## Dimension Number Crunching

Numbers for rear PCB access panel.

The number crunching to work out the dimensions of the MDF woodwork is coming to an end!  Thank goodness for that, it’s been mind bogglingly difficult and a long job.  You’d think it would be straightforward to work out but no.  I’m using the free, open-source software Inkpad.  It’s great, especially considering it is free.  But I can find no way of altering the origin of the measurements so x=0 and y=0 start at the bottom left-hand corner of the drawing, not of the object to be measured.  Also complicating things is that Inkpad measures to the edge of an object, not its centre.  I have to measure the distances of centres from the edges of the piece and transfer them to another drawing which shows the cutting details for getting the MDF laser cut.

MDF Laser cutting information: Front panel cutting dimensions.

So to find the centre distance of a hole from the edge of a piece of MDF I have to perform this simple calculation:

Centre point = (number for left edge of object) – (number for left edge of MDF) + (1/2 width of object) => (number for left edge of object) + (number for left edge of board on cutting drawing) – (1/2 width of object)

Bear in mind that the x, y, width and height numbers are all next to each other and x and y are especially easy to get mixed up after doing a dozen or so numbers.  It’s also easy for me to add half the width instead of subtracting half the width.

I have some decisions to make before finishing this part of the job.  The printed circuit board is attached to its access panel so it can be easily removed for service etc.  But that means adding connectors to connect the board to the outputs and inputs otherwise servicing and testing would be problematic.  I want to make this easy to work on by someone other than me, not make their lives difficult.  Everything goes wrong at some point, I need to plan for that so for example, changing blown output transistors is possible.  Once I have decided on which connections to use, I will know the size hole they will need and how far apart they can be and then use that information to add to the drawings.