Hey! This thing is still a Work in Progress. Files, instructions, and other stuff might change!

Improved Printrbot Fan Duct

by 50an6xy06r6n Jun 10, 2014
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Printed this off in TPU and it doesn't matter if it hits a failed print because it will flex. Great design!

Printed this in ABS, and, while it's only been a week since I've installed so I can't speak to longevity, I wish I would've printed this sooner! The difference in the quality of prints is quite remarkable. This seriously improves performance when compared to the old funnel-shaped shroud!

Thank you for such a brilliant design and simple modification.

Hello there, very curious to know what software you used for the airflow modeling?

I just used the basic fluids simulation features that come with SolidWorks

Awesome job on this design. Printed a treat and seems to work fine :)

Thanks for the file, it works great!

The metal version doesnt fit the hotend with the small fan on it.. Could you release a file to edit so I can fix it :)
The latest editable file is for the cheramic.. To small hole.. And cant edit that so easy :p so a file from the metal version and I could maybe fix it..
Had to heat and hand mold the PLA on the model to get it to fit.. ;)

I printed one of these today in ABS... Unfortunately it ended up getting pretty soft and sagging a bit during a long ABS print this evening. I'm sure it works great for PLA or other materials where the fan stays running, but I think it's just too close to the hotend if you print ABS regularly. The airflow was noticeably improved in the brief testing I did, I will probably keep one on hand specifically for when I print in PLA.

I solved this issue by putting foil tape along the inside of the hot end opening on the shroud

The fan holding portion of the hotend, in my case with only 2 holes, is at about 50 degrees from horizontal. I have tried another shroud and it did not fit at all.

Odds of this one working? Any idea what model printrbot simple metal I have if the angle is different than most of the pictures? Got it from a friend.

Thanks everyone!

I designed it with an angle of 60 degrees from horizontal, since that's what I measured on my machine. There does seem to be significant variation between machines (possibly a batch issue?)

Appreciate the prompt reply and props on the flow analysis. I'll just have to CAD up my own. Thanks for the great design idea!

I've included the source Solidworks files, so if you have that you can try to tweak the existing design. Should mostly involve changing the offset angle and fixing broken geometry. I unfortunately don't really have time to do these tweaks myself.

Got SolidWorks, was already in process. Thanks again.

Got the new Ubis 13 hot end. I printed the fan shroud for the new hot end yesterday on my old extrudedr. I have noticed that the fan duct for the extruder interferes with this fan shroud. Any way you could fix that?

Once again, this is a work in progress. It's hard because I don't have the new hotend on my printrbot

I'm with jdnec123, this shroud is amazing with the ceramic hotend, and I'd love to use it with the new metal! Would it be possible to mount the fan on the outside of the metal bracket to free up a little more room?

I would be happy to do a full sketch with dimensions of the hot end for you. The duct you made for the normal hot end worked wonders, and I would consider this an essential thing to have on a Printrbot. Doesn't look like anyone is helping you out much, so I will.

Works great! Unfortunately the top of the shroud interferes slightly with the all metal Ubis 13. I don't have Solidworks so I can't modify it. Can you take it in a little bit and post an updated file? Thanks!

This works amazing! My only problem is that it brings the hot end temperature down up to 20 degrees at times. It won't readjust either. Once the fan is on, it goes from 205 to 190-195. Is there a way to fix this in Cura?

You can try setting a higher temperature, but that's sort of a hack. It should come back up to the original temperature on its own.

It seems extreme to lose 20C from the fan and I think 50an6xy06r6n is right - it should come back up on its own. I've observed this a lot since I've been solving warping issues with print temperature changes & cooling and I've never dropped more than 3 when the fan kicks on.

I made one, but the hex nut depressions did not turn out quite right. What print settings (simple metal) works the best?

No Supports, 0% infill, 42mms, .2 layer Worked great for me

I made one yesterday and it works quite well. The only comment I have is that it interferes with the probe. Could you shorten it in that area?
Thanks for the plan. I see in the picture you posted that it appears to be much farther away from the probe, is that a revised version??

I haven't seen any reports of it hitting the probe. Can you send me a picture of what you mean? You might be mounting it wrong.

I slightly modified the solidworks file because the shroud hit the base when homing, and the tip of the shroud was pushing against the auto leveling probe. It's the normal version, not for the new hot-end. The STL is available here


Thanks, I printed the 7.2 version for simple metal, and the shroud hit the base when homing.
I will try this version.

cool! I think there are variations in angle between batches of the simple metal that are causing this.

Can anyone tell me the angle the fan bracket is supposed to have relative to the extruder platform ?
I suspect the bracket angle might be wrong on my machine.
I just printed this (prints way better than expected! great model btw), but it doesn't fit a brand new Simple Metal 1403 (it has the same hot end / extruder as in your pics, but the fan bracket has 4 screws instead of 2..

I measured almost exactly 60 degrees from horizontal on mine. I suspect they may have changed the angle slightly between batches. If someone gives me a value I can put up a new version of the model.

It works too well!

I had a failed print gum up my extruder insulator (red tube) and have been too lazy to replace it. After printing and installing this duct, my extruder temperature drops 30 degrees Celsius and can't recover back to 210. At 180C the duct cools enough that the PLA properties change and prints get clumpy (stuff sticks up) and fails.

So I've ordered a new insulator and will report back when that arrives.

For clarification what are the differences between the 7.2 and 7.2 Metal ducts?

Glad to hear it worked out!

Yep. I'm posting a "I made one!" of this. It works great once you get insulation set up correctly. I ordered some fiberglass tubing from McMaster Carr and had to use the "metal" model due to the increased thickness of the injector. The temperature dropping issue is completely gone.

Hmm that's not really what it's supposed to do. Ideally it would just cool the print, not the hotend (which is why it goes so low), but I guess it doesn't quite accomplish that. The 7.2 Metal is supposed to accommodate the new all-metal hotend, which requires a dedicated cooling fan to keep it operational (and has a slightly larger diameter).

I should mention this happens mostly when the head is very close to the print surface. During the first few, critical layers. It seems fine when the head is away from the surface. Also, I have no heat shielding on my hot-end so it makes sense that this would be an impact. I can probably do the same thing by blowing on it (though I might pass out). Anyway the heat shield shipped today. I'll have it tomorrow I believe. More then.

I just printed it and it fits almost perfectly on my Simple Metal (late 2014).
Just one thing: The walls are so thin Slic3r had some trouble slicing the model very well, even the 3D model got some small holes, and the print then as well. Could you maybe make the walls just slightly thicker? Should help with warping as well...
I printed it in ABS, but I am currently printing ABS @240°C hotend, the inner walls next to the extruder get so hot that the airflow manages to deform them!

The wall thickness settings are pretty finicky, and there is very little clearance as it is on the side closer to the chassis. If you want to do it yourself, the source files are provided, but at the moment I don't really have the time to do it myself. The deformation happens pretty commonly. I don't know that there's a good way to fix it. Luckily it's easy to print so you can always replace it...

Vastly improves print quality, especially on the right side! Thanks

Does not work for the new all metal hot end. the hot end fan is in the way no matter how you turn it.

I'm having the same problem. The end is large enough to fit around the metal hot end, but the hot end's fan won't let the shroud mount. Any chance you can modify the design to make room for the metal hot end's fan?

I'd like to, but I'm unfortunately pretty busy and don't have a metal hotend to test on. If someone tells me where the collision happens I might be able to just shave something off and fudge it. Or, someone else who does have the metal hotend can do a remix using the source file.

I'll try to describe as best as I can. I apologize for my imprecise language here.

The collision with your shroud is with the fan that is mounted on the metal hot end. If you imagine your shroud as it installs on the printrbot, and call the print table the front of the printer, the collision is at the top front area of your shroud. The fan is mounted on the hot end by its own shroud and they are actually slightly movable making precise measurements challenging. Together they can be rotated around the hot end slightly and at certain angles they can move up and down on the hot end from being tight up against the metal plate under the filament feed mechanism to about 5mm lower. The hot end fan is mounted square relative to the printer bed so its left side runs straight up and down vertically. The top left side of the hot end fan is roughly 5mm horizontally away from the top of the side fan your shroud mounts on. The hot end fan and its mount extend straight back roughly 10mm in front of the side fan and then slopes back around the hot end away from the side fan. At the bottom of the left side of the hot end fan it is roughly 20mm to the side fan as that side fan slopes away from the hot end.

Hopefully I've provided enough information here and presented it clearly enough that it makes sense. If not, please let me know. Thanks!

Has anyone tried it with the default hot end? Does it fit?

About 3mm to low for my Printrbot Metal. (using the 7.2 Metal version).

7.2_metal fits my Printrbot Metal but the clearance is too little. This causes it to rub against the print and destroy the print if there is any small bump at all. I have to artificially lower the hot end a few mm. Is it possible to have a version that is 2mm higher on the hot end?

Sand paper is your friend

7.2_Metal fits my Printrbot Metal perfectly. No issues homing any axis.

Had similar problems to those described below. It definitely hits when I go to X,Y,Z home and REALLY strikes when Z is home. Too bad because it is a nice design.

If someone gives me some exact measurements I can modify the solidworks file and push a modified version.

Hey! :D

Since you have the whole thing in SolidWorks, could you create an STL with a longer neck, for a setup where the fan itself is outside the metal bracket? :) Ie. the neck should be 10mm longer, to account for the fan itself.

Like this one: http://www.thingiverse.com/thing:367602

Thanks! :D

Printrbot Simple Metal Improved Fan Shroud
by EricY

I come back cause the duct hits the printer when I home Z, it is the side closed to X motor.

Well, I guess I am the second one reporting this problem.

Great design! Except I printed Fan_Shroud_v7.2_Metal.STL and put it on a brand new printrbot metal simple and it extends a little too far down, there's barely any clearance and I occasionally hear it dragging across the part it's printing.

I second this. I hear a lot of scraping especially after the first layers with no fan. Also, the shroud flexes a bit during homing. Nice design however! Thanks for the updates.

I'm beginning to think the platform the extruder is on isn't perfectly level (90 degree angle with the rest of the y axis platform). That might explain why the left side of the fan drags and also hits the base when it homes in z.

I had this issue with an Ubis (non-metal) hot end that I ordered in December. It seems the design is a bit different and the hot end is shorter. I switched back to my original hot end and haven't had an issue.

There isn't meant to be a lot of clearance, but it also shouldn't be hitting your prints. It might be a stray piece of filament stuck to the bottom (or sticking up off your print, or that the dimensions of your machine are slightly different that the dimensions of mine. Worst case you can edit the source files or just sand off a bit of the bottom.

Looks great! what did you use to make it?

CFD and all! I'm impressed! OpenFOAM? What package did you use to do the analysis?

Haha thanks! I must confess, the CFD is just done directly in Solidworks with the Flow Analysis package, and was mostly done so I could reassure myself that airflow was going all the way around the ring. I don't really know how to interpret it beyond that.

Can I make a suggestion?

As far as I can tell, PB's fan shroud has that recess in it to steer the air so it leaves the nozzle going straight, because if it was just an offset cone the air would go off towards the front side of the hot end.

Since your nozzle is doing plenty of steering I don't think it's necessary, and I think it might be restricting the airflow, as it narrows down that side of the duct, and obstructs that edge of the fan.

I think the recess is salting your game. Try it without and see if it improves the airflow. These little fans don't really have the power to pressurize at full speed so if there's obstruction it will just waste the air.

In both cases the recess is actually there to prevent the duct from colliding with the base of the printer when it homes. Not immediately obvious, but pay attention next time you home and you'll see there's only like 1mm of clearance between the part and your printer. A necessary evil, unfortunately.

I believe this is where the impact is occurring when people home XYZ. I had that problem with the initial one I printed before I switched to the Metal Ubis (I haven't had a chance to try version 7.2 with my Metal Ubis yet.) If there's a way to raise it another millimeter or two (and maybe reduce the fillet in the corner...that might be part of the problem), I suspect that would solve much of it.

(Note: this is more a reply to your question posted in response to rkburnside, but the context here made explaining it much easier.)

I just finished printing this and before I even use it I can tell I'm gonna love it! The height is perfect, just a couple of mm above the tip, but the hot end is not quite centered in the opening. I noticed in your pictures that the mount plate for the fan only has two holes, but mine has four. Maybe the fans are at slightly different angles?

Either way this looks great and I'm excited to see what it will do :)

P.S. I just noticed that the original stl has a complete inner ring, but after slicing with slic3r or cura, only the top and bottom are left. Any thoughts?

So it does work with the new hotend? If the fit isn't much of a problem, it's probably not worth it to overhaul the duct design to accommodate it.

The slicing issues I think are caused because the wall thickness on the inner ring is .5mm, so you need to turn on the thin wall settings in your slicer. Try that and see if it works.

I have the regular ceramic hot end, not the new metal one, and it does fit, but it is very close. There is maybe a millimeter of clearance on the left side. It should be fine unless the heat proves to be too much and causes it to melt. I don't know how one goes about making a customizable object, but maybe it would be worth creating an object where you can adjust parameters for vertical drop, horizontal run, and hole diameter for people who have different hot ends. Just a thought.

I will try the thin walls thing and let you know how it works.

Oops, I replied to the wrong comment! In reply to your original comment, it does seem like the newer runs of the Simple metal have a full plate for mounting the cooling fan as opposed to the half plate on the earlier ones. There is a tendency for the inner wall to warp somewhat, and I think that's just an unavoidable consequence of the design. I had mine printing for a couple of months, and the warping never got bad enough to affect its function, so it shouldn't be an issue. If it is, just print a new one!

RE: customization. I have considered doing that, but customizing a design requires that the file be created in OpenSCAD (I think). The current design is in Solidworks, and is probably going to be hard to convert over. Might happen eventually, but probably not anytime soon.

Oops, I replied to the wrong comment! In reply to your original comment, it does seem like the newer runs of the Simple metal have a full plate for mounting the cooling fan as opposed to the half plate on the earlier ones. There is a tendency for the inner wall to warp somewhat, and I think that's just an unavoidable consequence of the design. I had mine printing for a couple of months, and the warping never got bad enough to affect its function, so it shouldn't be an issue. If it is, just print a new one!

RE: customization. I have considered doing that, but customizing a design requires that the file be created in OpenSCAD (I think). The current design is in Solidworks, and is probably going to be hard to convert over. Might happen eventually, but probably not anytime soon.

Just printed it, and it looks great. I don't even care if it improves my prints... it's dead sexy.
Seriously, it is a well designed part that fits just right. I especially liked that the mounting plate was designed to hold the hex nuts in place so they won't spin as you tighten the bolt from the other side. Really looking forward to seeing how it will affect my printing quality above the standard Printrbot suggested duct.

Thanks! Glad you like it.

Note that this won't fit on a cartridge-style hotend because the diameter near the nozzle is too big.

Thank you very much! Love this thing- it really improves my printing results. Overhangs are nearly perfect now!
Will update some new printing results the next days.

Any chance for a all metal hotend upgrade for the official printrbot all metal hot end? I loved this fan fuct but it is too small to fit around the new all metal version

Took a look at the all-metal hotend, and I think the bigger issue will be accommodating the fan that cools the cold zone up top. Also not sure how much wider the opening will need to be/whether there will still be room for this to work. Can someone give me measurements for that?

