Cutting openings in brass?

[lab-dad]

Thanks John!
This is something I will try! someday...
-Marty

[DaKra]

Hey John

Do the etchers use the laser jet to print onto clear film for exposing the resist, or do they print directly onto the brass using the ink as a resist?   

Curious if/how high tech has made its way into commercial etching or if they are still doing things the old fashioned way.  Any info you have would be interesting to me!   

Dave

[Tom Neeson]

Anyone tried the photo etch setup from MicroMark?

Tom

[JohnP]

Dave, the hatch pattern I had to make for my source was on the areas to be etched away. I believe they used the printer to create a clear overlay of my pattern that was then sandwiched onto the resist-coated metal sheet. The sandwich was then exposed to UV light. The open spaces representing the shapes hardened on the resist to protect the metal from etching leaving the rest to rinse away. Then into the etchant spray tanks it went and out came etched parts. A bit old fashioned but accurate and repeatable.

Tom, I have the lil' etch kit. They provide the resist, developer, etchant, a laminator for applying the resist to the metal, etc. It works well in theory. There is lots of room for operator error though. The most difficult thing is to maintain alignment if you are trying a double sided etch. I bought it to make a fixture for drilling small holes precisely .030" apart for a rivet embossing fixture. It is better at etching very thin (.005") metal due to the problems in circulating the etchant. Even with the included bubbler it can still be uneven without rocking the container. Give it a try; you will have fun with it.

The images below of are the pattern for a small section of the part sheet on my previous post. One is the bottom, the other the top. One problem I had was in applying the hatch on my drawing areas that had rivets. My TurboCAD cheap version has a feature that applies a hatch around enclosed spaces, but it choked attempting to avoid the gazillion rivets. It may have been my weak computer. So I had to select each rivet and "cut" each hatch line with in the rivet. I was literally clicking for days in my spare time. If I did it again I would get a liquid cooled computer with the neon lights inside just to make sure it was big and tough enough.

John

[james_coldicott]

Hi All,

just a comment on photo-etching here in the UK which (looking at John's artwork) I assume uses a different system to that employed in the USA- maybe I'm wrong and I may be teaching y'all to suck eggs but I haven't seen this described in any of the US modelling magazines- maybe I just don't read enough of them...may still be of interest for those not familiar with the process...

Etching artwork here uses a three colour system-

Black etches all the way through
Red etches half the depth on the Face
Blue etches half the depth on the reverse- all colours drawn solid

In the olden days you'd hand draw your artwork which was photographed twice- once with a blue filter- only picking up the red and black areas, then with a red filter so picking up the blue and black. One negative for each side of the metal sheet. The transparency was then used to fix a photo resist layer on the metal.

This way you can put fold lines/ rivet punching centres etc. (or etch the surface and leave rivets full depth)  on either side of the metal which was etched just long enough to eat half of the material- the black areas of the drawing being exposed to etchant on both sides meet in the middle.

Now that digital artwork is the norm the drawing is still produced in the same way with three colours and two transparencies printed up- though my etcher will still work from hand drawn artwork and photograph it in the old fashioned way (or would last time I looked!).

James

[finescalerr]

Considering the immense talent represented on this site it is interesting that none of us seems to be expert in photo etching. Remember that airplane modeler Havard found a link to who photo etched hundreds of exquisite brass parts? And that lousy, sociopathic crook from Backwoods Miniatures made extensive use of etched brass parts before turning more of his attention to castings.

Those of us with CAD might consider drawing out the parts and sending them to a water jet outfit. Presumably that would obviate the need for etching.

Russ

[chester]

For those a little gun shy about photo chemical etching using something as dangerous as ferric chloride, here's the old fashioned way of electrolytic etching. I found this site completely fascinating.

http://steampunkworkshop.com/electroetch.shtml




   

[JohnP]

Hey James-
The method my etcher used eliminates the need for the black layer. If I put the hatch lines in the same area on both sides then of course it etches through. The rivets on the one sample drawing are white round circles. The bottom side sample drawing shows the same area as all white. So there is where the half etch occurs for the protruding rivets. I used lots of half etch bend lines on the model too. Using a separate layer for through etch and half etch probably would make it simple to design and analyze the pattern. Believe me I wished all they needed was a solid area, those hatch lines were difficult to handle in large amounts.

Chester-

I'll check out that site, thanks. I recall another guy who posted information about an actual pumped spray etch system he made in his garage. I'll have to find it.

Russ-
My question is, on what side of the fence do you need the photo etch expert? Doing the actual photo etch work to the standards we all are familiar with requires big expensive machines that are full of harsh chemicals and moving parts. That can be left to the experts who do it on a commercial basis and are familiar with the EPA and OSHA requirements. But the design of a sheet of parts to cut, bend and assemble into an outhouse or rickshaw is within the capabilities of anyone who has shown their work on this site. My project started as only a *dream* and ended up with boxes of etched brass sheets that could be assembled into an HO truss bridge even though I do not consider myself any kind of expert. I had no clue how it worked nor how to do it. I just wanted to get it done. But several years later I sold out two runs. The cash outlay for a big project like that was extensive but I took the chance.

