This sucks

I tried my homemade vacforming machine last night with disappointing levels of success.

I drilled a 32mm hole in the side of the box and attached my DeWalt shop vacuum.



I then clamped a sheet of 4mm acrylic into the holding frame



and placed an inverted ceramic pot on the vac bed as a test pattern:




And placed the sheet in the oven at gas mark 8 for 10mins. I was hoping to observe the sheet and, when it started to sag, remove it. The problem I had was that the sheet was too thick and didn't get hot enough before the MDF mount I was using started to char.

As the kitchen filled with the smell of cooking MDF I decided to give it a try anyway:



The thick, partially heated sheet was sucked down by the bed but was not hot enough to be pulled down onto the sides of the pattern. As a result I got this:




I also noted that the MDF mount had shrunk and was no longer gripping the sheet.

Next time I am going to:

1. Use thinner 2mm acrylic.
2. Make a metal mounting frame which will neither shrink nor smell.
3. Drill some more holes in the bed.

Going to be a while before attempt 2, my RepRap bits turned up today ;o)

Killing time

Whilst I am waiting for some parts to arrive for my RepRap, I found myself with an hour spare and decided to try making a vac forming machine.

It has a small footprint and is made from 12mm MDF. The clamping frame to hold the plastic sheet is 6mm MDF held together with 8xM4 bolts.

I haven't had chance to try it yet as I don't have any plastic sheet. We used to have a vac form department at work years ago but they outsourced it, so no free test sheets from there.

I intend to use it to make the domes for the Milestag sensors from acrylic sheet used on greenhouses.

Here are some pics:



Here is a side on view showing the clamping plate:

Finishing Touches

I completed the sensor head mounts this weekend. As I showed here I fastened hook velcro to the sensors. I attempted to sew some 50mm loop velcro to a camo hat I bought from Blue Moon Guns of York for £1.99. But after 30mins of inept stiching my wife caught me and with a Bradford 'give it 'ere' she managed perfection in 15 minutes what took me 30 to ruin:



Here's the complete system. I still need to cover the connecting PCBs on the hat and wire from the gun but I'll make some enclosures to do that when I've got my RepRap built:

Sensor testing

Today I tested my homemade sensor PCBs. I had made a mistake with the connecting curly cable in that the leads were reversed. I fixed this by simply reversing the connection order at the gun end PCB.

Here is a video of the test showing shot detection and hit LED activity@

The Last Parts

I completed the sensor connection PCB this weekend. I need to cover it with heatshrink to protect it but I need to test the full system before I can do that. Here it is connected to the gun complete with curly cable leading to the sensors:



Here is the complete assembly:



To test the system I need to construct another Milestag PCB. As mentioned before I bought 4 of these so I used my PCB jig to help me populate the boards:



This device holds multiple PCBs, allowing me to place components. When populated, a foam covered board is placed over the components and clamped in place. The jig then rotates to allow the components to be soldered whilst the foam prevents them from falling out:



Here are the completed boards:


I intend wire IR LEDs and trigger switches to the boards so I do a quick test. Before I can do anything with the remaining boards though I need some more gun housings, and for that I need my own RepRap......

Completed Sensors

Today I attached the two sensor housings to the new RJ10 PCB I made. Here is a detail of the junction PCB showing the two sensor leads attached with tie wrap strain relief:



Here is the assembly showing the two sensors attached:



I decided to attach the sensors to clothing with velcro. This allows me to flexibly configure the sensor positioning as required. I bought some 50mm velcro and stamped holes in it to allow me access to the sensor screws.



I've also designed a small PCB to hang from the gun to allow me to connect a RJ10 curly lead to the sensors:



I just need to make this and the gun is complete.

Sensor Connections

I've been trying to find the best way to mount the Milestag sensors to a headband and connect them to the gun.

I've decided that I'm going to mount a loop strip of velcro on a baseball cap or elastic headband and attach hook velcro to the back of the sensors. This gives me the most flexibility for sensor placement.

I've been unhappy with the way the sensors connect. They are traditionally soldered in parallel with a connection to the gun. I had concerns about the reliability of this as soldered connections break when flexed.

I decided to compromise and designed a PCB to connect two sensors to a RJ10 socket. Why RJ10 when others are using RJ11? Because RJ10 curly leads are available for less than 1UKP and these are ideal to connect the sensors to the gun.

Here is the headband sensor schematic:




It's very simple. I intend to place it in a small, velcro mounted box.


Here is a set of 8 PCBs ready for cutting and drilling: