What you will learn
- Lexan is polycarbonate, and it melts if you push. Low RPM, light touch, and patience are the only settings that work.
- Cut the wheel arches with a cut-off wheel, then finish with a sanding drum. The cut-off wheel gives you the line; the drum gives you the radius.
- Window masks come off last, after the body is on the car. Pulling them before paint removes paint with them.
- Polish the wheel arches with a felt bob and plastic polish. The arches are what people see from two feet away.
| Job | Bit | RPM | Watch out for |
|---|---|---|---|
| Mold lines | Sanding drum, 220-grit | 5,000 to 8,000 | Don't dig into the panel |
| Wheel arches | Cut-off wheel, then drum | 10,000 to 12,000 | Cut on the inside of the line |
| Body post holes | Small drill bit or diamond point | 6,000 to 8,000 | Mark the position first |
| Window mask edges | Sharp knife (not the tool) | — | Cut at a 30° angle |
| Final polish | Felt bob + plastic polish | 4,000 to 6,000 | Don't polish the painted surface |
Why is the rotary tool the right tool for this?
Lexan is too soft for a hand file and too tough for sandpaper alone. A rotary tool with the right bit sits in the middle: aggressive enough to remove mold lines, gentle enough to leave the panel. It's the workhorse of any RC body shop for a reason. The HARDELL Orange Pro 61pcs Corded Rotary Tool Kit has every bit this job calls for, cut-off wheels and drums included.
Most of the work is short, light passes. Trying to remove a mold line in one pass is how you cut through the panel. Three light passes is faster than one deep one.
How do you remove mold lines without burning the plastic?
220-grit sanding drum at 5,000 to 8,000 RPM, light pressure, and a continuous motion along the line. The moment the dust turns sticky, drop the RPM or change the bit. Sticky dust means the plastic is melting, not sanding.
Clean the drum every 30 seconds. A clogged drum cuts hot and the panel melts before you see it.
What's the right way to cut the wheel arches?
Mark the cut line on the inside of the body with a pencil. Then a cut-off wheel at 10,000 RPM, following the line on the inside (so the outside is the finished edge). Once the cut is done, switch to a sanding drum and radius the edge to match the original body line.
Skip the cut-off wheel and try to do it all with the drum. You'll either remove too much or burn the edge. The cut-off wheel is the rough cut; the drum is the finish. A HARDELL Black Gray Advanced 94pcs Rotary Tool Kit keeps the low-RPM settings you need for Lexan within easy reach.
How do you drill body post holes without cracking the shell?
Mark the position with a sharp pencil, then a small drill bit (3 mm or 4 mm) at 6,000 to 8,000 RPM with a sacrificial block of wood under the body. The wood gives the bit something to land in and stops the panel from cracking when the bit exits.
Skip the wood block and the panel cracks every time. The block is the difference between a clean hole and a body in the trash.
Can you polish the painted surface?
No. Polishing compound on a painted RC body removes the paint. Polish the inside (the unpainted side), the wheel arches, and the wheel wells. The painted surface should only be cleaned with a soft cloth and soapy water. Measure the arch during the radius pass with a HARDELL 6 Inch IP54 Digital Caliper, not by eye.
Even a soft cloth with a bit of polish residue will mar the paint over time. Keep the polish on the inside, keep the soap on the outside, keep the two separate from each other.
What's the order of operations?
Trim first, paint second, mask third, detail last. Trying to detail before paint gives you a polished surface that you then have to repaint. Trying to mask before trim means the trim cuts through the mask.
Most beginners do the work in the wrong order and end up doing it twice. The order above is the one that works.
What about a clear coat after polishing?
Yes if you want the body to stay glossy. A light spray of clear over the polished surface seals the polish and keeps the body looking new for months. Skip the clear coat and the polish dulls within a few runs.
Spray the clear in light passes, not one wet coat. A wet coat runs, drips, and clouds the polish. Three light passes, fifteen minutes apart, gives a gloss that holds up to track debris and washing.
How long does a first body take?
Two to three hours for a first body, including painting. An experienced builder does it in 90 minutes. The first body is slow because you're learning where the panel wants to melt; the second body is fast because you already know.
From the workshop: the body I painted twice
First body I ever finished, I polished the outside after painting. The polish took the paint off in streaks, and the streaks came off evenly only after I'd stripped the entire panel. I repainted the next weekend, did the polish on the inside this time, and the body looked like a different shell.
The lesson that took two bodies and a weekend of work to learn: the painted surface is for soft cloth and soapy water, full stop. Everything else happens on the inside, on the arches, and on the wheel wells. The body looked so good afterward that I left it on the car for the next race and beat a guy who'd been running the same chassis all year.
Common mistakes recap
Polishing the painted surface: removes the paint. Polish the inside, the wheel arches, and the wheel wells only. Drilling body post holes without a wood block: the panel cracks. Always drill into a sacrificial block of wood. Cutting the wheel arches with a sanding drum: removes too much or burns the edge. Use a cut-off wheel for the rough cut, then a drum for the radius. Pulling the window mask before paint: the mask pulls the paint off with it. Trim first, then mask, then paint. Going too fast on the mold lines: the panel melts. Light passes, lower RPM, clean the drum often.
If you keep the cut-off wheel and the 220-grit drum on the bench and the polish off the painted surface, you won't make any of these mistakes. The polish is for the inside.
| Hour | Stage | Done when |
|---|---|---|
| 0:00–0:30 | Wash the body, remove mold lines | Surface is smooth to the touch |
| 0:30–1:00 | Cut wheel arches and body post holes | Arches match the wheels, posts are aligned |
| 1:00–1:15 | Mask the windows, prep for paint | Mask is tight, edges are clean |
| 1:15–1:45 | Paint (outside) | Color is even, no runs |
| 1:45–2:00 | Let paint dry, pull mask | Edges are crisp, no peel |
| 2:00–2:30 | Polish the inside, wheel arches | Inside is glossy, no swirls |
FAQ
Can I use the rotary tool on a painted body?
Not for trim. The bit will cut through the paint and the body looks worse. Trim before paint, polish after.
What if I burn the plastic?
Stop, let it cool, and sand the burn mark with 1000-grit wet sandpaper. The mark won't disappear but it'll be less visible.
Why does my cut-off wheel wander?
The wheel is probably dull or you're pushing too hard. Replace the wheel and let the tool do the work.
Can I use the rotary tool to install the body mounts?
No. Body mounts need a hex driver and the right torque. The rotary tool is for cutting and polishing, not for assembly.
Is a 1/10 body easier than a 1/8 body?
1/10 is more forgiving. The panels are thicker and the curves are gentler. Start with a 1/10 touring car body for your first project.
What RPM for clear coat scuff?
Don't. The clear coat is too thin to sand. If the clear is scuffed, the only fix is to repaint.
How do I get the inside to look glossy?
Sand with 1500-grit wet sandpaper, then polish with a felt bob and plastic polish. The combo gives a mirror finish on the inside.
Can I use a regular drill instead?
You can, but a regular drill doesn't have the speed control. A rotary tool at 6,000 RPM is the right speed for lexan; a drill at 1,200 RPM is too slow and the bit walks.
