1:12 Heywood 15" gauge Brake Van...

[finescalerr]

If you use Printapart stuff for masters, please keep us informed about how they work out and how you account for shrinkage. -- Russ

[RoughboyModelworks]

Will do Russ. Basically they'll have to be oversize to account for the shrinkage which won't be too difficult to accomplish with the software. The questions will be: calculating the correct percentage and will the printed parts be robust enough to handle the molding process.

Paul

[W.P. Rayner]

Been a long time since I posted anything on the brake van superstructure. I've been concentrating on the metal components, preparing drawings for rapid prototyping. The superstructure drawings were relatively simple compared to the more organic shapes of the cast components. Today I prepared an exploded view of the frame and floor construction since these will be the first wooden parts to be cut and jointed for assembly. Goal is to replicate as accurately as possible the mortise and tenon joinery of the prototype. The floor boards are tongue and groove, as are the rest of the panels & roof on the van.



Paul

[nalmeida]

Wonderful looking piece of modeling Paul, very intricate design. Looking forward to see some prints.

[james_coldicott]

Paul,

really looking forward to seeing your progress with this project.

Regarding the use of printed parts as masters for casting... have you considered losing the printed part to get one brass master from which molds and repeat casts can be made?

Would require shrinkage calculations to be made for both processes but have seen printed parts successfully sacrificed to gain some very complex and largely hollow shapes- you obviously only get one chance at getting a 'hard' master but would make the molding process for repeat parts a little less fraught...

James

[W.P. Rayner]

Thanks James... me too I'm getting anxious to start cutting some timber here but until the weather moderates a little, my workshop is a little too cool for anything longer than a short stay. Hopefully by later in March it will have warmed up enough that I can spend some extended periods of time out there. In the meantime, there are still a few minor components to draw up for the van, truss rod brackets and the brake gear components, all relatively simple parts.

Ahhh... the lost resin master process. Shrinkage calculations are not a real problem and can easily be incorporated in the software prior to prototyping. The wheel I just sent off for prototyping is being used as a master for casting resin centers in 1:6 scale. As far as sacrificing a resin master to produce a brass master to produce perhaps multiple lost wax molds, it could probably be done, but I'm not sure it would be worth it unless you were planning a very large production run that may require several molds over a period of time. I'm not sure how the resin parts stand up to multiple moldings as it were. Perhaps if the parts were very delicate and you needed a large number of them, this might be a feasible alternative. The idea of sacrificing your original master in a one-shot deal to produce another master is a little disconcerting. Of course, you could always have another master prototyped, but then your costs increase. There is the question too of whether the resin would melt or burn away cleanly enough to leave a satisfactory mold.

Paul

[W.P. Rayner]

James:

I've done a little more digging around on this and it is possible to have masters printed in wax, eliminating the need for the original master and preliminary mold. This is taking hold in the jewelry business, naturally, and 3D thermojet wax printers are offered by Rio Grande, with an ominous "call for price" tag. In addition to the printer you also need an ultraviolet curing oven to cure and stabilize the model. The smallest version of this unit is $1470.00. The working area appears to be smaller than with the resin machines, but still within a usable range for most model work, unless you're working in a huge scale. Of course, it means that your wax "master" is sacrificed, so if the casting mold doesn't come out just right, you have to print another master and try again. Coincidentally a client of mine has asked me to look into this so I'm tracking down a provider who offers the service in this country. Shapeways is evidently testing the process, but I've seen prototypes from them that range in quality from good to dreadful. I'll keep you updated on what I find out.

Paul