With our house move behind us (thanks to my parents who came up last week to help out), I now have internet at our new house along with a small workshop area in my basement. We're still getting things situated and making some improvements to the house but I've been able to sneak in a few hours of work (albeit late at night) on my own personal projects. With the upcoming 3D Printing Camp WI this weekend, I have been focussing on getting my Prusa tuned up and making further progress on my other printers for the event. I eventually want to build my own design for a printer or mill or laser cutter, but I feel I just don't understand enough about these machines and the ins and outs of printing in order to create a smart design (as of yet). This means I need to build a few different ones to be able to analyze the intricate workings and figure out what it needs to be.
I have been following nophead's mendel90 development for a while and I found myself wanting to build a Mendel90 based upon the things I was seeing in his design. You have to hand it to nophead, as he really has engineered this design to a high degree. He has all the files on Thingiverse and it's a quality upload for sure (not like some things you find on the site). Honestly, it was not until I started printing the parts and putting things together that I realized how smart his design was and really began to appreciate his thought and skill. I recommend you take some time to review his work on his blog. He has a lot of great features built into the Mendel90 design.
I had decided a while back that I was going to build the frame in aluminum so as to make a super rigid frame and to eliminate the amount of hardware required by other reprap designs. I started with 1/4" 6061 aluminum sheet. I knew that this would probably be overkill, but I was hoping that I could eventually put the frame on a diet by cutting and drilling sections that aren't needed later once the machine was built up. As for now I have chosen to keep things as specified by nopehead. I imported the dxf files (from Thingiverse) into Rhino to be able to check measurements as well as to create CAM files for cutting on the Tormach CNC. The mill would help me to locate drill holes accurately as well as cut out the proper outside shape. The back frame supports were well under the size limits of the Tormach, but the frame upright and base were not. I would have to get creative, so I split the upright frame piece in my Rhino file and made sure I could reindex it and cut the other half. It worked out well and I was able to get the upright, y axis bed, and two back supports drilled and cut. One of the back supports has a large hole cut in it for a fan so the heated bed can be cooled down rapidly after printing.
The base for the frame was just too large for the mill (unless I reindexed it multiple times) and I figured I could just go the paper template route anyway). As a matter a fact I could have done this for all of the pieces and I'm sure things would have worked out fine. I guess sometimes I just get lazy... It was good to have the other milled pieces though along with the printed support brackets to be able to confirm the placement of the paper template and to make sure holes lined up properly.
I decided to drill holes and tap with the equivalent SAE thread size as I don't have a small set of metric taps and I happen to have a lot of extra 6-32 and 8-32 stainless steel hardware. I always use the drill press to asset with taping holes (not plugged in though as I don't have a tapping head....YET!). I just use the drill press to aid in getting the hole started square. The gun taps that I get from McMaster Carr are worth the money as I actually tapped the holes entirely with the tap held firmly in the drill chuck. The chip was pushed forward through hole and allowed for quick tapping just by gripping the chuck by hand as I fed the quill feed down with my other hand and then carefully backing it out by reversing the process. After the numerous tapped holes, my hands are tired, but it's a system that allows me to create straight threaded holes (without access to fancy tapping arms, tapping heads and the like). I also highly recommend a good tapping fluid such as Rapid Tap.
With the sheets full of threaded holes and cleaned up from all the tapping fluid, I set about mocking up the frame.
I took the frame parts home to my workshop area and got to work printing the axis rod supports. These are hollow and have a little recess in the inside for a M3 nut. They look so simple and to most people you would probably dismiss the "design" in the part, but they are an igneous design (hats off to nophead...once again) that utilizes the smallest about of plastic to print and they get the job done properly once mounted to the frame. Quite functional!
I continued printing parts and cutting screws down to the proper length two nights ago so I could mount the various parts. You'll see that the y axis utilizes printed lm8 linear bearing holders with zip tie slots. It runs on three bearings so no need to waste money on a fourth, plus you get to reduce costs further by using a shorter y-axis rod on the single bearing side. I plan on pocketing the under side of the aluminum bed to reduce weight since I made it out of the same 1/4" sheet, but right now things seem to move quite nicely. The z axis will utilize acme threaded rod and aluminum motor couplers. I printed the rest of the x-axis parts last night and and stayed up late getting things attached.
So far so good.
Once things are together and running, I'm going to plan some weight reducing cuts and then tear it down so I can lighten it up a bit. I can see a handle slot in the main upright coming so I can pick it up and carry it around with ease. I am also planning on replacing a few of the printed parts with aluminum parts to help even more with the rigidity of the machine.
I probably won't have it completed in time for the 3D Printing Camp, but hopefully it will be functional soon afterwards.
Look for updates in the future...