Small Batch Prototyping for 3D Printed Parts

3D printing enables rapid prototyping but lacks production-ready qualities such as smooth surfaces, temperature resistance and food safety. These attributes however can easily be added by combining 3D printing with casting silicone and urethane plastic for small batch production runs.

When selecting mold making materials for 3D printed parts, it is important to be clear about the intended material for mold and cast .

Some points to consider are:

  • Silicone such as Dragon Skin can be extremely difficult to stick to surfaces, except silicone itself. 
  • Urethane plastic such as Smooth Cast 310  is exotherm. This means it gets hot while it’s hardening.
  • Some 3D printing filaments are more temperature-sensitive than others.
  • Some 3D printing filaments are easier to post-process than others.

Having this in mind, the proper materials can be chosen basing on the desired material of the positive.

For PLA the following works nicely:

Final Positive Mold Seperate Seal Release
Urethane Plastic Silicone Monster Clay XTC-3D Ease Release 200 
Silicone Urethane Plastic Sculptex oil based clay  XTC-3D Universal Mold Release

Please note that urethane plastic is exotherm. This requires a non-wax based clay to define the two-part mold. Otherwise the surface in contact with the clay will be full of air bubbles due to the melting wax-based clay.

Applying multiple coats of XTC-3D with sanding (400…1500) in between is highly recommended.

Degasing the silicone and urethane before pouring significantly reduces trapped air bubbles and increases the chance of success.

Other useful items:

 

Amount Description Link
1 Medicine Cups to mix XTC-3D Amazon
1 Gloves Amazon
1 Mixing Cups for silicone and urethane plastic Amazon
1 Craft Sticks Amazon
1 Safety Glasses Amazon
1 Vacuum Chamber for degasing Amazon
1 Vacuum Pump for degasing Amazon
1 Clay Sculpting Tools Amazon
1 Hot Glue Gun Amazon
1 Durometer Amazon

 

PhoDrone 1 – Long Flight Time (1h), Aerial Photography Quad, 770mm 17inch

RC Groups

Centerboard

The center board has been glued with HK CA glue (HC-50-175). A small frame with screws through the four beam holder holes kept the sandwich layers aligned.
Note: Better do large areas with this glue outside as it generates a fume that is biting in the eyes. I assume it’s not healthy as well 🙂
Using nylon spacers and screws, the top and bottom sandwich were assembled.

Beams

The beams were machined with a 1/32″ flat end mill and cut to length in the last run.
M3 nylon screws lock the beams and act as breaking point when crashing.

Electronics

To attach the electronics to the center board, I chose two different approaches. Components which will not be used in every flight have been attached using Velcro. The other components were glued directly to capton tape I put to the center board. The ESCs were wrapped in capton tape to prevent short circuits. I hope the heat dissipation is reasonably low with the 30A ESCs.

Sandwich Glue

  • HK CA glue (HC-50-175)
  • Loctite Vinyl, Fabric & Plastic Flexible Adhesive
  • HK 30min Slow Cure Epoxy
  • 3M General Purpose 45 Spray Adhesive

Sandwich Bend Test

  • 100x10mm x 1mm CFK, 3mm Fill, 1mm CFK

CFK 1mm, 3k plain weave carbon, orientation parallel (0°/90°) to centerline
Fill +/-45°

Bend test showed best adhesion and no separation up to 6kg for HK CA glue (HC-50-175). All other separated well below this (usually at around 3-4kg). However glueing is tricky for large areas such as the center board.

Endurance

During the first flights, the flight time was reasonably high at a bit over one hour with 1555 props.

Crashing

Arms folded away during the first crash (I’d love to call it unplanned rapid decent though :-)) and the M3 nylon screws broke as planned, preventing damages to the rest of the drone.

Flight Time

With this setup, flight times above one hour have been achieved, even including the 180g 3-axis gimbal and GoPro.

In the diagram below various test flights for a 15″ 5.5 and 17″ 6.0 propeller were aggregated to show the effect the prop choice has on flight time.

