Finally getting down to business with sketchup

[finescalerr]

This suggestion may go contrary to the underlying reason for using rapid prototyping but maybe you should leave off the rivets and possibly the hinges if you try another test. As I study your photos, I see little ridges on every flat surface. You will need to sand them off both the boards and the steel strapping. But the rivets will create a big problem if you sand the strapping. Moreover I have no idea how you would adequately clean up the hinges or any other fine detail.

I guess the problem is that the resolution is not good enough to withstand a close look, especially the nut/bolt renderings and the hinges. At this point, were it my own model, I either would abandon rapid prototyping as too crude or I would pay a fortune for a higher resolution output.

Years ago I started work on a styrene pattern for an ore car with very similar hardware and planned to do resin castings. In the long run, that might provide more satisfactory results given your level of skill.

Russ

[Hauk]

I guess the problem is that the resolution is not good enough to withstand a close look, especially the nut/bolt renderings and the hinges. At this point, were it my own model, I either would abandon rapid prototyping as too crude or I would pay a fortune for a higher resolution output.

I have played around with the online qouting software now used by FineLines, and it seems that the price is significantly reduced if you order several parts  (different .stl files). My wagon consists of 4 different parts of around the same type, and this bring the price down from $133 to around $61 pr. part. another *identical* part will cost $18

If more people get together and order 10 similiar parts the price drops to around $52.

All this is based on the part shown above, and take into account that I might have overseen somethng that can influence the price. Go check for yourself, the app is fun to play with!


Still expencive, but close to worth considering...

[Chuck Doan]

I'll have to give it a look. When I was there last they would only quote the Micro res parts via a review (they never did get back to me)

[sd80mac]

When creating 3D drawings for printing, you mentioned that Marc suggested you have PAP print the part flat. My question is, if you orient the part on the XY plane of your drawing screen, and build it up or out along the Z-axis, is it safe to assume the PAP will orient and build the part this way as well?

Donnell

Another testpart has arrived from PAP, and it looks far better than the last one.
I think this is both due both to better control over the geometry of the SU part, and to Marc´s suggestion that I should make sure that PAP printed the part  flat.







In the extreme closeups it is easy to see that the part is by no means perfect, but I am planning to run a string of these cars on a layout some day, and without magnifying glasses I feel the quality might be good enough.

And the hassle-free dealings with PAP is a great bonus!

-Haavard

[JohnP]

Marc is right, it would be a pain to smooth surfaces with rivet or NBW details PAP'd in.

Now, one could also create a center dimple or even a hole where the parts go. Then commercial details would be added and come out aligned properly.

John

[RoughboyModelworks]

When creating 3D drawings for printing, you mentioned that Marc suggested you have PAP print the part flat. My question is, if you orient the part on the XY plane of your drawing screen, and build it up or out along the Z-axis, is it safe to assume the PAP will orient and build the part this way as well?

Donnell

Yes, that is correct. And it is best to raise the part slightly, ca. .050" above the x-y plane to prevent resolution problems with the underside. PAP will fill that gap and any other voids between parts with their wax support material.

Paul

[SandiaPaul]

Hauk,

Can you tell us about the process of getting the brass part made? Dealing with the company, costs, timing, etc...

I googled Korean Brass and one of the first hits was your web site!

Paul

[Hauk]

Hauk,

Can you tell us about the process of getting the brass part made? Dealing with the company, costs, timing, etc...

I googled Korean Brass and one of the first hits was your web site!

Paul

I can, and I will tell about the process, but I need to go through all the correspondance etc. first, and this will take some time. All I can say at the moment is that I have put brass casting on hold, and I am focusing at the printapart route at the time.

Regards, Haavard

[Hauk]

During all this testing my priorities have shiftet somewhat, and I am now focusing more on getting a string of these ore cars into operation.
So some compromises must be made. After priming the latest PAP-part (pictures will follow) I feel the quality is good enough for a train of say, 10 cars.

This also made me think about casting cost vs. printing cost. If I order parts for 10 car at the same time, the PAP parts will cost USD 315,-

But how much should one expect to spend on materials for making moulds and casting 40 bubble-free resin parts from two masters like the PAP part shown earlier in this thread?
(sizes are 63mm X 32mm  X 2,7mm and 52mm X 32mm X 2,7mm)

Could anyone give a ballpark estimate? It have to be taken into account that I have have no access to a vaccum chamber or a pressure pot. So the reject rate would be somewhat high, I fear.

Regards, Haavard

[eTraxx]

<snip>

Could anyone give a ballpark estimate? It have to be taken into account that I have have no access to a vaccum chamber or a pressure pot. So the reject rate would be somewhat high, I fear.

Regards, Haavard

Haavard. I should think that if Dallas turns back up he should be the one to answer that ..

[78ths]

Hi Haavard
The casting costs depend in part on materials used. I use smooth-on for all my resin and rubber. A gallon kit which goes a long way is around 100-125.00 - the resin is cheaper and again it depends on the resin used. I use a resin called Task by Smooth-on that is very strong and can be machined really well. For bubble free castings I do all my under pressure. (pressure pot) at 50psi until cured. I also use a vacuum chamber to vacuum the rubber. This is a must if you pressure cast. I like the route of casting myself - I get 1-2 masters printed in 3D then make molds as needed. The rubber I use varies depending if I cam casting in metal or resin. My resin molds will do hundreds of impressions before any sign of wear, the metal molds will break down after about 50 castings if there is a lot of small parts or details.
I don't mean to make it sound difficult as it is a simple process, however making perfect castings is an art that takes a bit of practice.
Here is a simple pdf I put together on casting a few years back.

http://www.78ths.com/index.php?action=downloads;sa=view;down=3
cheers Ferd

[Malachi Constant]

Haavard --

You certainly should be able to cast all the desired parts for less than the cost of having them all printed ... HOWEVER ... that would then mean that your "new hobby" becomes learning how to make satisfactory resin castings, at least for a while!

But I really wonder how they will turn out in print. For instance, will the grooves between the boards show? Or become too prominent?
I am also wondering if i should make triangular or square grooves. I have tried 0,1mm X 0,1 mm square grooves and triangular grooves with 0,3 mm sides. Input is welcome!

-Håvard

Early on, you made this comment.  Before you decide to print or cast the parts for ALL of the desired cars, it might be wise to assemble and finish one car to make sure: 
(a) all the parts fit together as desired
(b) the assembled car has the desired appearance
(c) the desired finishes can be achieved with the intended materials

But, considering the project as a whole, I'd have to say that I'd lean strongly to using the CAD/printing aspect of the project to produce the HARDWARE and assemble the wood components in a home-made jig.  I think that this would produce the least expensive ... AND ... most realistic appearance.  By doing this, you would have the precision of the CAD/printing to insure that the hardware is consistent, but you would gain the "modeler's edge" in terms of finish by being able to apply board-by-board weathering techniques, distressing, coloring, etc.

I think Chuck or one of the other PAP users indicated that the PAP pieces were a bit brittle.  I think this would be a serious concern for your project.  The most delicate parts of your pieces are the hinge bits ... and as those are intended to be functional, they would be subject to the greatest stress and the highest likelihood of breakage.

So, it seems like it might be wise to use a printing process to produce waxes as you described earlier and have all the hardware cast in brass ... or use one of the printing services that uses metals.

That's my 2 cents worth ... but it's only 8 am, and I'm not really a morning person! 

Cheers,
Dallas

[Hector Bell]

Why don't you just make brass masters of the hinged strapping, with nuts and washers and get someone to cast them in a good whitemetal or a lost wax brass, then fix them to the wooden sides. Cut out all this computer nonsense completely and make you more fulfilled as a model hobbyist.  Which I thought was the original idea.

Martin

[finescalerr]

After reading all the above, and as much as I love the potential of 3-D printing, Martin's suggestion seems to make good sense.

Here is why: You may recall I was concerned the texture of the Printapart "metal" straps was too coarse and would be very difficult to clean up for a master, let alone a series of cars; it would take about the same amount of time to produce a single brass (or styrene) master of that piece as to clean one. Also, the straps and hinges need strength and metal is the best material to provide that. Finally, individual wood boards will look far better than cast resin.

Back at the start of this thread I think I mentioned building styrene patterns for a similar car a decade ago, long before 3-D printing was a viable choice, and the plan was to cast the parts in resin. But even then I had serious misgivings about using resin in place of wood because, in my experience, it takes as long to get a satisfactory weathered wood appearance from resin as it does to build the whole damned thing from pre-weathered wood in the first place! And, at least in scales above 1:48, wood always looks better.

I guess, no matter what technology is available, we always come back to using the best material for the job.

Russ

[JohnP]

Jeepers Haarvard- Russ and Martin would have you cut your own trees and carve scale lumber from that! But those are the choices in the hobby; it should always be  about satisfying whatever modeling craving you have at the moment.

But if you do decide to cast just to learn a new technique and make 10 - 20 - 50 or more cars for yourself, friends, Christmas tree ornaments, etc., I would recommend an easy to use soft rubber like Smooth-On OoMoo or, even better, their new Mold Star platinum cure RTV. Both of these are a low viscosity and the bubbles will free themselves. Vacuum is absolutely not required- I used OoMoo extensively to develop my mold box and mastering techniques.  The 1:1 mix means you need no scale as well. Either rubbers are adequate for making 10 cars worth of castings.

For resin I found that the Smooth-On Smooth-Cast 305 cures better in a very thin section over the Task series. The Task resins are tougher though so if you need strength and have adequate mass to the casting they will cure just fine. I recommend a slower setting resin- this will give you time to mess with mixing and pouring, it will cure with less heating so it is easier on the rubber, and there will be no noticeable shrinkage of the finished part.

You will absolutely need pressure casting to remove bubbles. You will need a pressure pot used for spray painting and a compressor. I use 50 psi and never get bubbles in hundreds of thin castings. Don't use anything but a rated pressure pot for this application for safety. Some sources recommend higher pressure but I never have troubles at 50 psi. I dislike metal objects under pressure in my workroom so a lower pressure is better for me.

Do not use release spray on the rubber when casting. It is difficult to clean off, makes paint not stick and is unnecessary because RTV releases well. But if you are using a clay mold half layup, you will need a release for the exposed rubber on the first half of the mold when you pour the second half.

Have another look at my thread http://www.finescalerr.com/smf/index.php?topic=1024.0, ignore the vacuum part and feel free to ask questions.

John