Why 1.75mm filament?

Hi All

I see a number of people starting to use 1.75mm filament.

Could anyone please elaborate on what the benefit is over 3mm?

Thanks

Hi

I don't have my delivery of 1.75mm filament just yet, but hopefully it won't be long before I can start experimenting.

Other reprappers may be able to comment but what I'm expecting from it includes -

You can make all the extruder and Hot-end smaller and lighter, and also use a smaller (and lighter) motor.

Any weight reduction at the extruder end will make your RepRap able to run quicker.

It should also enable a faster feed / melt so you can speed things up if the rest of the printer can handle the speed.

Less pressure required to extrude as it's going from a smaller stock so less of a size differential.

It's also more flexible so you can wrap it in smaller coils.

It may make Bowden extruders easier to implement, but I'm really not sure about until I try it out. - That's the plan for my new set of extruders.

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[richrap.blogspot.com]

1.75mm extruders also allow you to run PP3DP and Stratasys filaments. I think the biggest benefit is in lowered feed pressures - this extrusion grade ABS is like trying to pump concrete through a garden hose, and it's no wonder there have been so many extruder versions to deal with stripped gears and the like.

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[haveblue.org]

The UP! printer uses only 1.75mm ABS and this I think is what started this trend. Initially the people who bought the UP! had to buy it from UP! directly from China ($ 70 for 1.4 Kg), then MakerGear started supplying the 1.75mm ABS that seems to work with the UP! printer ( ~ $ 22 per lb). UltiMachine also has 1.75mm PLA for $ 13 / lb. Based on the results of the people using the UP! printer it looks like using a smaller filament allows for better prints and permits to have a simpler extruder design and more reliable operation. It makes sense to use smaller filament, it requires less heat and power to melt and push and you can also use smaller nozzles.

Regards
Tayeb

This is a very important question, and I'm glad you asked. I see a lot of people touting the benefits of 1.75mm filament, but I'm not convinced. Maybe there is something superior about the chemical composition of 1.75mm filament, or maybe it's manufactured to better tolerances. But as to the other claims that have been made, I'm skeptical.

I don't think that 1.75mm geometry filament results in lower extrusion pressures. The pressure required to extrude will depend primarily on the flow rate and the nozzle diameter and length. The filament diameter shouldn't affect that. At best there will be a slight increase in flow efficiency because the transition from 3mm to 0.5mm is steeper than from 1.75mm to 0.5mm. But at worst, viscous losses inside the melt chamber will be higher, both because the diameter is smaller and the flow velocity is higher (to achieve the same volume flow rate). It's not immediately apparent which effect will dominate, but to my intuition, I think the 3mm filament will actually offer lower pressures in most extruders for the same extrusion rate.

It might help you get away with a smaller and lighter motor, because it will require less force to drive a finer filament into the extruder, even if the extruder pressure is no different. But since the cross-sectional area is smaller, to achieve the same flow rate, you'll need to run the motor at a higher speed. As a result, from the motor's perspective, using a finer filament is equivalent to changing the gearing.

As a consequence of the above, 1.75mm filament could offer superior resolution, because one step of the extruder motor will correspond to a smaller volume of filament. But as I said, this is no different than changing the gear ratio to do the same.

Compared with 1.75mm filament, 3 mm filament is ~9 times as stiff in bending, and 3 times as stiff in axial compression. That means that larger filament is much more resistant to buckling, and will be less springy in compression, so it should perform much better in bowden extruders. I wouldn't recommend 1.75mm filament to someone using a bowden extruder, unless they had a secondary motor on the end that offered fine-tuning control of the extrusion. I don't think anyone is doing this.

Edited 1 time(s). Last edit at 01/06/2011 03:41PM by jbayless.

Quote

But as I said, this is no different than changing the gear ratio to do the same.

Actually there is. The force goes down by the inverse square. The force is transmitted by the teeth of the pinch wheel and the limiting factor is when the teeth strip, so you will be able to feed smaller filament faster before that happens.

As you say it will be more prone to buckling but it is obviously not a problem with ABS at 1.75mm. Other plastics may be a problem at the smaller diameter. PCL certainly would be as I had buckling problems at 3mm, but it isn't a very useful plastic. PP and HDPE might also have problems.

The optimum diameter will be different for each type of plastic.

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[www.hydraraptor.blogspot.com]

It sounds like the 1.75mm filament is more expensive per pound/kilogram than the 3mm. I would want to see some real advantages before increasing the base cost of raw materials.

Mike

nophead Wrote:
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> But as I said, this is no different than changing
> the gear ratio to do the same.
>
> Actually there is. The force goes down by the
> inverse square. The force is transmitted by the
> teeth of the pinch wheel and the limiting factor
> is when the teeth strip, so you will be able to
> feed smaller filament faster before that happens.

I hadn't considered the pinch wheel teeth, that's a good point. The force on the filament does go down by the inverse of the area, but what determines when the teeth strip? That force is probably also a function of the filament diameter.

The pinch wheel will slip on the filament when the stress in the filament exceeds its strength. Assuming that the pinch wheel teeth size also scales down linearly with pinch wheel diameter, the stress in the system will probably remain constant... I'm not certain about that though, because it's not a simple problem. I'll think about this one. Maybe you're right.

And here I was under that the important benefit of smaller filament is:

There is less volume of molten plastic to pressurize and depressurize when starting/stopping printing, leading to more precise starts and stops.

Obviously there's much more disagreement on the subject than I had imagined. Obviously more data is required.

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I'm building it with Baling Wire

jbayless Wrote:
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> I don't think that 1.75mm geometry filament
> results in lower extrusion pressures. The pressure
> required to extrude will depend primarily on the
> flow rate and the nozzle diameter and length. The
> filament diameter shouldn't affect that.

Sorry, I should have said 'force' instead of 'pressure' - you're correct, the chamber pressure should be the same. "The force required to drive a 1.75mm filament through a 0.5mm orifice will be significantly less than driving a 3mm filament through a 0.5mm orifice" is what I should have stated.

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[haveblue.org]

Another benefit is that it should be quicker to liquify because the heat doesn't need to conduct as far to reach the centre.

Also, although it is similar to using a bigger gear ratio and larger filament, the last gear of the chain can operate with lower torque meaning it can be lighter and will wear less.

Also, thinner filament will be less drag on a moving head machine.

Edited 1 time(s). Last edit at 01/07/2011 01:07PM by nophead.

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[www.hydraraptor.blogspot.com]

To be clear - we do not stock 1.75mm ABS for Up printers. We stock 1.75mm ABS for use with MakerGear plastruders.

If you are curious about 1.75mm ABS then get a pound. Current pricing is $17.50 per/lb. plus shipping. We expect to have 5lb coils available soon and the prices should be comparable to 3mm filament.

If you have questions, stop by the MakerGear IRC channel (irc://freenode/makergear).

Rick