Category Archives: Engineering

FormFutura HDglass

A project I’m working on required some clear pieces, so I purchased some HDglass from FormFutura as I heard good things about the plastic’s transparency. This is a PETG plastic so use appropriate guidelines when printing it.

The recommended printing temperature range is 195-225 deg C. The box says nothing about bed temperature or fan setting, so I modified my PLA setting to adjust the temperature and went on printing.

First part I printed at 235 deg C. The detail was great, but the part felt very fragile. The inter-layer bonding was so weak that I could break apart the 3d printed part in my hands.

Thinking I went too high with the temp,  I next tried 205 degC. Same fragility. Part would disintegrate in my hands with very little force.

It turns out that PETG doesn’t like a fan (unlike PLA) so I proceeded to make another print at 225 deg C (the upper end of the recommended temp range) with a 10% fan setting however there was no noticeable difference in print

Next I decided to go much higher in temp and printed the part at 255 deg C, and the results were impressive. The clarity and transparency is much better then at the lower temperatures, and the part is now strong. It will not delaminate when it’s bent.

DIY optical lenses

For my AF Assist tool, I decided to make my own optical lenses to focus the light from the IR LED. I experimented with a few lenses I had kicking around (from other flash systems that I took apart) and looked online to see what I could purchase. The lenses I had kicking around did the trick in giving me a direction to follow, but were not prctical for several reasons. Sourcing is a big issue (these are custom lenses) and second they don’t quite fit my application constraints; too big, or need to be too far away from the light source.

After a brief search online (ebay, aliexpress, etc) I decided that I didn’t want to wait a month for some lens that was chosen just on a photo and scant technical info.  It’s too much trial an error for my taste. I’ve always been intimidated by optics. It felt like this black art/science that I knew next to nothing about. Having done some reading, I now feel a little more comfortable attempting to make my own optics.
Besides, learning something new is always great.

I’m approaching this from a couple different angles. 3d printing of a master (and then resin cast using optically clear resin) as well as cnc machining a mold and try to form some acrylic plastic sheet into the shape i want. I don’t quite know which will give better results which is why I’ll take both paths.


DIY Plastic lenses
– 3D Printing and CNCing Weird Freeform Lenses
– Bike pump Vacuum pump




A quick CAD sketch for a mold, and then a 3d print resulted in a


What tool to use for CNC mill or router?

Excellent three part series of articles talking about the right tools required along with many side articles providing more details.




VP multi-rotor: development testing

I figured I should put together a list of what the development tests I want to do before setting out to actually build a prototype of a VP quad. The temptation is high to just build something, but I know I will learn a lot more by doing some testing ahead of time in a controlled environment.

Would like to build 2 test stands. One based on Trex450 heli parts and another based on Trex500 heli parts. Both are available in belt drive or torque tube, both are available from HobbyKing and hence are quite inexpensive.
The rigs need to be modular enough to test both belt and torque tube designs.

What I would like to test:

– How much power can be handeled by either torque tube and belt drive

– Failure mechanism at high power. (what fails first?)

– How much does the boom flex (carbon vs aluminum) as this may impact the effectiveness of the torque tube?

– Ability to test out different blades (length, profiles) at different angles of attack, and record thrust vs RPM vs angle of attack.


What I will need:

– some sort of I/O card for data acquisition so I can record in real time things like RPM, blade angle, voltage, current, thrust, displacement/bending of booms,… (add more)
Preferably a USB solution so I can use a laptop to do the data recording on Labview?

– a test rig that can accommodate the data acquisition parameters. Also needs to be  inside a lexan or mesh enclosure so failure testing doesn’t hurt me.


Rig Design:

I will start with a heli body, since i will be using all the gearing inside the heli body and stick a motor in side
Figure out the gearing first.

Casting aluminum

Interesting thread on Casting Strength found here.

Now, if you want to experiment with casting an alloy of ths type, here’s how to get out cheap;-) Find somebody who does punch work and ask them to save the slugs for you. I have a 5 gal bucket of 3003 slugs that are 3/8×3/4″ ovals, punched out at a buddy’s shop. It is the perfect size for the crucible, doesn’t require breaking up, melts really fast, and being a weldable alloy, it flows and pours like you wish everything would.

Once cast, it machines just like 3003; soft, gummy, and gooey. It makes very solid castings using the lost foam process in dry sand. Much better than scrap waterpump housings and old VW pistons. That may be the best alloy for you to use, actually. It’s soft enough to avoid cracking and, as we all know is just rediculously easy to weld. It’s not as strong as 6061, but you’ll have a really tough time making a set of castings up that will mate well under load with 6061 T6 without the casting being as big as the engine block.


I worked for a few years with two guys who built custom racing bike frames as a side business. Short of going to graphite composite, their preference was alloy steel tube that was silver sodlered at the joints. They used reinforcement at joints by using two tube sizes that nested and put on a tube seat of the larger tube and then inserted in the frame member to get a double wall at structural joints. They also used swaged tube that was thinner wall at midspan and heavier wall at the tube joints. The swaged tube was strictly special order only.

the reason for using silver solder was to avoid destroying the wrought grain structure at the joint. TIG welding would change the grain structure from wrought to cast structure where the metal melted, making a much weaker joint.

From experience with truck frames in the 70’s, aluminum is no substitute for steel. Aluminum truck frames were made to reduce weight and increase payload in log and flatbed trucks. However, the aluminum frames inevitably cracked and had to have reinforcing plates installed, which made the frame heavier than the steel version and still prone to cracking. It is also much less stiff than steel by a factor of at least 3.

Last thing, 6061-T6 is cast, wrought, solution annealed and then precipitation hardened. The grain structure is not quite cast, but some of the wrought structure goes away during the solution anneal. Casting 6061-T6 with a precipitation hardening process won’t be quite as strong as the T6 processing, but will be better than as-cast and will machine better. There is another type of processing, T8, which is cast, wrough, solution annealed, wrought again and then precipitation hardened which comes out stronger and harder than T6, but no stiffer.

Laser Diffraction pattern research

Found a few sites/companies that manufacture difracion gratings. I should contact them and get some samples.

3d printed bevel gear-strength tests

Looking to make some 90deg gear trains, and wanted to know how much force 3d printed heard could resist.
After printing some gears, a holding block and some shafts, the testing began.

First few tries, the shaft to gear attachment kept falling. It was failing around 44 in.lbs of torque yet the gear teeth remained intact.

After redesigning the shaft to gear attachment, I was able to break some teeth at around 57 in.lbs of torque.