Ething brass with PPD.

[ednadolski]

I don't want to bother PPD with a bunch of back and forth e-mails.  I know people here have used this service and I'm hoping I can get some answers here.

You're better off getting your answers straight from PPD, since they know their own processes the best, and cannot be accountable for incorrect information that you might pick up from somewhere else.

I'm not quite clear what you have in mind for an undercut, but I agree that on a part this small it would not be noticeable without magnification, esp. on a painted and weathered model.   The cast-on louvers on a typical injection-molded plastic shell do not have any undercutting.

What would concern me is the thickness of the half-etch metal between the individual louvers.  That would be 0.004" thick (over 1/2 a scale inch) which would create a vertical 'line' along the sides in between the louvers that I don't think will disappear under a layer of paint.  Weathering could likely enhance the line rather than disguise it.

Again due to the small size it could also turn out to be tricky to install these sufficiently straight/square and parallel to any door edges or seam lines on the plastic shell.  They would also have to go on perfectly flat, and have very little tolerance for a layer of glue.

Does Archer have any louver decals that would work?

HTH,
Ed

[chessie system fan]

I bet you could easily etch a guide to keep things square.

[Sokramiketes]

I don't worry about undercut for parts like these. Unless you are trying to fold something into a box, or have tabs/slots/holes that need to accept a part, there's no need to worry about it.

Having said that, Ed's right on the thickness issue here. Archer may be best, full doors another option, or use thinner material.

[ednadolski]

I bet you could easily etch a guide to keep things square.

I would not be so sure.  First, you have to allow for tolerances which would introduce a certain amount of slop.  More so, the question then becomes, how do you accurately align the guide on the model (and keep it from moving)?   There has to be a way to transfer the precision of the drawing/etching to the actual model, that does not rely on manual/visual alignment.

I went thru this same thing with the BLMA grabiron drilling template, which was general purpose and did not allow for contours, raised areas, etc. on specific models.   So it was very hard to position accurately and keep it in the same place for drilling all the holes.   If it was off, then all the holes would be off too.  (For me it turned out to be more accurate to just mark & drill the holes manually under high magnification.)

Ed

[peteski]

I don't worry about undercut for parts like these. Unless you are trying to fold something into a box, or have tabs/slots/holes that need to accept a part, there's no need to worry about it.

Having said that, Ed's right on the thickness issue here. Archer may be best, full doors another option, or use thinner material.

I think PPD worries  that the undercutting will totally etch away the actual representations of the louvers (the thin horizontal lines).  The undercutting will cause them to be etched thinner than they actually are.  I see this type of problems with rivets - in some etchings the rivets are merely faint bumps on the surface due to undercutting (the part was either etched too long or the rivet mask was not large enough to compensate for undercutting). Same thing can happen to very thin shape of the louvers.

[wcfn100]

So to drag this thread back up, I got back to this project a few days ago and just heard back from PPD about some tolerances.  They told me to add 20% of the material thickness to account for the etching process.  I may still hedge my bet at about 25%.

Well see how it goes.

Jason

[craigolio1]

I started a mother thread in etching not realizing I was asking all the same questions so I'll add them in here now.

If I'm planning to etch in .20 mm brass, now wid a line should draw to make a 90 degree fold line?

Thanks.

Craig

[bbussey]

.10mm

[craigolio1]

Thanks. I figured half the thickness would be correct, but I wasn't sure if there was some that needed to be taken away in this case (maybe make it .008") to account for the process. Sort of the opposite of why I would add it to a rivet.

Thanks.

Craig

[bbussey]

Another tip — I work in metric, not imperial. It's easier, particularly since the contractor works with metric measurements.

[craigolio1]

I'll have to covert it. When it comes to model trains I can't think in metric! Haha.

Craig

[bbussey]

I do both the solid modeling and etching artwork in metric.  In addition to being base-10, millimeters are more precise than inches.

It also easier to deal with the various metal thicknesses in metric.

[CNR5529]

I do both the solid modeling and etching artwork in metric.  In addition to being base-10, millimeters are more precise than inches.

It also easier to deal with the various metal thicknesses in metric.

Agreed! @craigolio1 our 3D parts are all drawn in metric 

[wcfn100]

  In addition to being base-10, millimeters are more precise than inches.

You've said this before and I thought I got it, but really I don't.

How are MM more precise than inches as it relates to what we're talking about?

If I'm drawing a 3/4" rivet, I can just divide by 160 and get .0046875" or I can then multiply by 25.4 and get .1190625 mm.  What's the difference? 

I will say using MM is much better when trying to work with manufacturing specs or tolerances as those are always in metric. 


On a side note, I've sent payment for my louver sheet to run.  Hopefully I'll get it in a couple weeks and I'll share there results.  I didn't add any other parts to the sheet but just ran a full sheet of the louvers.  I did include a couple circles, and squares to measure to see exactly how much undercut happened.

Jason

[bbussey]

Because a millimeter is 1/25th the measurement of an inch, which means an eight-decimal-position millimeter measurement is 25 times more accurate than an eight-decimal-position inch measurement — very handy when working in 3D modeling programs. Also, all of the units of measure are in the same base, which makes conversions easier. And it's easier when all of your contractors happen to be on metric rather than imperial.