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Etching in 2mm


Lacathedrale
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Morning all (and a happy new year to you).  I'm currently playing with recreating the tall building in the background of this photo.  Apart from the covered conveyors, I've now got 2mm versions of all of the other main buildings, so this is the last I plan to tackle for the colliery.

image.png.11b2c3afd4aa98cf69c73b0fda71631f.png

 

All four faces of the building are the same as the aspect we can see, so it makes sense to me to try my hand at CAD and etching as the whole edifice is windows with the occasional brick!  My thoughts are to more or less build it out of clear acetate as the structural bits, with windows, walls and columns laid on top.  Each window consists of a 4x5 grid of panes, with the central 2x3 panes opening, as we can see on the 2nd window down, 3rd from the left.  I'd like to model several of these open, to relieve the symmetry and monotony.

 

So: I've dipped my toe into CAD today, using QCAD which I've found nice & easy to use, and come up with this...

image.png.e84ce3308476a6f605bcf3ab4fe067c7.png

...which pretty much covers an A4 sheet.  It's a tessellation of three elements: the frames of the left- and right-hand windows, which don't open; the frames of the middle two columns, which do, and the frames of the opening sections.  In a closer zoom, these are they...

image.png.15cf35e34c30c99308eec48f2eb7a118.png

The dimensions are in millimetres, so the frames are 0.5mm wide.  There's a semicircular notch where the hinges are of 0.25mm radius (my intention is to overlay the smaller window onto the hole for where the windows are shut, and to fit the former through the latter pivoting on the notches where they're represented open.

 

After all of this very long preamble come my questions:

- should I contain every element within its own frame, or simply frame the entire etch and add tabs between every element?

- is there a 'normal' spacing between tabs?

- is there a 'normal' spacing between elements? 

- there's a whole lot of holes in the etch: might the etcher object to this amount of waste dissolving into their acid soup? (I've not picked a specific etcher, although PPD are front runners at the moment)

- as this is my first attempt, can the more experienced folk spot anything I've not considered (fragility??)

(I haven't quite figured the sequence/contents of each layer, but I'm happy to work that lot out)

 

Thanks everyone

 

Richard

 

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I always draw each part in its own frame, this makes them easy to move around when filling up the sheet and also able to be copied for use elsewhere.

Most designers put far too many tags on, minimum number to hold the fret together is better - and most important never put them on the inside of a curve, they can't be cut out with snips in that case.

Spacing between depends to some extent on the thickness of material but I use .6mm normally, this is wide enough to do rough cutting with a slitting disc if necessary.

Our etchers (PhotoEtch and PPD) have never complained about large areas etched away but I usually make use od large "holes" to put in other or extra bits (in their own frame within the hole though).

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41 minutes ago, Michael Edge said:

 I usually make use od large "holes" to put in other or extra bits (in their own frame within the hole though).

 

Please could you show us a image of part of one of your etches as a picture tells a 1000 words.

 

Thanks

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I think that if I were setting out to create window frame etches for a very regular rectangular building like that in 2FS, I would aim to create a single window frame etch for each side, even if it meant that I had to have two (presumably identical) etches run off, and then just add (plasticard?) overlays to the etch for the concrete and brickwork. 

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3 hours ago, Ian Morgan said:

 

Please could you show us a image of part of one of your etches as a picture tells a 1000 words.

 

Thanks

No problem, this is a recent 4mm test etch in .015" material. The screenshots show what I acually send to produce the film tools, anything black will be etched away, where the black coincides on front and back it will be etched away completely. I send these as .eps files to PPD directly or to Phillips Digital to get films printed for PhotoEtch.

First one is the front etch

2011569925_ScreenShot2021-01-02at14_06_53.png.c34813df906efea4b797e0a3cb1e7ba8.png

The only part with tags on here is the large footplate top left, normally tags are on the back film but here the edges of the footplate are half etched underneath so tags have to be on the front. The centre of this shows how I use up space inside large holes.

