Advice, minimum size of etched objects

[mickoo]

Simples really, what is the minimum size one can get away with when etching, I gather it's primarily down to the material not the artwork as AutoCAD can go obscenely detailed.

Attached a small part of my current project, it's the checker plate for the foot plate, to the right is near scale, to the left over enlarged to ensure it etches, and the top is a halfway house that should hopefully etch and with the undercut end up near scale size? The lozenges stand proud so the majority of material is half etched away.


Now, I've seen peeps post up images of wagon plates and builders plates which are almost perfectly readable now that means by my guess work that the lettering has to be 0.1/0.2mm thick ?

PPD recommend a ratio of 1.2 to material thickness for minimum sizes so for 0.25mm that makes the minimum size 0.3mm which makes the tread more like Land Rover tread blocks than anti slip grating! I'm trying to keep all this on one sheet to save on tooling costs, it'd be a shame to have to make up another small auxiliary sheet just for these few small parts, mind PPD only go as low as 0.2mm (8 Thou) in NS, mind they do have 0.1mm (4 Thou) in brass so that might be an option.

Would like to get this off this week, only the grating and latch handles to solve which both revolve around the minimum size of etching.

Thanks in advance.

 

[Steph Dale]

Mick,

It's not quite that simple. For thinner sheets the tolerance is proportionally greater and so too the minimum feature size. There is info on the PPD 'site, although it does require a little thinking about with a specific application in mind.

The truth is that if you want fine features (and think about the height of the feature too) you have to go to finer material; try Phosphor Bronze or Stainless Steel rather than brass for very fine stuff as it etches much more cleanly.

Another thought might be to ask the etcher to offset the etch and take (say) 1/3 off the front etch and 2/3rds off the back - this is one way that fine text can be reproduced on etched plates without them becoming ridiculously flimsy.

Steph

 

[mickoo]

Steph,

Bugga, had a feeling that was going to be the answer, don't really want to go with a thinner material, but accept for these parts I might have too, Phos Bronze only goes as thin as 0.15 (6 Thou) but Stainless Steel goes lower, probably best with 0.125mm (5 Thou) not sure how you affix that, Solder?

Probably be best with an adhesive, which I'm rapidly coming to the conclusion will be the best medium for thin overlays.....might add a couple of solder spots on the rear just in case....small holes in the support material so that one can flood solder the hole and bond the overlay to the support material, very belt and braces!

Back to the original conundrum, as I have space on the art work I'm going to add some sacrificial items, I.E. etched with scale tread blocks and some with oversize that might still look acceptable. Not sure how the latches are going to work out either LOL.


Next task all the variants to sub cab compartments...and there's quite a few, I thought the doors (standard plug, plug with weather strip and thick winter variant) were a mine field, my own fault of course as one of the non negotiable aspects was sealed doors, I want either door to be posed open, not common in Canada LOL, but quite frequent in Florida and California. Then comes the bonnet, 81" and 88", oh and the SOU/NS high nose 81" version...a few more sundries like bell brackets (CN variants) intake snow covers (CN, SP, UP), tabs, borders and a major tidy up and compression of gaps before sending off to PPD.

If I get all that on a A4 sheet I'll be proper impressed


After that I'll tackle the Canada cab....kinda wish I'd started with that first as I've lost hours working out the spartan cab number boards folds and overlays.

 

[ZiderHead]

Does anyone have any pointers to detailed info for designing etches? The PPD site does have some useful stuff but perhaps not enough to get it right first time and avoid costly phototool revisions.

e.g.:
* How wide should the artwork etch line be if you half etch a groove for a 90deg bend, and how much should you add to the piece to take account of the bend?
* And likewise how wide should the artwork etch line be if you half etch a groove to seat another etched piece in it, and how much extra do you add to the inserted piece?

I'm trying to get my head round designing some etches and dealing with cusps is not making it easy for me!

 

[Steph Dale]

Does anyone have any pointers to detailed info for designing etches? The PPD site does have some useful stuff but perhaps not enough to get it right first time and avoid costly phototool revisions.

e.g.:
* How wide should the artwork etch line be if you half etch a groove for a 90deg bend, and how much should you add to the piece to take account of the bend?
* And likewise how wide should the artwork etch line be if you half etch a groove to seat another etched piece in it, and how much extra do you add to the inserted piece?

I'm trying to get my head round designing some etches and dealing with cusps is not making it easy for me!

Jon,
The answer in each case is to draw it at the width of the material.
Go on, ask me a tricky one...
BTW - have you seen the files on the Hollywood Foundry website? Well worth a read (bottom of this page: http://www.hollywoodfoundry.com/HowToPapers.shtm)
Steph

 

[adrian]

Does anyone have any pointers to detailed info for designing etches? The PPD site does have some useful stuff but perhaps not enough to get it right first time and avoid costly phototool revisions.

I used a combination of the PPD info, Hollywood Foundry guides near the bottom of this page
http://www.hollywoodfoundry.com/HowToPapers.shtm

and MRJ 228.

 

[JimG]

Likewise, Hollywood Foundry PDFs.

Jim.

