Insert one bolt into the drill hole and measure the error from the second drill hole to the second bolt with a pair of calipers.

A third dowel for the “short dimensions”, which are between 711 mm and 710 mm would be needed and bolts installed so that their center to center dimension is somewhere in between these 710 mm. Insert one bolt into the drill hole and measure the error from the second drill hole to the second bolt with a pair of calipers.

I suppose the same could be done with cheap carbon steel tubes to avoid distortion in the wood due to changing heat and humidity. One difficulty with this concept is fastening the bolts straight through the dowel with precision. A drill press would be required. Maybe a machine shop would make these for super cheap and shipping shouldn’t be too bad in the US. Another difficulty would be holding the dowel and calipers steady. Like the other methods, additional hands would help.

Example of the sleeve: