I’m following the Mark Method of building a RepRap frame, which involves using large Aluminum extrusion for the frame. The process involves cutting it, milling the faces flat, and then bolting it together. No wimpy 3D printed corner brackets here!

Adrian met me at Milwaukee Makerspace yesterday and helped me get my Aluminum extrusion cut down to size. I now have seven pieces ready for the next step. There are three pieces at 460mm, two at 480mm, and two at 500mm.


I started by cutting the extrusion to length (plus 6mm) on the band saw in the metal shop. We added 6mm so we’d have about 3mm on each side to mill down to get the final length. Cutting through the 45mm extrusion took some time but it wasn’t too bad.


I haven’t used the Bridgeport before, so Adrian got me all set up and walked though the process. I’ve used a few lathes in the past so the actual milling process wasn’t hard to do, it was mainly learning a new machine. I can see why people love the Bridgeport! It’s a nice machine that has some great capabilities. (I’ve got the old Enco mill at work, so I may need to play around with it a bit more.)

Milling took some time, but there was nothing too difficult about it. One thing I learned about milling is that it’s a messy, dirty process. I mean, the oil and the chips and the metal and all that. Being such a digital fabrication nerd probably doesn’t help.


Neat trick I learned from Adrian. Use a black marker to draw all over the face of your piece so you can easily see if you’ve milled off enough material. (I guess that’s why there’s a container full of Sharpies in the Metal Shop.)


Next in the process will be tapping the ends to accept bolts, drilling holes through the extrusion to get a hex wrench to reach the bolts, and then screwing it all together. The whole process of cutting and milling the pieces took a little under two hours. I still need to clean up the extrusion a bit, take care of sharp edges and remove little bits of metal. Adrian suggested using a Scotch-Brite pad for that.

(I’d like to thank Adrian for all the help, and Mark for the good price on the Aluminum extrusion!)


I’ve been experimenting with casting for the last year or so and typically my “experiments” come out terrible, mainly because I try weird things, but sometimes I sort of get it right…

This time I made a silicone mold of a model of a glue stick for a hot glue gun and it mostly worked fine. I modeled a glue stick and tall cylindrical container for it using OpenSCAD and then 3D printed the two pieces. The idea being I’d place the “stick” into the container and then pour silicone in to create the mold.


I had a small amount of silicone we were going to throw out at work because it wasn’t enough to do anything useful with, and it was just enough after scraping everything out of the two containers and mixing it together.


Once again I had to destroy the original mold master to get the mold out, but since it was printed using PLA I just smacked it with a hammer a few times and peeled away the plastic to get the silicone mold out in good condition.


I could not find the cheap little cooking pot I bought a Goodwill a few years ago for melting things so I grabbed an old metal can, made a makeshift gaff tape handle, and melted down some old candle wax to pour into the mold.


Hey, it worked! A wax stick the same size as a glue stick you would use in a hot glue gun. ;)

Oh, see those rubber bands? They hold the mold together because I split it down the side to allow for getting the wax out of the mold. I may have wrapped the mold too tight or not aligned properly because the first stick wasn’t totally straight.


Here’s the second one… much better. You can see the split in the mold. I just ran an X-ACTO blade down the sides to split it.


Now, to ramp up production I may need to make a lot more molds, or come up with an alternative. Here’s a method using a metal tube and parchment paper that might work. Honestly I think I prefer silicone molds but this might be a good way to get really long sticks.


The next part of this experiment requires a hot glue gun, and most likely, disassembling it for the heating element. Stay Tuned!


In my last RepRap post I had modified the design to be much wider in the x and y planes, and as I did that I started to realized that it would cause a number of issues with the build. I mainly did this because I have plenty of Aluminum extrusion to work with, but as I thought about it more I started to remember why 3D printers are mostly the size that they are.

When you go beyond the typical build envelope of most 3D printers things get complicated. You can’t use 8mm rods because they’ll sag under the weight they carry, and if you make them long enough they’ll even sag under their own weight, so you need to start using other methods of linear motion. I thought about following some of Mark’s lessons from SoM, but things get expensive when you start doing that. (He does manage to scrounge and buy used things, but that can be tricky as well.)

I will definitely follow some of Mark’s techniques though. For instance, look at this build for the BA3DP. Start counting the amount of hardware used for those corner plates. Crazy! The Mark Method is to tap the (milled square) extrusion and screw it together. Simple! And you can always add some corner brackets if you want, but they aren’t as necessary and definitely don’t need as many nuts and bolts.

Some printer designs use T-slot frame members joined together with printed plastic parts. Avoid the temptation to do that. If you want rigidity, you have to bolt/weld metal to metal. T-slot extrusions are designed to accommodate standard sized screws. All you have to do to join two pieces is drill one hole and tap the end hole to receive the screw. Likewise, attaching things to the T-slot can be done by using nuts designed to fit the slots (or by making your own).

That’s my plan for assembling a rigid square frame using 40mm Aluminum extrusion. Speaking of the extrusion, here’s a test fit for some of the printed parts. I’ll probably start with these and tweak if needed. Mark suggested I make the motor mounts from square Aluminum tube, and that might be a future upgrade, but I’m okay to start with some printed parts. I do want to try to reuse many parts from my old RepRap, and use parts I have on hand, so I’m going to try to stick to that plan.


One thing I don’t have is 12mm linear bearings for my y axis. I’m going to try igus drylin linear bearings. I’ll need to make mounts for them that compress them a bit so they fit properly. I’ve read enough to know you can’t just zip tie them into place, (To be honest, wires are the only things I plan to zip tie into place.)

I still need to shop for hardware. Either 5/16″ or 8mm bolts, depending on what I’m ordering from BoltDepot or buying locally in the coming weeks.


One thing I’m still not totally sure of is where the vertical pieces of the gantry will sit yet. I’ve tried to calculate where to place it so that the extruder will reach the front and back of the bed properly, but I still don’t have that nailed down… partly because I’m still not sure how the x axis and carriage will work as far as mounting the hot end, connecting to the smooth rods and lead screws… I also want the carriage to be easily removable, and possibly replaceable with, another end effector. :)


Since I’m going to avoid going wider than I need to for this printer, I can get away with 8mm rods for the x axis like I did with my old RepRap. I’ll probably sacrifice a little rigidity and precision, but that’s a price I’m willing to pay right now to avoid paying more for a proper linear guide on a square Aluminum tube. (Future upgrade?)

I’d like to keep the x axis motor within the envelope of the machine, and not hang it outside as many printers do, but I’ll need to design that as I’ve not found a solution yet that fits what I want. Time for more CAD work I guess.


As the RepRap build continues, I designed some motor mounts that will work with the 40mm extrusion I’m using. The Nema 17 stepper motors I’m using are about 43mm wide, so they hang just outside the extrusion if centered, so I’ve designed the mount to be slightly off-center so the motor do not hang outside the frame.


I’ve incorporated the model into the overall render of the printer. I don’t have the hole yet for the smooth rod to fit into the mount. I’m looking at models like this one to base my work on.


I’ve also worked on the full model a bit, and made it slightly larger for reasons I’ll get into in a future post. I’m currently thinking of a few ways to make this machine a bit more flexible in its capabilities, and a larger frame made sense for that. (And it means I can waste less extrusion when I cut it down to size.)


Things look wonky in this photo because that’s actually a piece of 38mm (?) extrusion I had handy, since all the 40mm is at Milwaukee Makerspace right now. I’ve got a few projects to wrap up before we cut down and mill the extrusion, so I’ll probably keep working on the printed parts for a bit.


You may have already seen John’s post about our Velocity exhibit, and I must say, he did an amazing job with all of the CAD and CNC work to build it.


For my part, I handled the technology that went into the exhibit. (Which sadly, you can’t see much of in these photos because some were shot after things were powered down.) For three of the five components, I spec’d the hardware and worked with a software developer to upgrade the old version of the software to something more modern, stable, and easier to calibrate and support.


I can’t even tell you how many golf balls I rolled down all of those ramps. At one point we had an issue with a projector overheating and I set up a time lapse camera to run all day and overnight to give us some idea how long it was staying on before shutting off. We eventually fixed it by adding a duct to the projector housing to draw the heat out and away. We’ve used earlier models of this projector with no issue, but this is why we do extensive testing… you never know what problems are going to pop up.


If this exhibit looks familiar (!?) it might be because there are now three copies/versions of it. Besides this one which was a “for sale” item, we’ve got two on the road, one of which will be returning to the Betty Brinn Museum this summer.


By the way, if you occasionally have a bunch of old golf balls you want to get rid of, let me know… There’s a non-profit in Milwaukee who would love to take them off your hands. ;)



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