Archive for September, 2013

Building Mendel 90, so far

Well, I have a Mendel 90 well under way. I have it printing and I have lots of fun time calibrating and designing better parts and such ahead of me. Here’s how getting parts and such went.

Assembled Mendel 90

Assembled Printer

Printed herringbone gears

Printed herringbone gears

Printed small audio equipment

Printed small audio equipment

 

 

Build options
I chose to go with the “Sturdy” variant of the Mendel 90 because I don’t have access to a CNC mill and don’t want to buy a frame. One of my original goals for choosing the Mendel 90 was to be able to make all the parts for it myself so that the Stana Barbara hackerspace could use this design for a 3d printer build fest. It also seemed like a good design considering the thought nophead has put into getting it to operate for many hours without parts failing or needing to be replaced, or even tightened.

The frame was pretty easy to cut and drill, but I failed the first board. I had the drill templates printed at Staples in actual size on 3 pages of 18″x24″ paper (two copies each) for about $11. The MDF was available in 2 foot by 4 foot sheets from Home Depot for $10, hiding way in the back. I failed the first sheet because the cuts I made through the wood weren’t at a perpendicular angle because of the way my circular saw was set. I didn’t have access to a table saw to do this right. The second set of holes were cut fine. I used the piece of MDF for the bed, and the cuts for the bed and hole in the gantry were cut (poorly) on a bandsaw at the hackerspace.

I didn’t update the configuration to have a 12mm thick bed plate, so the screws included in the BOM were too short and I had to buy more.

When building the Bill of Materials I took the full BOM text file and pivoted the columns so I could put it into a giant google doc. This was really helpful to find where each part went and such because the column headers in the text file are absolutely unreadable. That said, there are a bunch of places in the BOM and the google doc where I wish I had better options to see how a part was used or fit together, or able to better select options for it. For example, RepRap electronics are typically sold in bundles that include the main board, motor drivers (optionally 4 or 5) and endstops. Sometimes this bundle can include more things like the heated bed, heated bed thermistor and such (for example the gadgets3d bundles…). This wasn’t usefully represented in my spreadsheet.
Vitamins
Here’s where the vitamins on my printer came from:

  • Linear Bearings: Amazon (some really slow merchant shipping from china, so I bought extra)
  • Rotary Bearings: Amazon (VXB)
  • Most fasteners: Bolt depot
  • McMaster-Carr:
    • Smooth rods (I didn’t cut the smooth rods. I think I have 5 of the 400mm ones and one 500mm. I have cut none of them)
    • 8mm threaded rod. I cut this with a hacksaw and the bandsaw. I like the results from the hacksaw better.
    • Star washers
    • Bronze M8 nuts
    • Plastic tube and sheet
  • Maker Farm:
    • Magma nozzle. I need to write more on this later, I think it does jam a lot
    • Hobbed bolt
    • RAMPS and LCD
    • Z threaded rod couplers
    • Probably more plastic. Always need more plastic.
    • Polybelt
    • T5 belts. Their $15 min order size is annoying.
  • Misc:
    • Glass sheet from Home Depot. The local one doesn’t have it but the ones in nearby towns sell 8×10″ glass sheets for $2 each. A glass cutter is $12. I haven’t cracked any of these with heat yet, but catching the nozzle on the edge can cause problems.

Printing the parts
I printed all the printed parts myself on my 8″ i3 with .35mm nozzle in Orange ABS from Maker’s tool works on Kapton covered glass. I didn’t have much trouble following the instructions for how to slice the parts. I did have trouble with them not staying on my bed when I printed large plates, but I think that should be fixed now as I’ve leveled the bed on that printer better.  My i3 is leveled using washers and nylon spacers, but the bolts weren’t long enough to add more washers. This has now been fixed.

The X motor is really annoying to print on this printer. I printed at least 5 full ones before getting one that I thought was okay. At 15 hours each it took a while. It didn’t help I was printing ABS too hot. A box helped, and a 5mm brim helped, but there’s probably more required to get things working right.
Assembly notes:
I spent a bunch of time reading and watching different people’s instructions. I ended up watching watching maddyplays videos on youtube: http://www.youtube.com/playlist?list=PLNUL7DzXzp_JqA92h6eeVH8XwwLVZ_C0Z
then I followed http://reprap.org/wiki/Mendel90_Build_Manual. I wish I had read the instructions on the RepRap wiki more because a bunch of the mistakes I made were mentioned on the RepRap wiki build instructions.

I broke some parts during assembly and soon after so it’s nice to have a working printer to print better replacements. Here’s a quick list:
The extruder fan was quickly broken because it is a thin part with poor layer adhesion (ABS was printed too hot). The replacement was a little awakward to install because the fan duct nut traps didn’t hold the lock nuts in place (they spun in place). I’ve installed the new mount with the bolts going in the other way (the bolt head sits in the nut trap). This doesn’t work great because the bolt on one side runs into the X belt tensioner.
I’ve split a few rod holders by tightening the bolts too much. Part of this is that most of my rod holders were printed at the wrong temp and don’t have good stick between layers. When the bolt gets into the lock part of the nylock nut, the nuts twist and break the rod holders apart. I’m probably going to leave this for a while because I have only broken one bottom Z holder and one Y rod holder.
Don’t drill holes (at least by hand) in your pulleys or gears. I had originally drilled holes in the belt pulleys for X and Y, and these wobbled very badly. I printed new ones and just pushed them on backwards and they have been working well enough I leave them alone. My extruder gear probably also needs to be replaced.
I wasn’t able to etch or assemble the PCB for the extruder connector because I couldn’t find what I thought was the correct D-15 connector. I have the wires run in a bundle now which is fine and I may leave it that way. I used a thicker ziptie around the motor for strain relief, the bundle of wires is connected to this ziptie to direct them upwards and so the wires don’t take all the bed force themselves.

First prints

I managed to get this printer working reasonably quite quickly. My first few prints were in ABS with the 60mm duct fan on full time. This duct has the inner part removed so it blows both upwards and downwards on the extruder. (actually the duct didn’t stick on the print and I held on to the part because I thought it might fit better around the magma’s ceramic heater. I was right). I didn’t have the Z max value tuned so my first week or more of prints had me turning the Z rods at print start to get the right height and approximately level.

Pretty quickly however I started having jams, usually near when I started a print.

I tried a bunch of things (PLA jams also), and now have something reasonably working. I have a duct for a 40mm fan which I intended to use on my i3 zip tied to the extruder motor blowing air on the heatsink of my hot end. Except for sometimes at the beginning of prints I haven’t seen as many jams. I don’t currently use the 60mm fan or duct but I may in the future. I think the right option for me may be a small board or fan controller living on the X carriage so I can manually switch how the fans are configured. I do have the wires and pins to control them though, I just haven’t set that up.

I still have a number of tweaks to make happen:
On my bed my bolt heads stick higher than the glass plate. I need to get some different M3 bolts (I have M3 socket head cap screws now) that don’t interfere with the nozzle around 0,0.
I need to design a different extruder fan duct that holds two fans (one for the barrel and one for recently printed
Consider building the extruder PCB and replacing X and E wires with the fancy ribbon cable from nophead’s design.

Extra fan duct for cooling magma nozzle

Extra fan duct for cooling magma nozzle

Up next, ramble about ALL THE CALIBRATION.

Some time spent tuning retraction

Some time spent tuning retraction

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