Todays result: A full set of Mendel90 parts

I now have one or more spares for every printed Mendel90 part.

I have lost count of the number of parts on my original Mendel Prusa style printer that I have replaced. It now is made of more replacement printed and electronic parts than original parts. After a period of being broken, once operational again the first thing I did was to print a spare for every printed part. 

The reasons parts have broken

• PLA parts warped when printing ABS,
• Extruder gears broke from ware,
• Parts broke from stress or over tightening,
• Generally delicate parts - the manufacture appears to have reduced the printed volume of many parts.

The same applies to the Mendel90, I have had to make at least four repairs now. The broken parts have either been PLA warping at ABS temperatures or bad prints to begin with. The Mendel90 is a much more reliable design. 

Having a 'spare' printer has reduced the need to backup the Mendel90, but I am also keen to one day convert the Prusa style printer into a Mendel90. I have been using periods between large prints to print a spare or two. The majority have been in PLA. I got carried away trying to print everything quickly and used PLA for some items that need to be ABS. I now have a few PLA spare of spares.

When printing ABS or for long periods in an enclosed chamber, parts near the extruder or in contact with the X Y or E stepper warp if made from PLA. PLA seams fine for the other parts.

In my experience parts that should be ABS

• x-motor 
• y-motor bracket
• d_motor_bracket
• wades_block
• wades_gear_spacer
• wades_idler_block
• x_belt_clamp
• x_belt_grip
• x_belt_tensioner
• x_carriage
• x_carriage_fan_bracket
• x_carriage_fan_duct
• x_motor_bracket
• y_motor_bracket

Full set of Mendel90 v2 printed parts (grey PLA, black ABS)

Mendel Prusa style printer, Note that the original part colour was dark grey.

Todays result: Carbon filter

I have created a filter to add to my printer. It helps by removing some of the bad plastic odours. The filter medium is activated carbon pellets purchased at an aquarium shop.

It is a box shape with a fan at both ends and a diagonal wall of carbon through the middle. The intent was to double the force moving the air through a large area of thin carbon. It was designed to mount on the side of my Mendel90 it fits neatly on the inside of the right stay. I directed the air flow downwards. When the printer is operating in enclosed box it will pull warm air back down from above.

The y length is 17cm, almost the full length of the printer bed. The z height is 70mm - the fan size, and the x width is fan size + 2 cm wall of carbon. The filter grill is spaced with 3mm gaps to hold the 3.6mm diameter pellets.  I used 70mm fans due to a surplus from a botched order and 2cm of carbon seamed a useable thickness. Each end has m3 nut traps to attach the fan, and a slide cover to hold the carbon. 

The very bottom layer is mostly missing. The second layer droops a little when printed and restores a flat bottom. All but a few mm around the perimeter of the bottom layer have been removed. This reduces the adhesion to the bed otherwise it would be very difficult to remove.  To avoid severe warping the bed needs to be heated. I used PLA, ABS is a different beast where a complete bottom layer would probably work better.

The top came out well; I have to admit I was surprised, but it is not air tight. Along the sides of the top there are gaps between strands of plastic. This is where the largest bridging was. I suspect in 1 or 2 more layers it would have completely sealed. Painting it should resolve this. The model has inbuilt support structures and does not need generated support when slicing. The supports for the top branch off the filter grill and walls. They snap away easily after printing allowing access to the nut traps. The nut traps are still fiddly to use as they face into the chamber.

This is my third filter attempt; the previous filters had too much carbon and almost no air flow. 

The model is available here, though I am not releasing the scad files due to objections to thingiverse. I may produce stl files for other configurations if you leave a request it in the blog comments (no promises!).

 Mounted filter box on Mendel90

Failed filter attempt #2, converted broken PC power supply box. 

Electrical tape covered the screw holes and a tissue was placed inside the box over the vents on the far side.

Failed filter #1, printed mesh tube ends, designed to hang off my spool holder rod.

Todays result: 72 playing tiles

I printed a set of game tiles for a friend. They are in a gift box waiting to be discovered.

They took about three weeks of evenings to print which included a lot of failures. This print taught me the importance of correct extruder settings. I probably lost a half a spool of plastic to failed or poor prints. I noticed by chance that Cura was setting its own extruder steeps and overriding the correct value in firmware. Prints would use too much plastic and cause infill to bulge up. The bulges would catch the end of the nozzle and either cause the X/Y motors to miss steps and misalign the extruder or just knock the tile free of the bed.

