More etching / the smallest rivet I can etch?

[craigolio1]

Hey all. I've got some parts for the Royal Hudson done but before I commit to finishing more parts, and making multiple versions of tender sides, etc. I want to be sure I'm on the right track as far as what will successfully etch.

The smallest rivets are .75"  (.005") and spaced 1.5" apart on the model. I was hoping to use .012" or .010" brass (or the closest to that in mm that they have) . PPD's website states to multiply the thickness by 1.2 to calculate the smallest hole we can etch.

Does this apply to half etching as well?

Will a rivet that small just disappear and should I increase the size? I'd rather not due to the close spacing.

Would I be better off with a thinner material to start?

This is my first time etching. Thanks for your interest and assistance.

Craig

[bbussey]

Depends on the thickness of your material.  I generally have the diameter of the rivets the same as the thickness of the metal.  That should give you rounded rivet heads.

Also, go with .20mm on the brass thickness, which is roughly .008" thick.  That's thin enough for delicate relief but still sturdy enough (at .004" half etch) to handle.  Then make your rivet heads .008" in diameter.  They will etch down in the process and will have a smaller diameter when finished.  I would not go much smaller than that because you won't see them in N.  Keep in mind that paint and decals are a factor as well.

[craigolio1]

Thanks for the reply Bryan.

Is that a rule to make all details a little over sized? For example there are some 1" rivets. Would I be wise to make those say .009" or .0100", or would you even notice the difference?

What about something like a weld line or a panel seam?

Craig.

[peteski]

Yes, this applies to every half-etched surface detail.  The acid will undercut every surface covered by the mask.

[craigolio1]

Is there some kind of formula to apply based on the thickness of the materials?

Craig

[peteski]

It feels like deja-vou all over again. There was a recent discussion ab out the amount of undercutting. Let me see if I can find it. The PPD online instructions also cover undercutting.

Found it - still on the page 1 of this forum section (few posts below yours). 

https://www.therailwire.net/forum/index.php?topic=41638.0

[craigolio1]

I read that. Sorry I didn't realize I was also talking about under cut. I'm still learning.


Craig.

[peteski]

The undercutting that occurs during the etching process will cause all the masked features on the surface of the metal to be thinner/smaller than the actual artwork.  regardless whether it is the actual edge of the etched part, a line representing a louver or a rivet.

[craigolio1]

Of course that makes complete sense.

Thanks.

Craig

[ednadolski]

One thing that I did for etched details like rivets and grille lines was to make (on one fret) several versions of varying size, then choose the one that came out best.

Hopefully the etching process is consistent and repeatable, but if not then you won't get reliable results anyways.

Ed

[craigolio1]

Would you mind sharing your results?

I have made the adjustment that Bryan suggested and plan to get a test print of my tender side before I move on to other variations of it. I also plan to add some other details as well. Perhaps I should add a pile of test rivets.

Craig

[bbussey]

Would you mind sharing your results?

I have made the adjustment that Bryan suggested and plan to get a test print of my tender side before I move on to other variations of it. I also plan to add some other details as well. Perhaps I should add a pile of test rivets.

It's best economically to utilize one sheet of brass regardless of the size of the part (unless it is small and can "piggyback" on another job), so the cost is negligible to add more parts to your fret — or variations of the same part, particularly if this is for building a small amount of the same model.  The artwork charge would be constant for the job.  So you can have additional tender sides with different sized rivets and select the one best to your liking.  I wouldn't go smaller than .006" diameter on the rivets, as they would disappear if the metal is over-etched even just a slight amount.

Now, if you want to have many multiples of the same part, such as a component for a kit, then you'd want to have as many on a sheet as possible to make it cost effective.  But for the purpose of a single model, put all the variations in your artwork and then you can choose the the variation best to your liking.

[bbussey]

Also — while the rivets should be slightly oversized for all the reasons stated above, keep your scale 1½" spacing as there is no reason to change that.  If you feel it looks too tight, increase the spacing to 2".

[craigolio1]

Thank you. A couple of us are working on a locomotive and there about 4 versions of the tender. In the final revision we plan to include all variations on the fret but I would like to nail down what size of rivets look the best otherwise I'll have to include two or three versions of each set of sides to allow for various rivet size choices. This is why I was planning to do a test.

I thought of including my side that I have done, also some other various sizes of rivets, a few panel lines and finally some folds so I can test how wide fold lines need to be, and how best to account for how they affect the length of a piece once folded.

Unless this information is available somewhere.

I did adjust my drawing as you suggested. I changed the .005" rivets to .008", and the .006" rivets to .009".

Craig.

[ednadolski]

Would you mind sharing your results?

Best pic I have is this:



This is actually made from two etched parts layered over each other: the bottom layer is the vertical grille lines, and the top layer is the doors/hinges.   I wasn't sure which sized grille lines would match up best with the other grilles on the shell, so I made several of various widths/spacings, and used the one that looked best to my eye.  They are all on the same fret, which uses up more real estate but avoids potential process variations.  The metal is 0.010" phosphor bronze and the raised grille lines are the full metal thickness.  (note, both top & bottom parts were etched with an overlapping border frame, to help align them.)

As you can see, the etching process isn't quite as fine as the tooled plastic shell, but a thinner metal might work better.

Ed