Re: 1/12 scale R-40-23 reefer Dreadnaught end


Charlie Vlk
 

When I was visiting the Kato factory I reviewed the CNC milled positive aluminum trial of the N Scale RDC body. 
Over the 3D aluminum object we discussed the roof curvature and marked it up for correction to the 3D CAD tooling files....
The following morning (!!!!) I was presented with the first plastic test shots of the corrected body shells!!!
Reviewing 3D renderings of designs is vastly preferable to trying to absorb and index twenty or more paper drawings covering all the parts in a product.  You can peel away elements to look at every aspect of an assembled model and rotate in it to view at from any perspective.  The 3D design programs have built-in fit and interference features that make engineering and review much simpler.
It is still possible to miss nuances of contour but still it is a lot easier than looking at old fashioned multiple plane views on paper prints.
The review process within a company and the interaction between the project manager and the engineers at the factory is critical.   If the engineers do not make recommended changes the product suffers.  Too many times the designer (in China or even in the US) won’t listen and insists on doing it their way, even though the reviewer has direct end user input or experience.   
Importers need to write detailed outline specs covering the full range of quality, performance and feature characteristics to avoid problems, but too many put all in the hands of the factory and are surprised when products don’t measure up to what the market expects.
Charlie Vlk
Railroad Model Resources


On Dec 12, 2019, at 11:42 AM, Dennis Storzek <destorzek@...> wrote:

On Thu, Dec 12, 2019 at 08:45 AM, Andy Carlson wrote:
I think that in some very important ways the old-school methods of panto reducing down over size patterns with a pantograph can produce parts which the best of CNC tooling has not shown an even match.
-Andy
And I totally disagree. Anything that can be cut by a 3D pantograph can be cut by CNC. In fact, you'll be hard pressed to even find a pantograph in a modern day tool shop, unless the owner is almost retirement age and never gets rid of anything. Toolmaker time is expensive, and a pantograph is a manual machine. The question becomes do you want your toolmaker to spend hours sitting at the pantograph, or be doing something else while the CNC machining center cuts the part unattended.

Pantographs can't reverse the pattern; that is they can't cut a cavity directly from the model of the part. The usual way that was dealt with was to wax the part model, and then pour epoxy around it, thereby producing a pattern of the cavity.

The real problem is one of visualization. It is difficult to see contours in a cavity that are very evident on the part.  In the case of the 1/12 scale end, the pattern maker had the positive pattern to compare to the drawings, and most likely photos of the real end. In my toolmaking work, I cut graphite EDM electrodes, that, while small, are a positive copy of the part, so if contours are strange, they are evident, at least under magnification.

The problem with the IM end is it was most likely cut as a cavity directly into the mold plate, relying on the computer graphics to inspect the shape of the surface, and obviously the programmer got it wrong and didn't catch it. This could have been avoided by using the opposite side of the surface geometry to cut a positive part in plastic or wax. Since CNC files are scaleable, the positive check piece could have been made oversize for easier inspection.

Dennis Storzek

Join main@RealSTMFC.groups.io to automatically receive all group messages.