Saturday, 23 April 2011

More Sensor Housing

I'm still trying to find a way of making sensor domes from acrylic sheet. After my last attempt destroyed an A4 sheet trying to make just one dome, I made an A6 clamp so I can make 4 domes per A4 sheet:

I still need to make a mold.

In the meantime, I discovered these:

On the left is a single seedling propagator that can be bought at gardening centres. They are not as hard as acrylic, but compared with the milestag dome on the RHS they are just about the right size. The flange they have at the bottom also makes for easy mounting.

They may be of use to someone....

Friday, 22 April 2011

DIY Milestag UMT boards

Some time ago I decided to design my own version uf the Milestag UMT board but using components easily sourced in the UK.

I used KiKad to re-engineer the UMT schematic:

And designed a PCB using surface mount components. The PIC micro is through hole so it can be taken out for re-programming. I could have put a programming header on the board but I decided not to as it would have made the board bigger:

I've sent the gerber files to Itead Studio for manufacturing. They charge only $28 + $5 delivery for 10 boards which must be the cheapest service on the planet.

I have no idea what quality they will be, but for a $32 punt it's got to be worth a try.

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

Sunday, 10 April 2011

Dome, on the range

Whilst awaiting my RepRap extruder to be delivered from Germany I've re-visited vac forming.

I made a new clamping frame from 1.2mm steel, and used M4 dolts + wingnuts to fasten it:

I also drilled some more holes in the bed of my vac former, and attached sealant gasket gasket to the bed to improve the seal:

I made some molds by casting plaster of paris into the acrylic domes I got from Milestag:

Here's the molds after they had set:

Unfortunately, this was no more successful with 2mm acrylic than it was with 4mm. The problem is that the acrylic is not sufficiently flexible to be sucked completely into shape by the vacuum. The plastic failed to form around the vertical edges of the mold.

So I decided to try another approach. I constructed this phallic object:

The idea being that I push the frame down around the mold, I should be able to exert more pressure than the vacuum.

Here's the result:

And after cutting:

Which is almost what I want. To improve I need to:

1. Change the mold so that the acrylic can't fold underneath the mold. I'm thinking of a wooden pole with a rounded end.

2. Make the frame smaller. I used an A4 frame this time, but to make just one dome it's a bit too big.

3. Cut the dome out with a power saw. I used a hacksaw and cracked it.