I used green for the base and grey for the top. I stole the idea from images of other people’s prints. The tiles came as separated models for the base and tops. My printer has a single extruder. To achieve two colours I printed the green base for a plate first, changed the filament, reset the z value back to zero, and then printed the grey tops. The base and top where sliced independently with different settings and printed as separate jobs on top of each other.

The tiles where arranged in plates of 9. Often some of the tiles where ok while other printed poorly. To replace failed tiles I ended up cutting up the plates then reforming my own arrangements.

The grey top didn't always span the same horizontal area as the green base. This would lead to misalignment as Cura would centre each job. When I figured out what was going on I started using cooling cones at each corned to force the equal horizontal areas and ensure alignment. The cooling cones also produced better prints of towers and cloisters.

Some of the pieces had tab/sockets that where too small and needed to be made larger. Other model changes included adding a shield to the four way city, trim the corner walls to match the other wall heights, add corner wall to cities, elevate city shields, and add a termination to the T intersection. Use rounded corner roads.

Changes to slicing settings for the base

• Leave the heater and bed on at the end of the print, remove M104 S0 and M140 S0
• Leave the Z height at the level it finishes printing, remove G1 Z+0.5 or similar

Changes to slicer settings for the top

• Set Z to 0, G92 Z0
• Turn off skirt
• Do not home Z, remove Z0 from the G28 line, but leave G28 X0 Y0

The model is available here

All 72 tiles

Close up of connected tiles

Todays result: Business cards

I made some business cards. They look good in transparent ABS. I made them to try and connect with other 3d printing minded people. I have been rather impressed with them and have made about 10 now trying different things. Most of them have ended as melted puddles of plastic as I "refine" the abs finishing process.

The cards are 0.6 mm thick for the background and the text is a further 0.6 mm. I have printed them at 20mms speed 0.2 layer height, but not noticed much difference printing them at 50mms 0.3 layer height. They take 15-30 min each so I won't be producing boxes of 500 any time soon. The text works best when viewed through the card, this means that it need to be printed backwards. The cards are made in OpenSCAD with the text imported. The background needs to be printed at 100% fill. The extrusion rate needs to be exact or the outcome is poor. The cards look good straight off the printer, but even better when acetone finished slightly, [then poor again if over finished]. Some trial and error is needed to get the text right, too fine and details go missing.

 Card just after printing.

 Card after acetone

This isn't a fair comparison as the before shot was lit from above and the after shot lit from below. The point is the lettering is more rounded, the lines from the diagonal fill pattern has been smoothed out, and the card is more see through.

Todays result: Printing in the sun

Its such a lovely autumn day I think I will go outside and print in the sun.

Todays result: Big blue lady

This is a test print to ‘quickly’ evaluate how the Pink panther woman model would print in layers. The model is a hollowed out version of the original and not just a ‘shell’ print. It was the precursor to the filled in version that I am currently working on.

It is printed in blue PLA at 0.2mm layer height, 20mms print speed, and took about 2-3 hours for each of the eight slices. The final height is 40cm tall. This was the limit my printer could manage, further and the horizontal foot print of the slices would exceed the print bed dimensions. 

Clips where necessary for the model to stand upright and balance the layers. The print has very little surface area for the next piece to sit on. I printed tray of clips but ended up breaking about 1/4 assembling everything.

The model was produced by:

1. Scaling original to 40cm
2. Offset surface inwards
3. Repair and clean
4. Invert model
5. Merge with original
6. Slice in to layers
7. Flip some layers to print better

I used MeshLab for cleaning and merging parts and Netfabb for scaling, repairing, inverting and slicing into layers. Custom software of mine offset the original surface.

The hollow model is NOT available here.
Update: I'm sad to say I pulled the files. I didn't realise that the original was"All rights reserved" so I shouldn't be copying or distributing it.

The final model on top of my netbook for scale.

The nice lighting is from the sun shining through glass bricks at my front door.

Todays result: Cooling cones

I have been using specifically designed cones to lengthen print times without decreasing the actual printing speed.

Models with a small amount of material in one vertical section can print rapidly over the same spot. This builds up heat in the part and leads to warping. This occurs frequently at the very tops of prints. Slicer and Cura have print speed limiting settings but I have found this changes the consistency of prints and appears as visually discontinuous vertical regions.

The cones are wider at the bottom with a single layer base for stability. Thin tall columns eventually get knocked over and make a mess. The cones are thin with holes cut in the sides as the delay comes from making the head move and not wasting extra material. By placing cones as far as possible from the object once per layer the print head will need to take time traveling to the cone then back again. This adds a cooling period between layers and gives the part a chance to solidify.