Sorry for the delay,

It is a 30mm fan and is about 20mm deep while it stays 30mm square. The hot end fan holder does taper near the back but I'm not sure that'll help you or not. The red cover part on the hot end for me is about 19mm while on the hot end. Your new metal version fits, but the fan has to be installed cockeyed and at the very top so the hot end fan holder doesn't hit the fan duct. Here is a picture gallery that will hopefully help you out: https://imgur.com/a/jgJtn
The first two pictures are with the hot end fan installed and where it hits on the fan duct. The 3rd picture is the shape of the fan. The last picture is the fan somewhat what it would normally be on it to show you how much overlap. Feel free to hit me up over twitter, email or something that I get notifications from and I'd gladly test print versions or try to get you the measurements you need. ( dattasmoon via gmail (email) or @dattas (twitter) )

TL; DR: the hot end fan holder hits the fan duct, looks like a steeper angle is needed or a cutout for the fan so the fan can sit closer to the hot end.

See the reply to the most recent comment. It was directed at your comment originally.

See the reply to the most recent comment. It was directed at your comment originally.

looking into putting out a version with a larger inner diameter. Also might make a configurable version of the source file to make those changes easier

looking into putting out a version with a larger inner diameter. Also might make a configurable version of the source file to make those changes easier

I would also love to see a respin for the new all metal hot end. It doesn't seem like the interior diameter would need to increase much more than 1 or 2mm in order to accommodate it.

I can't get this thing to slice. Out-of-the-box slicer settings as downloaded/recommended by the printrbot setup guide, done a few prints just fine from STL files, but when I slice this half the inner section of disappears.

Indeed, I'm running into the same problem when using Slic3r, but it looks like enabling "Detect thin walls:" works around the problem. That said, it generates other junky bits while slicing, which is why I generally keep that option disabled.

Still, I suppose it's worth printing out a version that just needs some cleanup, rather than one that blows air directly on the heating element. :P

I seem to be having the same issue. part of it is missing.

Thanks for that, especially the SLDPRT version! Printed out pretty good, and seems to work good. On my V1/RevD model, its not centered on the print head, but maybe just due to manufacturing variances of the printer? - actually looking at your picture, looks like its a bit off center for you too... regardless, thanks for sharing - Nicely done!

Hey, I'm a 3d printing noob, but it occurs to me - are we trying to cool the print or the premelt chamber area? If we are trying to keep the upper bit cool, should the cooling bit be up higher? That said, seems to work good

Made one for my 1312 PrintrBot Simple (Wood). The angle is a bit off, but I think a simple adapter to adjust it should work.

Printed the best that anything has ever printed on our printrbot simple, but it is 15mm to short because on the Simple, the bolts mount the fan from the back, not the front. Is there any way I can get the original file (before STL export) so that I can modify it? I use Inventor, and I haven't found an easy way to mess with STLs. Thanks

I've posted Solidworks files in addition to the STLs for every iteration of this model. Unfortunately, you'll need to have Solidworks to mess with them. (They're use the .SLDPRT file extension)

Thanks a lot. I should have been clearer when I did not specify metal v wood printer chassis/model.
I have been meaning to get Solidworks for a while (through FIRST robotics as a student, free), so I'll look into that. In the meantime, would it be possible to convert it to a .step/.stp file? That is generally a pretty universal file type that most any program can open.

I'm not too familiar with .step files, but I'll try to upload a version when I get the chance

You need to mount the fan on the other side of the support, then bolt the shroud directly on to the fan.

That's impossible because of the nature of the mount on the Simple; the bracket that the fan normally bolts to is on the extruder side of the fan, which is not the same as the metal version that this print is designed for. I would attach pictures, but I'm on my phone. I'll try in a few hours.
I don't mean to come off as being critical or mean, it's just that I tried that already and found that it simply isn't possible.

