Monday, June 13, 2011

Why decorate the back?

It seems odd to put decorative details on the back of a printed part.

The bezel has patterns all over it. While I do think it looks cool that way, there was a more practical reason.

Large, flat parts printed on my machine tend to weld themselves to the support structure in at least a couple of spots. This results in a long, frustrating cleanup process, and usually several gouges in the part. I found that adding 1/32" x 45° v-grooves in the bottom, and chamfers around the edges, makes the process easier. If it does stick, it's usually only between one pair of grooves, and is more easily dealt with.

I've also discovered that the support material separates more easily during marathon printing sessions. The only explanation I have is the heat. I will take more care in the future to heat my printing platform before printing large parts.

Friday, June 10, 2011

Fastener Improvement

My first set of fasteners had a high failure rate. About half had their head pop off while either removing them from the support material, or with only mild torque while using them. I had been using standard print settings, and found that they worked better when printed at highest fill and  print quality. But many still sheared off more easily than I found acceptable. I've found a solution.

 The gray bolts are the original style; the gold are new and improved. Notice that the gold countersink head has a continuous slope, where the gray one is disjointed.  On the button head bolts, the gold has an undercut at the head interface, while the gray head is flat and just "stuck on top".
Here's why this makes a difference. In the sketch labeled "flat", you can see what the printer does at the transition from head to shaft. It makes an outline around the head, then fills it solid. The shaft outline will then be laid donw in the middle of the fill surface, and proceed to print the rest of the bolt. There is not much structure, poor adhesion, between the layers.

On the other hand, when the shaft of the undercut bolt starts to print, three outlines are printed, with two fill areas. This makes the print have more structure, and better adhesion. When I tried breaking a "flat" bolt, the head popped off easily. When I tried breaking an undercut bolt, it was considerably more difficult, and it snapped where the threads start, rather than at the head. In the photo above, you can see the sheared head of a "flat" bolt, and a nice set of "undercut" bolts. Looking closely, you can see the slight groove on the head, where the undercut is printed.

And thank you, TeamTeamUSA, for your suggestion to print them at a 10° angle. As you said, this causes the printer to "outline" the entire skin of the bolts, covering all the fill. Perfect! :)

Wednesday, June 8, 2011

Ideal Harmonic Transformer Evolution

Discarded Parts

First print of complete butterfly dome

Here it is, right off the printer table. It's filled with support material, a necessary evil for my machine.

After some patient cleanup work, here's the finished dome. Happy! :)

Not a great photo, but here it is on the partially-assembled Ideal Harmonic Transformer.

Ideal Harmonic Transformer prototypes

These are my first two working prototypes for the Ideal Harmonic Transformer. I learned a lot from them, including how to make a fit with friction, snug but sliding, and loose. Also played with techniques for making parts that separate more easily from the print base structure. On the Up!, it's the same as the print material. It's very disappointing to spend 30 min to separate an intricate part before getting to use it, and having a marred surface for all of your care.

These prototypes use #6 machine screws. I had reasoned that they are already designed, readily available, and quite strong, so no need to reinvent. However, I could not find any off-the-shelf hardware that let me do what I wanted with the arm pin and yoke pin. After spending too much time in front of the fasteners at Lowes and Home Depot, I decided maybe it was possible to make plastic screws after all.

Once I got the hang of it, I converted all of the screws to home-printed rather than OTS. This let me eliminate all the nuts, by "tapping" the holes, which made the whole design cleaner. It also let me decorate the heads to go with the overall look, not to mention saving me the frustration of sorting through the store's wares.

One limitation, at least with my printer, is that threads must be printed vertically in order to work. The down side is that a print is basically a bunch of laminated heat-welded layers. I think this gives a certain grain to the finished material, and is contributing to the failures I'm experiencing. Some of my bolts snap off at the head right as I'm taking them off of the machine. Others turn out fairly strong. Setting the Up! print settings to fill=solid and quality=fine helps, but does not eliminate, this problem.

Introducing the Ideal Harmonic Transformer

I needed a simple project to use while getting more familiar with Alibre. My husband suggested I make a simple sin-cosine machine. We were inspired by a documentary of a mechanical fire control computer for a ship that we had recently seen posted on Boing-Boing. Simple. I keep thinking about that word. But all designers know that simple is not easy. I will eventually post more of the intermediate steps of this design's evolution.

