Spring loaded extruder for Leapfrog Creatr

by Rob65, published

Spring loaded extruder for Leapfrog Creatr by Rob65 Mar 16, 2013
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The Creatr from Leapfrog (www.lpfrg.com) has a fixed idler ball bearing. I wanted to replace this by a spring loaded type to allow better control over the filament feed and allow for an easier filament change.
After a few different ideas, the Mk7 minimalistic replacement extruder seemed a nice design to start with and here is the result.
Now changing colors is actually a fun thing to do ;)
Update: I found that the pressure on the filament was not always enough so I moved the spring and compressed it a bit more resulting in more pressure on the spring. I've tested this for > 100 hours with ABS, Taulman Nylon and PLA and had no problems at all.
Also added a longer filament guide towards the hobbed wheel, making a filament change a bit easier.
note: photos with the light green parts are v2, red parts are v1
You could consider building http://www.thingiverse.com/thing:321258 instead, this adds the possibility to print flexible filaments like Arnitel and Ninjaflex


Print and follow the instructions in the PDF document. The PDF document contains detailed instructions on how to remove the old extruder parts and install the new one.
N.b: the instructions are still for v1 but v2 is almost the same (except for the washers when mounting the stepper motor).
You do not need to remove any wiring or cut or change original parts. Everything can be restored to its original state if needed.
Besides the printed parts (and some tools) you will also need:

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I have some trouble with the pressure on the filament. I've printed the new parts in PLA with the original extruder.
Our leapfrog has a standard 3mm drive gear pulley. Any ideas how to get the feed rate of the filament right?
I tried a stronger spring but it doesn't seem to make a difference. The original parts seem to give enough pressure but the curl up to often and its hard to change the filament. Should i try a 1,75 driver gear? Or is the problem with the flexibility of the PLA when bending?

I am not sure this will work with PLA. The parts get work enough for the PLA to become soft.
But this should not matter when the motor is still cold - so it should work at least for some time ...

I had a bit of a problem getting the right springs and I ended up adding a washer under the spring in order to get more pressure on the drive wheel. I think my Leapfrog also has a 3mm driver gear so that should work - on my new printer I also mounted the 3mm driver gear on a 1.75 extruder since the 1.75 gear was sold out when I ordered ...

Hi !
Nice work you did.
I had problem extruding with my leapfrog creatr, so i try your solution.
It is better but i still have some problem: sometimes (often) the filament stops extruding during an instant which mean at the end i had gap in my piece. Te motor is running but the wheel stops and so i had no filament coming out.
Do you have an idea? Im using a diferent spring than yours, do you think it can be because of that?

Hm... motor is running but the wheel stops ?
If this is true, you should see the axle of the motor rotating while the wheel is not. In that case the wheel slips on the axle and you have to re-tighten the little allen screw (imbus) of the wheel. If I remember well this is a 1.5mm allen screw

Sorry i did not want to said that. I was talking about the ball bearing which is not rotating whereas the wheel of the motor is rotating.

If the wheel at the motor is rotating and the ball bearing not, then the transportation of the filament stopped.
This is most likely due to not enough pressure from the spring. I had a few problems with this myself - try another spring or increase the pressure from the washed by placing a large washer or a thin piece of steel under the spring so it becomes stronger.

Hi again,
I replace your spring by a stronger one, it works really well now.
Thanks for sharing that Rob !

Working like a charm! Thanks! Grabbed out a spring out of an old garden scissor. :-)

Hi, Thanks for this nice Add on! Well done....What a force the spring has to have?

Hi Rob,
thanks for sharing your extruder. My Leapfrog (received a month ago) had
problems with filament tolerances I guess. During a print job, the filament was
from time to time not transported and the nozzle clogged. Therefore I made your
extruder. I had to remix it a little, because I wanted to use the original filament
feeding. Now it works very well and the filament change is much easier.



I want make this to know , you have use how many parts.
Would you help me about the Spring dimension is correct spec? and Screw spec.


