A '91 Stealth RC10 project

[mikea96]

Looks awesome!

[sandkil]

Great metalwork

[bluewormx]

WOW!!! amazing work! The chassis looks CNC cut, but is it?
Cant wait to see the rest of the parts!

[Sticksnpuck]

This is ridiculously awesome, amazing work! I can't wait to see each new step.

[XLR8]

Thanks for the compliments guys. I’m not sure I would call it “awesome”; I’m hoping to save the awesome stuff for the replica. But thanks again for the kind words.

No CNC here, just a drill press, coping saws, files, etc. -- just common hand tools and a lot of patience. The chassis plate alone took me about 6 hours to finish.

So, a little update: The top deck and trans brace are finished so it’s time to start the trial assembly process. So far, everything fits like it should (holes lineup, etc.). It definitely pays to invest the time needed to make an accurate CAD model before cutting material. At least it has for me (I hate tweaking parts to make them fit after they’re finished).

I’m struck at how rigid this assembly is. That very thin top deck, while off the car, is very flexible but once it’s screwed to the rest of the assembly, everything becomes amazingly stiff (maybe too stiff?). Remember the broken top deck on Masami’s car, was it an accident or was it deliberate? Did any of Masami’s teammates manage to break their cars?? Has anyone ever spoken to him about this??? Anyway, I think it’s an interesting possibility to consider.

I went ahead and cut the trans brace from the same 1/16” G10 material. Like the top deck plate, most of the forces applied to this part are coplanar so the actual thickness of the brace is somewhat irrelevant. The material cuts and shapes like butter with hand tools. I wish I could use if for shock towers but it’s just too flexible for that purpose.

I’ll need to make a couple 5 degree wedges for the front bulkhead to compensate for the difference in kick angle (25 vs. 30 degree). Think I can cut these from my other favorite building material; styrene.

I’ve mentioned before how much I dislike the color of the 3D printed parts so I will try painting them with Krylon’s “Ivory” paint (it seems to be close to the blonde natural nylon AE parts). Anyway, that’s the plan; I guess we’ll see how well that works out. It’s a runner so I’m not gonna be too fussy.

Next up are the shock towers and battery strap. Stay tuned.

[mikea96]

That looks great nice job!

[XLR8]

thanks again Mike.
I've gotta say that I'm very disappointed in the quality of that 3d printed bulkhead. Not only are the hinge pin holes oversize but the screw holes are as well. I've just fitted the shock tower and all the screws turn in as though the holes have been tapped (with very little to no resistance). Once they've bottomed, I'm afraid to apply very much torque or they might pull-out. I'll drill the holes deeper and fit longer screws and see if they'll tighten.

[mikea96]

Which company did you get the parts from?

[XLR8]

Which company did you get the parts from?

This is the NIX 91 "racer" set from i.materialise. For this build, I wanted durability so I chose the MJF material.
Mike, I know that you're planning to build a replica so you'll need to order your parts from Shapeways (i.materialise only sells the racer set). I also have the Shapeways NIX 91 "replica" set and the holes are correct or maybe slightly undersized.

[mikea96]

Ok i figured that was where you bought them. I have ordered all the shapeways parts and i think i will machine delrin arms and a front bulkhead and maybe more at work on our manual mill.

[Niki]

Hello Doug, your project looks great!
I have the same MJF front bulkhead and when drilling hinge pin holes with 3.2mm, I really got a lot of material out. Take a closer look at the first picture.
Also screw holes had enough material. I cleaned them first with 2.0mm and tapped 50% of screw lenght.
Too bad there is this much variation between parts. Well, we can still use the same 5-40 or M3 trick as we do with injection molded kit parts. Hinge pin holes are harder to compensate.
Did you allready drill the rear arm mount hinge pin holes? Is it better or worse? Just wondering if the part size have effect on it.

Tip for every SLS/MJF part builder:
Clean the screw hole with a small drill all the way but never tap a hole all the way. 50% of screw lenght is a good compromise.

-Niki-

[XLR8]

Since I don’t have access to any CNC equipment to make parts, accuracy can be a real challenge.
One technique I’ve found helpful for drilling screw holes (especially for composite materials that can be difficult to center-punch) is to mark the center on the pattern with a 1/16” circle; I think this provides a more useful target point for the bit than a simple cross which goes away the moment the bit touches the material. I have the circle and cross saved as a group (or block) in CAD with the insertion origin at the center point so I can easily drop it everywhere I'll need to place a hole. Regardless of material, I’ll always begin by drilling a 1/16” pilot hole prior to drilling the hole to its final size and having a circle marked on the pattern that matches the size of the pilot bit helps me accurately locate the hole. Using the cross/circle CAD block is useful for both metals and composite materials. For aluminum parts, having the cross helps to accurately locate a center punch while also having the circle as a reference helps to confirm that the pilot hole is on target.

I’d very much like for everyone who wants a ’91 Stealth RC10 to be able to build one so I’ll be posting some detailed instructions for making the chassis parts after completing this runner car. The time spent writing the instructions might offer a nice break before starting the replica build. Maybe by that time, CNCrc (aka Seabass) will be producing chassis parts again and it won’t be necessary to make your own parts.

[NomadRacer]

That's very nice, using a pattern. I have an old drill press with a cross slide vise. I know it wold be time consuming but this is my technique...

Once I've made my marks on the piece I clamp it in the vise. Then I take a 1/4" (new) counter sink bit and using the cross slide vise, get it centered on the mark. Drill very lightly and make sure I'm spot on. Once that's done, switch to the correct size drill bit and get it done.

You have a lot of holes to drill so it might not be the thing for you.

[XLR8]

Yeah, I totally forgot about it but my Dad had such a vise in his shop. Don't know whatever happened to it though. As for being time consuming, I'm more concerned about accuracy than time so using a slide vise is a very good idea. I'll look for one at our local Harbor Freight.

Thanks Nomad, you're number one!!

[NomadRacer]

Cheers mate!