First, I made one that I thought would work. It sort of did, but lead to a series of improvements until it worked nicely. Then I got thinking how pretty that bracket was, and how cool this simple design could look if I added a few aesthetic features. Well, here it is. The dome is printing right now. I have the bezel assembled, with the central arm in place. There may be a few minor issues that I'll need to address, but I'm ready to call this done!

I don't think it's simple any more, but I like it. :)

Parts for making Ideal Harmonic Transformer

What is it?
Ideal Harmonic Transformer
AKA Analog Sine/Cosine Calculating Machine
It is a thing to hold, enjoy turning the crank, and look at. If you can't find your calculator, and need to know the sine or cosine of an angle real quick, you can dial in the angle and read off of the Scotch Yokes. It also works in reverse.

Assembly Instructions:
Assembly instructions are here.
Print Plates:
Here is a screenshot of each stl file for 3d-printing my Ideal Harmonic Transformer.
Don't have a printer? You can order the parts from here.

Ideal Harmonic Transformer Assembly Instructions

Get the stl model files Here
You can order the parts from here, in a variety of materials.
Here are pictures of the part files, with their names. 

Step 1

You will need two of these. Check the fit of the Yoke T and Yoke Extend, and trim if necessary to achieve a tight fit and a straight part. Separate the parts, put glue on both, and fit them back together. Wipe off any excess glue, and allow to dry thoroughly, possibly overnight, depending on the glue. I used "household cement". Despite the tight fit of the parts, gluing really is necessary. There's quite a bit of bending load on it. Not gluing will allow too much flex, and it really needs to be stiff.

Step 2

Look on the back of bezels 1 and 2, and find the index marks. Piece them together, as shown in the figure, then turn the grouping right-side-up.

Step 3

Slip the bezel ring screws (csink head) through the bezel ring, and loosely thread into the support base. Make sure the notch in the support base is oriented as shown in the figure.

Step 4

Piece together and slip Dome Capture Segments between the Support Base and Bezel Ring, as shown. The Support Base should fit into notches in the Dome Capture. Do not tighten the screws yet.

Step 5

Carefully turn the assembly over, and slip the Bezel sections under the Bezel Ring. The Bezel Ring will lock into the groove in the Bezel segments. Tighten all three screws until snug.

Step 6

These are the voyages of...
Fit the Mount Extensions onto the Support Base. Lock them together using the Support Bushings, as shown. Both Hi bushings go on one Extension, and Lo's on the other. Either way is fine. Make sure to use the correct length screw, and slip an angle roller under each screw. Slip a Scale Clip into place on each before tightening the screws. Leave the screws out or very loose on one side for now.

Step 7

Push Knob Bushing all the way into the knob until seated. A very small amount of the bushing should show through the bottom.

Pus the Arm Pin all the way into the Arm. Push the Arm Bushing onto the part of the Arm Pin that extends through the bottom. The Arm Bushing should contact the bottom of the Arm.

Step 8

Insert the Yoke Pin into the Arm until flush. Insert the Arm Pin into the hole in the center of the support base. Push the Gear Blank onto the Arm Pin, then secure into place with the Key.

Step 9

Assemble Yokes, et all onto the Yoke Pin, as shown in the picture. The Angle Rollers create a v-track for the inside of the Scotch Yokes. Tighten the Acorn Nut.

Step 10

Slide the Zero Scales onto the Yoke arms, and secure each with a Zero screw. Lay the lower Yoke into the Low Bushings, and secure with Angle Rollers and Low Bushing Screws. The Rollers and Bushings create a v-track for the Yoke to slide in. Secure the higher Yoke in the same manner, on the High Bushings.

Step 11

Align the Dome notches with the assembly, slip it into the Dome Capture Ring, and rotate it clockwise until it stops. I found it helpful to line up the screw holes first, then look at the notch that lets it fit over the support base/mount extension frame. Then clock it to the other edge of that notch, carefully push the dome edge into the slot, and clock it back until the holes line up again. I found it to be tricky, and might try wetting the edge lightly with water next time, to slightly lub it. Insert the Dome Screw to secure the dome in place.

All Done! Now wasn't that easy? No? Well, then doesn't it look cool?

Ideal Harmonic Transformer Extents

Here it is, with the angle at zero, 90, 180, and 270°. The yokes move in and out, letting you read values of Sin and Cosine for each angle. The teeth around the bevel edge are 1° apart from peak to vally, ie there are 180 teeth. I would have liked to post this as an animation, but my version of Alibre does not have that feature.

We're thinking this might be helpful when the kids need to learn Trig. We're also planning to paint it up and hang it on the wall.