Reproduction PP1 Battery

[greensleeves]

I have constructed a reproduction PP1 battery for one of my Roberts RT1's

I'm pleased with the results but am having trouble printing a paper sleeve, just can't seem to get the scaling right !

Wondering how other members achieve this ?

Colin

[Dave Moll]

I must admit that my fairly unsophisticated approach is to use trial and error: having estimated a scaling factor, I print out a trial version and compare its dimensions with those which I am trying to achieve. I then multiply or divide by the ratio accordingly and try again. If it is still not quite right, I tweak the factor a little in the appropriate direction - and so on.

[Herald1360]

That's very neat and in this case it doesn't really matter (it's only a low power battery circuit), but relying on the integrity of wood (or plastic or other compressible material) to maintain the electrical contact between the solder tags and the nut/bolt/battery studs isn't good engineering practice. In a high current application, any heating of the connection would lead to a progressive increase in resistance as the material creeps- potential positive feedback to failure.

[MapperleyTop]

I modified a PP9 by very carefully unrolling the turnover at the bottom a dead battery, removing the original cells and wiring 8 rechargeable AA cells into the case re-using the top with the snap clips for the connections.
This gives 9.6 volts and still looks like the genuine Ever Ready PP9 but it is not a suitable solution if you need to use primary cells unless the bottom can be made removable.
The solution I use for the print scale problem is to include a 100mm reference line away from the wanted part of the printout and measure this when printed. I find drawings done with Microsoft Word always needs to be set to 103% for the printer scaling (The 100mm comes out at 97mm) but every other program is correct at 100%

[Phil G4SPZ]

I use the same technique as Dave. I use plain paper for the drafts, and once I'm convinced the dimensions are bang-on, I print the final version on thicker paper or even photo paper.

[greensleeves]

Thanks for all your replies, much appreciated.

Printing drafts (in eco B&W) is the method I had been using and sometimes only the right size after 4 or 5 tries, I must admit I hadn't thought of printing a scale line but definitely will do next time.

Chris I agree with your comments re. my connection method and if I attempted this in my day job I would deserve to be shot. but as you say in this case the current drawn is low enough to be of no concern.

The attached picture is an attempt at a PP9 in an RIC2, this one came out OK, but haven't printed a top yet.

BTW what method do you use to cut the larger holes in the paper for the terminals?

[Herald1360]

A method I've used with some success for largish round holes in paper etc is to draw the circle then punch multiple holes inside its circumference with one of those multisize leather punch tools.

A small pair of curved nailscissors can also be used if the hole is not too small or if you're careful, a scalpel (#10A blade is good) whilst carefully holding the paper down on a sheet of card like the back of an A4 pad.

[crackle]

Try this file, it should print the right size on A4, check that the PDF viewer is set to NOT print to fit printer margins.
The battery cover design may not be in keeping with the age of the radio.
Mike

[pmmunro]

For cutting holes, larger than the common sizes on rotary punches, in card cutting compasses such as these work quite well. http://www.jakar.co.uk/knives.html. These will cut a variety of materials, even - with care - synthetic rubber up to a few millimetres thickness

Another option is a wad (or wadding) punch, e.g. http://www.smithfrancistools.co.uk/wad.htm but you might have to invest in several sizes.

Herald's point about the compressibility of materials like wood and plastic compromising electrical connections is very valid.
PMM

[Phil G4SPZ]

For cutting holes, I use a 'leather punch set' that contains a dozen punches, from about 2mm up to 12mm, and cost me under a tenner from ebay. I bought them to cut washers out of leather, oddly enough, for my other hobby of restoring vintage blowlamps, but they have proved surprisingly useful for other tasks!

I'm attaching a pic of a replica AD14 large 1.5 volt battery that I recently made; one of the larger punches made a neat job of cutting the hole for the 2-pin socket.

Phil