This is the back film

1343983426_ScreenShot2021-01-02at14_06_29.png.746888beef97be85fc8547f68f183790.png

Now all the parts (should) have tags, no more than necessary and all designed to got at with snips - much the quickest and easiest way of dismembering an etch. PPD ask for the corner markers and scale, PhotoEtch don't seem to need them. If I get the films done myself I check them visually for missing tags - if there are any missing the black can be scratched away with a scalpel to create one. It still happens from time to time though no matter how carefully I check.

This isn't how it looks when I'm working on the drawing, at that stage everything is on one drawing with colours to make the layers visible and easy on the eyes.

This is the original form

1829537799_ScreenShot2021-01-02at14_21_37.png.bc5c960ddb29c710b2b301ba790c244f.png

There are six layers (all of them can be switched on or off) grey is for etching both sides, blue from the back and red from the front. There are also three "white" layers (they are shown on my screen in three shades of yellow - you can't see white on a white screen) corresponding to the first three. These are used to cancel them out, for example when creating tags or correcting small errors. Generally speaking (there are exceptions) there are no lines on the etch drawing, all the shapes are fills. There were lines used on the original drawing to create this but they are left off for etching.

Hope this helps.

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I would agree with much of what has been said, though I do things a little differently from Michael.  It would certainly be easier to etch all the windows on a side as one piece and then add the structural parts on top as @bécasse suggests.  Otherwise it will be a bit of a fiddle to get all the windows perfectly aligned and square.  One out or position will be very noticeable.

 

I tend to leave parts c1mm apart and I cut tags with a curved X-Acto craft knife on a brass block.  I occasionally go below that if I'm a wee bit pushed for space to squeeze something onto the sheet.  One benefit of using PPD is that they will do small sheets.  PEC, for example, have a minimum of A3, which needs a lot of 2MM stuff to fill it!

 

I've gone down to .25mm for the width of window bars and although that is below PPD's preferred tolerance for .25mm n/s I haven't had a problem.  I always tell them that I'm happy for them to go with that.

 

Jim

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Thank you all for the pointers.  I like @bécasse's idea of etching each aspect as a whole, or even the entire building as a oner - three half-etched score lines and it'll fold very neatly.  As @Caley Jim says, it'll prevent any problems with alignment. Plus significantly fewer tabs.  I think I'll take the process one step further and have the concrete columns and cross-members etched too.  Laminating them onto the window frame layer will be a much neater job than cutting lots of lengths of plasticard.  The brick infills will remain as plastic card.  Hmm, and as I type this, can I have these etched too?  Although I suspect they may be well below tolerance, I might have a bit play with that...

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8 hours ago, Michael Edge said:

 

This is the original form

1829537799_ScreenShot2021-01-02at14_21_37.png.bc5c960ddb29c710b2b301ba790c244f.png

...

Hope this helps.

 

Thanks Mike.  What’s the dotted lines?  Is that metal sheet size?  How do you handle different etchers different boarder requirements?

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The dotted line there is the print margin in the CAD program, nothing to do with the drawing, this is just a screenshot of what I can see. I do stretch border requirements quite a bit - PPD ask for more than PEC do.

PPD almost always warn about parts too narrow but I also just say it will be fine, just do it. We do normally only use PPD for test etches though, nearly all our production is with PEC so if anything doesn't work it's not important.

With regard to cutting out etches, I've been a full time professional modeller for 44 years now (kits are a recent sideline) and I want to cut out parts as quickly and efficiently as I can (time is money after all). Most of the quoted methods of cutting frets result in a beautiful piece of etched brass lace at the end with a completed model - however this is just scrap, it's far better to cut it up and throw it in the scrap bin as you go along. Cutting with snips is a different art involving exactly where and in which order to make the cuts, if it is planned correctly (and there are no tags on the inside of curves) all parts, including the most delicate, can be snipped out with no distortion.