Bill of Material

Amount Description Link
6
rctimer 5010 360kv
NA
3
Multistar Lipo Pack XT90
Amazon
4
Flyduino KISS
Amazon
4
1760 Folding Props
Ebay
1
Flight Controller and Power Module
Hobbyking
1
GPS witd Compass
Amazon
1
Receiver
Amazon
1
Damping Balls
NA
1
Folding GPS Antenna Base/Black
Ebay
1
Lipo Voltage Checker
Amazon
1
FPV Camera
Amazon
1
VTX
Amazon
1
Telemetry Radio
Amazon
1
Skyfpv Video Switch
NA
1
OSD
Amazon
2
LC Filter
Amazon
1
FPV 3 Axis CNC Metal Brushless Gimbal With Controller For DJI Phantom GoPro 3 4
Banggood
1
GOPRO
Amazon
1
pigtail
Amazon
1
Silicone Wire
Amazon
1
FPV Antenna
Amazon
1
Transmitter
Amazon
1
Goggles
Amazon
2
Goggle Battery
Amazon

 

LiPo Battery Value and Capacity

Flight time depends mainly on the drone weight. In order to get flight times above 1 hour on a single charge (as shown here), the weight has to be minimized. Typically the most dominant weight hereby is the battery.

  • Value can be calculated by Capacity / Price)
  • Density can be calculated by Capacity / Weight

The diagram above is sorted left to right by Ranking = Cap /Weight * Cap /Price

Raspberry Pi 3B+ Enclosure

Thingiverse

Cloud Server

The above setup is used for a Nextcloud setup. The installation script can be found on github.

Backup Server

The above setup is used for a backup server which regularly backs up all Raspberry Pis in a rolling backup un a daily and monthly basis. The installation script can be found on github.

Bill of Material

Amount Description Link
1
1TB HDD
Amazon
1
Hard Drive Adapter
Amazon
1
Raspberry Pi 3
Amazon
1
Memory Card
Amazon
1
Power supply
Amazon
1
Y-Cable Extension
Amazon
1
#4×1/2 Pin Head Phillips Zinc Screws
HomeDepot
1
#4×3/8 Pin Head Phillips Zinc Screws
HomeDepot

 

 

Parabola Tool

This tool will help you to design a parabolic trough and give you the information you will need to build a simple one on your own.
Download ParabolaTool_v190

ParabolaTool v1.9:

Compiled without source code guarding. Exe will start correctly on machines without additional DLLs.

ParabolaTool v1.8:

Export functions are available now.

ParabolaTool v1.7:

By ” Print 1:1 ” functionality you are now able to plot the parabola at its real size and to use it as a template for cutting the beams or to cut a solid beam.

Reflector Width:

You can enter the width of the reflector here. (Real/plain width of the mirror)

Supporting Beams:

To stabilize the parabolic shape, it is useful to place some supporting beams along the curve. The middle is always fixed to x=0 and the outer one to the highest point of the reflector.

Focal Point Height:

Parabola Tool calculates the curve by selecting the damping of the parabola. The height of the focal point is the most important variable you have to select to get good results. The higher this value is, the lower are the shadowing effects. Keep in mind that this will also increase the vulnerability to inaccuracy. A good starting point should be 30cm-1m for 1m x 2m base frames and 3/4 ” absorbers.

Parabola Width:

Is the shortest distance between both ends of the reflector. You can use this as a starting point for the width of the base frame.

Parabolic Trough

Currently I’m building a low cost 1000mm x 2000mm parabolic trough for experimental purposes, which is split into four 1000mm x 500mm segments. Polished stainless steel is used as reflector material.

The tool used to calculate the support structure can be found here.

Up to now there are no building instructions here, but I will update the site from time to time.
If you are interested in more technical drawings please write a mail. If there are enough requests, I will upload further material.

Update 20110511:
A technical drawing (1:10) is now available: parabolictrough_technical_drawing

Update 20110508:
Today I did a series of tests, which should view the capability of the new mirror mounting.

Here are the results:
To get 700ml water to boiling temperature, one of the four modules (500mm x 918mm) took 7min.
If the absorber is preheated, the water already starts boiling in less than 5min.

The next test setup was filled with cooking oil to determine the maximum temperature of the module.
The highest temperature was 138°C after 4-5min with the poor, quickly black lacquered aluminium tube.

In my opinion it’s not that bad and I will continue to optimize the absorber.

Further steps are:

  • Try to get a ” cheap ” vacuum absorber tube. (DONE)
  • Try different materials for the tube.
  • Aluminium has good thermal conductivity (235W/(m·K)) but it is cooled down too fast by the fluid inside the tube and shadowing effects.
  • In my opinion it woud be better if the tube acts as a capacity and could store the heat, which could then be transmitted more steadily.