The model is a OpenSCAD file. The height and width can be changed. The height should be set to the same height as the part. Increasing the width slightly increases the delay, uses more material and may take up more room.

To use set the height of the cone then include the model with the object to be printed. Place the object and cone in opposite print bed corners. More delay can be achieved using multiple cones. I prefer placing the cone in the corner closest to [0, 0, 0], this will make it the first item printed on the first layer.

The OpenSCAD file is available here.

 Various cone from past prints.

 Cone used to print Carcassonne Cathedral

 Cone plated with Mendel90 x_motor_bracket

Todays result: Part 3, 4 and 5 of 6, the abdomen, hips, and but

The last week has been busy printing parts for my version of the pink panther woman model.

The patterns for part 3 and 4 appear more disorganised than the other parts. They don't have a simple geometric shape as the basis for the pattern. Part 5 has one one the best patterns I have worked with so far.

I have fixed the Y belt issue that caused undesirable ripples in part 2. The ripple effect could be interesting in the right place - but not for this print

Producing this model has been a lengthy involved process.

1. Make an inside shell for the Pink Panther woman model
• Hollow out the original Pink Panther woman model
• Shrink the outer shell of the model by offsetting each triangle along its normal
• Trim triangles against neighboring triangles
• Repair
2. Slice into 50mm layers
• Slice up the inside shell into 50mm layers
Save each piece
• Flip the triangles of the complete inside shell
Merge with original unmodified model
Slice into 50mm layers
Repair slices
Save each piec
3. Generate cellular patterns
• Run algorithm to generate patterns 
• Filter duplicate patterns
• Inspect and select patterns
• Find good pattern orientation and size
4. Combine model slice and cellular pattern
• Break the pattern into wall planes
• Create an OpenSCAD script and render each wall as a stl file
• Propagate the wall stls over the space occupied by the modle
• Use OpenSCAD to intersect the internal model shell and pattern walls
• Merge the resulting walls and outer model slice
• Trim erroneous triangles
5. Slice and print
• Print a test piece in a surplus colour
• Fix model if necessary
• Print final in Natural transparent ABS
6. Finish

All up I have worked on this solidly for two months now, not including the mass of resources I accumulated previously. I have had to tweak the process a lot to work around various limits in skills, my code, OpenSCAD, and time. OpenSCAD handles simple stl csg operations ok, but sometimes it just fails.

The internal walls in the resulting models overlap at the seams. I haven't been successful at combining the walls into single shells so the final stl is a collection intersecting shapes. Cura seams to handle this ok, but I believe that an accurate model would achieve better results than I am getting.

Each piece is printed at 20mms with a 0.2 layer height. This produces nice results but takes an average of 9 hours per print.

Todays result: Modified Mendel90 y-idler-bracket

I tweaked the design for the bracket to add extra tension to the y belt as it is done up. The y bracket is responsible for the tension on the y belt. The y belt can be installed to within one tooth accurately. I used T2.5 belt so that is +/- 1.25mm as the belt doubles over. The last mm or so is achieved by the screw tension holding the y idler firm against the printer base. My printer is MDF. The screw hole for the bracket is stripped, and it quickly works its way free after tightening. Wood glue will hold it in place but only for a print or two. The belt being just a little loose has caused noticeable ripple patterns on prints as the bed wobbles back and forth.

The modification adds a slant to the back of the bracket. When tightening the screw the bracket acts as a leaver adding tension to the belt slightly. Trigonometry reveals that for T2.5 belt an angle of about 6 degrees will pick up the remaining slack.

I printed the bracket right way up, and then filed off the messy overhang. Flipping the model long way up would prevent this but also reduce the print area touching the bed. As the bracket screw hole on my printer has stripped I used a zip tie instead. The new bracket has removed the ripple effect on prints.

The modified scad file is available here. To use the Mendel90 repository is needed. Substitute the modified file for the original y-idler-bracket.scad in the directory Mendel90 \scad.

To install

1. Setup the printer as follows 
   
   • Y-motor and bed in place
   • New y idler on the belt but unfixed to the base
   • Y-belt tighter than necessary
   • One belt clamp on the bed done up, the other tight enough to hold the position of the belt, but loose enough to give when pulled
2. Place the y bracket on the base with the bearing side flat and screw hole elevated. Slide the bracket with the screw toward the screw hole until it is just able to reach. This should be the correct belt length to within one tooth.
3. Tighten the belt clamps on the bed.
4. Tighten the bracket screw until secure and the belt is tight

Angle to achieve desired tension

 Installed on my printer, this is before I did the math and has a 20 degree angle.