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I am often asked how I do my 3D models and turn them into slot car kits. I have put together a quick tutorial and some information in case some of you are interested. Note: this is my method and isn't to show you the only way to do it. You can use a printed part just fine with some finishing. My kits are ready for volume production and paint and that's the reason I do it this way.

Wanting certain bodies that I knew I was not skilled enough to carve out of wood, I found a NextEngine 3D scanner while watching MythBusters one evening. They used it to scan a 1/24th scale model of a Chevy Impala and then 3D printed it in the size they needed. That was my "Eureka!" moment and I immediately contacted NextEngine. They offered to scan a body for me and recommend a 3D printing service for me if I was interested in purchasing the scanner. (BTW - If you watch this episode on YouTube, you will actually see my Cougar interjected in to show off their scanner and the results. This was done as the show glossed over the computer portion of the process)

Here is the Cougar model once the scanning was complete:


They resized the 3D model to the 1/32nd scale specs I gave them and with proof that this worked, I shelled out $2500 for the scanner and sent the STL file off to be printed. That ran $350 for the ABS part.



The part was fairly rough and required quite a bit of hand sanding, the rocker panels to be made deeper as they did not translate well when re-sized, and the windows had to be cut out. This was not done on the original printed part though, as I was not about to cut on a $350 model. I made a 2-part mold of the original and after popping out a few resin copies got to work on those.



After quite a few hours the Cougar was finally ready.



How did I do? Not too bad when compared to the Scalextric version in my opinion!



The Datsun 510 was the first model I scanned and it turned out well.



It still cost about $350 to have printed and unfortunately during the copy process of the original part, it shattered into about a million pieces when I took it out of the mold! Thankfully the mold turned out well and I was able to keep working on the resin versions. This is a picture before it shattered:



The Datsun was still fairly rough and since I decided I wanted separate grill and bumpers I had lots of chopping to do:








But finally it was done:


I began experiencing computer issues that almost put me back two years on scanning. By the time it was resolved, I’d lost what little skills and interest I had and sold the scanner for what I paid for it.

Around this time I began talking with our own Choc-ice (Gareth is his real name) and we discussed the process he was using as I was starting down a similar path. The new path was purchasing a completed 3D model (he has made his own!) and having that printed off in SLS formatting. Both the Chevy II and the Corvair have been done this way.

As has been discussed here, there are several 3D printing options, all have their place, but as a comparison to the Makerbot or other printers, SLS is fairly smooth and getting smoother all the time:





I purchased a 3D model of the car I wanted for about $55:


Had the CAD work done to "shrink it" and remove the chassis, wheels, etc. from the model for about $90

Had it printed for about $85:


Did my normal copy of it:


And finished it:




So there you have it. Not a completely comprehensive look, but since people are always interested and numerous folks are now playing with this in our world, I wanted to put it out there.

David, That is amazing stuff! I had no idea you went to all that to make a car.
That's a far cry from pouring some silicone over a die cast car! :lol:
No wonder the quality of your casts are so nice. Great stuff, thanks for sharing this.

Bob

This is a true keeper of a post.

Thanks for the behind the scenes look Doc, what a process.

Wow, that sounds a lot easier than the way I have been doing it. I need to find a way to convert the models so my CAD program will let me make changes to it. As it is now, I print out the body and spend a couple hours with the dremel removing material from the inside of the body, then I start sanding to smooth out the ripples in the printed finish.
Great article, I'll be going back to read this more often now.

As David says, that's all there is to it ;)

I've got a range of 20 resin bodyshells and of those 15 were made by 3D printing the master bodyshell. All my different chassis and steering units over the years have been done as 3D prints and as David says, none of that would have been possible if I had to rely on my abilities of carving and fabricating or soldering. My typing speed would also be slower as I'd be missing at least 3 fingers due to burns, power tool accidents etc.

I used to get my bodyshells made as a solid block and from there they were slush cast. Now I get them hollowed to a given thickness and a 2 part mold is made so it's a lot more precise. That work is done by a bureau service as I don't have the software and can't justify the payback as a "hobby" user.

