mk7 ball bearing extruder drive
Derived from
Description
I just don't love having that delrin plunger dragging on the filament and I like to be able to quickly release the tension so that you can pull the filament out and replace it easily without having to run the stepper.
Instructions
Either print out the parts separately or print out one of the plates (with or without the quick release).
Remove the support from the lever (where the bearing goes, it's just two thin walled cylinders)
Remove the support from the underside of the body.
Remove the support from the quick release (two cylinders again)
If you have a 3mm tap, you might as well run it through the holes for the tensioner and the bearing.
Install a 623 (or R2) bearing (3mmx10mmx4mm) in the arm with an 3mm x 10mm countersunk screw
Put the pin for the quick release in the quick release and install the screw (3mm x 20mm)
Snap the lever onto the drive and install the tensioner screw or quick release.
Install the drive the same way you would the normal mk7 block. Tighten the tensioner screw until the stepper misses steps when you hold onto the filament (as opposed to just slipping).
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Just made this and I love it! Got the bearing from amazon and here's the link if anybody would like.
http://www.amazon.com/gp/produ...
Its prime eligible so that means 2 day free shipping for whoever has prime!
I would suggest an improvement -- I have already stripped the threads in the plastic because it is plastic (duh). A better solution would be to put a recess for a nut on the inside of the drive plate for the tensioner. Then we could add a 3mm nut (glue it in) and not have to worry about the plastic stripping out. By the way, I tried just putting a nut on the inside, but there is not really room.
Second, I attemptyed to put a spring in between the release lever and the tensioner. I found some 3mm "fender washeers" but even they were too small -- they slipped inside the slot in the arm and then when I took it apart again, the arm was split in two. I may try a larger washer after I print it
again.
So I am back to the stock configuration right now. I do not have the program to modify the plate for a nut, so I may not try again.
Here's a video of it in action using sdp-si spur gear S10T05M020S0505 in place of the MBI special part. There's some flex on the tensioner (it's using a spring so the spring is overpowering the ABS). I am going to modify this design to have no overhang on that side (for dual extrusion) so I'm not too worried about that part:
Also works with a 77R2 bearing (available at Ace Hardware) which is 1/8" bore, 3/8" OD and 5/32" wide, or 3.175mm x 3.97mm x 9.525mm compared to a 623 3x4x10.
The bearing screw is M3x10 (remember flathead screws count the head).
This is a very clever print! I think it may need some more room behind the tension bolt in my application but other than that it's almost perfect.
I've since learned that the size is just "R2", not sure what the 77 prefix means. I ordered a second one from McMaster (for about $6.25) and I'll post the McMaster p/n if it works out.
Thanks! I never got around to measuring that screw, I just put one in and then cut it off to length with a abrasive disc. I'll update the instructions.
What size are the other countersunk screws? Source for them?
Do you mean the little one for the bearing? I would guess that one was 12 or 14 mm. I thought they were 8mm and ordered some from mcmaster carr but the I didn't realize that for the countersunk screws, you measure the length from the top of the countersink, not just the length of the screw. I ended up using one that I had left over form my aluminum build platform since I only used 3 of them to hold the platform. I just shortened it with my dremel tool. I'll try to remember to post the actual length of that screw when I get a chance (or I could look in the cad files). You could probably also use a 6-32 or 5-40 screw from your local hardware store.
This is great stuff and I will be attempting to print my copy. I was wondering what others have used for Object infill (%), Number of shells and Feedrate? My Base Profile is set to SF35-Thingomatic-HBP-MK7 with the extruder temp at 230C and HBP at 110C.
Any info/recommendations are appreciated!
I think I printed mine at around 50% infill. I'm not sure what the extra shells setting was. If it's anything other than 0 you will probably have a little open space in the arm where the hole for the bearing is. It doesn't really matter though.
You could probably just print it with the base profile and up the infill a bit. My extruder is at 220c and my HBP is at 110.
I love my new filament drive! It would get in the way of dual extrusion, but I'm not planning on that for the foreseeable future.
A great addition to it would be a filament dust remover. Just four thin walls surrounding the input hole, where one would put two pieces of sponge to keep dust away from the filament drive...
I made a untested mod for your extruder to make it compatible with the ultimakers bowden system...
Instead of using a skateboard bearing, I'm thinking of using one of these: http://www.thingiverse.com/thi...
It looks like its designed so you can do filament changes, unlike the stock mk7 (see http://www.thingiverse.com/thi... )
Can anyone confirm?
I think I'm going to tweak this to use a standard skateboard wheel bearing.
Also, what is the difference between the mk7_drive_plate.stl and the mk7_drive_plate_qr.stl???
The bearing is ~22mm in diameter and ~7mm in depth. The center hole is the perfect size for a nylon spacer.
I was thinking about pulling the stl files into OpenSCAD, Blender, or Sketchup. I'll decide which one once I decide how things need to be tweaked. Anyway, see the photos below. It is a "Lucky Hardball (Reds)" bearing.
the qr one includes the quick release parts
what are the dimensions of a standard skateboard bearing?
I like the drive and I like the fact that you provided the Alibre part files. I was able to download then and make an assemble to better understand the drive. Dave
I've uploaded updated files along with the alibre files.
There are now STLs for plates either with or without a quick release.
This looks really good, I'll need to make one I think. Keep us posted on printing results and heat effects.
That's my main concern now that the heat is so much closer to the stepper than it was on the MK6.
Regarding the dual extrusion-mirror the drive concept. The mirrored one would place the bearing on the "other side" of the motor pully, but coulldn't a clever person make the extruder motor turn the "other way" ? The current motor goes clockwise for foward and ccw for reverse. Isn't the "sense" of the extruder motor a motherboard parameter? It could easily be done in the wireing, of course.
It just occurred to me that this design may not work for dualstrusion, would that be accurate?
I have mk7 and thinking the same thing... I don't like the plunger.
I will give this a try when I get the bearing!
Let me know if you need some help testing it out...especially if you can solve the color-change problem.
Awesome! Awesome! Awesome! Cheering for you! If you do upgrades please link them to this page so I don't miss any :P. Whoohooo! this is great! Thanks!
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is there any way to make this work with a 608 bearing, the kind that skateboards use?
Not really, a 608 bearing is half the width of the stepper so, it would need to be a much bigger assembly. The mark 5/6 filament feeders could be tweaked for a 608 but they use a different hot end.