posts tagged with the keyword ‘dcrlmtm’
If you’ve been following any of my adventures since I first mentioned a Turntable Drawing Machine, this is the result. The Turndrawble is a machine that uses a spinning platter and a movable arm to create drawings.
Unlike many of the things I’ve been working on lately, the Turndrawble leans more towards the “art object” side of things than the “here’s all the files/you can easily make one” side of things. That isn’t meant to say you could not make one, but the prime objective was to create an aesthetically pleasing machine that was unique. (I hope I did that!)
I also wanted to build a machine I could bring to events and allow people to use in order to create drawings. Often in the past I’ve brought drawing machines places but I’ve ether operated them or they’ve operated (semi-) autonomously. The Turndrawble presents a chance for the viewer to become a participant.
(I’ll be posting photos of some of the drawings soon as well. There’s also a video.)
Check out the Turndrawble project page for more info, links to files, etc. if case you want to try to build your own. (I’ve been thinking of building a much smaller and simpler version as a kit you can purchase and assemble. Stay tuned for updates on that.)
One of the pieces I needed for my turntable drawing machine was something to hold a bearing in place underneath the platter to support it and let it spin easily. If you’ve ever taken the plate out of your microwave oven to clean it you may have seen a “Microwave Roller Wheel / Turntable Support” thing. (Really, that’s what it’s called. Check Amazon.)
I decided to use 608 bearings, mainly because I had a lot of them on hand, but they’re also really easy to get for a low price. (I think I got 30 608ZZ bearings for under $20 from Amazon.)
I designed these two arms that would fit into slots cut into the base of the machine, below the platter. Each piece would be locked into place with a 3mm bolt, so there’s holes and t-slots for those. The extra piece you see on the bottom (with the 4 slots and 2 holes) is the mating piece. This was designed based on the arm pieces fitting into it, and I would only need to cut one (hopefully) to test the fit.
The arms are slightly different. The one on the right has a hole large enough for the 8mm bolt to fit through, while the one on the left has a slightly smaller hole. The plan was to tap the smaller hole so the bolt could screw right into it without needing a nut. Do a search for metric tap drill size and you’ll see that a 6.8mm hole is needed to tap it for an 8mm bolt. (Sometimes you can just look on the tap and it’ll tell you what size to make the hole.)
As a bonus, when I share the files for this you can decide which pieces suit you better, depending on the availability of an 8mm tap in your workshop. No tap? Just use the larger hole version and a nut instead.
When you’ve got a laser cutter and lots of scrap acrylic, it makes a lot of sense to make your own washers and spacers and standoffs. (Assuming acrylic is up to the task of what you’re designing.) The spacers were sized to match the inside part of the bearings allowing the outer part of the bearing to spin freely.
I originally was going to make acrylic nuts as well, but decided on tapping the holes with threads. I still wanted the “hex nut” part of the design, as it’s used to hold the platter in place. So that, in conjunction with the tapped parts, prompted me to make the hex shape at the top of the arms. (It’s the details, right?)
The one thing that making and using acrylic nuts would have allowed would have been adjusting the height of the bearing. I could have created a slot for raising or lowering the bolt and bearing combo, so with this design featuring the tapped holes, there was no room for adjustment. Luckily I got it right by the second (or third) attempt.
Here’s a shot of the spacing of the bearing holders below the platter. It worked out well and I got the math (mostly) right. I may end up making a new bottom in the future to account for other faulty measurements this time around, but I’ve already adjusted for them and things work well enough.
(For other posts about this turntable, check the posts tagged with dcrlmtm.)
You can’t have a turntable without an arm! Well, I guess you could, but where would you put the pen? Here’s some of the design files for the arm. The hole pattern on the larger part was made to match a servo hub from SparkFun, which is also from ServoCity, which provided a STEP file. (Ignore the heart-shaped thing for now. It’s experimental!)
Luckily I was able to open the STEP file in both Rhino and in FreeCAD! It’s like I won the CAD file lottery or something. But seriously, if there’s ever a competition to convert from one format to another and then another and another… I think I can win.
I was able to get what I needed to get the hole spacing right, which is all I really needed this time. The holes are tapped for 6-32 screws. Once again I’m mixing Imperial and Metric. Sigh… Mission (somewhat) accomplished, I guess.
The arm consists of three layers of laser-cut pieces stacked up, and screws to hold them together. I played around with materials a little bit, trying wood in the center, but finally choosing the red acrylic. I thought about clear, but there is at least one other red element right now, and possibly more to come, so I chose the black and red combo. Always a good choice!
There’s also a hinge I cut from a 1mm thick plastic I got from the Midland scrapyard. (Windell from EMSL thinks it might be polypropylene.) The laser cut it fine once I figured out the proper settings… and covered it with masking tape on both sides.
And yes, I did borrow a few ideas from the Egg-Bot design. Sharpies, FTW! Pen holder designers unite, and all that. There’s a 8-32 square nut in there, really snug. I do not have a nice thumbscrew like EMSL uses… yet!
There comes a time when every designer who designs things in two dimensions that get assembled into something that has three dimensions wants to have a diagram with some… dimensions.
If I were to provide assembly instructions I’d probably want such a drawing. Here are some notes on the process, so I can do it again next time.
In Inkscape, each piece must be an object. The ‘holes’ cannot be separate objects, but must be cut out (differenced) from the main object. (This is the same method needed when bringing a 2D drawing into OpenSCAD, so nothing new there.)
Sadly, Rhino cannot import SVG files. (Mini-rant: I’m always surprised at the number of applications that do not support SVG. The SVG specification has been an open standard from the WC3 since 1999!) Rhino can import PDF files, so export your Inkscape file as a PDF. Your PDF should be a vector PDF, by default. Inkscape should do the right thing unless you’ve done something silly to your file. (Which is possible, I’ve done it.)
Our vector file is now in Rhino! Double-check to make sure each line/object did not get doubled-up. I’ve had it happen a few times but could not conclusively determine what causes it. It may be the width of the stoke of the objects in Inkscape.
You can now extrude your object(s) in Rhino. I make them the height of the material I am using. Oh, I’ll be laser cutting these pieces with 4.45mm acrylic. YMMV.
Change the view in Rhino from wireframe to solid and you’ll see your new 3D object(s)…
Make sure the holes are really holes! If not, re-read the part above about objects and holes and such. You need to difference any cut out things!
Now you can move your new object(s) because the original vector lines we imported in are probably sitting right underneath them. Swing your object(s) into the view you want… get that angle just right, and then choose “Make 2-D Drawing” from the “Dimension” menu.
You should now have a 2D version of your 3D object. Rhino should also select it by default, so you can use the “Export Selection” menu to save it out as… A DXF file. :( Sadly, Rhino cannot export as an SVG or vector PDF, or even an EPS file. Rhino can export as an Illustrator file (.ai) but Inkscape cannot open those. The AI file it exports starts with “%!PS-Adobe-3.0″ which is probably a format from that was popular in the 1990s.
Anyway, we can certainly import that DXF file back into Inkscape and work with it, and make it look like a nice vector drawing. Mostly. Sort of. I mean, if you want to just fill it with a color or change the stroke, it’s not quite that easy. If you just want a line drawing that isn’t too fancy, mission accomplished!
Oh, and not that I want to turn Inkscape in a 3D application, but I could see great value in being able to extrude and change the view angle of a vector drawing… maybe through an extension?