Saturday, 22 March 2014

Chinese Conundrum

I've been buying IS1790 playback chips from AliExpress. These are about 1/3rd the price of the 'official' chips from DigiKey. Lately though I have been experiencing failures of around 50% of the chips that have been delivered.

The supplied chips are obviously copies, and when they work they work 100% of the original. However, the only way to check if they function or not is to solder a 28 pin SOIC down and hope for the best. A bit inconvenient if it proves faulty.

So to allow me to check the chips before sticking them down I came up with this:

It's a Tagbits UMT board wired into a 28 pin SOIC ZIF (Zero Insertion Force) socket. This lets me plug in a chip and test it without requiring me to solder it to a PCB.

Monday, 17 March 2014

Punch Drunk

I started work on my CNC router over the weekend. It's a moving bed design with an aluminium frame fitted to a 25mm base of MDF.
To get the holes for mounting the linear rails and extrusion I printed a huge 1500x600mm 1:1 print of the CAD drawing of the base onto vellum. This was then stuck to the MDF with spray mount.

I used my optical centre punch to get the holes centred. These are fantastic. Here is a 1:1 print of the mounting holes at the end of one on the linear rails. The holes are M4.

And looking through the centre punch:

It's easy to see how accurately the holes can be positioned when using a tool like this. The one I use is from Dankroy Ltd.

Here is the base made up with a piece of MDF used for the moving bed. Once I'm happy with the layout I'm going to drill some 15mm aluminium plate for the bed itself.

Saturday, 8 March 2014

Ivor Biggun

Now I've acquired an A0 printer, I've been able to start on my CNC router. It's a moving bed design as I believe this kind is better suited to milling metals. It's a bit big at around 1500mm x 600mm and I need to drill some accurately positioned holes.

So I've printed a 1:1 scale diagram of the SBR20 linear rails and the machine bed so I can start drilling some holes.

I got several different kinds of paper when I got the printer. I'm using HP Vellum paper for the engineering prints as this is a dimensionally stable paper which is translucent. This will allow me to overlay it onto the parts I wish to drill and align the outline of the part with the real thing.

Here is the print for the linear rails:

The holes each have a cross-hair which I will use in conjunction with my optical centre punch to get precise hole positioning.