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3mm Direct Drive Extruder / Bowden Extruder

by tosjduenfs, published

3mm Direct Drive Extruder / Bowden Extruder by tosjduenfs Nov 28, 2012

Description

3mm Direct drive extruder compatible with Prusa Mendel and similar printers.

Recent Comments

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Does it work with 1.75mm filament ?
I'm using a 50:1 ratio geared stepper motor to drive 3mm filament through an extruder mounted on the x-carriage, and so far I've also found the Raptor tricky to work with. I've experimented with a variety of filaments and idler pressures, reduced speeds, disabling retraction, etc., but haven't been able to make it very trustworthy. My old reliable NEMA 17 Wade is still the champion.

There is some heat from the motor transferring to the Raptor gear, and this could be contributing to the problem. There's also the issue of possible jams because at 220°C a lot of heat is creeping up as well. So far I've found PLA more reliable to print with, and I'm sure the lower temperature range helps.

Ultimately, you want just enough pressure to grip the filament, not enough to distort it, which requires more torque anyway, and if it does jam up, I'd rather the motor skip than gouge a groove in the filament, but that's hard to achieve. The same things that prevent jams on a Wade should apply equally to direct drives.

Anyway, it's all just experimentation. I'm building a couple of other extruders that may work better with the Raptor (especially for 1.75mm filament) but I will soon have a couple of MK7 gears to try out also. The groove on the MK7 is more like the groove on my trusty Wade's hobbed bolt, so I expect much better results from it than the Raptor in this setup.
Hey you know those cheap Venetian blinds that you pull the string on to make them go up and down? they gave a small brass floating gear looking thing that traps the string. Kinda looks like a ready made filament drive to me.

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Instructions

I have now succesfully used this extruder with a DIY drive gear. The parts have been upgraded to have a stiffer filament compressor arm and a fully supported stepper shaft (I bought 20 of these bearings so why not).

My calculated steps per mm (132.285) are pretty close but I still need to calibrate it (It's late and I'm tired). I'll post some examples once it is fully calibrated. The one test piece I have printed looks to have the same quality I have come to expect.

Run it in reverse and it can be used as a bowden extruder. The filament runs through 1/8" teflon tubing threaded into an M5 nut which is held by the nut trap.

For this extruder you'll need: M3x12 screw x 3 3/4" 4-40 screw 1" 4-40 screw and nut x 2 625z bearing x 2 *#10 brass or steel spacer, 5/16" OD, 3/8" Length for the drive gear.

Assemble as shown in the photos. The extra hole and nut trap on top is for a filament guide attachment.

You may need a 3mm ID 5mm OD spacer for the compression bearing. It just so happens that my 4-40 button cap screw fit right into the bevel inside the bearing enough to keep it centered but would not go all the way through so the spacer was not necessary.

The assembly is easy and I'm sure the photos are enough for you to figure it out.

To make the drive gear:

A drill press comes in handy but is not necessary.

Hob the #10 spacer as shown in the photos, placement of the hob is not critical since you can easily adjust its placement just make sure you have enough room for the set screw. Drill and tap one or two holes like in the photos. I used 4-40 1/8" set screws. Finish by drilling out the spacer with a 5mm bit so they will fit on the stepper.

A note, I didn't use any of the gears shown in the photos. I ended up making one that was cut more shallow than those. I only hobbed it enough to get good teeth in the brass. I used a 6-32 tap.

Since I am running 3mm filament through a 0.35mm nozzle a great deal of torque is needed to have reliable extrusion and in order to get more torque you need more amps. I added a larger heatsink to my extruder stepper controller to ensure it stays cool. After about an hour of testing the extruder the stepper was pretty warm so I plan to add some heatsinks to the stepper itself.

The printer you see in the photos is my HaMendel printer. My last name is Hamende (Ham-end) so putting Hamende and Mendel together I got HaMendel. I designed and fabricated it myself with some inspiration from the mendel. It has a full 200mm z height with 12mm z smooth rods and 10-24 leadscrews. This means ZERO z wobble. The two plate design keeps the whole thing incredibly stiff. I will eventually add this to thingiverse but it will take me some time to get all of the part files together.

