Scratch building an aluminum chassis - Printable Version

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Scratch building an aluminum chassis - KensRedZed - 29th-Dec-20

Before I started scratch building. I had seen and heard about chassis being made out of brass/wire, popsicle sticks, or even hockey pucks. I'm not sure how competitive the hockey puck chassis was. But it must have been funny to see.

Brass, wire, and solder were strange to me. I was more comfortable with a drill press, disk sander, and bandsaw.

We have a store in Canada called Home Depot.

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I have searched their metal rack many times before for other reasons. Might it be possible to find something that would work for a slot car?

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Make sure it's 3/4" inch square aluminum by 1/16" wall thickness. I have recently found out that there are a lot of thin imposters out there.

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A length of tubing was cut a bit longer than the space for the chassis.

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One end was sanded square to measure and mark all the holes from that end when the part was flipped 90 degrees.

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The wheelbase had to be figured out first. Tires were glued onto the aluminum wheels and trued on a tire-truing machine to fit the car. That's another thread in itself.

The wheels were laid down on a bench or table. The body was slid into the wheels until they centered themselves in the wheel arches. Then the distance between the center of the axles was measured. It doesn't work this easily for every car. But it will usually be close. Measure three times if needed. It's worth triple checking.

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The guide and body posts need to be figured out by checking how much room you have inside the body. Don't forget to allow extra distance for the guide to turn.

I made a drawing for each car before drilling anything.

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Several different cars may show up for this tutorial. It's not about any one car. This method can be adapted to many different bodies.

Now that we have measurements and metal. The measurements need to be scribed onto the aluminum.

A permanent marker was used to mark the general area where the lines would go. This helps to see the scribed lines clearly. The metal was measured with a digital calliper. The calliper was set to half the distance. Then another larger piece of metal was used to set the callipers against while the callipers were slid down the tubing to scribe a line. Then the 3/4" tubing was flipped 180 degrees and scribed again. The small distance between the two lines is the closest thing to center I can get without more complicated measuring equipment.

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The tubing was turned 90 dregrees, and the guide/body post distances were marked.

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Here is the aluminum tubing measured and ready for drilling.

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The next section will show what tools are required, and how to go about the process of machining.

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RE: Scratch building an aluminum chassis - KensRedZed - 29th-Dec-20

I generally use 3/32" axles, and 3/16" OD single flange bearings. (or Oilite bushings)
Slot.It univeral guide part number CH10.
4-40 brass inserts with #227 Evergreen styrene tubing.
4-40 countersunk screws and washers. (90 degrees)

The tools required.

#2 pilot or center drill (before every hole).

Guide hole = Number 27 drill bit (and pilot drill).

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Body post holes = 1/8" drill bit and 1/2" countersink (90 degrees)(and pilot drill).

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Bearing saddles = Number 14 drill bit and a 3/16 reamer (and pilot drill).

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Now you can take a short cut and just start free-hand drilling. But the likelyhood of the axles being aligned would require a bit of luck. I found a very cool tool that allows me to move the part while keep the axles in line with each other during the machining process. It's called an XY-compound table made by Proxxon out of Japan. It gets bolted/fixed to the drill press.

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My first several cars were made by clamping the tubing to the compound table. A bit crude. But functional.

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I eventually located a larger drill press that would accept a precision vise mounted to the compound table. Clamping the tubing just became much easier and quicker.

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No matter what equipment you use. The machining process is the basically same.

The pilot drill is interesting in that it's very small in diameter. The large shank supporting it won't allow it to bend or wander. It's used to gently "spot" where the hole is located before commiting to drill. If you are a bit off center from the mark. Only a pilot drill can be corrected for position. All other drill bits will wander back to the original spot.

I started with the body posts first.

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I test to see how deep the screw sits before moving to the next hole and do the same process. The part does not get moved until all three machining processes are completed. Only then can you move to the next hole, or the centering is thrown off.

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The guide hole is easy. Pilot hole first, then the #27 drill bit.

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Bearing/bushing holes are next.

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RE: Scratch building an aluminum chassis - KensRedZed - 29th-Dec-20

Now that the main chassis holes are done. Flip the part 90 degrees and start the process of locating the center of the bearing marks using the pilot drill.

Same theory applies for the bearing holes. Don't move the part until all three machining processes are completed. Start with the pilot drill. Then move up to drill bit #14. Then use the reamer to remove the last 0.005" of an inch for super precise accuracy. The bearings/bushings fit like a glove using a reamer.

