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Questions about measuring filament diameter

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Hi there,

Something has been bugging me for a while now. I am hoping someone can help clear things up for me.

My UM2 wants 2.85mm diameter. My Colorfabb filament says it's 2.85mm. I read that it is good to measure one's filament to get the best results. But when I measure my Colorfabb or any other filament with my digital calliper, I consistently get around 2.54mm or less. And sometimes I think I am getting over-extrusion when using my measured values.

So, questions:

Is this normal?

Should I be getting closer to 2.85?

Should I be doubting my calliper?

Or is there some difference between cold and hot filament, or measuring horizontally vs vertically (relative to the curvature of the filament)?

Basically, what I am missing?

Does it really matter that much?

How precise should I be for best results?

Does my 2+ upgrade change how I should think about this?

I can add that when I first got my printer, the 2.85 default worked just fine. I did not discover the idea of measuring filament until I got to the last 1/3 of the spool and was having under-extrusion issues (as was common before 2+).

Measuring also led me to always edit the filament diameter whenever I changed filament (Material -> Customize -> Diameter), which was fine but less than ideal, I guess.

Anyway, any wisdom shared would be much appreciated. :) Thanks in advance.

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If you are using colorfabb then it should be within +/- 0.05mm of 2.85 as advertised. if not you should contact them.

i have measured mine regularly and it has always been bang on 2.85.

Measure the filament in a few places and rotate it also to check to see if its round.

Does it matter? well this depends, I have found that it doesn't matter that much but it will depend on how far out the dimensional accuracy is out, what you are printing and if its very inconsistent then you will see more issues.

I would check your caliper first. make sure you zero it with a light force that is the same force you measure your item. Measure something which is larger that will show if the scale is correct.

Some calipers are inconsistent when the battery gets low and some don't work correctly if the slide gets grease/oil or water on it. so you could try cleaning it with alcohol.

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Thanks Labern. (Love your fan shroud btw) :)

It's good to crosscheck with other people's experiences. From what you have said, I think I will have to take a much close look at my caliper and my measuring technique. I have gone through several Colorfabb spools and not one has ever been above 2.54 by my measurements, so I am pretty sure it's not Colorfabb, it's me. :)

Thanks again.

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also when measuring, make sure, you don't use the sharp edges close to the tip but the flat area more in the back so that you get a larger contact area.


Interesting! I would not have thought it would make much of a difference. I would expect the sharp area to be more precise, but I guess the flat area takes the maximum diameter over a wider area.

I will see what kind of a difference that makes. Thanks! :)

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Hi folks,

Just wanted to post an update to this.

I had replaced the battery in my caliper, but it did not change the measurements. Now I have finally got around to buying another (and a bit more expensive) digital caliper. Sure enough, it's measurements are exactly what is expected and what @Labern gets.

So my original cheap calipers are off by 0.4 - 0.5 mm. It's possible this only happens on measurements under 5mm, but I would have to test that further and frankly, I like my new caliper better anyway. :) Maybe they can be recalibrated? Meh. Project for another day.

Anyway, just wanted to conclude this topic with a result and to say thanks again. :)

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