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Upgrading stock drive gear and idler
Things you'll need:
Mk7 drive gear
3x8x3mm bearings
8mm drill bit
Drill (recommend using a drill press)
Small file
T10 Torx screwdriver

Concept is pretty simple, so I'm not going to write-up step-by-step with pictures here. You'll need to remove the hot end. Disconnect the idler lever spring. While holding the stepper motor so it doesn't drop on your glass bed, remove 4 T10 torx screws, pay attention to where they came from because there are 3 different lengths! Remove stepper motor. Remove idler lever. Remove metal plate behind idler lever and the hot end mount plate. Carefully slide off the E-clip holding the idler wheel on. Remove idler wheel, drill out to 8mm, press in 2 bearings (one on each side) with a vice. The drive gear is pressed onto the stepper motor... you have a couple options: 1) remove with small gear puller 2) carefully cut it off with dremel. Rather than risking damaging the motor, I quickly made a small gear puller and removed the drive gear. Don't install the new drive gear yet. On the idler lever, there is a small slot that is used as a stop... use the file and lengthen the slot on the square end a couple mm. Re-install the idler wheel on the shaft and replace the E-clip. Re-assembly is reverse of removal. Careful not to over-tighten the stepper motor screws... doing so will warp the extruder carriage and cause it to bind up on the rails. Before you put the hot end back on you'll want to install the drive gear. Loosen the set screw on the new drive gear, pull the idler lever back, and slide the new gear onto the motor shaft. Line up the grooves on the drive gear and idler, let the idler gear sit on the drive gear, and tighten the drive gear set screw. Put the hot end back on, and you're done.

Initial observations - filament feed seems more consistent, less blobby. Still have to try some things other than ABS with it and see how it does.[Image: 20150228_134427.jpg][Image: 20150228_164905.jpg][Image: 20150302_090340.jpg][Image: 20150302_090347.jpg]
So far it's working flawlessly with ABS, some of the best prints I've had on this machine!

But, not so great with other filaments. Since the new drive gear is grooved, the gap is too large to grip all the filament types well. I'm having a machinist friend cut me a new idler wheel with a flat surface (still pressing in the 3x8x3mm bearings).
Did you finally install the custom made idler wheel? I have purchased an MK7 but reading this I'm doubting whether it'd be a good idea to install it. Perhaps using a printed idler would work too?
Friend made it as a favor and actually just got it done today. Haven't picked it up yet.

I don't see why a printed wheel wouldn't work. I have a couple drawings for it, just haven't had much spare time to play with it.
You also might be able to just flip the OEM idler around since the groove is offset a bit.
Tom, try zipping your file that you wish to post.

Duh, thanks Keith.

Attached are sketchup files for two rollers... one with teeth, one without.
Can you also post those as an stl for peyote that don't use sketch? If so that would be great.

When I get time. Working 60hrs a week, a dozen hobby projects, and a wedding rapidly approaching (May). lol
Thank you Tom! I'm probably going to try and print these. I need to find the bearings first though.
See my first post, links to bearings
I put 3x8x3 ball bearings in my idler weeks ago. They were scavenged out of an old Trex 450. I used a lathe to bore the idler. Way better than a drill press. With a lathe you can use a slightly undersize drill bit and then deflect it to get a nice snug press fit for the bearings. The hole will also be perfectly centered.

The mk7 drive wheel is an improvement over the original brass wheel, but an even better drive wheel for maximum bite is a wire EDM cut high carbon drive wheel. They are only $3.50 at robotdigg. It uses a setscrew, but I put on the green loctite (for cylindrical parts) to make sure it was perfectly centered and locked in place. This drive wheel was exactly the same diameter as the original and required no extruder feed re-calibration. More importantly, no need to modify any stops or make any new parts.

For pictures I took of the idler bearings, look at these posts in the liquid cooling thread.

I also posted pictures of the EDM cut drive wheel in the PLA thread, here it is again:

Don't waste time making a puller to save the original drive wheel. It's junk. Just slice it down both sides with a dremel (just short of hitting the shaft), insert screwdriver in slot and pop it off.
[Image: OldDriveWheel.jpg][Image: EDMDriveWheel-2.jpg]
So the MK8 is of the exact same diameter as the stock gear? Damn, I read something different in another thread, hence why I ended up purchasing the MK7... and it now seems that the MK7's diameter (in the hobbed part) is about 1mm smaller than the stock gear, which means I might have to readjust the position of the E3D to line it up perfectly :unsure:
What? No. The Mk8 gear is much smaller. The mk7 overall diameter is nearly the same, but the "effective diameter" where the hobbed section is is about 1mm smaller.

Which is why I'm working on a flat idler wheel w/o the groove. Makes up for the difference.
Quote:Don't waste time making a puller to save the original drive wheel. It's junk. Just slice it down both sides with a dremel (just short of hitting the shaft), insert screwdriver in slot and pop it off.

I didn't make the puller to save the gear. If you actually read my original post you'd see that. Not everyone is going to be able to cut the OEM gear off without damaging the stepper.... plus, think about where all the filings and cut-off wheel bits might end up (ie. in the motor).
No issue with brass powder from dremel. Pay attention to direction cutoff wheel is turning to throw filings away from motor. I also taped up the end of the motor so that only the shaft was protruding. With basic precautions and a steady hand (no drinking and dremel driving Wink ), it was very easy. I had the old wheel off in about 2 minutes.
The wire EDM cut drive wheel I described - and pictured - is the same. 10.8mm diameter. Direct replacement with no modifications needed. Don't use a hobbed drive gear - they are inferior. I've used the wire EDM cut drive wheels on three Kossel printer builds and they are awesome. They don't slip.

Scroll down and look at the pictures comparing it to the hobbed drive wheel.
Technically, it's not really an Mk8 drive wheel, but I think they did call it that on their invoice when I ordered them it.
For Keith, STL files of the roller/gear models
For clarification... the gear Greg is referring to is 10.8mm OD, which is smaller than the OEM 11mm.

I've made no adjustments for steps or multiplier with the mk7 gear I'm currently using.

The pictures below are -
3 gears stacked: mk8, OEM, mk7
mk8 OD
mk8 hobbed section OD
oem OD
mk7 OD
mk7 hobbed section OD

[Image: drivegears.jpg][Image: drivegears-2.jpg]
Tom, what material would you use to print the wheel? I suppose ABS would work but I have some samples of exotic filaments like bronze and carbon fiber, and I'm wondering if those would work better (I'm doubting because I believe they are made with PLA and thus temperature in the build chamber could be an issue).

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