Keeping things locked tight is important during this step. You need to use the pilot drill for the top hole only. Then carefully plunge the #14 drill bit through both sides of the tubing.

This is just before reaming both holes.

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This is the reamer after removing 0.005" of an inch from the pre-drilled holes. Barely a few small aluminum hairs left on the reamer. Both holes are perfect and in line.

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Now we need to remove the excess material from the top of the chassis. Whether you use aluminum channel or tubing makes no difference in the fact that you still need to use the bandsaw to remove the excess material to get the motor to fit. The difference being, square aluminum tubing is much more square than the aluminum channel. You end up with a much better product using square tubing. Aluminum channel is also a pain to hold in the vise.

I mark the side of the chassis with a thin marker. I use a popsicle stick to mark where the bearings are located. Pretty fancy eh?

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Time to start cutting. I found there is a way to cut the chassis while also keeping the bandsaw blade as far from fingers as possible. I like my fingers. A lot!

This is the pattern.

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Now the hardest parts are over. It's time for the details.

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RE: Scratch building an aluminum chassis - KensRedZed - 29th-Dec-20

I mark the area around the guide hole with a large permanent marker. Then set my callipers to 1.65mm and scribe a line around the guide hole. This is my safety zone. Cut too close to this line and the chassis is scrap. I've already scrapped several chassis that were 95% finished. Oops.

Take your time with this area. I use a combination of bandsaw for rough cuts, and a quality hand file to finish it off.

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I install a sample body post at the rear of the chassis and mark around it. Then draw lines for the bandsaw. The sanding disk is used to give it that "store bought" look.

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Every once in a while I'll substitute a Slot.It guide for an NSR. The NSR guide can turn a bit more when the guide is very close to the axle.

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Chassis is assembled. The motor is glued in with 5-minute epoxy. This method of fastening the motor freaks a few slot car people out. But I'm an old RC aircraft guy and this works so well, that a lot of members in my slot car club now glue motors in too. Water flows downhill. It's hard to fight simplicity. It's now a well proven method.

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Body posts are attached to the chassis and tested for overall body height. The posts are removed and shortened slightly and re-tested many times until the body sits at a proper height. Once they are too short. It's a bit late to go back and add material. Once the body sits properly. They are epoxied to the inside of the body.

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These two cars were used for this tutorial. Lightweight aluminum chassis's still require weight to be added to corner properly. Either brass, or stick-on lead works great. Note that a relief had to be cut in the Triumph chassis to make room for the crown gear. Some cars have short tires, or tall gears and require a crown gear relief slot. It's simply 3-holes drilled in a row, and then file finished to fit.

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Always remember to put safety first when machining anything. Safety glasses are a must when drilling into metal.

Best of luck with your build!!!

Thank you very kindly for looking.

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RE: Scratch building an aluminum chassis - JasonB - 29th-Dec-20

Great stuff Ken, thank you.

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RE: Scratch building an aluminum chassis - Tibbs - 22nd-Mar-22

Once again another great thread.

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RE: Scratch building an aluminum chassis - JasonB - 23rd-Mar-22

I have the great pleasure of owning one of Ken's wonderful chassis.

It's a brilliantly engineered bit of kit.

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RE: Scratch building an aluminum chassis - KensRedZed - 23rd-Mar-22

Tony and Jason,

I humbly thank you both.

It was fun to share these experiences with everyone.

An update to this thread. In an effort to save time and also be more accurate. I bought a vertical milling machine and digital readout accurate to =- 0.001" of an inch. These are too cheap today to ignore. It was around $650 USD. A basement machinists dream.

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A milling machine meant I had the freedom to make side and cross cuts. The aluminum is typically 1.5mm thick. A pocket 1mm deep was milled out from both these chassis for an offset motor set up. I could not do that with a drill press.

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Three racers in my club helped me to buy the equipment by purchasing more than 2-dozen aluminum chassis. I was able to buy tooling with the extra money. I can now make a very precise chassis in less than half the time.

Warm regards,
Ken

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RE: Scratch building an aluminum chassis - Tibbs - 23rd-Mar-22

Oh that looks so handy, precision for sure.

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RE: Scratch building an aluminum chassis - Kevan - 23rd-Mar-22

How I miss access to a Bridgeport...

Square channel is useful stuff, box brass tube is great for rear axle/motor mount and solders very well.

Sadly I haven't made anything in metal since I went 3DP, metalwork is very much hands on, new era stuff is the opposite.

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