Ask the "PRO's"

[RacerX]

What better way to get help than from our own panel of WIRL and PDDR winning Pro's.

These guys have years of experience and ton's of race proven knowledge so let them be your personal assistant.


Race Fast

Racer X

[FAST Racing]

When turning/machining a wheel on a lathe, what type/style of c
cutting bits/tips should I use?

What about spindle speeds? How do you compensate for the
plastic "growing" in size from cutting heat?

I'm trying to improve my builder skills from sandpaper & a drill
press to making the leap for a hobby lathe....

[HogWild]

How do you avoid the dreaded front end wobble? My son's car last year in district took everyone right off the start, but because of the front end wobbling so badly it lost energy within the last 10 feet and cost us every race. I could not figure what I had done incorrectly. Any advice for future builds would be most appreciated.

[builderjim]

Hogwild,

You will have to describe the wobble better for most to be able to reply.

Questions for you:
1. Was the front end moving side to side on the track?
2. Could you tell if the cars was moving in an up and down direction on the front or rear?
3. How were the wheels treated on the tread? bore?
4. What process did you do to the axles?
5. Where was your center of mass located?
6. Could it have been the track, was is it's condition?

Ask these questions to yourself and you just might be able to find the answers somewhere in that particular car. Remember each and every car is different and reacts to the track in a different way that the last one you built.

Jim

[dsracing]

Hogwild - most of the cars I have seen do what you describe have too much weight behind the rear wheels causing the front end to "float". You can check the ratio by making a platform the exact height of the surface of the scale you are using to weigh with. Then set either the rear wheels or front wheels on the platform with the other set on the scale. Thus you can weigh each end seperately. The total should be the same as the overall weight of the car. The front end weight should be around 15% of the total weight. Hope this helps.

[dsracing]

Fast racing asks about lath work. I use the slower speeds on my lathe. I don't get melt that way. I use a TAIG micro lathe which will do anything I need except making threads. The cutting bit depends on what you are doing. Both left and right hand cutting are needed, a parting tool is nice and a thread cutting tool works well for making tapers (hub coneing). As you get more skilled, you will "invent" different tools and ways of making what you want.

Good luck!

[builderjim]

Fast Racing,

Here is a pdf that might help you out
www.littlemachineshop.com/Info/MiniLatheUsersGuide.pdf#search=%22lathe%20tooling%20guide%22

Jim

[FAST Racing]

Thanks for the info guys,

ds, when you say slower speeds compared to what? Some of
the web sites I've checked list what i would call exotic plastics-delrin , urethane etc- to cut at high speeds. Of course no listings for abs,styrene,PVC or other common plastics.

I've found that the common sets of lathe bits at HF tend to
chatter and dull fast. I guess I'm asking is the indexable re-
placement carbide tip cutters a worthwhile investment?
(Carbide is a stinker to sharpen!)

builderjim,
Wow! Thirty five pages, a lot of info to absorb. Again a quick
look does not seem to address plastic.

What I'm trying to do is turn 2 wheels at the same time on a mandrel. A "matched set" per axle. I think would help take one
of the variables out of alignment. Alignment has been my weakest area.

By the way, in the short time since I asked my question I went
to Harbor Freight and bought a mini-lathe. Only $359.00 on sale
this month. Guess I"m in this Pinewood Derby thing deeper than I thought.....Maybe I need to start a thread about explaining to
Mrs. FAST?

[dsracing]

Fast Racing - I use the slowest speed available on my TAIG and Carbide tipped cutting tools to work on wheel cutting or shaping. The tools are about $5 each at the hobby shop or tool center. The only time I increase speed is when polishing or buffing. Then I go to as high a speed as will run smoothly. Play with the different speeds to find what works best for you.

When you clean up wheel perimiter, a lathe will allow you to set the finish diameter and then duplicate that setting for as many wheels as you wish to run. If you have a micrometer you can reset that diameter at a later date by cutting a trial wheel - start oversize and reduce to desired finish. Micrometers aren't cheep but I use mine all the time (checking axle diameters for instance).

[dsracing]

I apologize, the measuring tool is called a calliper. This is for larger diameters - wheels. A micrometer is usually for item smaller than 1 inch including axles but the Calliper is the most usefull.

My Bad

[pwgrasshopper]

fastracing said:

Thanks for the info guys,

ds, when you say slower speeds compared to what? Some of
the web sites I've checked list what i would call exotic plastics-delrin , urethane etc- to cut at high speeds. Of course no listings for abs,styrene,PVC or other common plastics.

I've found that the common sets of lathe bits at HF tend to
chatter and dull fast. I guess I'm asking is the indexable re-
placement carbide tip cutters a worthwhile investment?
(Carbide is a stinker to sharpen!)

builderjim,
Wow! Thirty five pages, a lot of info to absorb. Again a quick
look does not seem to address plastic.

What I'm trying to do is turn 2 wheels at the same time on a mandrel. A "matched set" per axle. I think would help take one
of the variables out of alignment. Alignment has been my weakest area.

By the way, in the short time since I asked my question I went
to Harbor Freight and bought a mini-lathe. Only $359.00 on sale
this month. Guess I"m in this Pinewood Derby thing deeper than I thought.....Maybe I need to start a thread about explaining to
Mrs. FAST?

I don't know what the market would be for an instructional DVD on turning wheel and axles but if Max V or some of the other vendors are paying attention I would buy it. I am not sure how long the video would be but if it is only 15 minutes or so it could be added to a new addition of maximum velocity, the movie. That is if a new version is in the works? For me a picture would be worth a thousand words.