Tuesday, March 30, 2010


Best of both Worlds

I'm using RapMan 3.0 for a while now and it is a great machine. I did tweak it a lot, but however I tweak it, and however I change more or less important parts or the way some things work on this Darwin based kit the few things I cannot change and they bug me big time. Major issue I have with it is size. And as I'm printing a lot of PP/HDPE there is no way I can use that big table (PP warps 10 times worse then ABS)...

This is the left third (almost half actually) of my desk:

From RapMan
now it would be cool if I only used this desk for printing but that's not the case. I found solution in Mendel, the second generation reprap machine. Mendel is super cool reprap, it has small footprint, it requires less power... but all the extruder designs I seen for Mendel are not comparable to those of rapman's designed and sold by BFB. Getting your nozzle to 260C and extruding at high pressure will render PFTE tube based extruder tips unusable, and standard extruder drive has no way of applying enough pressure. dr. Bowyer recently published YAGE that IMHO had potential to push with enough strenght (I did modify the drive a bit and added some very sharp 2mm pitch pulley as drive instead of that M4 inset) but still, the PFTE tube design and 260C don't really go together, not to mention glued PFTE and high pressure so I looked at the hot end piece of rapman's extruder. BFB sells hot end kit for some reasonable price, and as I have few spare and I know this hot end can take a beating (the first one extruded kilograms of different filaments and is still in prime condition) I decided to give it a go.

BFB hot end is "wide", it is ~80mm diameter so I had to change the x-carriage so it can fit.


I heated the hot end to 270C and let it be hot for 2h before I checked if the x-carriage (made out of PLA) is getting soft - and, to mine surprise, it was not. I was afraid I will have to print the x-carriage using ABS or HDPE and that requires heated bed that I still don't have.


Testing the extruder, it is bit slower then original bfb extruder (because bfb one is 1:1 and this one is 5:1 and because I'm using some second hand stepper of unknown manufacturer) but is pushing filament at more then 2-3mm/sec of filament (not the 0.5mm but the 3mm filament) per second and that's what I was aiming for.

Now I need to try to modify the bfb pcb to run Mendel so Mendel can also be stand alone printer and I can truly have best of both Worlds, but for now, Mendel is, with this new powerful extruder, ready to replace the dear chunky rapman from my desk (and rapman, as stand alone printer, can go to back room)

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Great work!
Looks great! If I ever make a Mendel, I will probably use that same design :). Or maybe with a bowden cable.

One question, what does your Z travel end up being with that setup?
Bogdan: Im working on the same thing!
Although a bit slowly, and hadn't time to finish my design.

Here is a photo of mine:

Best regards,
any luck going to a stepper with less torque with a setup like that.?
@Marcus, thanks

@Mike, design might need a bit tweaking, I heat press nuts on the inside of the x-carriage but it might be better to make a trap nut space. I also plan to use the bowden cable that's why I did not spend too much time on that adapter.stl as it might be nice to have it go the whole width of the carriage.
The max Z is what you see on the image, there is 2mm clearance from big gear to the plexy sheet. Removing the plexy would increase the Z but I think the bowden cable is the proper solution.

@Laszlo, from the stream, what I see is you are making pinch wheel extruder holder for the rapman. I love the original rapman extruder (it is as powerful as this one and 5 times faster) so I do not plan to change it, I just wanted to use rapman's hot end on the mendel.

@dissidence, no luck, I first mounted a "small" nema17 (half the lenght, 5V 1A) and I drove it hard (12V 0.95A) and it had no strength to push pla trough nozzle at any speed at 200C and was skipping steps at 220C so that's unusable imho hence I replaced with "normal size" nema17 that gets the job done properly.

I need to find springs and add springs to the 4 screws pressing the idler holder as if you over tighten the screws the filament comes out deformed / flat :D .. that and the "big size" of that gear wheel practically yell bowden cable ..
i am hoping that it means that i would not have to find a high torque stepper though, but i do like it overall though

i have a 24v one here, but i dont know what it will put out just yet
The design of the "hot end" will make a big difference to the amount of torque required. The shorter the transition zone, the less it will need.
Bogdan: Im working on the bottom half of the extruder too ("hot end"), so it will be a complete extruder, which fits both on the Rapman and also on the Mendel too.

Also the pinchwheel design has a serious advantage: it is more tolerant to the filament width or the variation of it.

@dissidence, the "normal size" nema17 stepper works perfectly .. the ones on my mendel (including stepper) are MINEBEA 17PS-C055-G9, I have no idea what the characteristics are but I drive them 12V 1A and they work and don't get hot and have enough torque to drive both mendel axes and extruder

@nophead, I tried few different designs and the bfb hot end "works best for me" .. now this is subjective but ..

@laszlo, good luck, hardly wait to see it finished :D .. one of the things I really like with bfb hot end is - I send 25gbp they send me hot end .. and it works .. proven :D .. with no lathe at home making my own is next to impossible
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