Category Archives: Extruder

Experiment Extruder Transmission

Experimental Off-Carriage Extruder Motor

There was a recent thing on Thingiverse called the Vert-X-Belt-Truder by Johann which describes a way of moving the extruder motor off the carriage. The benefits are a lighter, and potentially faster, carriage. The Bowden cable is another way of achieving this goal. A comment by Martin Price (martinprice2004) caught my eye:

…keep the x axis as current prusa, but turn the extruder 90 degree around the z axis. Drive the extruder using a motor mounted at the end of the axis with a square or hexagon bar mounted horizontally. The extruder drive gear moves along the shaft when the x axis moves, but can still be driven by the motor at any point.

I had already done something similar for moving the X-axis motor off the carriage and so I quickly threw together a proof of concept to thrash out how a design would work.

Sketchup Design

The results are shown in the following video (please excuse the varying focus, the many “er”s, and the fact the audio is muffled between 2:10 and 3:35 – I didn’t realise I had my finger on the microphone – but I don’t say much of value here anyhow, only that it seems to work and the drive gear moves through the drive shaft. Also that the test “print” is running at 200mm/s (travel:250mm/s))

I utilised the Compact Geared Extruder by Matt Roberts (Thingiverse) because it’s small, modular, and as it is designed in OpenScad it’s easy to hack with. I went through a couple of iterations to come up with a bracket that would hold the drive gear in place as the extruder moved along the square drive shaft. As I put the parts together I realised the same effect could be achieved using herringbone gears, so long as the drive gear is held close to the driven. The coupling is a rubber roller from an old Xerox laser printer, as is the square rod. The NEMA 11 motor is simply zip-tied to the X-axis motor end, and the idler is simply a bearing zip-tied to the X-axis Idler end.


A few things I learned as I put it together which might be worth considering if anyone recreates this.

  • Positioning of the motor and idler dictate where the drive gear will be placed, and so I would align these precisely with the X-axis rods and place the drive gear with a bracket. Then I would make position of the extruder flexible (using slots for the bolts for example) so it can be accurately pushed back in line with the drive gear, giving a good fit.
  • The bracket holding the drive gear would be made more robust – reducing lateral movement and possibly adding bearings or bushings either side of the drive gear to support the rod.
  • The bracket should have a way of removing and inserting the square rod, otherwise it’ll be a pain to disassemble the whole thing. Of course if bearing or bushings are used then it might be easier to design it so the rod slides out along the X-axis when disassembling.
  • As mentioned above, using a helical gear such as a herringbone might remove the need for a bracket at all. I guess this would depend on the amount of flex along the driveshaft, and whether the drive gear keeps engaged during the back and forth.

If I get chance to fix the hobbed bolt of the compact extruder then I will try to get this setup printing for real. Here’s a couple more photos and videos just of the running.

[gallery include=”942,946,944,943,941″]

 

Extruder

Hobbing nuts and bolts

Whilst printing an extruder for my huxley/mini-mendel test printer (NEMA 17 bowden extruder drive by jmgiacalone), I realised I didn’t have a “M4 toothed insert”. Not wanting to pay, nor wait, for one, I decided to hack something together from parts I already had.

Not being able to hob my own bolts has irked me for a while – I don’t own a slow enough drill, nor do I have shop tools to machine a part. However, the recent purchase of a Dremel brings with it many opportunities! My previous attempt at hobbing a M8 bolt had worked, but it was non too pretty, and I thought a M4 nut would be too fine to hob by hand.

Still I decided to give it a go – trying both standard M4 nuts and coupling nuts – which turned out to fit perfectly in the extruder.

First I ground the coupling nut a little to round off the edges, then slowly worked along the length with a fine cut-off attachment.

Bolstered by these results I then attempted another M8 bolt, with much better results.

The steel of the bolt was much harder on the attachments though.

Extruder Printing

Building Matt Robert’s Compact Geared Extruder

I wanted an extruder to use for my experimental hot ends so I took advantage of the long weekend and had a go at Matt Robert’s Compact Geared Extruder.

I like the small, modular design, and particularly like how he’s approached the transfer of torque in the main gear.  This requires three set (grub) screws to go the radius of the gear, and I didn’t have any lying around.  A few minutes with some M3 bolts and a hacksaw though yielded sufficiently long and stable screws.

Extruder Printing

Improved Calibration of Extruder

After finding the Extruder Steps Calculation Spreadsheet on the brokentoaster blog I calibrated the extruder to produce better results.  The important thing it seems is to measure everything on your own gear, and don’t take it for granted that the default settings will just do.

My gear ratio is 3.55 (not 5); the extruded filament diameter is more like 0.9 mm (not 0.5, although I will measure this again tomorrow); the Pinch Wheel Diameter (PWD) is 6.7 mm (not 8) and the steps per revolution is 3200 (after taking into account the 1/16 microstep setting).  Consequently, the E_STEPS_PER_MM comes out at 48.5 according to the spreadsheet, a much higher value than the original setting of 22 in the Tonokip firmware I am using.  The initial results seem much better.  Still much room for improvement – but I was able to print a (rough) replacement end-stop holder, after my Z axis holder broke from over-zealous tightening last night.

Hopefully I will find time to formulate the process I went through and add it to the wiki, or add to an existing page if it already exists.  I think these calibration steps, together with getting the right firmware/host combination, is a potential sticking point for newcomers, and providing clear directions and help would really help.

Extruder

Makeshift PLA Feeder

Two spare skateboard wheels
+ smooth rod from an old printer
+ spare shelf parts
= Makeshift PLA Feeder!

Extruder Frame

Print Head

I’m not too happy about the position of the extruder on the print head.  The motor rubs against the X axis belt when mounted in one direction, and the large cog rubs the belt clamp in the other.

Also, the two bearings that hold the hobbled bolt, in the extruder, are not perfectly parallel, and this causes the bolt to be slightly stiff when turning.  We shall see if this causes problems and needs to be revisited.

Extruder

Building the Extruder