3mm or 1.75mm?
I’ve just started designing a compact (275x275mm footprint) printer which will focus more on precise prints (think small nozzles and dissolvable supports) and less on speed and size (obviously), and it’s becoming clear that it’ll have to be be a bowden design. Now, the question is whether it should use 3mm or 1.75mm filament, as i see some advantages and disadvantages in each of them. What are your experiences - which one gets you better print results overall?
The biggest reason why I use 1.75 is because 3mm simply requires a lot of pressure. I was too worried about pneumatic fittings not being able to hold the tube in place. I don’t think either gives you better print results, but I do believe that 1.75 is less of a hassle.
As this is in design phase, is there any value in a machine that could push either. I don’t know if technically, this is possible! I know someone setting up as a UK filament reseller, he says he’s stocking 3mm after his research showed that most consumer products required it. Might be worth doing this research too, see if you find similar. His study must have been done last summer.
@Jo_Bigger i’ve seen some numbers on the 3mm vs 1.75mm market, too, and they indicated that the 1.75mm market was about 3 times as large as the one for 3mm filament.
My current machine is 3mm, as that’s simply what i’ve always been printing. Availability of the two sizes seems to be almost identical.
If small footprint is a design goal then 1.75mm might be necessary. The additional flexibility of the smaller filament may give you more options on where you place spools, smaller spool size etc.
Although 1.75 requires more extrusion steps than 3 to get the same amount of filament out the nozzle, 1.75 is my choice. It is becoming more and more popular everyday and, in my opinion, is a better choice for smaller nozzle diameters. It’s a little more wear and tear on the motor but doesn’t require as much of a step down for smaller nozzles reducing back pressure and molten plastic creeping up the tube. I would go with the 1.75 personally.
@Thomas_Sanladerer sounds like there’s a business case for 1.75 and also a technical one. I posted a 3 versus 1.75 question in here about a month ago, there might be some more interesting comments on it in there. I’m sure that most posters noticed little difference in outcome between the two.
I had a lot of issues blowing pneumatic fittings with 3mm. The only ones I found that worked well were high pressure brass fittings from McMaster that were screw on connections.
I have found some filaments only available in 3mm but for the most part 1.75 seems to be easier to deal with
P.s. love this community
@Sanjay_Mortimer , you’ve probably been handling and using using more hotends than any of us here. What’s your opinion?
I think it makes sense to go 1.75 for precise applications, as the surface area of the filament is smaller you have more control over the flow. Only pro I can think worth choosing 3mm in a Bowden setup would be if you print slowly you may be able to use some elastic materials, other than that 1.75 SEEMS better for finer work… I only have experience with 1.75
3mm is more reliable than 1.75mm. If you’re inexperienced and have a bit of a clunky bot. This is due to the springiness and being more buckle prone. The springiness can really take away the “punch” of the extruder when un-retracting in a bowden system. When properly confined from hob to nozzle 1.75mm is just as reliable.
3mm however is actually a bit easier to exert retraction and pressure on through a tube, in hookian terms it’s a much stiffer spring than 1.75mm so transfers force with more immediacy. This coupled with more mechanically robust (versus PTFE) PFA tubing is why UM do so well.
@ThantiK The strength of the coupler is a bit of a red herring, if you get any of the couplers on the market (and I’ve tried LOADS) and insert some PTFE tube, then pull, what happens is the teeth bite the PTFE, until the PTFE deforms/fails at the point where the teeth are biting it. We use the couplers we do because they have large teeth with a good gripping area, as well as being easily modified to pass tubing through them and a bunch of other generally nice factors. If you want to get more pressure in your tubing before it pops out at the coupler change to PFA, or nylon. It’s the tubing failing, not the coupler.
There is no noticeable performance difference between 3mm and 1.75mm in most normal printing situations. However, top end continuous extrusion speed can be a little better in 1.75 (more favourable volume to surface area ratio in the melt.)
You can’t print flexi filaments in 3mm or 1.75mm bowden systems. It’s a lot easier to print 3mm flexi filaments in a direct system than in a 1.75mm direct system.
1.75mm is about 65% of the market, and this is rising continuously in favour of 1.75mm. Around when we started out selling last year this ratio was around 50-55% in favour of 1.75mm. This data may be biased because I am judging this from my sales, and I our market tends to be a little more “invovled tinkerer” than “I just want to print stuff”.
Overall for @Thomas_Sanladerer 's needs I would say to go for 1.75mm bowden, get the tubes short as possible, and confine your filament well. Also, use a Kraken. I can loan you one for free if you like 
@Sanjay_Mortimer r I’m interested in the kraken for an upcoming build loosely based on the prusa i3. I’m assuming it is made for a Bowden setup. Any suggestions for electronics to run four extruder set up with a heated bed? Also looking at running nozzle fans for pla. Any suggestions?
Aye, the devil @Sanjay_Mortimer is temping me again. I just had a look at the dimensions again, and The Kraken really does make sense because it’s just so compact. But then again, four extruders is not going to happen on a Melzi board, so i think i’m going to stick with a pair of (slightly modified) v5s for now. Thanks for the offer, though.
It looks like everyone is recommending 1.75mm (thanks for all the feedback!), which was my initial plan as well, mostly to allow a direct-drive extruder and get tight radii on the bowden tubes. The one thing i’m still afraid of are filament tolerances - like when a nominally 3mm filament vendor proclaims a ±50µm tolerance, that means the area of the filament can increase or decrease by 7% from one moment to the next. On 1.75mm filament, the same tolerance translates to a possible 12% deviation. Is that actually something to worry about or is 1.75mm filament generally manufactured to higher standards?
@Sanjay_Mortimer covered it pretty well. The one thing I would add is that some of my recent testing indicates that due to the difference in the pressure required to extrude, 1.75 is much easier to control for changes in extrusion rate with acceleration. Where 3mm tends to lag behind these speed changes a bit, resulting in solid fill having slightly more material at the ends of the straight lines where it changes direction, the nozzle pressure of 1.75 equalizes much faster (and with much less material pushed out of the nozzle to do so), so the results look cleaner. This testing was done with identical hot ends (other than the internal bore). The 3mm extruder had a carriage-mounted geared stepper motor, while the 1.75 was a (short) bowden which should have given the 3mm extruder an advantage. The speed (100mm/s), acceleration and jerk settings were also identical. Using a larger nozzle diameter (.5mm instead of .4mm or .35mm) also seems to enhance this effect.
@Thomas_Sanladerer the two brands of 1.75 we’ve measured so far, have been 1.71. Taken with pair of digital calipers.
These kind of deviations are easily handled with a spring loaded extruder assembly.
@Michael_Spano_Jr_Ama true, but it will still mean that the amount of plastic coming out the nozzle will deviate.
Think single-wall thickness. On one layer the filament could be at the lower end of the tolerance, on the next one it could be at the upper end, resulting in a 12% difference of single-wall thickness.
@Thomas_Sanladerer true didn’t think of that.
Filament tolerance may be listed in millimeters of diameter on the packaging or website, but in my experience it is actually specified in percent of diameter. A 5% deviation from nominal diameter will result in the same percent deviation from nominal cross-sectional area, regardless of what the nominal diameter is.