Comments on: Airtripper Extruder Filament Force Sensor – Introduction

By: Mark Heywood

Mark Heywood — Sat, 19 Oct 2013 00:18:29 +0000

I’ve only used 1.75mm filament so far, mostly because I use a bowden type set-up.

The problem with small diameter hobbled pulleys is that they can constantly slip on the filament at higher force. A larger diameter pulley is more likely to stall the stepper motor than slip on the filament. Larger pulleys tend not to dig into the filament like the small pulleys at higher pushing forces.

By: James

James — Thu, 17 Oct 2013 15:55:10 +0000

Ah! I meant a 5.5 cm radius, which would be a 11 mm hobbed pulley. Although, hobbed bolts definitely go way smaller than that, and I’m pretty sure I’ve seen people directly hobbing the motor shaft somewhere on the reprap wiki. Having hard numbers on the actual force required to push filament is very beneficial — the reprap wiki recommends >40 oz in motors with a Greg wade extruder, which translates to a whopping 42 kg of filament force after all gearing and the much thinner hobbed bolt.

Would you happen to have numbers on 3mm filament as well?

By: Mark Heywood

Mark Heywood — Wed, 16 Oct 2013 22:48:59 +0000

Hi James,
The numbers are good, stepper motor effort is directly transferred to the load cell.
2.5kg would be enough as long as the hot end and other components are in the best condition. However, using a drive pulley as small as 5.5mm may be an issue due to the reduced contact on the filament compared with the 10.56mm pulley I use.

By: James

James — Wed, 16 Oct 2013 21:02:13 +0000

These numbers look great! Are the values on the axes absolute? If I’m reading it correctly, a 1.4 kgcm nema 14 stepper with a 5.5mm drive pulley would generate 2.5kg, which is plenty to push 1.75 mm filament through the hot end. Since nema 14′s can be as light as 180 g, this could really open the possibility of using light direct-drive extruders…

By: Kalle Pihlajasaari

Kalle Pihlajasaari — Sat, 13 Jul 2013 08:11:11 +0000

Would be interesting to see the temperature of the thermistor and/or the PWM duty cycle on the graphs.

The extrusion rate could also be interesting.

These would allow one to try and see what effect the amount of material to extrude has on the force required.

By: Mark Heywood

Mark Heywood — Mon, 24 Jun 2013 02:50:20 +0000

I’m using an insulated heater block which is probably close to the temperature I’ve set for PLA filament. However, the hot end nozzle tip will be much cooler. But, without a thermal camera, it will be hard to tell what the temperature difference is; I reckon it’s more than 10 degrees C difference.

I have to set a high enough temperature to compensate for the temperature difference between the heater block and the nozzle tip.

It’s unlikely that the filament would create a friction variance of say 500 grams inside the PTFE tube to cause a sine wave under a constant force. This is why I think the temperature at the nozzle tip has more to do with causing the sine wave than any friction in the bowden.

The sine wave could be unique to my nozzle design so I’m looking forward to seeing graphs from other printers for comparison.

By: Peter

Peter — Mon, 24 Jun 2013 01:28:15 +0000

The temperatures seem rather high for PLA. But I cannot claim this since I never used PLA (only ABS and only at the stock 230°C). When you used lower temperatures and got the sine wave in the force chart, was the filament nicely straight in the bowden? The point is that when higher force is required and the filament is not tight in the bowden all the time even just after the airtripper drive gear then a wave can appear in the filament (especially when retracements happen) and this can increase friction in the bowden which can be irregular. Although it probably would not create a nice sine wave in the force chart. Just want to be sure this cannot be the reason for the “sine signal” in your force charts.

By: Mark Heywood

Mark Heywood — Sat, 22 Jun 2013 21:53:15 +0000

Hi Peter

1.75mm PLA was used through a nozzle size of 0.4mm and extruding a layer height of 0.25mm.

The PLA filament was bought from ReprapWorld and has been the best filament I’ve used so far. It sticks well to glass and oozing is controllable.

A 3mm bowden will be supported later with a new extruder design to fit the filament.

The good weather and the dreadful PLA filament I got from Ebay has slowed things down a bit but a new post will be out shortly after some editing.

Mark

By: Peter

Peter — Sat, 22 Jun 2013 10:43:57 +0000

Very interesting measurements. Thank you. I have two questions:
What filament material was used? ABS? PLA? Something else?
What was the nozzle size of the head you used?

By: Mark Heywood

Mark Heywood — Mon, 10 Jun 2013 21:57:04 +0000

Thanks William.

The project should be fully published within the next two weeks; I’m looking to get the next part out in the next few days. I’ve been testing different load cells to define a calibration strategy that will work for most people. I’ve got more testing to do tomorrow to practice calibration methods with different load cells which will hopefully provide a more solid guide.

G-code settings are mostly not transferable between different 3d printers so having good feedback from the extruder will be useful, especially on bowden extruder systems. With the extruder filament force sensor, you would only need to print a few layers to get enough data to recommend new g-code settings.

Your blobs could be at the Z axis travel positions. If you do not have enough retraction distance set then plastic extrusion would continue while the nozzle moves up to the next layer. Retraction usually happens during Z travel as well as other areas. You would need to check your filament diameter in different areas just to make sure it is not oversized; if the blob issue continues that’s not related to retracions.