Wheel Sanding Techniques

[TurtlePowered]

How do you sand your wheels? I prefer to get a small strip of sandpaper and fold it in half and then loop it over the wheel but some prefer sanding the wheel against a wood block. I would think the former would be easier for young children, what do you think.

[Da Graphite Kid]

Since the intent of our rules do not allow for re-shaping the stock BSA wheels we use sandpaper over a block of wood. This keeps the wheel tread area flat so that we no problems come inspection time.

If you look at the stock BSA wheel tread, it is not flat but convex in shape and yet the rules we race at District state: "Wheels may be lightly sanded to smooth out molding imperfections in the tread area. This light sanding is the only modification allowed. Beveling, tapering, thin sanding, wafering or lathe turning of the wheels is prohibited". Go figure...

By the way, isn't "lightly sanding" the wheels also a form of "lathe turning" if it done with the wheel being spun by a drill?


Da Graphite Kid

[Stan Pope]

Since the intent of our rules do not allow for re-shaping the stock BSA wheels we use sandpaper over a block of wood. This keeps the wheel tread area flat so that we no problems come inspection time.

If you look at the stock BSA wheel tread, it is not flat but convex in shape and yet the rules we race at District state: "Wheels may be lightly sanded to smooth out molding imperfections in the tread area. This light sanding is the only modification allowed. Beveling, tapering, thin sanding, wafering or lathe turning of the wheels is prohibited". Go figure...

By the way, isn't "lightly sanding" the wheels also a form of "lathe turning" if it done with the wheel being spun by a drill?


Da Graphite Kid

Good comments, Da.

If your rules require an essentially flat tread cross-section, then be very carefully about supporting the back of the sandpaper with something soft. It will abrade the edges of the tread more quickly than the center, resulting in a "crowned" tread cross-section.

BTW, our district rules take the condition of "out of the box" wheels into consideration... some inspection steps are skipped if the wheel is "unmodified." Our belief is that unmodified kit wheels must be satisfactory, since the fallback solution to improperly modified wheels is to allow acquire and race on fresh kit wheels. In fact, we ask the DE to bring a modest consignment of wheel replacement kits to the district derby!

Also, our district rules don't dictate or prohibit a method... they regulate the result! That gives each the freedom to use the tools that they have available.

[TurtlePowered]

Since the intent of our rules do not allow for re-shaping the stock BSA wheels we use sandpaper over a block of wood. This keeps the wheel tread area flat so that we no problems come inspection time.

If you look at the stock BSA wheel tread, it is not flat but convex in shape and yet the rules we race at District state: "Wheels may be lightly sanded to smooth out molding imperfections in the tread area. This light sanding is the only modification allowed. Beveling, tapering, thin sanding, wafering or lathe turning of the wheels is prohibited". Go figure...

By the way, isn't "lightly sanding" the wheels also a form of "lathe turning" if it done with the wheel being spun by a drill?


Da Graphite Kid

Good comments, Da.

If your rules require an essentially flat tread cross-section, then be very carefully about supporting the back of the sandpaper with something soft. It will abrade the edges of the tread more quickly than the center, resulting in a "crowned" tread cross-section.

BTW, our district rules take the condition of "out of the box" wheels into consideration... some inspection steps are skipped if the wheel is "unmodified." Our belief is that unmodified kit wheels must be satisfactory, since the fallback solution to improperly modified wheels is to allow acquire and race on fresh kit wheels. In fact, we ask the DE to bring a modest consignment of wheel replacement kits to the district derby!

Also, our district rules don't dictate or prohibit a method... they regulate the result! That gives each the freedom to use the tools that they have available.

Wouldn't the stiffness of the sandpaper act like a flat surface to prevent the crowning of the wheel?

[ExtremePWD]

My experience with sandpaper is that it is not sufficiently rigid to remain flat and that it will tend to conform to the existing profile even if it is evenly loaded. The coarser grit papers have heavier paper backing and will stay flatter in a relative sense but the finer grit papers are fairly flexible. Even when looped around the wheel it is possible to apply more pressure on one side resulting in uneven sanding and rounding of the corners. I also recommend backing the sandpaper with a flat block of wood or something similar.

[Jungle Jim]

BTW, our district rules take the condition of "out of the box" wheels into consideration... some inspection steps are skipped if the wheel is "unmodified." Our belief is that unmodified kit wheels must be satisfactory, since the fallback solution to improperly modified wheels is to allow acquire and race on fresh kit wheels. In fact, we ask the DE to bring a modest consignment of wheel replacement kits to the district derby!

Also, our district rules don't dictate or prohibit a method... they regulate the result! That gives each the freedom to use the tools that they have available.

Stan:
I'm pleased to see other Districts & Councils giving some of the same levity in design that ours does. Granted, we have had to change our rules almost every year for the last 8 years (I suspect the internet here ), but our only other choice would be to allow only out-of-the-box wheels to be used.

As far as "Wheel Sanding Techniques" go, I'd say that one method well suited for a scout would be to use a wheel arbor in a drill press with fine sandpaper attached to a block of wood.

