Sunday, August 1, 2010

I need design advice? And who better to ask than a community of Developers?

I have a choice, and I can't really figure out which direction to go.  If I keep the build plate 6 inch, and continue to use 608 skate bearings, & place the extruder on the X trolley, Brutis will only have +- 50mm travel in the Z axis.  I could very easily end up with only 40 mm in the Z axis by the time I give myself some margin.  This is enough travel to be able to print all the Mendel parts, which is the main design goal, but it would give a build area of 150mmx150mmx40mm which looks really sad...

I see a few directions I could go here, any advice?

a. Since the top vertexes are already different than the bottom axises, I could make those vertex much bigger (same size as the Mendel, but with only 6mm/ 1/4 rod), and turn the gear motor sideways and design a whole new extruder that can fit between the upper threaded rods.

b. Forget having the extruder on the trolley and just go back to assuming bowden extruder (which adds cost, reduces print quality, and makes this harder to calibrate).

c. Make the build area bigger, therefore adding 5mm in the Z for every 10mm I add in build area.  I have to be careful here because the point here is to keep the print time below 20 hours.

d.  Since 40mm is enough for Mendel say the hell with it and just let it be.

e.  Something that I am missing that you would be kind enough to share?

I know I need to alter the placement of the Y motor (needs to go lower), to allow more room for the smooth rod supports.  Also I need to move the cross beams that support the Z axis down below the side bars to again allow more room for that y stage.  But she is looking good in my opinion.  But I am at a point where either I have a lot more work to do, or I get to start making printed prototypes on Monday.  What do you say?


  1. With all the trouble I've been having getting the bowden extruder going, I would not make a design that can only be used with it. My plan is to include an extruder that can be used with a bowden cable to decrease carriage mass and increase build height, but can also be used without it for increased reliability.

    Also, rather than lowering the y motor, consider moving it to one side. Moving the belt clamp closer to the 360 bearing should increase stability anyway.

  2. What if you were to change the angle in the upper and lower frame vertices, so that the frame becomes an isosolese triangle rather than an equilateral triangle by decreasing the angle in the lower vertices, and increasing it in the upper? This would probobly give you the ability to make the print area as tall or short as you like, just by changing the angle in those 6 parts. It wouldn't require any more print time either.

  3. That's why I ask the questions :)

    I think I will just move the motor and see how that works. Good thing about Heekscad, and the size of these parts, if it doesn't work I can fix it in like 15 minutes.

    As far as the vertex angles... would an isoscele triangle be any more prone to warpage from motion than the current equilateral?

  4. I've been thinking about an isosceles triangle too, but I was thinking in terms of lowering the top (45°/45°/90°, maybe) to make a very large build platform without making the machine too tall.

    The problem with deviating from the equilateral triangle, or indeed, with changing the horizontal bar spacing for one set of vertices, is that it makes cutting the rods to size and squaring them a lot more difficult. When I built the triangles for my frame, I simply lined them up and made sure that the vertices matched, then rotated one of them 120° and repeated.

    This would be harder to get right with an isosceles triangle, and you'd be more likely to end up with a rod applying pressure to the inside of its hole. This stress combines with vibration from the motors could eventually cause the vertices to delaminate.

    If you do go with an isosceles triangle, choose your angles carefully to make the rod lengths easy to cut accurately.

  5. How about making a cube or trapezoid frame? Call it Darwinish or Mini-Darwin? Would still have the weight at the bottom instead of suspended in mid air.

    Would require two more corners and two more threaded rods , but you would have no problem with the extruder hitting until the entire z height was used.


  6. Triangles are more stable than rectangles. A rectangle can turn into a parallelogram without changing the studding lengths, only the angles. This means that you either need the corner pieces to be strong enough and tight enough to resist any bending, or you need diagonal bracing like darwin's (turning squares into multiple triangles).

  7. I am keeping it a delta. Going square would really up the RP mass. And then I end the point of this project.

  8. "The RepRap Breeder project has in mind to branch off a Replicating Rapid Prototyper with only one focus, reproduction."

    I vote (d), go with 40-50mm height. Most people are probably going to print a mendel anyway.

  9. That sounded a bit rude, sorry.
    What I ment was, most people are probably going to use your printer to print themselves a mendel at some point. So I would gladly sacrifice some build height if it makes the design easier to construct.

    Note to self, use the preview button.

  10. Keep at it Neil! :)