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1/12 scale R-40-23 reefer Dreadnaught end
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Andy Carlson
Hello- Pictured is a tooling resin 1/12 scale PC&F R-40-23 Refrigerator car Dreadnaught end. This is a classic example of an old-school method of tool making. An individual rib is carefully shaped and upon completion a 2nd generation part is mated with 5 others and skillfully joined together to make the 1st generation tooling resin reefer end. A time intensive large scale model of the end is used as a tracing pattern for cutting a hard tool aluminum mold using a Deckel 3-D pantograph. The pantograph allows several different scales as recipients for this large scale design. 5.33:1 reduction gives you an S scale part, and a 7.25:1 reduction yields an HO part. The parent large pattern is pictured below. I have also included a picture of a pair of R-40-23 HO ends. The NP numbered part is from an Intermountain R-40-23 kit, and the grey resin part is a next generation part from the parent large scale pattern. The IM part is from a mold made with CNC tool cutting technology, and the resin HO part is from the old-school method. Regards, -Andy Carlson Ojai CA
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Dennis Storzek
On Wed, Dec 11, 2019 at 11:51 AM, Andy Carlson wrote:
The IM part is from a mold made with CNC tool cutting technology, and the resin HO part is from the old-school method.If you compare the two, it is obvious that IM screwed up the geometry at the end of the ribs. CNC is only as good as the programming, and the computer visualization of the surface sometimes makes these errors hard to spot. Dennis Storzek
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mark_landgraf
Andy
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If you have a Deckel photograph available, wouldn't it have been easier to make the first generation master rib and then use it to panto all 5 ribs, using an offset method into a ABS sheet? I model in 1/8 scale and have done steel tooling for 5 rib Murphy end panels. Now insert a piece .030 thick steel and apply 40 tons. Are you envisioning resin or vacuum formed or fiberglass sides and roof? What ever your choice, I'd recommend making sure it is UV and age/heat stable. Sometimes it is easier to make your master 2 or 3 times larger and then panto it down to the correct scale. Mark Landgraf Albany NY
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Andy Carlson
Hi Mark- I am not a tool maker and have never played one on TV (Ha HA). Most of what I know is just from listening to actual toolmakers talk. I have had a fair amount of resin casting experiences and those traits i can speak about more informedly. The only work I was involved with those 3 ends I sent pictures of was the resin HO end, I poured that casting in a mold I poured with RTV about 16 years ago. Even further back in time, I once saw the work from another old-school tool maker. This guy had the acrylic 4-1 sized positive of the Athearn Blomberg EMD truck which Athearn had commisioned for the replacement styrene sideframe for the BB Zinc out side bearing early Athearn Blombergs. That plastic sideframe is still held in ultra high regard decades later. That original toolmaker has since passed away. I wish I had bought that acrylic pattern from him when I had the chance. 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
On Wednesday, December 11, 2019, 8:08:23 PM PST, mark_landgraf via Groups.Io <mark_landgraf@...> wrote:
Andy If you have a Deckel photograph available, wouldn't it have been easier to make the first generation master rib and then use it to panto all 5 ribs, using an offset method into a ABS sheet? I model in 1/8 scale and have done steel tooling for 5 rib Murphy end panels. Now insert a piece .030 thick steel and apply 40 tons. Are you envisioning resin or vacuum formed or fiberglass sides and roof? What ever your choice, I'd recommend making sure it is UV and age/heat stable. Sometimes it is easier to make your master 2 or 3 times larger and then panto it down to the correct scale. Mark Landgraf Albany NY
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Dennis Storzek
On Thu, Dec 12, 2019 at 08:45 AM, Andy Carlson wrote:
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
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Charlie Vlk
When I was visiting the Kato factory I reviewed the CNC milled positive aluminum trial of the N Scale RDC body.
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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:
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