My apologies, I misunderstood your original post. I thought you were mounting this to a Simple Metal (1403), not the wood Simple Maker (1405).

Looks super useful! Will be printing one for my Printrbot tomorrow!

Has anybody had any issues with the shroud crashing into the 'bot's body at XYZ home? It just slightly hits the body on mine. You can see the Y-arm assembly twist slightly when it happens. It's only a problem at the home position, so it doesn't get in the way of prints, but I'm worried that over time it might deform the Y-arm and throw off the 'bot calibration.

Yes, I printed it and it does crash into the unit in home position, it also throws off the sensing of the table...

I fixed it by sanding the sides down now it seems to be ok.
I think I will edit it and scale that side down a bit.

could you make one for the 1405 maker's kit edition? it would have to have one end clamped in between the wood and the fan itself, i like the design, i just cannot use it

I've printed this a couple times and, on each print, the inner cup is too close to the hotend on the front. This causes the interior to deform and the tip to droop, pulling up prints. Any suggestions? Should I try to get it printed in ABS instead?

Great design and appreciated that it requires no supports. If you're going to further develop it, I do second Gareth's suggestion for probe-side support to minimize the droop. Great work.

It was going OK until I got to the steep part and then it started drooping! I am printing this with my simple metal (first day on the 'job'). Do you have any tips for print settings to help this turn out better?

I am using the settings suggested in the quick start guide:


Will adding extra perimeters in the slicer settings help here? Or tweaking the fan settings?

A little bit of drooping is fine and doesn't affect the functionality unless you start getting holes or something. extra perimeters probably won't help if it's already slicing the walls properly, as they're only 2-3 layers thick in most places. I'd definitely recommend enabling the cooling fan, and if you can see it starting to droop you might want to turn the fan to 100% manually from your host software (probably Repetier).

thanks for the tips. I figured out that the walls turn out much better when you decrease layer thickness. I was using 0.3mm. 0.15 mm seems to work well.

Printed one, and it works great

I've been using you fan shroud for a while and the design is very good. The only change I would make is to include a ring on the side of the sensor probe so that the right part of the fan duct would be supported by the sensor's lower nut. As it is, when printing for extended periods without fan, the duct deforms and droops down on the right.

Hmm, will take that into consideration. My main concern is that I designed it to print unsupported, and adding that part would almost certainly require some kind of support, which I would probably have to add manually, unfortunately, I'm away from my Printrbot for the forseeable future, so I probably won't be able to make those kinds of major upgrades anytime soon.

So I've been reading that some people have had no issues and that this fan duct has really improved their print quality, while others have had issues of it not fitting properly. I am confused as to how this can occur, especially since these are all printrbot simple metals we are talking about here?

The fit is pretty close (<1mm), and I think the differences come down to slight differences in assembly combined with manufacturing tolerances on the printer and printing tolerances on the part.

Would you be willing to add another shroud for the PB LC and Plus, I really like this design, but the fan isn't angled on the pb lc and plus mount.

I'd love to, but unfortunately I don't have access to a Plus for measurements/testing (I don't even have access to my SImple anymore!). If you're willing to provide measurements/feedback, I can try to design one remotely with you. Send me a message, and I'll give you my contact info.

Just installed, the left side (looking from the intake side of the fan, is too far over and hits the body of the printer.

Yeah, for some reason these two things seem to vary from printer to printer. If you're willing to, I'd appreciate it if you could send me pictures and maybe rough measurements documenting the problem. I'll PM you with my contact info.

Additional. Bottom hits prints sometimes and tears up thin layers. Will have to file the bottom down a bit and see if that helps.

This thing printed pretty damn well on my PrintrBot Simple Metal. Very impressed. Thanks for the upload!

The interior cup seems to thin and too fragile. I'll see how it plays out in actual usage, but it is so thing that Slic3r didn't treat it as a solid surface.