Does it work with 1.75mm filament ?
Hey you know those cheap Venetian blinds that you pull the string on to make them go up and down? they gave a small brass floating gear looking thing that traps the string. Kinda looks like a ready made filament drive to me.
What version X-axis carriage are you using in your photos?
Nice gears. I think I'll try that too. I've been using my gearless extruder (http://www.thingiverse.com/thing:21728) for almost a year. The key, in addition to cooling the gear and motor with a fan is to use a well-designed hot end that requires very little force. So far, I've had success with the 0.5 mm Budaschnozzle 1.0 and the 0.35 mm J-Head Mk V-BV. With the J-head, I can extrude 3.0 mm ABS at 150 mm/min and higher.
Direct Drive (Gearless) Extruder
by brnrd
i am currently using a direct drive extruder with a 3mm filament and 0.35 mm nozzle... the extruder motor has a 40 mm fan constantly running on it. But the extruder randomly skips steps in the middle of a print and end up with missing bands on the wall of the prints... i tried everything including higher current and higher temperature to make it reliable for the last two months .... but finally i am giving it up in favour of a greg's extruder......:(
hi,
i have a direct drive extruder for a 3mm filament and 0.35 mm nozzle... it works well only with a fan on the stepper... also it tends to skips steps sometimes due to a variation in the consistency of filament... ie sometimes the filament need a lot higher temperature to push through the nozzle....in short this type of extruder can work fine either at a higher temperature or a 0.5mm nozzle
I agree, with a higher temp and larger nozzle this can work very well.  However,  I did this more for experiment than out of necessity.  My gregs accessible extruder works very well so I'll stick with that for now.
Update:

I calibrated the extruder today and printed some test parts.  They turned out well but my stepper was getting very hot.  For the sake of my printer I switched back to my gregs extruder.  There is a reason most people use mechanical advantage for 3mm filament.  If I ever switch to 1.75mm filament I will revisit this idea but for now I'm throwing in the towel.  If you have a 0.5mm nozzle you can probably use this with more success than me.
SUCCESS!! See above.
Great job! How are you liking the Raptor filament drive gear?
It did not work out as well as I had hoped.  It would grab the filament ok but I had to use a lot of compression force.  It says it is universal but I think it works better with 1.75mm filament.  

I'm experimenting with making my own drive gears.  I bought some zinc plated brass #10 spacers 5/16" OD and 3/8" long.  I hobbed a few with a 4-40 tap and some with a 6-32 tap to various depths. Then I drill and tap some holes for set screws and drill the spacer through with a 5mm bit.

I also got some 625z bearings to compress the filament with.  Since I had some of the extra 5mm bearings now I also decided to support the shaft like Misha suggested.  I'm not sure it is necessary but it should extend the life of the bearings and it does give me warm fuzzies knowing the shaft is fully supported.

I've added some pics of the filament drive gears I've made.  Since the OD of the spacer is ~8mm and then hobbed to an even smaller diameter it should also give the extruder >60% more torque than if I used a makerbot or raptor drive gear.

I'll be testing tonight.  If it doesn't work this time around I'll likely abandon the project since my gregs extruder works very well as it is.
I'm using a 50:1 ratio geared stepper motor to drive 3mm filament through an extruder mounted on the x-carriage, and so far I've also found the Raptor tricky to work with. I've experimented with a variety of filaments and idler pressures, reduced speeds, disabling retraction, etc., but haven't been able to make it very trustworthy. My old reliable NEMA 17 Wade is still the champion.

There is some heat from the motor transferring to the Raptor gear, and this could be contributing to the problem. There's also the issue of possible jams because at 220°C a lot of heat is creeping up as well. So far I've found PLA more reliable to print with, and I'm sure the lower temperature range helps.

Ultimately, you want just enough pressure to grip the filament, not enough to distort it, which requires more torque anyway, and if it does jam up, I'd rather the motor skip than gouge a groove in the filament, but that's hard to achieve. The same things that prevent jams on a Wade should apply equally to direct drives.

Anyway, it's all just experimentation. I'm building a couple of other extruders that may work better with the Raptor (especially for 1.75mm filament) but I will soon have a couple of MK7 gears to try out also. The groove on the MK7 is more like the groove on my trusty Wade's hobbed bolt, so I expect much better results from it than the Raptor in this setup.
You will likely need to add bearing support to the motor shaft to counteract the force from the idler.
Not needed. I've been running my extruder (see below) which works the same way for over a year with no issues with the motor.
Perhaps, but for now I'll test without support.

The load from the idler is only offset 6.5mm from the base of the shaft so the moment is actually pretty small.  Even with 20 pounds of compression force (which is a lot) it is well within the limits of the bearings.
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