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Thanks to everyone for their advice (as ever!).  I've ended up trying to recreate the entire building in 0.25mm n/s.  It's been a steep but rewarding learning curve.  The whole building is a single piece, square in plan so each wall is replicated and separated from its neighbour with a fold line.  I've added some right-angled triangles to assist in making the square actually square (and it's just occurred to me that I should have added half-etch lines for them to sit in - ah well).  The rest of the pieces are the concrete elements, which when laminated will be either a quarter or half millimeter proud of the surface.  I had considered doing these in plasticard which would have significantly reduced the cost, but the sharpness of the lines and the accuracy of the measurements clearly gives etching the edge. The holes under/above the window apertures will be infilled with brick-embossed plasticard.

 

image.png.1661563359da80a831582c3c5b1484cf.png

 

I've emailed it to PPD for them to validate (or otherwise) and give me a quote.  I'm quite etchcited!

 

Richard

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  • 2 weeks later...

Well, my etch came back from PPD. First three lessons:

- use the bare minimum amount of tabs. Every one of them needs cutting, twice, and filing, twice.

- my window ledges (the horizontal red lines on the body of the main building above) ain't never gonna fold without bending the narrow window frames they're attached to (see pic). 

- next time, use the trick of fully etching (invisible) folds, with a couple of tabs, to make the folds much easier.

 

20210121_195805.jpg

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2 hours ago, Geordie Exile said:

Well, my etch came back from PPD. First three lessons:

- use the bare minimum amount of tabs. Every one of them needs cutting, twice, and filing, twice.

- my window ledges (the horizontal red lines on the body of the main building above) ain't never gonna fold without bending the narrow window frames they're attached to (see pic). 

- next time, use the trick of fully etching (invisible) folds, with a couple of tabs, to make the folds much easier.

 

 

I did say most etch designers use far too many tags..... - and they are often unnecessarily thick as well.

How thick were your fold lines? I have been making them quite a bit wider recently, especially where they will be difficult to fold because they are too close to a hole. Your last option works but doesn't need nearly as wide a gap as you might think. Sometimes (etching varies quite a bit) it won't etch right through but it's easy to slice it with a knife to allow it to fold.

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I always make long fold lines with gaps in them.  As michael says, they don't need to be the full width of the fold line.  When making the folds it helps to run a knife along the line a couple of times to help it to bend.  Can you grip the window frame in bending bars or a vice and then use a steel rule to bend over the small ledge?

 

Jim

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9 hours ago, Michael Edge said:

I did say most etch designers use far too many tags..... - and they are often unnecessarily thick as well.

How thick were your fold lines? I have been making them quite a bit wider recently, especially where they will be difficult to fold because they are too close to a hole. Your last option works but doesn't need nearly as wide a gap as you might think. Sometimes (etching varies quite a bit) it won't etch right through but it's easy to slice it with a knife to allow it to fold.

I thought I'd been quite canny with a minimum amount of tabs, but having seen how (relatively) solid the sheet was I could definitely have used fewer. I kept them all at 0.5mm width, although two etched through so I'm going to check my artwork to see if those were narrower.  Fold lines are 0.2mm, and again I think that might have been too narrow.

7 hours ago, Caley Jim said:

I always make long fold lines with gaps in them.  As michael says, they don't need to be the full width of the fold line.  When making the folds it helps to run a knife along the line a couple of times to help it to bend.  Can you grip the window frame in bending bars or a vice and then use a steel rule to bend over the small ledge?

 

Jim

The body of the building is too large to fit in a vice, so I've tried holding it flat with a steel rule while attempting a bend. Not bad, but not great. I hadn't thought of weakening the fold with a knife, so I'll give that a go, although I've accepted the possibility of adding (a lot of) microstrip ledges once everything else is done.

 

Thanks, both, for the benefit of your experience. 