 

[Steph Dale]

Mick,
I'd think the thicknesses you're talking about are okay and stainless can be soldered (Carr's Brown Label, I think). I'd expect the cab side blanking plates (in reality just a thin skin of steel sheet) to be done in the same thin detailing etch.
Are your battery box covers supposed to be the same size? I'm not sure they are.
The latches should be okay although I note no screw heads and that you've gone for the later pattern - careful how you organise the fills otherwise the handle won't etch as you've currently drawn it. You also might want to etch rebates in the layer the latches will sit on so that the handles are in full relief.
Other than that all looks good. I've no doubt the multiple doors will come clear in due course...
Steph

 

[mickoo]

Jon,

Steph is right, for an internal bend the half etch slot should be the material thickness, in my case I'm using 0.25mm material so my slot needs to be 0.25mm wide.

Actually in my case I've made it 0.3mm wide, that's because my AutoCAD snap setting is 0.05mm and half of 0.3 is 0.15mm, I use the half mark to get the middle of the fold for measuring. If I'd used 0.25 then half of that is 0.125 which would mean a snap setting of 0.005 and that's bloody painful to work in!. Working out the length of material from fold lines can be awkward, for some odd reason I haven't really got my head around that part, hence the blundering with the number board, it's the mental juggling of where the bend will occur in relationship to the lines drawn on the art work, there's plenty of good advice and tutorials out there, but for me, at this moment in time, it eludes me.....easily To be fair, I'm fretting over 0.15 and 0.2mm here and there, which are a mere simple brush with a file thickness.

The extra 0.05 doesn't matter, just means that there will be a small gap when the parts are folded up and does ensure that you can get a true 90° bend, if for some reason the etchers don't etch deep enough then you end up with a slot too shallow and cannot easily get a 90° bend, ending up with 85° or something, real pain having to file the groves bigger.

A slot or half etch groove to position another piece in will be the material width, same as an internal bend half etch.

For an outside fold, I.E. where you want the material to fold back on its self 180° then make your half etch 1.5 times the material thickness.

There are other factors and the hollywoodfoundry papers are really good, to be honest when your down as thin as 10 Thou then undercuts and such like I find really have very little effect on the fit and final etch.

 

[ZiderHead]

So I might be over thinking it?

OK on the widths, how about the length of the pieces? I guess the folded piece needs to be the width of the material longer so the edges of the groove meet on the inside of the bend?

How about the seated piece? Imagine a ladder structure with grooves etched inside the stiles for the rungs to seat into. If the rung length is the inside width between the stiles they will slop around, if its the inside width plus the width of the material (ie. half etched groove depth at each end) the cusps on the rung and the groove will push the stiles apart.


Edit:
Several replies while I was typing/eating my dinner/distracted by the cricket Thanks chaps, I'll have a look at the Hollywood Foundry stuff

 

[mickoo]

Mick,
I'd think the thicknesses you're talking about are okay and stainless can be soldered (Carr's Brown Label, I think). I'd expect the cab side blanking plates (in reality just a thin skin of steel sheet) to be done in the same thin detailing etch.
Are your battery box covers supposed to be the same size? I'm not sure they are.
The latches should be okay although I note no screw heads and that you've gone for the later pattern - careful how you organise the fills otherwise the handle won't etch as you've currently drawn it. You also might want to etch rebates in the layer the latches will sit on so that the handles are in full relief.
Other than that all looks good. I've no doubt the multiple doors will come clear in due course...
Steph

Steph, no they are not the same size LOL, I drew the scale etch first and then when adding the oversize treads needed to lengthen it by 0.4mm to get a equal space around the tread blocks in reality both will fit over the engineers battery box with ease, one just having and extra 0.2mm space at each end.

Not sure on the latches myself, I'll color one in shortly to show what I mean, I did want to try and get the latch to sit lower than the face plate but that'll require a half etch from the rear to open out the area around the handle.

Screw heads are dome headed on the ones I've looked at, slotted or cross head, yup spotted two types and quite a few locos have doors with both types on, old on the left, new centre and right.

 

[mickoo]

So I might be over thinking it?

OK on the widths, how about the length of the pieces? I guess the folded piece needs to be the width of the material longer so the edges of the groove meet on the inside of the bend?

How about the seated piece? Imagine a ladder structure with grooves etched inside the stiles for the rungs to seat into. If the rung length is the inside width between the stiles they will slop around, if its the inside width plus the width of the material (ie. half etched groove depth at each end) the cusps on the rung and the groove will push the stiles apart.

X = Material thickness
Y = Space between ladder uprights
Y + X = length or rung etch, don't worry about the cusp as in 10 Thou you can soon smooth that off with a file.

 

[mickoo]

Latches

First is a simple half etch around the handle and then a little half etch in the top to simulate where the latch is recessed all sitting on a half etched surround with raised treads.

Second is a little more complex, half etch in red and full etch in black, my only concern is the small gap between the handle and face plate and may not be enough for the etch from the rear to break through and define the handle stirrup.


We're talking a stirrup thickness of 0.2mm and a gap down the sides between stirrup and face plate of 0.2mm, all in a material 0.25mm thick, according to PPD you need 1.2x material thickness to break through, that means I need a gap of 0.3mm or more.

