Starting a Prusa Mendel build

It works!!

First print is far better than expected!! Might even be usable.


First print is a gear for an extruder...didn't expect it to work :-)

So that gear was printed on paper...just regular paper I took from my 2d printer.

I just installed the heated build plate covered with kapton tape. Printing the bottle opener now and it is gorgeous so far. Will post pics when its done, so we will see :-)

So happy with this quality :-)

Ohh yeah, I didn't use a micrometer, plumb bob or spirit level when I made this. I used a level app downloaded on my iPhone and counted the threads instead of using a micrometer :-)

z-axis is a bit jittery. sometimes the x-axis won't move up when the z-motors turn for one layer (0.25mm). when the next layer starts, the x-axis bumps up two layers. this caused the bottle opener to delaminate when i removed it. it also caused the gear to have a periodic skinny section that would gradually get back to the normal size as the axis moved smoothly again.

i think i can fix this by aggressively heating the z-axis PLA bushings on the smooth rod. should do the trick. if it doesn't, i'm getting some linear bearings that i may use to replace the PLA bushings.

another problem...110 degrees c for the heated print bed seems to be excessive. it's the value pronterface had in there by default, but it caused a print to be mushy on the bottom layers and made for a very difficult removal. i'm going to try 80 degrees or so instead and see how that goes.

finally, my print bed is not properly positioned, the print head is starting too close to the bed, will need to adjust that tonight.

Tuning the printer has been going fairly well.

I got some 20x20 cm glass for the print bed so that I could properly level it. I couldn't find springs for the z-axis, but I did find some 1/2" vinyl tubing that I re-purposed as a spring for the x-end-idler.

Last night I put together a plate for a few parts from Greg Frost's Prusa branch and started printing; I'm getting ready for the linear bearings I ordered.

Things didn't go as planned...

I found out why I have to keep leveling my bed. The four bolts holding the top print plate to the bottom print plate have a tendency to loosen up during a print. This happened during my epic print last night. The parts being printed kept traveling upwards as the screws loosened and the springs pushed up on the top print plate. Eventually the extruded plastic interferred with the x-axis ability to move, so the head got stuck on one side. Shortly after, the y-axis was unable to move.

So I woke up to a nasty mess of plastic. Thankfully there is no damage to the printer, just my ego.

My first thought is to use two M3 nuts on the bottom of each of these four bolts. I hope that would be enough. These are bolts that I need to adjust to level the bed, so I am reluctant to use locktite. However, when all four bolts are tightened all the way, the bed appears to be level within 0.2mm.


Photo of the failure:




Photo of the bolts holding the bottom print plate to the top:




Anyone else have this problem? Any ideas?

Edited 1 time(s). Last edit at 10/03/2011 12:07PM by hardtoe.

Another thought: should I just remove the springs on the bolts connecting the bottom print plate to the top?

It seems like it's going to cause a lot of wobble between each layer and it also seems to exacerbate the bolt/nut loosening problem.

If I do that, I'll need to make sure that the vinyl tubing I am using as a "spring" in my x-ends is springy enough to push the x-ends down, but not so firm that it could break the glass if the z-axis makes a nose-dive.

EDIT: I should also brace the rest of the frame with a motherboard sheet or some of these: Braces to Stiffen Mendel Frame by brnrd. That would help my x-axis accuracy.

Any other thoughts?

Edited 2 time(s). Last edit at 10/03/2011 02:06PM by hardtoe.

printed out a brace and it seems to help out. will probably print out one more.

i used 6mm MDF for my top print plate. because it's only 6mm, the belt doesn't run horizontally and it pulls up on the plate when it gets to the extremes of the y axis. i think that stress caused my PLA bushings to come un-done over a print today. glued them back up and i'm going to print out a pair of Prusa Y-Axis Belt Tensioners. this will raise the belt up a couple of centimeters to match the height of the pulleys as well as allow for a better tensioner system than the s-shaped Belt Tensioner.