Just have a look at the instructions - your questions are answered there

I got a Creatr last week, having many problems with filament feeding, jamming and curled below the pulley. I will print and install your project, I believe it's a big helper. I miss a better guide bellow the idler/pulley, I believe the distance is too long and the heated 1.75mm filament is weak, bends very easily. I´ll try a ABS prototype conical guide, let´s see if it works. The ideal is a bronze or aluminum guide.
I´m a mechanical engineer, power solidworks user. If you need opinion in your designs please let me know.
from Brazil

Hi Paulo,

Without extra conical guide most materials work fine. ABS, PLA, PET and even Nylon print without problems. I just have problems with Arnitel (a flexible co-polymer).
I think it is more likely that you are having a problem with the drive gear alignment. It should be perfectly in line with the guide tube - see page 45 in the user manual.

Hi Rob

I have tried both the first and second versions on my Creatr and the design keeps getting better.

find with both designs, especially with the stiffer springs I prefer,
that I get jammed or curled filament escaping out of the extruder area.

I tried the the thing-o-matic drive block (thing 72215) I found it fits
the leapfrog with some spacers, and solves the issue of filament
squirming out of the side of the extruder by having a small guiding
section beneath the idler/pulley, but it's not such a strong build or
good fit as your design.

Maybe a hybrid of the two might be perfect?


thanks for the hint. Is this "squirming out" occurring during printing or only when feeding a new filament ?

I am currently working on something like 72215 but for a different reason. I have no problems printing ABS, PLA or Taulman Nylon but the Arnitel (aka Flex PolyEster or FPE) is too flexible and needs some extra guidance.

I am hoping to have a new base-plate next week that does the job for me.

Hi Rob

Squirming usually occurs after printing for a while so maybe I need to adjust feedrate to fix.

cheers and thanks for all your work

I have been printing ABS and PLA at 60mm/s without problems. I can almost do Arnitel but that still squirms out while printing the raft.

> thanks for all your work

I took something from the community, adapted it to my needs, provided it back into the community and now it's giving me a lot of nice tips on how to improve the design (and my print quality).
This makes us all happy :)
Thanks for the heads up.

How's it going?


unfortunately my attempt have been unsuccessful up to now. I can't yet create a reliable printable part for this. As added difficulty, the inlet of the hot-end is not in line with the drive wheel on the motor.

That's a pity, did you do the design in Openscad?
I may try and mash together your backplate with 72215 in meshlab and see what happens!

The design was done in SolidWorks and not one of the nicest thing I made ...

I'm having trouble getting mine to feed correctly. Is the spring you used really stiff? I found a pretty stiff one at Lowes (Bi Folding Door Replacement Hardware) that I cut to size. The spring is strong enough that it is difficult to assemble. Without filament, the drive roll spins the idler bearing, but with filament the bearing does not turn. It may be that I need to clean my hot zone, as it is fairly difficult to manually push the filament in.

I love the design though, I hope I can get it working!

just measured my spring. Uncompressed it is 25mm long and 10mm wide. When I compress the spring to about 16mm (that;s approximately how long the spring is when compressed in the extruder) it develops about 1.5 kg force.
I just measured this by placing the spring on my kitchen scales and then pushing it until it is about 16mm long. The scale now shows 1500 grams.
And that actually is a bit on the low side. I currently have the spring compressed a bit more to develop about 2 kg force.

you should be able to push the filament in with a bit of pressure. Keep in mind that different colors have different pigments and they may need different pressures to be pushed through. My white and black ABS go in very easily, green takes more force and orange is in between those.

Are you using ABS or PLA ?

I think the issue was with my hotzone requiring too much force. I switched to the other extruder and only one moderate spring was sufficient. Printing great now! I'll have to clean the one hot zone thouroughly and see if it is easier to push filament through. I print exclusively in PLA these days, directly on the heated glass with a bit of hair spray.

Nice to read it works. I am still working on a design with a longer lever and an adjustment for the spring force but I am not yet convinced about my new design.