3D Printer Filament is not round!

I noticed that people were saying that you should measure the diameter of your filament and enter that value into your slicer software. I had seen various values for the diameter of the filament, so I decided that I should measure mine, which is nominally 3mm.

As I started to measure the diameter of my filament with a digital vernier caliper, I noticed that I was not getting regular values. They ranged from about 2.92 to 2.98. At first I thought it was my bad technique, then it dawned on me that filament is an extruded product. I began to take my measurements with more care and attention to where I was measuring. I found that if I measured the diameter from topside to bottom side, I consistently got values around 2.98mm. When I measured from side to side, the values were around 2.92mm. Then it dawned on me! The filament is not round. It is oval. I was measuring the major and minor diameters of an ellipse.

I took two sets of ten measurements from both directions and averaged them. I found that from top to bottom, the average diameter was 2.98mm, and from side to side it was 2.91mm.

Using these values, I calculated the area of the ellipse (pi * r1 * r2) to be 6.81 sq mm. A circular filament of 3mm has a cross-sectional area of 7.07 sq mm.
Then I calculated the radius of a circular filament with a cross-sectional area of 6.81 sq mm and found the diameter to be 2.94mm.

Why is this important?
When you load an object's *.stl file into a slicer program, one of the items of data you give the software is the diameter of the filament. From that diameter, the program calculates the amount of filament required to make the object. If you are doing printing for profit, then this figure is important to you for costing the job.

Using the nominal 3mm diameter under-estimates the amount of material required by approximately 4% compared a diameter of 2.94mm.

I do not have any nominal 1.75mm filament to test whether it is oval, too.

Old Man Emu

Moved to relevant category.

Good job Old Man Emu !

I finally realized why your filament is oval. It is laying on a solid surface before it has cooled enough. I have not checked our filament yet, but I doubt this is a consistent thing.
If the filament extruder is at an elevation high enough, or the filament is cooled rapidly enough this will not happen. A lot of commercial extrusion companies run the extrusion through a water bath directly after it exits the extruder nozzle, this is not a good thing for filament that will be extruded again later. So most just air cool it. I suspect Old Man Emu's filament very well may be home made, or come from some one with their own filament extruder.

I purchased the filament from a well known supplier here in Australia (BilbyCNC). There is no place of manufacture on the reel. Unless there are manufacturers of inexpensive filament in the Americas or Europe I guess that this filament comes from China. Bear in mind that the differences in dimensions were of the order of 0.05mm. An extruder nozzle hole could be that much out of round.

The point that I was making was that it is important to know the diameter of your filament if you are involved in commercial production, and that you should not use the nominal diameter in your slicer software configuration. I would suggest that the figure of 2.94 be used for calculations.

Old Man Emu

There are variables that cannot be accounted for, and that small of difference is very small indeed. Even air flow can account for that variation.

As filament is extruded it expands to a larger diameter than the size of the orifice it is being pushed through, this happens with all plastics, at all stages, whether it is during the making of the filament, or the printing of a part. That makes calculating actual usage very difficult at best. Your discovery is still something that is helpful, as it lets us be aware of possible hang ups from distorted filament, and other problems that may arise. I would have never even thought to look for out of round filament. I still thank you for your discovery !

Your filament is probably of high quality, I did not mean to imply otherwise. Home made filament can be as good, possibly better than factory filament, depending on the reliability of the supplier. You definitely know what you are doing, keep up the good work. Your contributions are greatly appreciated !

Another issue is with the amount of filament being extruded. Your software will use the diameter you input to calculate how much plastic to extrude.

Sorry to Hi-Jack, but.. What do you think of the quality of BilbyCNC??
I have not used their product yet and was going to grab a sample.
With the update of oval filament.. :confused:

Last few rolls I purchased have been TERRIBLE (NOT from Bilby).

One roll was actually even larger than 3mm!!
Another roll (two actually) did not bond to itself...

Out of 6 rolls, 2 were good.

I can't give you any info re the printing characteristics of the filament from BilbyCNC as I haven't fired up my printer as yet.

I was not making comment on the filament obtained from them. It was just that I noticed this difference in the values for the diameter that I was measuring, and formed the opinion that everyone had misinterpreted the shape of the filament. The calculations were done to show a commercial effect of that misinterpretation.

Old Man Emu

Thanks OME!
Champ.

I have not used my new printer yet, either.. I've started building one but had many hold ups and setbacks.. Software was my recent problem, fixed. Now its X Carriage. Was not printed flat, so my extruders are off center :(

I see a lot of people saying to measure your filament and use that number, I have had better printing performance not doing that. I honestly have no idea why. The few times I have measured and used those numbers I end up with over extrusion. It's important to recognize that all filament has different tolerances. The Filament I sell has a diameter within +/-0.10mm and roundness of +/-0.07mm and you should find the same to be true with any high quality filament. Before I found a good source of filament I bought some stuff on amazon with poor tolerances. The biggest problem I ran into was filament that was thick enough to jam my extruder.