To make a few copies of something for your own models would probably require using the Micro-Mark kit. The commercial places charge for set-up, then for the run. Once they are running your job the cost per sheet goes way down as the quantity goes up. So if Marc wanted an etched brass model of one of his bikes he should do it himself, but if we all wanted a few a vendor could do it.

If there is someone here who wants to know more and/or who wants to know of a commercial place that works with model makers on a regular basis let me know via message or right here. I am working through the resin casting process right now but would not mind if my experience with etched brass does not go to waste... or get flushed by likes of this beautiful Brooklyner-Schneider Hopfen-Weisse I am currently enjoying.

Thanks, John
A few more parts pics are attached, a little low on resolution but that's all I have saved that I can find

[james_coldicott]

John,

so do I understand correctly that you have to produce two drawings- one for each side of the metal sheet being etched? The UK system is one drawing that produces two (different) negatives so making referencing much easier when it comes to making the drawing and after reading your comment on producing hatched lines saves an AWFUL lot of time. Or have I got it wrong?

James

[JohnP]

James,
There is only one CAD drawing but it has two layers. As far as the computer is concerned there is only one file. But that file has pattern or image for both sides of the sheet. The etcher software will sort that out when they run it on their system.

I you can print out each side on paper and check the alignment of the patterns. I put the top sheet on the bottom and looked at them on a light box the old-fashioned way. Just for my own reassurance. But the computer is far more accurate and easy to see.

On the CAD drawing you probably know the user can assign colors to each layer. It is easy to see the alignment while looking at the drawing on the screen with both layers turned on.

The hatch lines were a pain because of the size of my drawings and the many, many features on them. I needed a bigger computer (speed and memory) to do it easily. I personally did not need to draw them, the hatch feature did it for me.

My laser cutter provider has a system where the machine recognizes red for through cuts and blue for scribing cuts. In the same way, I make a CAD drawing with two layers in the different colors, but can view both to see what the result will be.

I hope I answered your questions.   

John

[finescalerr]

Wowsers! That is some beautiful photo etched stuff, John! The little folded up piece looks much better than a casting. Most impressive. -- Russ

[james_coldicott]

Ah, I've got it- thanks John. It all makes sense now- baby induced sleep deprivation must have been numbing my brain for a while!

Just trying to get a handle on the (very different) systems used on each side of the pond.

I still thing the UK system has advantages over the US one- I imagine all the hatching makes interpreting the alignment- even on a cad drawing a bit of a pain- that's where the single layered, three colour CAD that UK etchers use is so much easier.

Finally, ditto Russ' comments above- the bridge is GREAT.

Thanks for taking the time to explain how you got the parts etched. A fantastic result

James

[DaKra]

Happiness is a big photo etched part with rivets all over it.      And it looks like everything fits perfectly, very nice work there, John.   

That cross-hatching seems slightly insane.  I wonder why it was necessary, does some sort of oddball machine interpret that as a solid area, and how?     

[JohnP]

Gee, thanks fellas *blushes*.

I have this thing for bridges and rivets and always wanted to model them accurately. My lil' business through which I sold the brass bridge is an outlet for my experimentation, and an attempt to supply real bridges to modelers who care. The brass bridge looks great and assembled accurately but the .010"/.005" brass was a tricky material for modelers to handle in such an extensive way. Also, I had first thought of layering the etchings so the lacing strips attached on the surface of the beam flange angles but costs prohibited that. The overall look of the thin sections and lots of accurately placed rivets was a success though.

The crosshatching is spaced as I recall .005" apart because their artwork printer prints lines .006" wide. That will make the etch area solid. Why it is I do not know. The insanity rests with me for making my own actual etch files- most customers make a regular CAD drawing and they translate it into the artwork. I save a good amount of set-up cost that way.

A few years ago I decided to continue my riveting quest using resin in rubber molds. Again I stumbled into it blindly, which is the best way- no limitations. My concept and design of the D&RGW truss model is very sound, but I have found that even the best RTV is not dimensionally stable. I am learning to compensate for it so the parts are all within tolerance. My masters are all thin section with decent rivets so even with the resin casting I am avoiding the heavy metal look. Even the rare imported scale bridges seems to use heavy lost wax castings for the lacing strips. I am hoping the Print-a-Part technique will help with mastering the tough parts while maintaining a good cross section.

Thanks!
John
I kitbashed a double-track version for a customer (below). Lookit them rivets!

[finescalerr]

The bridge is jewelry. It would surprise me if the cast resin parts are as "perfect". -- Russ