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.

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.

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.