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I'm designing a new extruder (again) and before I get too married to a design with specific dimensions, I thought it would be interesting to do a comparison between the different drive gears and hobs that are out there. I've got the SeeMeCNC gear of course, picked up an E3D HobGoblin of each size, and snagged a few others from Chinese sites that my wife would tell you I spend way too much money on...

What other drive gears should I include in my shootout? Do you have a favorite?

I'm also open to ideas on the test rig. My plan was to make something that allows me to clamp the drive gears into a fixture and apply a consistent pressure against a piece of filament with each of them (either by hanging a weight or by using a strong spring), and then see what tensile strength they can each hold before slipping, stretching, or cutting the filament. Are there other traits and properties that you'd be interested in having me look at (deformation, knurl spacing, etc)?

The Bondtech has been used a lot by MHackney and I purchased two of them. I believe the url is http://www.bondtech.se.
They use a geared stepper and a counter rotating gear set for the filament.

It would be great to have some real data on this. There are other factors at work too though. For instance, in traditional designs (i.e. not a Bondtech) the presser bearing can be flat or grooved. I've had problems with flat bearings allowing the filament to move laterally across its face. Similarly, grooved vs unproved drive gears. Flex in the system also causes problems and even if the gear and idler were "perfect" flex in the idler arm can create problems. And don't forget filament support out of the extruder. Simple pull tests are not going to test any of these but it would be great to figure out how to do it.

I now have enough time with the 7 QRs that I have to really appreciate their design and extrusion power. I've not had a single extruder related issue. It is the only extruder that will completely reliably push PLA through a Cyclops dual hot end. And I mean 100% reliability. I am extremely impressed with what they can do. Now the only open issue is their long term reliability. I don't anticipate issues but it does have to be tested.

Brian from TrickLaser just got in a BondTech as well. Man, they're beautiful extruders. I'm sure it's not as nice, but PrintrBot has a dual gear extruder like that, too. http://printrbot.com/shop/gear-head-extruder/

Trying to quantify the grippiness of the drive teeth themself is what I first intend to do. The design of the extruder and its arrangement is a whole different bag of hammers

I also got the bondtech QR installed on one of my max v2 with e3d v6 hotend.
i printed with it for the past weeks and it works very good no skipping, no jams at all.

I also have this on other max v2:
http://www.aliexpress.com/item/3D-print ... 18400_6149 and it works just fine but will not work for flex filaments like TPU, NINJAFLEX and so...

Looks like the "MK7" drive gear (their description mentions 7 and 8). I should have one coming.

That extruder looks like it could jam very easily. There's a lot of open air between that drive gear and the bowden tube. You ought to design an insert to slide into it that supports the filament better. That would be a cool mod.

I just added a new one to my machine about a week ago, direct drive with a NEMA 23 stepper. I got the stepper for like $8 from a salvage website; I think they take the steppers out of whatever machines they can get and resell them dirt cheap. Mine came with dampers already installed!

So far no problems, the extra NEMA 23 torque got rid of all stalling problems I was having with NEMA 17 steppers. Direct drive is fast and has no backlash, and with enough torque you eliminate all of the stalling. I made this design nearly air tight to prevent moisture absorption when leaving nylon in over the course of a few days or weeks. I don't have a cover on it now though.

Uses a standard hobbed drive gear like every other extruder. No gear train, no backlash. It feeds great without slippage or grinding, no filament buckling, not a single print flaw with or without retraction since I've installed it. One of the few times I nailed a design on the first attempt. I guess the key to it's performance is simply using a motor with more torque.

The downside is that it needs two PTCs, one is optional for airtight feeding from a sealed bucket. It also needs several holes to be tapped for correct fits. The pinch bearing is 624zz, held against the drive gear by a screw on the outside.