Hi Hardtoe

Great thread, I have just started building my Prusa Mendel (installing electronics now) and this looks like some great info on things to watch for.

Keep it up.

Tony

PLA only needs a heat bed temp of 55C to stick to glass, I have built a Prusa with linear bearings and they slide real nice, not tested properly yet as my pololu chips haven't arrived yet

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Experimenting in 3D in New Zealand

Hey Guys,

In the middle of my Prusa build at the moment too. Thanks for all of this info, will keep an eye on this thread for some more pitfalls.

Cheers,

Adam.

The x axis pulley chipped a tooth ;-)

I had previously printed the parts necessary to use linear bushings, so I'm converting to those as well as machined XL pulleys.

Probably get those on Monday.

hardtoe,

You have the nuts installed on top of the bottom plate below the springs. You should install the nuts below the bottom plate instead and either use locking nuts or double them up to keep them from coming loose: Since your spring has a small diameter, it would might work better if you just add another nut at the bottom so you have spring-nut-bottom plate-nut. This way the screws won't move side to side if the springs aren't giving much tension.

I can highly recommend the linear bearing versions.

I replaced my Y mounts and the X-carriage with ones using LM8UU linear bearings (Greg Frost's version) and it has made a big difference to the accuracy and repeatability of my prints.

Just in the process of printing X-end-motor and X-end-idler versions using LB's, that should improve it even more.

Geoff

Man, this is a good read. Any updates?

the new pulleys and belts come tomorrow, should have something then!

got the new linear bearings on x and z axis. still need to get them on the y axis.

i also replaced the x axis pulley and belt with a cast XL pulley and fiberglass belt.

printer is working well! i have been printing with ABS since I had finished it, so I thought I might try some of the free PLA I got from ultimachine. it's really goopy stuff. it just goops and gops all over the place, and if your extruder stays in one spot for more than a millisecond it is guaranteed to make a nice little blob.

anyways, i was feeling really adventurous last night. so in addition to printing with PLA, i got the latest Skeinforge (44), latest pronterface and i swapped out Sprinter for sjfw.

i love the new "Skin" script in Skeinforge, pretty slick feature for making things a little nicer on the outside. i also really, really like the way acceleration is implemented in sjfw. in Sprinter, i would get small but noticeable bumps between line segments on curves. this was due to Sprinter accelerating from stop and decelerating to stop for each line segment. sjfw is a bit smarter and merges each move together such that the speed is kept up as much as possible while not violating any of the acceleration settings. pretty slick, and a noticeable improvement in quality.

however, sjfw seems to be a little flaky sometimes, so i'm keeping a close watch on it while it's controlling my machine.

got some green PLA and white ABS squirrel pics. maybe someone can help me figure out how to take care of the excessive oozing the PLA has.


Green PLA, Skeinforge 44, sjfw




White ABS, Skeinforge 41, Sprinter (going to try this guy with 44 and sjfw soon)

another note, my x-axis linear bearings sometimes make a rattling sound whey the carriage moves in the negative direction...i think maybe the bearings are not perfectly parallel? any other possibilities?

i also switched from lithium grease to a much lighter oil to lubricate the smooth rods.

Did any of you have issues getting the X axis to glide properly? I bought a metric prusa mendel kit and it seems like when you mount the printed pulley backwards that it will tend to track toward the motor until it is rubbing against it. This may be due to having to mount the motor on the linear model opposite what it is on the conventional prusa. I put in 4 washers to try and pull the motor out so it lines up with where the belt tightens on the carriage, but it still doesn't quite do the trick. Making the belt tight causes it to require a bit of force to make it go back and forth. Could it just be a bad printed pulley? What is the standard pulley size for these printers and is there a good store to buy them? My belt seems fine so I'd prefer not to have to replace that as well.

Just as a reply to my issue, it turned out to be a weak soldering job on the RAMPS board. The end stop seemed to switch designation for some reason but that works too. Fingers crossed for some happy printing!