It is a bit thin, but if you enable thin walls in slic3r it slices and prints quite easily. It's plenty strong enough for what it needs to do.

This is a great idea. How well does it handle air backflow?

Better than the original shroud, but still not optimally. That's something I'm still working on. Someone suggested that I widen the entrance a little, but I think I'm going to try messing with the flow simulations in SolidWorks first. If you have suggestions I'd love to hear them.

Building 1.7 right now, crossing my fingers I've got enough PLA left, printing on a Printrbot Simple Metal 2014. Hope it works out!

When I sliced the fan shroud with slic3r, it generated a void just past at the lower front bolt cavity. Have you encountered this or are you using another slicer?

If I understand correctly, you're saying that there is a hole in the shell where there's a large cutout for the bolt (only in version 7.1)? I am using slic3r, but have not encountered this problem. These are the settings I have for layers & perimeters: http://puu.sh/9vIFd/0afa84993f.pnghttp://puu.sh/9vIFd/0afa84993f.... Regardless, I'd like to see what the problem is. If you're willing, I'll send you my email address privately so you can send me screenshots of the problem. Good luck!

Thanks for the reply!
My bad, when the print went further and got to the hotend's inner wall, there were holes in it. The thin walls option was not enabled in slicer. It prints correct now and works well though I should get it printed in ABS, Nylon or other more resistant plastic.
The duct's opening at the tip of the hotend could be a few millimetres higher as it is very difficult to grasp bits of filament off the tip before a job starts. The effectiveness of the cooling may be decreased though. I still have to change my fan for a new Noctua unit which is much more efficient.

Glad to hear it's working for you! I realize that it doesn't leave a ton of room to grab things out from under the hotend, but I think it does improve the cooling performance, as you want the air to be directed mostly at the the extruded plastic. I use the pliers on my Leatherman to help with that. If you swap out the fan, do be careful about how thick it is, as that might affect the positioning of the duct, as it's mounted directly to the fan. If I ever get around to figuring out Open SCAD, I'll definitely try to make this thing customizable to account for all these variables.

That's a great idea to make it customizable. As for the fan, one could use a more powerful unit but these are deeper than 1cm. The Noctua NF-A4-10 is a 40mmx10mm fan which is quite powerful due to its blade and frame design but it costs about 15$. Thanks again for this great design.

The short one is too long as well by at lest 5mm, mine hits the bed and bend before the z end is found.

Have you tried the newest version? I've done the measurements, and extends less than 2 millimeters lower than the original shroud provided by Printrbot.

Yep this extends past the hot end tip. looks mostly usable needs more design. good first start.

Yeah, i'm working on updating that. In the meantime, I'm pretty sure the file labeled "short" actually does work. If you try it let me know if the centering works for you.

I printed this on my Simple metal and mounted it up. Looked great, but the hot end tip does NOT extend below the fan duct....

How much room is between the bottom of the duct and the tip of the hotend? I suspect that since the Printrbot clamps onto the back of the hotend, there's significant variation in hotend length from printer to printer. I'll try to upload some versions of varying length in the next few days. I would make it customizable, but I don't know how to use Open SCAD yet.

you can fix the back pressure issue to some extent by making sure the cross section nearest the fan is slightly larger then the fan for a short distance. The air is spinning off the blade tips and bouncing. To balance the airflow at the nozzle you can use channels that direct the amount of air your want around to the far side. These would just consist of spline extrudes in the airpath. However, I that would mean expanding the volume around the nozzle especially around the side that carries the air for the far side.

Hmm, I'll keep that in mind for the next version

Hi, What kind of sensor are you using there? the one with the yellow head.

It's some kind of proximity sensor (induction I think?) that comes with the Printrbot to act as the Z-endstop and makes the auto-levelling possible. Works pretty well. I don't know much more than that, but they sell them here: http://printrbot.com/shop/auto-leveling-probe-2/http://printrbot.com/shop/auto...