From there I get the 3D data, pull it into my CAD system and add body posts where I want them and sometimes extra strength features in the shell. Then it gets printed as an SLS, the last few have been polished which cuts down on the hand finishing. I do all the finishing on the 3D printed master which saves me one stage of silicone mold over David's method, however if something goes wrong with my master model it's pretty much all over unless I get a new one made. David can just pop a new one from his mold and start over.

It's a great mix of new technology and old skills - I still use vacforming for my interior and windows for example. But there's no doubt that this method of creating a slot car has given me huge freedom to make things that the big players don't do.

Again, just trying to show my way. What is funny is how long I've been doing this - 2006 is when I started. While technology has improved, pricing has improved, it still takes a great deal of work to get them to where I'm happy with them. However, it does let me makes stuff not done before. Having almost no CAD skills is a killer and that costs me $ and time. Luckily I've got a great guy that does that and the printing service is fabulous that I use.

As for finish - the recent 2J thread is awesome - those folks have mass produced a needed body, but requires finishing. That is a genius marketing method and one that keeps their hands out of the resin dust. I was only jesting when I suggested I do that. I get complaints occasionally that my kits are too hard to build. If I took their approach I probably would not still be in business after all of these years.

Now that things personally are settling down I hope to get caught up on some new projects and start releasing things faster.

Gareth - I figured you'd jump in here! Great stuff!

*waves*

One other thing - the advantage of David's method of making a mold from the initial 3D print is that resin is easy to work with; you can sand it or you can add paint and sand it. With the SLS method of 3D printing your only choice is really to paint, sand, paint, sand, paint, sand. Making a master from a modified resin part has plenty of advantages, but here in England the cost of silicone is very expensive so it would just push out my payback time.

Good thread, David! Making the technology easier to understand makes it more interesting I think.

Great information here, thank you for posting.

Rick V.

Just here to help. I do mold it as Choc says since resin is easier to carve on besides not wanting to break the part. Luckily, the costs of printing have come down and now my service polished it for me as well. Super nice! I've got another body on the bench that had this done.

True enough, and I was only using that print to show the differences between types of printing. Interestingly enough though is the same file was used for both prints. Not being a CAD guy though, all I can tell you is that I can spell STL..

So to us laymen that don't know anything about 3D printing, what causes one to look like Chicken *%$# stacked with chop sticks, and the other to be smooth?
Some of the bodies look ready to run when done!

Bob

As an addition...

I have seen in person both RMS and MT Resins shops and processes. Over they years these artists have improved and today bring us the best castings in the genre they offer IMHO.

Looking at the kits in front of me and seeing the quality, it's a reminder of how lucky we are in our hobby. Mark makes each mold BY HAND using his own technique that is nothing short of pure artistry.

Using the CAD system is it's own art form as well. One thing is certain, Dave knows it well.

I also think the folks who bring these model to us need to be commended on working together. There are some out there who feel they know it all, and the end product shows they do not. Others like Gareth, Dave, Mark, Shotgun...these folks help one another and the end product proves it.

Now about that Limited "Drowning Mona" Yugo.... :lol:

I didn't know about different printers needing different settings on the stl file, can you expand on that?

I've found that build orientation on the platform makes a difference; if the bodyshell sits on the platform with the roof facing up you get visible build lines on the hood, trunk, roof and a little on the sides. It looks like contour lines on a map and it's why most 3D printer manufacturers don't showcase model cars, instead they show widgets that hide these contour lines.

If the bodyshell is nose down (or up) the layer orientation is different and the gaps across these gentle curves are hidden better. I only found this out by accident of course! You still get the contour lines around the nose and tail but the front usually has details like a radiator grill and headlights that hide these lines better, they show up worse on large, gentle curve areas.

The STL files I buy can and are manipulated. My CAD guy does it in SolidWorks...so now I'm confused.