I am in the process of rebuilding my Prusa Mendel RepRap

I bent the Z threaded rods pretty bad learning about the various ways to not use the printer. The Z wobble isolators helped, but it still had issues.

I had a few parts left to print out for an 'upgrade' that allows the printer to print much taller. I printed these in the last of my red ABS, because it was already loaded.

Slic3r just came out, so I used the wizard to create a new set of profiles. WOW, did the prints come out nice. Well, except for one weird thing where parts where embedded into the neighbors.

I tweaked some of my smooth rods that had some bow in them. They aren't perfect, but once bent, they never will be!  Rolling them on my surface plate shows the bends. Straighten them like a wooden arrow shaft, but without the heat.

I used a ROMER arm to square up the frame. The frame is pretty square. I am working out how to square the printer's motion now. I have an idea, but the math is beyond me. Hopefully somebody will help me with that.

In album Slic3r 1.0b Default Settings

I’ve never had such a perfect bridge in 2 years of printing on this printer!

This part is ‘designed for manufacturing’ with break away bridge supports. Awesome!

The leg on the bottom left is designed to break away as is the upper bridge arch. Very clever. Makes good use of the good bridging.

I try to get all ‘points’ directed towards the inside so that I have no long, thin fingers which are prone to lift when printed in ABS. I also use a fairly wide brim to keep all the bits connected to each other.  These two tricks has helped me print directly to heated glass with ABS reliably.

Note the highlighted part has a good gap between the main part. The top left part is basically lined up with the big part.

A fairly clean part. The problems visible here are not Slic3r’s fault but mechanicals on the printer such as some Z issues from bent Z rods and a thermal issue near the top of the tall tower where the printer somehow doesn’t get updated temps and the hot end temp climbs.

This is a problem, these two parts are buried into the next part. There was a good gap on the plating screen.

All the little parts are shifted. The part that was on the upper left in the previous screen is now strongly overlapped. Two of the parts have been shifted into the big part body.  It literally printed the overlapping areas twice – as if Slic3r thought they where properly spaced. Bizarre behavior.  I wonder if it’s a repeatable bug? Possibly related to the 3mm brim?

The heat climbed up crazy high again. I jiggled my wires, the printer ‘caught’ the right temp and thermal shut down the hot end as it was near 300c!  I figured out this ‘jamming’ issue i’ve been having at last. Good thing this is the LAST part print for printer upgrades. The printer will get tore down and get the Z issues fixed and the temp probing will get double wired so hopefully this won’t happen again unless both sets of wires break.

I just moved the Z down manually and let it pick up. I lost about 1mm but I think that’s OK. I hope that’s not a critical measurement in this part.  Ugly print, but good enough for now. I may re-print this part when I get the printer rebuilt.

Stripped the printer back down to the frame.  A sad day.

I had to cut the printed parts apart from the shift. How bizzarre.

At least the part I needed (the big one) is in a good way. The little bits are basically junk. Too much removed from one side to be usable.

I’d tried the tablets on the bench here to run the printer before I tore it apart, no luck. Maybe after it gets put back together?

Lots of measuring. Lots of moving the carriages about and re-measuring. Trying to make sure that they track straight. Ideally, I’d like to know that they are tracking perpendicular to each other, but I can’t figure out how to measure that directly. Going to need to measure a calibration print and check that for squareness I guess.

Here you can see the whole of the arm I used to measure the RepRap. It’s about all the arm wanted to do to fit in and around the printer. Being able to work off the surface plate sure did help a lot.

5 Replies to “I am in the process of rebuilding my Prusa Mendel RepRap”

  1. The irregularity is the sides seems to indicate that your hobbed bolt is slipping during printing.  This is not the fault of the hobbed bolt, or the tension on it.  The problem is most likely that your melt pot region is very long.  What hot end is that?
    A lot of people building RepRaps think that there has to be this huge force behind the extruder, along with deep cuts into the hobbed bolt.  You can spot these ppl when you see them putting heat sinks and fans on the stepper motor of the extruder.  In truth, the extruder motor current does not to be very high, and the hobbing on the bolt only needs to provide enough friction to push the filament.  The tension on the filament should not deform the filament drastically either.

    If you can afford to replace the hot end, try a J-Head from Brian Reifsnyder.  He designed it, and sells them on his site.

  2. The irregularity is Z wobble and whatever they call it when you have Z isolators and they give you variable layer height. 95% of the reason for the rebuild is to swap out those Z threaded rods.

    This is my 3mm MakerGear hotend & extruder. I don't have melt zone issues with it like I do my 1.75. The printer is running fast enough to not have have these issues anyhow.

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