With the first example I may not get full half etch depth but at least I'll get something, where as in the second, if it doesn't break through the sides then it'll look odd, I think worse than the first option.

 

[Steph Dale]

So I might be over thinking it?

OK on the widths, how about the length of the pieces? I guess the folded piece needs to be the width of the material longer so the edges of the groove meet on the inside of the bend?

How about the seated piece? Imagine a ladder structure with grooves etched inside the stiles for the rungs to seat into. If the rung length is the inside width between the stiles they will slop around, if its the inside width plus the width of the material (ie. half etched groove depth at each end) the cusps on the rung and the groove will push the stiles apart.


Edit:
Several replies while I was typing/eating my dinner/distracted by the cricket Thanks chaps, I'll have a look at the Hollywood Foundry stuff

P'raps. For example, I wouldn't aim to trap the rungs between the stiles during assembly as you'd never hold the lot together, much better to fold the two stiles from a single piece, drop the rungs in from the back, clean up and then separate from the fret. If you take into account Mickoo's diagram and thoughts then you're away, you can make any adjustment as you assemble the parts.

Secondly (and I might get shot for this) you don't have to exactly scale everything. The lead dimensions are important; people can measure axle spacings and tell if something is square or not, but probably couldn't say whether something was an arbitrary 0.010" too long or short. The measurements are only critical when assembling items that need accuracy and come in component form. One reason my drive components take a while to reach a test etch. I can pitch out the centres pretty quickly from empirical data, but producing something that will repeatably fit together and take allowance for over- or under- etching, can be written up in instructions and be assembled by your 'average modeller' takes a bit of thinking about.

Steph

 

[Steph Dale]

Second one Mick.

Even Athearn wouldn't be too proud of the first one. Have alook at the websites of either Sunrise Enterprises or Plano to see how they're doing etched latches in HO.

And it will etch through!

Steph

 

[Richard Spoors]

Steph,

Bugga, had a feeling that was going to be the answer, don't really want to go with a thinner material, but accept for these parts I might have too, Phos Bronze only goes as thin as 0.15 (6 Thou) but Stainless Steel goes lower, probably best with 0.125mm (5 Thou) not sure how you affix that, Solder?

Probably be best with an adhesive, which I'm rapidly coming to the conclusion will be the best medium for thin overlays.....might add a couple of solder spots on the rear just in case....small holes in the support material so that one can flood solder the hole and bond the overlay to the support material, very belt and braces!

Back to the original conundrum, as I have space on the art work I'm going to add some sacrificial items, I.E. etched with scale tread blocks and some with oversize that might still look acceptable. Not sure how the latches are going to work out either LOL.
View attachment 29783

Next task all the variants to sub cab compartments...and there's quite a few, I thought the doors (standard plug, plug with weather strip and thick winter variant) were a mine field, my own fault of course as one of the non negotiable aspects was sealed doors, I want either door to be posed open, not common in Canada LOL, but quite frequent in Florida and California. Then comes the bonnet, 81" and 88", oh and the SOU/NS high nose 81" version...a few more sundries like bell brackets (CN variants) intake snow covers (CN, SP, UP), tabs, borders and a major tidy up and compression of gaps before sending off to PPD.

If I get all that on a A4 sheet I'll be proper impressed
View attachment 29784

After that I'll tackle the Canada cab....kinda wish I'd started with that first as I've lost hours working out the spartan cab number boards folds and overlays.

Mick, it's been a while, but what was the result of your checker plate experiment? I'm just about to embark on something similar and in researching CAD posts came across yours.
Cheers

Richard

 

[mickoo]

Richard,

It really depends on what material thickness your working with and whether it's for construction or visuals.

The final checker plate with anti slip lozenges on used 10 thou nickle silver, so 5 thou half etch with 5 thou raised parts.

I posted this on the Bagshot build the other day so will repeat here.

This battery cover is 11 x 26 mm, each anti slip lozenge is 0.06 x 0.65 mm in size, the stirrup latches are 1 mm wide and 2 mm long and o.2 mm thick.
This is on 10 Thou Nickle Silver material.



I can also post up some detail shots and information on the W1 fall plate if it'll help.

MD

 

[Richard Spoors]

Mick, very helpful, thanks.

Richard

 

[andrewb]

Here's a quick (and hopefully simple) question that I hope a CAD-savvy ninja can help me with, and which seems to make sense as a codicil to this post rather than a new one:

When making allowance for etching tolerance, is it sufficient to draw the line thickness in CAD software at twice this? - for example, if I want - say - an accurate 10mm dimension with 0.7mm NS, and a quoted tolerance of +/- 10-15% of thickness, I draw the critical lines at 10mm centres but make their thickness about 0.18mm (0.07-0.105 tolerance, roughly averaged, x 2)

I use TurboCAD 10 Deluxe for Mac, where the drawing certainly looks like it'd do the trick...

 

[Steph Dale]

Andrew,
That's one of those questions to ask your potential etcher I think.
I can imagine scenarios where it might work, but it'll depend on how the film is generated.
Steph