Sunday, June 30, 2013

Printrbot Mechanics

This next printer build is necessary for an on going project and also it’s to act as a dedicated printer for future clay extrusion experimentation. I plan to highlight the assembly and make note of anything interesting as I move through the building process.

All of the parts were printed with my RepRapPro Mendel.

 I purchased the LM8UU bearings from an eBay seller and as the saying goes, you get what you pay for. I paid $5.27 USD for 10 bearings and got a poorly manufactured product. The tiny ball bearings pop out if extreme care isn’t taken. They still work, but I’m not sure if I’m getting a smoother ride than printed PLA bushings.

The base is a solid design and is easily leveled.

I found a lot of 5 used NEMA stepper motors with T2.5 pulleys on eBay. The shafts are short, but work well for the Y and Z axes.

I used a clear acrylic sheet for the bed. The only major design change I made was with the Z axis threaded rods. I swapped out the 5/16" rods with 1/4" rods. A similar feature of the RepRapPro Mendel.

There were a few problems which had to be solved to adjust the X axis carriage. I had a difficult time in lining the 2 bearings parallel on the X axis rods. I ended up cutting out the bottom end of the carriage and zip tying the bottom bearing in place.

I’m using an accessible Wades extruder that I made on my first printer. I switched out the hobbed bolt with the Arcol hobbed bar, Hyena 1.0.

Overall, the mechanical assembly was easy and much faster than a Mendel printer design.

Addendum 22July2013

Getting the mechanical functions tuned to perfection has been a pain. This has been primary due to imperfections in the printing of the plastic parts. I originally printed them in gray ABS on my RepRapPro Mendel, but they’re not working out. I'm not getting good prints because the X and Y belts on the  RepRapPro are slipping. This I plan to rectify once and for all which I’ll cover as an addendum to my last RepRapPro post. For now, I reprinted the parts in black ABS on my Prusa Mendel.

Next, the low grade LM8UU bearings have been replaced with better bearings. I think the cheap ones would probably be fine, but I prefer to keep the performance higher on this printer.

Next, I decided to ditch the Wades extruder and go with  the MakerGear Brutstruder and hot end. I have tested this system time and time again with no problems and I prefer to keep with what works. However, I did print the Brutstruder parts and assemble the hot end to be fed with 1.75 filament. I really believe that 3mm is better, but for the purposes of an on going project, I’ve made this decision.

Last, I decided to add the components needed for a fan. I printed the fan system designed by erossman and posted on (thing:32605). I cut out the ducting which cools the hot end with some snips to give the nozzle full usage of the air.

Wednesday, June 19, 2013

RepRapPro Mendel (part 7)

The RepRapPro Mendel has been a great printer, but it’s been plagued by a number of issues which arise from prolonged print runs and constant use. This, I believe, is not indicative of an inferior machine, but just the nature of DIY printers in general.

This entry will survey more of the problems I’ve had with the RepRapPro Mendel. Some of these problems must be prevalent with their printers at large since RepRapPro has made some recent design changes to correct them. Most of these problems, I’ve had to solve on my own.

Here are my recent issues:

I’ve had problems with the parts which are exposed to the heat of the bed. This is probably because the parts are made with PLA rather than ABS. PLA has a lower tolerance for heat.

The Y belt clamp has been a continual headache. The heat from the bed softens the clamps and this causes the belt to slip. The screws are instrumental in this problem by conducting too much heat through the clamp. I’ve had to make several adjustments or modifications to keep the belt properly tensioned.

The Y axis motor mount has warped considerably over time and had to be reprinted. RepRapPro now sends this out as a laser cut wood part in their kits. I remade the part in ABS which should hold up fine for my use.

The next problem I’ve had is with the bowden cable attachment at the extruder side. The clip which holds it in place would wiggle its way out and the cable would detach. I lost several long print runs because of this. I fixed it by simply tying the clip in place with a zip tie.

The next problem is with the Melzi controller. I just haven’t had much luck with this board. This time it's with the mini USB connector. It separated from the PC board. Fortunately it wasn’t damaged and I could solder it back in place, but it wasn’t a very easy task to accomplish. The 5 pins are very small and it  required some very steady work and I think some luck to get it in place.

The last problem has been a reoccurring failure of the heat resistor, but RepRapPro has made a component change and now sells a more robust ceramic heat resistor. The replacement part I found as a substitute has been easier to install, but hasn’t provided any longer service than the OEM part. I’ve purchased replacements for all my RepRapPro hot ends with the new ceramic resistor.

Once again, I think the RepRapPro Mendel is a great machine and I would recommend it highly to anyone who is looking to purchase their first printer. It’s a very nice system and it’s continually improved.

There are just inherent weaknesses in the DIY system. I hope that by finding these weaknesses in all of my printers, I’ll be able to perfect the technology for my use in creating sculpture. This has been my underlying rationale for building the printers I have so far.

Addendum Aug. 18, 2013

I can't seem to keep the belts on my XY axes tight. My best solution was to drill holes in the X carriage and run the belts through them and then clamp with nylon ties.

 I did this also for the bed.

I also had a problem with one of the PLA printed pulleys. I replaced both XY pulleys with aluminum T2.5's that I found on eBay. Since the pulley diameter is larger than the OEM versions, I had to re-calibrate the axes.