What is the proper filament diameter to use?

[Moby Disk]

I have a stock Makerbot Replicator Dual extruder, and it came with a black and a natural reel of ABS.  ReplicatorG defaults to a filament diameter of 1.82mm, but MakerBot sells the filament as 1.75mm.  What is the correct filament diameter to use in ReplicatorG?  Searching around, any discussion of this deals with optimizing or modding.  But I don't see any explanation for why it is sold as one value but configured as another by default.  If you buy the filament separately, does it come with something that tells you the *actual* diameter versus the "marketing" diameter?

[c f]

Most filaments have a 'nominal' diameter (1.75mm, 1.8mm, etc.), but due to manufacturing tolerances may vary from that by some small amount. Additionally, plastics can absorb moisture from the atmosphere which cause them to swell over time. The software is designed so that you can measure the filament precisely with calipers and input the actual value, since it depends on so many different factors.

On Sun, Nov 4, 2012 at 3:50 PM, Moby Disk <moby...@gmail.com> wrote:

I have a stock Makerbot Replicator Dual extruder, and it came with a black and a natural reel of ABS.  ReplicatorG defaults to a filament diameter of 1.82mm, but MakerBot sells the filament as 1.75mm.  What is the correct filament diameter to use in ReplicatorG?  Searching around, any discussion of this deals with optimizing or modding.  But I don't see any explanation for why it is sold as one value but configured as another by default.  If you buy the filament separately, does it come with something that tells you the *actual* diameter versus the "marketing" diameter?

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[Moby Disk]

I just noticed the spools say 1.8mm on it.  So by having it set to 1.82, what is the side-effect (however minute)?

[c f]

The software is figuring out what volume of plastic to put into the extruder to generate a given output volume (since it knows the diameter of the nozzle) as it goes about generating the print. If the software thinks the filament diameter is larger than it actually is, it will wind up outputting less plastic than it intends (as it will not have fed in enough filament to generate the intended output). This can sometimes make prints look 'stringy'. If the software thinks the filament diameter is smaller than it actually is, it can output too much plastic unintentionally and your print can look 'blobby' and have poor surface finish (sometimes the nozzle can 'catch' on the molten plastic blobs that get generated and move it around like peanut butter).

You can tweak the number to output more or less plastic as desired as you tune your machine.

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[Dan Newman]

On 4 Nov 2012 , at 3:03 PM, Moby Disk wrote:

> I just noticed the spools say 1.8mm on it. So by having it set to 1.82,
> what is the side-effect (however minute)?

As the diameter increases the input volume to the extruder increases.
As the diameter decreases the input volume to the extruder decreases.

So, if you claim a larger diameter, then SF feeds in less filament for the print.
If you overstate the diameter, then insufficient plastic will be extruded and the print will look anemic.

If you claim a smaller diameter, then SF feeds in more filament for the print.
If you understate the diameter, then too much plastic will be extruded and the print will bulge.

Mind you, you need to do tuning. Until you do that, you will find that to get
good prints you need to under or overstate the filament diameter. (Some people
tune by under or overstating the filament diameter; others by tweaking the packing
density in SF; and others still by tweaking the stepspermm for extruder axes.)

Dan

[Cymon]

I found with a brand new roll, give 1.79 a try. Of course you could always test it.

[JohnA.]

Man, I've never had to go that low...  I almost always have to over-estimate to get smooth top surfaces.   Right now my roll is set to 1.835....

John A.

[hellphish]

I bet your packing ratio is at .85 if you are over estimating your diameter. 

@moby disk, You will want to buy some digital calipers to measure your filament. There is never a guarantee that your filament will be what it says it is. You should always measure at several places and average to find what to enter into your slicing software.

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[Moby Disk]

Okay, I need them for other reasons too.  Thanks.

[Moby Disk]

Based on dnewman's statement that this value is used to calculate the volume of plastic, that would mean that when your plastic swells due to moisture you should not update the value in Print-O-Matic.  The volume of plastic per mm of filament did not actually change.  Updating this setting as your abs swells would merely cause your prints to get thinner.