Ed, a long time ago I did a little home etching of copper clad circuit boards using resist and ferric chloride with very variable results. I would suggest that trying to do coach sides this way is unlikely to be successful, especially using ironed on photocopy toner. I know that some have advocated this method, but I've only seen it used for small components.

I'd suggest having a look at the Worsley Works web site. They do a large number of etched coach sides in a variety of scales, and will scale up or down as necessary to 7mm, so if you find one in 4mm scale, they can do it for you in 7mm. If you already have the sides drawn, Worsley may be able to work them up and produce the sides for you. This way you know you are getting something that will work.

I have produced etched parts in 16mm scale doing the artwork myself and then having it commercially etched. I have found that the thickness of metal depends on the degree of detail you want. So for example, you cannot etch a hole for say a handrail that is smaller in diameter than the thickness of the brass. Similarly things like nameplates have to be etched onto thinner material in order to keep the sharp edges of the lettering. Most of the etching was done for me by PPD – they have a website which has guidance on how to design and draw for etching.

So, my advice would be to have a commercial company do the etching of your design. They will look at your artwork and decide the best thickness to use.

Edited By Jonathan Mead on 18/02/2016 18:16:37

I have found the laser transfer process to be rather hit and miss. Large black areas tend to have low density.

For me dry film photoresist sheet exposed through a master made by printing in reverse on overhead film with an ink jet printer in photo mode gives better results.

Russell.

Here is a picture of an etched brass box we used to make at the old salt mine about 20 years ago. It is 0.25mm brass shim stock and was made as a 4:1 enlarged version. The artwork used sprocket tape from an old pre-CNC tool and the perforated holes meant it always folded correctly along the dotted line. We made dozens of different screening boxes and other parts in house as we had our own PCB plant and could make double-sided boards very cheaply.

The secret is to etch from both sides at the same time, so you need a double etch resist pattern screened on the sheet. Without this the holes have a distinct taper and need attention with a fine file. The tricky part is to get the two etch resist screens lined up, but we did this all the time and the jigs catered for this operation.

The box has been kicking around in my junk box for almost 20 years so the nickel plating is a bit scruffy now.

By making the artwork 4-times bigger we could reduce the size in incremental steps, this box is a 1/4-scale version of the full size one. It measures 3" x 1". Our LittleJohn plate camera could enlarge or reduce in 0.1% increments, so making different sizes was easy, one artwork did for all of the boxes..

Edited By John Fielding on 22/02/2016 16:08:13