posts tagged with the keyword ‘machines’

2015.05.03

Arm

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!)

Servo Hub Rhino

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.

Servo Hub FreeCAD

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.

Arms

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!

Arm Hinge

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.

Pen Mount

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!

2015.05.02

Parts

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.

Above is a dimensional illustration of the parts of the mount for the shaft for the machine I am building.

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.

Parts in Inkscape

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.)

Parts in Rhino

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.

Solids in Rhino

Change the view in Rhino from wireframe to solid and you’ll see your new 3D object(s)…

Extruded in Rhino

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!

Make2D in Rhino

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.

2D from 3D

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.

3D/2D in Inkscape

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?

Note: Lots of comments about this post are on Facebook.

2015.04.22

Lathe

Just a quick follow-up to the previous shaft post… I cut the shaft to length on the horizontal band saw, and then chucked it in the lathe (and had Frankie do a quick check before I started) and then cut down the other end so the bearing would fit. It’s not perfect, but close enough. I’ve still got some of the shaft left if I need to make another one. The main thing is, I got some good experience using the lathe, which will come in handy if I end up turning my own knobs to fit on the potentiometers.

Shaft

One bad thing… we had thought the shaft was steel and would work well for the magnets I plan to use, but… it’s not magnetic! I’ll probably end up drilling (er, lathing) a hole in the shaft to thread a steel bolt into so I’ve got some material I can stick the magnet to.

2015.04.22

Electronics

I finally got the electronics for my Turntable Drawing Machine working. It wasn’t easy…

I decided to use a DC gearmotor controlled by an Arduino and potentiometer for the speed. I did a quick test of this with a Leonardo and a DRV8835 Dual Motor Driver Shield for Arduino. It worked fine for controlling the speed of the motor, but I didn’t really want to use the shield, so I used a DRV8835 Dual Motor Driver Carrier I had on hand. (Since I’m only using one DC motor, I probably could have used a DRV8838 Single Brushed DC Motor Driver Carrier.)

Pololu has an easy-to-use Arduino library for the DRV8835 Dual Motor Driver Shield which worked fine for the shield, but doesn’t (I mean didn’t) work with the DRV8835 Dual Motor Driver Carrier. I ended up hacking the library a bit to make it work. All was well until I added a servo. Since the Arduino library for the shield is hard-coded to use pins 7, 8, 9 and 10 there’s an issue because the default Arduino servo library disables PWM control on pins 9 and 10. I then changed the library to not use pins 9 and 10, but that still didn’t quite work… Seems that the servo library and the motor control library both need to use times, so there’s some weirdness there…

I ended up digging through the forums and eventually found some useful posts and a link to ServoTimer2.zip. (It’s worth noting that there are a number of ServoTimer2 libraries, but I tried this one and it worked.)

Once I had the ServoTimer2 library in place, getting it to work with the my hacked ‘DRV8835DualDriver’ library was simple. (I’m saying “simple” but it took a few hours of screwing around with things that should have worked but didn’t) If I had used one of the Arduino Megas I had lying around, I probably could have avoided some of the issues the Servo library causes.

Alright, well… electronics seem good! Next step is to build things, and get the turntable portion constructed to test if the DC gearbox will work out. I think it will, as it’s got plenty of torque, and there shouldn’t be much resistance.

2015.04.13

Platter System

For my turntable drawing machine I’ll need the platter to spin. In a “real” turntable (the kind used for vinyl albums) there are three methods, idler-wheel, direct drive, and belt-drive. The illustration above shows my original idea for direct-drive, which I quickly abandoned in favor of belt-drive, on the bottom.

Rod & Bearing

Typically I use 8mm rod for things because, well, I have it handy, and lots of 608 bearings as well. For this turntable shaft, Frankie gave me some 6003Z bearings, which have an inside diameter of 17mm. I found some 17mm steel rod from McMaster-Carr, but I didn’t need very much, so I asked Chad about making a piece on the lathe. He said it should be easy if we had some stock just a bit larger, and well… Frankie did indeed have something! (Oh, if I used 17mm rod I would have added shaft collars… luckily by machining the part, we won’t need them.)

Frankie gave me a crash course in the metal lathe. (I last use a lathe back in the 1980s, and it was a wood lathe!) I learned how to face off the material, and then he showed me how to narrow it down to size. We got it to a perfect fit for the bearing!

Plastic pulley

I also had some plastic pulleys on hand from when MakerBot sold off all their old Cupcake CNC parts… I knew they’d come in handy someday! We managed to drill out the center on the lathe so it fits tight over the steel shaft. I may need to add a set screw or some locking collars, but it’s a nice tight fit right now.

Parts

Here’s the shaft, bearing, and pulley all properly sized. Once I determine the length of the shaft we’ll put it on the lathe, cut it down, and then get the other side to the right size. I’ll make some pieces that hold the bearings by either laser cutting some material, or 3D printing something, or maybe via the CNC router.

Perfect Fit!

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