Printed HO Chassis

[1976Cordoba]

Here's a test print for a TYCO body project. It's a real world print to verify the dimensions of the virtual design chassis, that can be fitted to virtual 3D bodies before printing . . . If you follow me.

[NicoRosberg.]

printedtyco.jpg

That is cool.

What is the material?

What is wear like around the axles holes?

Is the wheelbase 1.7'', as in set for the Group C Porsche Tyco did?

[HO RacePro]

A coupla criticisms...

One, the axle holes appear oversized. To achieve a better fit the holes could be printed undersize and reamed to spec. Or the holes could be bushed, possibly with eyelets. But the holes still might need to be resized to fit the bushings, and may still need reaming to achieve tolerances.

Two, the chassis is designed as if it were an injection-molded part. Thing is, 3D printing has its own design "best practices" which are very different than those for injection molding. While the designer may have intended to simply duplicate a specific injection-molded design using 3D printing -- and achieved that -- a design that is good for injection-molding may not be at all good for 3D printing, and vice-versa.

When designing an injection-molded part good practice is to keep wall thicknesses the same. You also want to create features to help the ejection pins push the part out of the mold. Both practices are evident in this part. But they are irrelevant in 3D printing.

I've been on a bit of a personal journey discovering the differences between good design for injection molding and 3D printing. One example is thick walls. In a 3D print thick walls can be printed with a low-density infill -- typically about 20% of full density. You can't do that with injection molding unless you use a resin that contains a blowing agent to create a foamed core with a solid skin. That works, but not with the precision you can do it with 3D printing.

You don't want to create large fillets between walls in injection-molded parts. They make for thick sections that don't cool as fast as the rest of the part. Not only does that increase cycle time in the molding process, but the interior of that thick section may form voids as the plastic shrinks and cools. It may also create molded-in stress that can make the part prone to failure under load. A 3D printed part has none of those issues.

If the idea here was to print a chassis just like an existing injection molded part, well, at least in terms of geometry it does look like the designer succeeded. Whether the part performs like its injection-molded cousin, however, is not at all certain. For one, 3D printed parts tend to be weaker than injection-molded parts. If this is intended to be part of a magnet car some of those thin walls might need to be beefed up.

Good design requires an intimate understanding of the requirements and limitations of the processes used to manufacture a part. You can manufacture a metal part by casting or by welding, but the two designs won't -- and shouldn't -- look at all alike. Same goes for printing and injection-molding plastics.

I'm not trying to dump on the designer of this part. It appears they have achieved what they set out to do. What I am trying to do is share some insight into how a designer needs to think when the goal is to design the best part for the intended method of manufacture. Sometimes it can be very challenging. Which makes a good design satisfying and something to admire.

Ed Bianchi

[NicoRosberg.]

tboi

[model murdering]

Good one 'Doba!

So, it's a buck to hammer out and refine body fitments. Nifty

B

[NicoRosberg.]

It appears they have achieved what they set out to do.

Which appears to be to check that a file inside a computer matches the original in the real world, for future body projects.

Having said that, if this was an attempt to print a chassis, surely it would be smart to commence with an existing design, which is then crash-tested?

[model murdering]

No.

Existing chassis designs are already crash tested.

[NicoRosberg.]

Not in a new material like Doba has presented.

Crash testing it would reveal if it needs strengthening, and where, just as running laps would reveal if the axles need bushing.

[model murdering]

Were he testing, that would be testing the material, not the existing design.

[NicoRosberg.]

Well, it is testing both, if they suit each other, or not.

[1976Cordoba]

Mr. Hall is correct when he calls it a buck. I'd have to look up what material as it was printed in a couple different materials. I appreciate the tips anyone can offer.

Thanks,
'doba

[model murdering]

The dead give away was the humongous frame connector that notably crosses the centerline of the armature. Well, and that fact that you told us as much. Still, a good thing your bench top "go, no-go" gauge has now been pencil whipped and crash tested by experts.

When ever you pop in, I reminisce on the "Deckert Ring". Based on the few bread crumbs you've dropped, I'm long shot betting the bar tab that there will be "corrected" road graders.

If you havent already, the best advice is to hook up with Jim Miller aka "High Wing Pilot". So far out front, he's not hard to find. His trail is pretty easy to follow.

[1976Cordoba]

Yes, Jim makes really great stuff

[1976Cordoba]

[Eagle Racing]

Here are a few pics of the Eagle Racing USA, printed 3D chassis. The last photo is of the new narrow chassis.

CIMG1980.JPG