This is, I am proud to say, the single greatest upgrade you can possibly print for your MK5 print head. Seriously... download it and start slicing it now while you read this, you're not going to want to lose any time!This tensioner provides MUCH stronger grip than is possible with the default delrin plunger setup. In addition, it doesn't require the same constant adjustment the delrin plunger does. Just put it on once, and go. It'll eat anything. And it can hold with MUCH more force against the motor shaft than the delrin plunger could ever DREAM of.This thing is a MONSTER FILAMENT EATER and will take your arm clean off if you get in the way. Well, maybe that's not true. Or maybe it is. Just don't go sticking your arms in any loops of filament while printing; I don't want to be responsible.This is advertised as "MK5" and it is - I'm not going to make any assumptions about whether YOU are using a stepper extruder or the DC motor ... anything MK5 goes. In fact, I'll give 100 bonus internets to the first person who tries it out with the DC motor and posts some photos. Most of my photos are of a stepper configuration, but it's just because that's what I'm using.I've intentionally tried to design this using only parts you'll have on hand and can find at the local hardware store.The design of the tensioner is of course inspired by every variation of Wade's extruder I have seen. The design of the mount is mostly inspired by natetrue's printable MK5 ( http://www.thingiverse.com/thing:5169 ). I'd have liked to have made it a proper derivative by starting with his design, but sadly I couldn't get it to render in CGAL via OpenSCAD, even after his recent fix (it did fix the error I had gotten, and replaced it with a nastier one!).So this is a fresh design 100% by me in OpenSCAD.Motivation: Now that I have a stepper extruder ( http://www.thingiverse.com/thing:5797 ) and I've found a way to make it pull strongly with my weak motors ( http://www.thingiverse.com/thing:6362 ) now I need a better tensioner. The bolt-driven delrin plunger on the MK5 doesn't supply constant pressure; just constant position. The tensioner from the Wade's style extruder seems like a brilliant design to me; a spring-pressure 608 bearing can press against the filament with a good, strong pressure, and the springs ensure it can supply pressure even if your filament isn't 100% consistent, or you have worse problems like a bent bolt or whatever. Here's a youtube video of my first actual test extrusion with it. I've since gone on to print, and have the most AMAZING consistent filament flow I've /ever/ had. It's beautiful enough to make me weep. The mechanical noise I point out in this video vanished during my first print. http://www.youtube.com/watch?v=54xrG96qoJMUPDATE: (2011-03-09) I've been printing great with two of these ever since I put it together in the first place. But I usually print with a fan on - and I think my dual extruder setup bleeds a lot more heat than a single one would, and is more confined.Long story short, I tried a print without a fan on, and my filament pusher melted down! Well, melted UP, actually. Photo posted. I may redesign this with a thicker base, but really I think the fundamental issue arose out of my cramped dual-heads, and can be cured with a fan, so it's not such a big deal. If it should happen to anyone else though, I'd like to hear about it - and keep a spare printed just in case!FINAL FILES UPLOADED. This is a working design in production use now. If I make any improvements, I'll post them under a new derivative. The -final files are the complete design, which differs from the photos only in that the space for the 608 has been /slightly/ enlarged, leaving a window for it in the back of the idler block.Other required bits:4 springs; I am using 1/4"x1/2"x.035 compression springs which I picked up for a couple bucks at my local Ace Hardware. They just fit a M3 bolt head, something a shade thinner might be even better. You can go to the Ace, get your bolts, then just go to the springs and see what fits, if you have any trouble. If you get springs that fit the right width, the length is not too important; you can use aviation snips to cut them to size. You can also use a nut or washer to help hold them under the bolthead if you're worried they are too thick.4 M3x40mm bolts, (x45mm or x50mm will make assembly and filament changes much easier) 4 M3 NYLOCK nuts. (my photos are normal nuts but I'm sure they will come loose someday) -- ALTERNATIVE (not tested): 4 6x32 2" bolts, plus matching nuts.1 608 bearing (rollerblade/skateboard)1 m8x25 bolt.IF you are using a narrow STEPPER motor mount like mine, or TheRuttmeister's, you may want to make sure you have 2 M3x10mm on hand to fit behind the idler block. If you are using the DC motor, you might want 4 of them to fit the motor on with.You should be able to find all the above parts between your local Ace Hardware and your local skate/rollerblade shop. The "Play It Again Sports" near me sells the bearings for $1/ea!This part is a bit thicker than the original, to make room for a nice thick idler block. This means your pusher gear needs to be moved up a bit on the DC motor shaft. There should be just enough room left to seat the end in the bearing. I took a photo to show the clearance I've got, which you can see on the side here. (Incidentally, the 'NOISY' sticker? That's the way it came to me from MBI, I didn't label it.)I think I took enough photos for you to see how to put it all together. After you've got it in place, if you used the M3x40mm bolts like I did, you might need to use a screwdriver or something to wedge the idler block to the side to fit in your motor, and the filament. That's how I did it. You might otherwise make sure you put the motor and shaft in BEFORE attaching the 608 idler block, but I dunno if that'll have it's own complications.