 

Richard 

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7 minutes ago, Graham R said:

If you really can’t fold the ledges, at least you now have consistent rebates to take pieces of microstrip, tedious though adding them might be.

Our posts crossed, but as you can see from my reply above that's my Plan B. Great minds!

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2 hours ago, Geordie Exile said:

 Fold lines are 0.2mm, and again I think that might have been too narrow.

0.3mm is what I always use. I once drew out what a bend looks like very much enlarged and it showed that to be what was required. On my phone at the moment, but I'll post a drawing later.

 

Jim

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The Association etch for steel wagon solebar conversion involves bending a fine edge along the length of the solebar. There is a special bending tool for this (2-350), formed from two pieces of paxolin with a sliver of etch between them. It works quite well. Perhaps you need to fabricate a similar tool for your window sills?

 

 

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26 minutes ago, Caley Jim said:

0.3mm is what I always use. I once drew out what a bend looks like very much enlarged and it showed that to be what was required. On my phone at the moment, but I'll post a drawing later.

 

Jim

 

0.3mm is what I use, and what I was told when I started out etching. If you do the maths, this is about right (0.35mm is minimum needed for 0.25mm material if you don't expect the metal to stretch, but I presume it does a bit).

 

Chris

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3 hours ago, Caley Jim said:

0.3mm is what I always use. I once drew out what a bend looks like very much enlarged and it showed that to be what was required. On my phone at the moment, but I'll post a drawing later.

 

Jim

I too use 0.3mm wide fold lines for 0.25mm thick metal. 0.25mm isn't wide enough to get a right angle bend. I think the rule of thumb is to use 1.2 times the material thickness for the fold lines. I'd agree about running a knife blade along the fold line to make bending the metal easier, especially if one side next to the fold is quite narrow and hard to grip. I score along the bend until a faint line appears on the other side.

 

Nigel Hunt

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As promised, here is a drawing which illustrates that 0.3 is the correct width for 0.25 metal.  The arc length is that of the middle of the thickness of the half-etched bend line (shown dotted). Presumably the metal on one side of the bend line stretches and on the other side compresses.  Either way this is what works!  I've used a similar drawing to work out the width for less than, or more than, 90° bends.

 

image.png.340be28f1cb37f119c505e3248e6a560.png

 

Jim

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4 hours ago, Caley Jim said:

As promised, here is a drawing which illustrates that 0.3 is the correct width for 0.25 metal.  The arc length is that of the middle of the thickness of the half-etched bend line (shown dotted). Presumably the metal on one side of the bend line stretches and on the other side compresses.  Either way this is what works!  I've used a similar drawing to work out the width for less than, or more than, 90° bends.

 

image.png.340be28f1cb37f119c505e3248e6a560.png

 

Jim

 

This assumes a K factor of, I think, 0.5. Ever sheet metal shop seems to have their own ideas on this for the same materials. What matters is that this works for us. 

 

On a 180° bend I use a longer tag with a 'hourglass' shape (narrower right in the middle) that encourages the bend in the centre of the tag such that the part alignment is close to begin with. I also put them on the opposite side to a 90° bend, which Chris and you both do iirc.

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4 minutes ago, richbrummitt said:

On a 180° bend I use a longer tag with a 'hourglass' shape (narrower right in the middle) that encourages the bend in the centre of the tag such that the part alignment is close to begin with. I also put them on the opposite side to a 90° bend, which Chris and you both do iirc.

That's correct, Rich.    You can even arrange for pars not to align edge to edge, where you want that to happen, (e.g strapping to land in the centre of framing) by putting the 'waist' at the mid point between where you want the edge of the part to end up and where that edge lies on the etch.  For example on this etch for some fencing where I wanted the half-etched horizontal bars to line up with those on the fence, but letting the posts extend down below the bottom of the fence itself.

 

image.png.4783dfd78f859933f334e7b28de83e25.png

 

The full thickness pieces lying horizontally are extra layers for the posts.

 

Jim

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