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Post by big train james on Oct 3, 2019 19:37:26 GMT -5
I'm waaaay late to this, but I was looking at the Onshape drawing for the step treads. The dots in a hexagonal pattern around each larger hole are actually raised pimples with small holes in the center, rather than holes themselves. The step material is actually Morton open grip walkway material, the same as is found on many covered hopper roof walks. Here is a link to there catalog pages for rail products, if you scroll down to the bottom or go to the second page, you will find locomotive steps. They may or may not match exactly what you need for the gp30, but they all have pdf's which you could download and presumable pull into Onshape to trace. The hole and pimple pattern is the same for all, it's just the overall shape of the step that varies. The second link is to a generic cut sheet for the open grip safety walkway, and it has dimensions for all of the center to center distances. Very useful stuff. catalog.metlx.com/viewitems/railroad-car-running-boards/running-boardscatalog.metlx.com/category/open-grip-safety-grating-standard-channelsThe running board catalog also has info for all of the walkways they offer for various rolling stock types, including covered hoppers, well cars, and coil cars. Plus there are PDF's for crossover platforms as well. I'm not sure how far you want to take things, but you'll see that the toe kick plate at the back of the tread should be integral with the tread, folded up either 4" or 6" typically. You'l also see that there is usually, at least on most steps other than the earliest that I've found, a row of smaller holes that is half on the top of the tread and half on the front face of the tread, spanning over the fold. Lastly, the two squares on either side of the tread should be right at the edge of the tread surface, and open edge. I'm trying to do the same sort of thing that you are trying, creating etch artwork for better parts in O scale. In the following link, you'll see the 3d cad I worked up, which basically matches the prototype, and then the 2d cad interpretation for etching. There are some quirks and nuances for the artwork, but once you get the rules down, it becomes pretty automatic. www.westernthunder.co.uk/index.php?threads/etch-artwork-a-first-attempt.7405/#post-177033I tend to use links because I don't have a photo hosting account. Probably should do something about that, maybe. Jim
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Post by ctown2 on Oct 7, 2019 22:06:28 GMT -5
Been pretty busy with the back to school routine (I'm a teacher) so I haven't had much time to work on this project lately. I kind of stalled out with some designs of new radiator fans, so I need to work on those parts again as well. I really need to just bite the bullet and order some Cannon and Co parts so that I can use them as a basic design. I've got the replacement steps all ready and done to be sent off to the etching service, but I need to finish the other etched parts so I can do them all at once. These should be a vast improvement over the stock steps. I have done a little bit more on the cab interior, but will wait to post photos until it is all the way done. Craig
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Post by ctown2 on Oct 7, 2019 22:13:32 GMT -5
Jim, Yes, I'm aware of the raised dimples. What I was thinking was having the smaller raised dimples half etched from the bottom, then I could take my NWSL riveter and punch the half etch holes into raised dimples. And yes, I have added the kick plates to the top on the main steps, but the engineer and fireman cab steps, I believe don't have kick plates.
I will have to go back and adjust the center to center spacings using that information you linked. I kind of just was guessing based off some photos I had. The other thing I have to consider is the requirements for etching service. I was able to find EMD drawings for some of the safety steps, and had to kind of adapt on the fly as I don't think my model dimensions exactly match the prototype either. I haven't figured out a way with Onshape to create the holes on the folds of the sheet metal, so either I can try and copy/paste the pattern when I import it into Inkscape or just call it good enough. Most people won't know.
Edit- It looks like my center to center spacings are within a 1/8 of an inch or so of the prototype plans. Making them any closer creates problems with the etch (not enough space between etching of parts)
Craig
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Post by big train james on Oct 8, 2019 9:22:11 GMT -5
That is correct that the cab steps don't have integral kick plates. It didn't occur to me that the Onshape drawing was a cab step. Also correct about having to balance the proto dimensions against the model dimensions. I had to do the same thing on my model. The pilot end sheet on the Atlas frame scales out to about 3", and there are some other areas with extra material, which is likely a concession to the diecast process.
On the raised dimples, that's an interesting idea to punch them from the back. I'll have to reconsider now. Although that's a lot of dimples to punch! I was trying to achieve the same effect by half-etching the top of the tread, leaving the raised nubs. The problem is that I couldn't half etch the tread without blowing out the fold lines. There are ways around this, namely to scrawk your own fold lines. Or you could go for a four layer etch, but that's supposed to be pricey. In the end I decided not to bother. The reality is that I could only pick up the nubs with magnification, or in a tightly cropped photo. I'd love to have them, but I let this one go. It would certainly work better as the scale increases.
As far as the holes on the folded edge are concerned, it's fairly simple. If you are creating artwork in 2d, the holes are just circles, with the half-etch fold line running through them. You can see that in my 2d drawings on the Western Thunder link. If you are drawing them in 3d, then I'd suggest using a sphere positioned more or less with its center point coincident with the folded edge, with minor adjustments to account for material thickness. Subtract the sphere from the step, and you should be left with essentially a semi-circle on each face. They may not be exactly a half circle per face, due to material thickness. I'm making a presumption that you can do that with 3d solids in Onshape, if its capabilities are anything like Autocad or Solidworks.
