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1/20th Scale Burrell

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Larry G.

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Ferric chloride is a widely used and thoroughly understood industrial process. Very little needs to be re-invented.
We used a ferric chloride spray etching system to produce deep- and through-etched clock parts in brass and tool steel. Working on a small industrial scale we used Kodak KPR dip-coated resist and litho negatives of original artwork. Thorough degreasing and oxidation removal are key. Warming the solution accelerates the process. If we weren't spraying with PVC and titanium built equipment we would have added aeration.
For limited production the references cited are very good, particularly VON Industrial and nontoxicprint.com.
 

awake

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Ferric chloride works well, of course ... but there is a much-cheaper alternative that home-shop folks may be interested in. Two caveats: 1) this is much cheaper for me where I am - maybe not true elsewhere, and 2) I use this to etch printed circuit boards, i.e., copper - I believe it also works on brass, but I have not personally verified it.

The etching solution is made by mixing two parts drug-store hydrogen peroxide with one part hardware store muriatic acid (hydrochloric acid - often sold as brick etch, or in pool supplies). "Do as you oughtta, mix acid with watta" - always put the water (or in this case, hydrogen peroxide) in first, then slowly pour in the acid. The etchant can be used once and then disposed of (safely - do NOT pour it down the drain!! I mix with concrete to "solidify" the dissolved copper and then dispose of as per county regulations), or you can go on to to create cupric chloride by dissolving in more copper. This solution can be reused over and over again simply by re-oxygenating it (bubbling air through it). Again, a caveat - I have read many reports of this process, but I confess that, given the limited frequency and quantity I need, I find it easier just to mix up a fresh batch each time.

One other word of warning - don't store your muriatic acid inside your workshop; the fumes will make everything rust! I store it in a covered plastic container outside my garage - seems to have worked just fine for many years now, and I am still nowhere near to using up the first container of acid that I bought.
 

glue-itcom

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I've been designing and machining the front axle, then today finished the hub caps

20210110_135038.jpg


This next image gives you the scale as my hand can nearly wrap around the axle and smokebox.

The front wheels are 70mm in diameter

20210110_135018.jpg
 

glue-itcom

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Have struggled getting the 1/20th scale door hinge correct, lots of parts in the bin. Finally I have something that I think looks ok.

In essence I went back to basics and broke the problem down. Then looked again at the assembly. Plus I bought and tried some silver solder paste - not cheap at ~£16 for 10g, but wow. Maybe it is cheap as you only need tiny amounts, well on this size of parts tiny amounts.
 

glue-itcom

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I used two countersunk 10BA bolts to fix the plate to the front door. I should probably add 2 more, but space is very tight.

I'm pleased with the look of the hinges now, just need to add the towing eye to the front and add the steering links onto the axle for this front part to be approaching a good level of completion. OK, still lots more to do even then.
 

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