Sometimes I wonder if people aren't becoming too anal about the accuracy of their machine's output. Afterall, these machines are supposed to be for prototyping, not for producing museum quality one-offs.

Old Man Emu

Hurrrmf ! ! Almost choked ! Ha ha !

Not sure about 3mm spools as I use 1.75mm, but the variance has been pretty minimal in all but 1 of maybe 20 rolls I have been through, so that's not so bad really.

I found the new HIPS ABS (the limonella dissolving filament) after some time took in moisture very easily and parts of it expanded which led to some clogged nozzles, so I had to set my filament diameter to 1.85mm but even then, it slipped a little bit, but I generally find if you keep it in a nice dry airtight container it stays uniform.

That being said there is some cheap filament out there, ive had some rolls with all sorts of garbage thrown in with it :/

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Originally Posted by old man emu

..... Unless there are manufacturers of inexpensive filament in the Americas or Europe I guess that this filament comes from China. ...

Old Man Emu

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Thanks for the insight on the cross section calculation. I was well aware that filament could be oval, but had not thought much about the volume of material and how that is affected. I would have assumed that if the filament left the extruder nozzle round and sagged into a different shape, like an oval, that the resulting cross sectional area would remain constant. Is it safe to assume that you have a perfect oval? I'm not sure. Maybe it's egg shaped. Who knows. I guess you have to use an oval to get an estimate of what the theoretical round diameter would have been though.

But I wanted to comment about Chinese filament. People are pretty quick to associate it with poor quality, but there are many producers of filament there with a variety of ability. I sell and use filament from a supplier in China who has manufactured engineered plastics of many types for nearly 25 years. Sheets, bars, billets, filament, etc. I personally have 32 spools of it because I wanted to see and test everything that I offer on my site. The roundness and average diameters have all been within their stated tolerances (which are identical to nearly all other manufacturers worldwide). I have had no issues with contamination and the PLA and ABS print with very low odor. In fact I can barely smell the PLA at all. I have very good consistency between colors.

I sampled some filament from a US producer and the 3mm filament was way out of round and oversize. I really wanted to buy American for several reasons - freight costs being a big one - but the Chinese filament I found was great quality and reasonably priced. (Not the cheapest mind you - there are some REALLY cheap offerings from Taiwan and China. I suspect these are the ones selling on Amazon for well under $30.) Not everything made in China is poor quality.

I just did a video that discusses how to deal with filament that is out of spec. I only recommend going through the trouble if you have 2+ rolls that are out of spec.

https://www.youtube.com/watch?v=HLJdAHpQmOo

I have not had PrinterNinja's experience with Chinese filament but it doesn't surprise me that there is at least one good manufacture out there. The problem is that there are large variations between all the chinese manufacturers, not just in size but in formulation as well. You have to kiss a few frogs before you find your princess or prince.

I agree that there is a good deal of China bashing going on in all fields. I suppose the best estimate of how good Chinese filament is, is its price. If it is selling at an equivalent US of European price, then there is a good chance it is OK. If it is cheap, then expect it to perform cheaply.

Old Man Emu

I think there is something that goes something like you get what you pay for. Like any country, there are a few shady characters that want to make a quick buck, or Yuan, and don't care about repeat customers, or quality. However there seems to be developing a supply base of quality products coming out of China, maybe. I seem to remember something like this in the early 60s (I know the Jurassic) when Japanese products were really poor quality, now Japanese stereos, and cars are some of the best. Do the Japanese make 3D printers ?

Your filament is not perfectly round because of the production line.
For high quality filament, the tolerance should be less than +/- 0.05mm.

Most of the filament on the market is average quality which is +/- 0.10mm.
This roundness will have an impact on the printed products.

Daniel Poon
BotFeeder Canada

If the truth be told, I don't think that the cross-sectional shape of the filament means a hill o beans. After all, the filament feeds into a heated tube where it melts and is squeezed through the extruder orifice.

Old Man Emu

Don't mean to bump up an old post for no reason, but I just realized this too. My filament was not round, I think because of the way I was storing it. What would be the best way to store it to preserve its roundness?

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Originally Posted by MessierGoal

Don't mean to bump up an old post for no reason, but I just realized this too. My filament was not round, I think because of the way I was storing it. What would be the best way to store it to preserve its roundness?

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I doubt that it is due to how you stored your filament. Most likely it wasn't round when you got it.

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Originally Posted by jzatopa

I doubt that it is due to how you stored your filament. Most likely it wasn't round when you got it.

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Oh really? I would think that if I stored it in a hot humid place kinda packed together with other spools, it would compress. You don't think that's the cause?