I'm curious if Onshape has a function to allow you to unfold a 3d sheet metal model into a flat part?
I'm also trying to get more etch artwork completed before sending off. I'm planning on using PPD in the UK, and I'd like to be as efficient with international shipping as possible to keep the costs down.
Jim
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Post by ctown2 on Oct 8, 2019 16:34:49 GMT -5
Jim, The beauty of Onshape is that it allows you to unfold a 3D sheet metal model that has built in the thickness needed for fold lines. I haven't quite figured out how to then draw on the flat sheet metal drawing, but I'm sure it is possible. I've created some complex folds with Onshape. The only downside is that that etching service (PPD) wants you to place the drawings on a 2D file with all the half and full etched marks noted. So I have to export that .dxf file into Inkscape and then create a line drawing. So it becomes a multi step process. Since I can fill a hole A4 sheet of paper, I will probably include a couple of different versions of the cab steps. One with small half etch holes, one with no dimple hole, and maybe one like you suggested, half etching from the top down. As for the fold lines, I might experiment with no half etch fold lines because I think it is thin enough material that I don't need them. But I've got room to experiment. I've got cab steps, and pilot steps that I'm working on at the moment. I started with the simple cab steps. I'm even tempted to try some small diamond tread etch as well, but that introduces a whole new issue with the latches on the diamond tread near the cab. So far my list of photo etch for just this project is.. Cab steps Pilot steps Radiator grills if I can find some good reference information Fans Fan covers (I will 3D print the rest of the fan housing) More grab iron attachment NBW things. Diamond plate? I figure if that doesn't fill a A4 sheet or two then I can quickly make replacement cab steps for my GP9 and F3 units as well. I also have a huge photo etch design for a GN Snow Dozer that PPD will eventually get as well. I will probably include a few sheets of those parts as well. The problem with designing these parts is that 90% of the time you can't show progress, then boom that last 10% gets done in a few days. If you're curious, here is the full file of steps. I still have some tweaking to do with the pilot steps (move the square holes) cad.onshape.com/documents/7bc7ebf27b4ee5f6f130d221/w/4f3633de79089d082de7c0dc/e/c57cedb273c501fbc8b19138Here is the grab iron bracket I was talking about. The smaller hole gets a NBW washer, the larger hole gets the grab iron. cad.onshape.com/documents/0c11683cb6ca5d45a71e991f/w/ce4ad2bb8bb71c9995a17b71/e/6798678d593504f075f67aabThis is my large Snow Dozer project. Basically everything is either etched, 3D printed brass, or K&S metal shape. cad.onshape.com/documents/d6a7c3328ca42805d62a3117/w/6441b6e268f09a15fb4a5881/e/7e31f23d55cb266244a6b77fCraig
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Post by ctown2 on Oct 8, 2019 23:44:52 GMT -5
Well 2 steps forward, 1 step back. I went back and looked at the cab step design and realized that I was making a major mistake. I wasn't leaving enough spacing between the dimple holes and the larger holes according to the requirements for the PPD etching service. Thankfully I can save most of the drawings, so it is just a matter of tweaking some things here and there. Glad I caught this now instead of when I tried to send it off and it was rejected.
Craig
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Post by big train james on Oct 9, 2019 10:09:32 GMT -5
I can reply with more later, but for now I'll say that the tolerances as specified on the PPD website can be exceeded. They will ask you about it first, and you will need to sign off that etching failures aren't on them where specs are exceeded. But it can be done. So don't change all of your drawings just yet.
That being said, bar and gap width equal to the material thickness is about as narrow as you can get away with, no matter what. Maybe just a little bit narrower than material thickness. I measure from the edge of the large through hole to the edge of the dimple/nub on my drawings at a little over .007" at 1:32. So that would theoretically limit material thickness to .007" as well, which is about 1/4" at 1:32. That's pretty thin, and I would be concerned about the strength of the parts in nickel silver or brass. They would be much stronger in stainless steel, so that may be an option.
All food for thought. More later.
Jim
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Post by ctown2 on Oct 9, 2019 11:14:50 GMT -5
Jim, I redesigned the bar spacing between the large hole and the smaller holes to be 1.2x the etch material thickness. Onshape has a feature that you can make a measurement a variable. So my variable is #Etch * 1.2 Right now the etch material is set at .3mm or about .010" as I think that is going to strike the balance between strength and scale thickness.
In 1/29 1" = .0344", so .010" is about as close to a 1/4" as I can get without losing too much strength.
Stainless steel might be an option, but I was worried about making bends without having half etch.
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Post by ctown2 on Oct 17, 2019 15:27:38 GMT -5
A few photos of the CAD process... The fans as of now... The steps that are to be etched. The smaller holes will be half etched from the bottom, and using a NWSL riveter, will be raised as rivets on the top surface. I may try 3D printing these as well, but I'm thinking they won't be as strong as brass etch. Craig
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