[Stan Pope]

I'm pleased to see other Districts & Councils giving some of the same levity in design that ours does.

I'm not following the meaning here... "levity"???

As far as "Wheel Sanding Techniques" go, I'd say that one method well suited for a scout would be to use a wheel arbor in a drill press with fine sandpaper attached to a block of wood.

Works well, but subject to some runout. Without shimming the arbor, runout of 0.005" typical on my drill press. Waaaaayyyy too much!

[terryep]

Re sanding wheels. Instead of a mandrel I use a steel bushing with a 0.250" inside diameter mounted in a drill press. Place the wheel on the table face down and press fit it's hub into the bushing. Use a combination square resting on the table for a true 90-degree surface to back the sandpaper. Use a low speed. Hold the square to the table, move it toward the wheel gently. Sand with 220 grit sandpaper until the wheel is flat. No pressure on the wheel, only to the table. This will insure the wheel is round (fix any runout) Then use wetted 320 grit sandpaper and finish with pumas polish on a cloth. Slow and gentle so as not to over heat the plastic. This method won't harm the axle hole and you can do 4 wheels in 10 or 15 minutes.

Terry

[Stan Pope]

Instead of a mandrel I use a steel bushing with a 0.250" inside diameter mounted in a drill press. Place the wheel on the table face down and press fit it's hub into the bushing.

I've thought about this in the past, and was interested when you mentioned earlier. Now seems a good time to dig more deeply!

Have you been able to measure the concentricity of the hub ID and OD?
Have you been able to measure the runout of the inside of the bushing?
Since the total runout in the wheel needs to be way under 0.005", then you need to make sure that the chuck runout and the bushing runout and the hub runout don't gang up on you.

Here is an eternal trugh: When you are turning PWD wheels, errors never cancel! They add in the worst possible manner.

[Jungle Jim]

I'm not following the meaning here... "levity"???

We do not tell them what to do - only what they can't. Knowing this, someone will invariably test the flexibility (hence "levity") of the rules. When this happens (and I'm talking about gray area stuff here), I'll usually ask the Scout if he knows why that "modification" was made. If I receive a good answer, he races. If not, the car is put into hock until all members present at that race see and vote on it.

Works well, but subject to some runout. Without shimming the arbor, runout of 0.005" typical on my drill press. Waaaaayyyy too much!

Perhaps now's the time to talk to the little lady about that new drill press.

Yeah, there's going to be some runout. My theory is that unless you are going to teach a kid all of the pertinent ins and outs of whatever particular components are being prepped, and the tools and/or cost of are not excessive, then a more "accessible" means of building should be used. And these cars (at least in Scouting) are to be built by both the Scout and parent together.
Knowledge is a commodity that can be priceless. If you have kids who really want to learn what it takes, GREAT! America needs more like them.

[terryep]

I went out to the workshop and measured two spare wheels I made last fall. Using a vernier caliper I measured at 4 places around each wheel from axle hole to the rim:

Wheel 1) 0.539, 0.538, 0.539, 0.538
Wheel 2) 0.538, 0.537, 0.539, 0.538

I will need to borrow a dial indicator from work to measure the runout of my drill press and bushing. (I'm not uning an arbour, the bushing is good for 0.0001) The axle hole to hub dimension should be spot on from the mold as long as the hole hasn't been compromised. I can possibly get a better measurement on the wheel using the dial indicator but would need to figure out how to set it up in a meaningful way.

Terry

[Stan Pope]

Using a vernier caliper I measured at 4 places around each wheel from axle hole to the rim:

Wheel 1) 0.539, 0.538, 0.539, 0.538
Wheel 2) 0.538, 0.537, 0.539, 0.538

Those 0.001" & 0.002" runouts are good for a drill press, unless you took special care to eliminate the runout when you did the setup!

I'm not sure that I would trust the molds to give good (<0.0005")concentricity for hub ID's and OD's. Anybody measure that for many of the molds?

[terryep]

To measure wheel runout I was thinking I could set up a car on top of my cast iron table saw and put a dial indicator on top of the body close to a wheel. Set up a stop for the car and pull a piece of paper under the wheel to spin it without the car moving forward. This should give the definitive measure of wheel runout. I might need to weight the car to keep it down.

Terry

[Stan Pope]

To measure wheel runout I was thinking I could set up a car on top of my cast iron table saw and put a dial indicator on top of the body close to a wheel. Set up a stop for the car and pull a piece of paper under the wheel to spin it without the car moving forward. This should give the definitive measure of wheel runout. I might need to weight the car to keep it down.

Terry

Clever!

What to watch out for? How to minimize effects of:
paper thickness variations.
flexing the wheel/body/axle.
axle "riding up" on the side of the bore.
axle not in contact with bore.
paper not pulled parallel to table top.

[MaxV]

A set-up like this would be more accurate:


Deviation from circular trueness


Deviation from lateral trueness

Rotate the wheel by hand and note the deviation on the indicator.

You should be able to adapt the technique to a drill press instead of a lathe.