All around my hat.....

When I made my first Reprap'ed Milestag gun I designed a small PCB to allow the IR sensors to be connected to the gun housing with a curly RJ10 lead. I initially fastened this PCB to the baseball cap by fastening them with tie-wraps. Hardly satisfactory.

I didn't advance on this rather crude method until now. I designed a small box to contain the PCB with mounting tabs to allow it to be fastened to the basball cap with press studs. It has two slots on the top and bottom halves for the PCB to slot into and some tabs for studs to be attached:

Here it is fitted to a cap. Much neater:

More domes

I've almost completed my Mk4 RepRap Milestag gun and I needed to make some sensor domes with mountings that allow me to fasten the sensors to a baseball cap. I started out by maing six more domes from acrylic sheet as detailed here. To do this I modified the dome mount I made some time ago. I needed to modify the dimensions slightly as my domes have an internal diameter slightly larger than the ones I got from Lasertagparts. Here are the two parts:

Rather than potting the PCB and dome in place, my design uses three screws to hold it in place. This allows it to be dismantled for maintenance.

I SPI

I've been doing further assembly on my Milestag UMT PCB. I bought a serially driven 7 segment display module from Sparkfun. This module is the one recommended for use with the Milestag UMT board. It is used to display clip rounds remaining and life. However, I could not get the display to function correctly. I sometimes (about 80% of the time) got a corrupted display. I resorted to removing the PIC MPU from the PCB and wiring it up on a breadboard with just the display and run from a stabilised PSU. I still got the same results:

This should be displaying " 042". I made various attempts to fix it: Rewiring, shielded cable, more filtering caps, shorter sires. Nothing worked. I then noticed that when I picked the display up, it changed. I noted that this module has both SPI and TTL level serial inputs and when I touched the TTL input the display became corrupted. TTL level serial idles at logic 1, so I tied the serial input line high and I haven't seen any corruption since. The module accepts segment level commands. i.e. You can send 4 bytes of data representing the segments in each digit. Obviously the serial input was getting noise and this was being interpreted as a valid display command.

ABSsolutely fabulous

Now that I have my PLA extruder up and running, the acid test for me was the ability to switch between PLA and ABS easily. I swapped the extruders around in about 10 minutes. Most of this time was waiting for the heaters to get hot enough to allow me to remove/insert the filament.

With the ABS extruder in place, the first print I did came out perfectly without any need to re-calibrate. It's a picatinny rail sight mount for my Milestag lasertag gun.




Here it is sprayed up and with a sight mounted on my MK3, RepRap printed gun:







My wife is an avid photographer so I printed her one of kitlaan's lens cap holders.

It was printed with white ABS but I sprayed it black with the same paint I use for my guns. It came out very well.




The quick change extruder mount that I got from wolfgang has allowed me to change extruders without undoing a single bolt, and, more importantly, maintain calibration between changes.

PLA

I've recently been trying to print PLA. A hard, transparent plastic that nophead has used to print parts for me in the past to diffuse light from LEDs.

When I started with ABS, to save time, I bought a pre built wade extruder from Wolfgang and this has served me well. However, I've heard on the grapevine that this design needs to be thoroughly cleaned with acetone before it can be used for PLA if it has previously printed ABS.

Being lazy I simply ordered a second extruder. Wolfgang's parts are top notch. I have a lathe and could make extruder parts myself but for the price he charges I can't be bothered.

I initially tried printing a 10x10x10mm cube. This came out OK but sagged in the middle. The reason for this was that I had created the gcode previously for a 0.4mm layer height, and my new extruder has a 0.35mm nozzle.



I re-skeinforged(?) the STL with a layer height of 0.25 (~=0.35 * 0.8) and printed some LED diffusers that I had designed. They all warped at the corners:




The temperature I used for this print were:
Extruder = 220C
Bed = 55C

My PLA is 4043D and has a lower melting point so I reduced these to
Extruder = 200C
Bed = 50C

My wife makes greetings cards as a hobby. She has previously bought kits where a pre-cut card is supplied with paper to layer behind the card. They look quite nice:






She asked me if I could print a template to allow her to cut the card herself. To do this, I photographed the card, then used GIMP to convert the wine glass shape to be pure black.

I then imported this image into AlgoLab Photo Vector and converted the image to a DXF file.

I then imported this to CreoElements and from this I was able to scale the design to match her requirements and print a template she can use for cutting:

Dome Goal

I got my homemade Milestag UMT board working this week. This has forced me to think about acrylic domes again. I bought 4 pairs of acrylic domes from LasertagParts whilst in the USA last year, but now I've used them all.

As mentioned previously my neighbour made me some dome molds from a weird slate/resin composite. These are just right but I needed to create a hole in a sheet of wood to allow me to force the soft acrylic sheet around the mold.

The problem I had was that the outer diameter of the mold is 36mm and the nearest hole saw I have is 44mm. A 44mm hole is too big to force the soft acrylic sheet around the bottom of the mold.

To solve this I drilled a 44mm hole in a sheet of 6mm MDF and then printed a bush to reduce the internal diameter of this hole. Here is the CAD:



And the printed part:



It has a flange at the bottom to prevent it from being pushed out of the MDF:



Top down you can see the diameter reduction:






I cut a second sheet of MDF to provide a flat surface to place the mold on. Here it is forcing 2mm acrylic, heated at gas mark 9 for 4 minutes, over the mold:



And with the forcing plate removed:




I'd previously sprayed the mold with PTFE to aid removal:



The molds have a threaded hole underneath. This allowed me to hold the mold in the vice whilst I gently prised the acrylic free. As this mold has a draft angle it came off quite easily:






The remaining problem was now the removal of the dome from the sheet. To do this I used my 44mm hole cutter on two 15cm square pieces of wood which I then placed on top of each other with the holes aligned. With the hole cutter in my drill press this prevents any downward force being applied to the dome, which might crack it. I applied very little force whilst cutting and I let the acrylic soften from the tool friction as this seemed to prevent cracking. I destroyed one dome by pressing too hard:



Here are sheet and dome after separation:



I cleaned the rough edges on my belt sander:



Here it is after grinding:




Total time is about 15 minutes, 4 of which is waiting for the acrylic to soften.

Can I repeat it? Of course!

These are now available at Tagbits.

DIY Milestag UMT board

I managed to get some ISD1790SY sound playback ICs for my homebrew Milestag UMT PCBs.
I've spent the last couple of days populating the PCB and programming the sound chip.


This board will soon be available at Tagbits.co.uk



Whilst doing this my RepRap has been idle, so I printed this castle from Thingiverse just because I can.

It came out very well:



A pre-built version of this board is now available at Tagbits