How are the wheels this year ?

[quadad]

We are out of the game, but a friend shared their out of roundness measurement data on a large set of the current wheel crop and the results were surprising. Larger numbers than I have ever seen before (up to 10/1000th's ) for a fair number of molds. #2's still look best overall (bore diameter, OOR, spin all very good) but the overall quality level really seems to be going down quickly.

Is this what others are seeing ?

[68sportcoupe]

that is what i was thinking so i bought two big rig kits each came with 2 #2s runout was .0007 on 2 of them.
the reason i bought the big kits is that i believe they have been sitting st the scout shop since last year or whenever they came out meaning earlier wheels in the run.
maybie i should go back and buy the last couple they have.
im not sure if the kits are old but i think they are.
does anyone know if they are still making the big rig kits they say 2010 on the box.

[whodathunkit]

does anyone know if they are still making the big rig kits they say 2010 on the box.

68sportcoupe,
You Might try http://www.scoutstuff.org" target="_blank for the big rig kits.
Thay still have them listed in stock.

[sporty]

Sorry,

I guess there is not a real reply to the initial post.

Hopefully some one will have some data from wheels, that perhaps were made more recently.

I knew pretty much, that the new wheels were the best they were gonna be. Due to new molds.

Working back again at a plastic / mold injection place again. I can pretty much tell you. We never check that fine of detail.

We have a range most of the time, of .010 for many of the products that do require inspection and thats every two hours. But the dies, molds. Ugh, They do not get redone unless there is actual damage to the die.

Which can happen by a stuck runner hardening and the press closing while it's still in there.


Regrind and material seem to be the biggest varience's to cause issue's like you ask about.

I am mentioning all of this, as I feel perhaps it provides a tad more insight into plastic's and molds.

Regrind, is most often the grond up bad parts and the runners.

(the runner is a piece of material that was the liquid plastic fill tube thru the cavity of the mold. it comes out with every part pretty much.

Many places, grind this up and mix it in with new material to save money and not loose as much money, But this material once used before, can cause a bunch of issues.

Because it now melts and cures and at a different rate than the new plastic material it's being mixed with. Which causes the two to not mix as well together or cure at the same time as they should.

I mention this, as it might also explain variences you see when checking the wheels.

Then there is also a big factor in moisture and temp of the plastic. Some parts we use driers to dry the material and its slightly warm before its fed into the mold machine.

You will see allot of varience when you use a drier to not using a drier on a run.

Now, the machines, need the dies polishes and cleaned, ect. the ejection pins are where the most issues comes from. they pop the parts off.

If they stick slightly or the speed cycle times differ and they do. when they start them up and during a run and ect. Often too, the auto feed of the material, but often is manual mixed. meaning a clear or white plastic, mixed with small amounts of color plastic.
Depending on how well its mixed, the flow into the press. slightly changes color and softness and hardness also.

The cleaners, the parts are still goo, most often, this is a floor job or op job and they just open the press up, spray a little bit of cleaner or ect, non mold stick or ect. and wipe and start running it again.

those parts are likely saved and used. but those parts will have different tolerances.

Most often, the material comes in large vats. Well when you use one up and go to another. You can run into a slightly different batch of mix or size of pellets, moisture, chemical varience in the material as it was made. Which also effect tolerances too.

These guys, would really have to spend allot of time and be on top of the production run and check every 15 minutes to ensure a awesome wheel !

Opps, also most of these parts, likely just drop or fall into a table / box. how those parts cool depends on where they land ! if they do not get picked up or moved every 5 to 10 minutes,. the heat from the parts they are all piled up on one another, can also create different curing times or distortion in the product.

We got some parts that fall into tanks of water to cool them fast and they sit in there for so long.


I wanted to share all this, since I know it. Perhaps you liked the little indepth look at mold machines, the process a bit and plastics.

I deal with allot of john deere parts and more.

Sporty

[*5 J's*]

Sporty - very intesting insight. Thanks for the post.

[sporty]

Of no problem, I really did not start off thinking to mention it or so much.

There is more I could mention.

You can adjust the slow of the purge, the melted plastic that flows through a nozzle into the mold cavity.

you can adjust how fast the mold closes and opens, the same for the ejector pins, that pop the parts off.

naturally the cycle time, how fast or slow or long, to inject, how long to let it cool before opening the mold up.

You can adjust about everything on a decent mold machine.

If I can get permission, perhaps I can get a few photos sometime.

[Teeeman]

Sporty, I worked in injection molding more or less for a time at my first 2 jobs (we designed the parts, I spent quite a bit of time in the mold facilities).

I don't know the processes as you do, thanks for taking the time to share!

Great stuff!


And, bet you would know what gas assist injection molding is...

I bet gas assist would help some with tolerances (if you kept things like cooling time and ejection stress in check)...

... would also lighten the wheels.

That could be a showstopper, if there were significant differences in the mass of wheels.



Probably should not say this in this manner, but I literally have discussed with Stan before that it suprises me some of the vendors have not pursued getting specialty wheels run to be highly deceptive cheater wheels.

I have seen interior tread cuts that were obviously meant to be hard to spot in inspection before, so there are very deliberate "cheater" wheels being sold (wheels meant to deceive).

I am glad to say that if it became known that gas assist light-weight, but totally stock external dimension wheels were available, I would pull the wheel weigher off the shelf and tell everyone to plan an extra 1.5 hours for District inspection as we would have to weigh wheels even when they had passed visual inspection.

-T

[murphken]

There are quite a few good mold numbers to choose from. We leverage #2s for Pro Racing. Unless you are really good at building PWD Cars, the mold # is not the area that will get your Scout lower or increased track times. Alignment is key. Don't hurt to have good prepared axles, along with nice, shiny bores. Most graphites are good.
Murph
Shining Light Tribology

[quadad]

Unless you are really good at building PWD Cars, the mold # is not the area that will get your Scout lower or increased track times. Alignment is key.

I agree Murph. From what I saw though, some of the wheels might be so bad now that those that can really prep a wheel (and are allowed to by their rules) might get way ahead of those that can not. Skill with the other keys (alignment, et al) seems to follow.

I'm just wondering if my quick impression from one set of wheel data is being seen by many others.

[rpcarpe]

We haven't started in earnest on the wheels yet. Most kids are just cutting the bodies.

I still agree with others, ALIGNMENT!!

Might try wheels on the new lathe this year instead of the hand Derby Worx version.

Will re-post when I see more of the wheels from the recent builds.

[FatSebastian]

Perhaps you liked the little indepth look at mold machines, the process a bit and plastics.

MaxV also has an insightful newsletter article about the injection molding of the MV wheels. Consistent with Sporty's post, MaxV notes that "a major reason why there is so much variance in most pinewood derby wheels, even within a given mold number" is "the cycle time is a little too fast," resulting in wheels that "will still be soft when ejected, leading to a slight warpage." (This would account for our own data implying that mold numbers are not always a consistent predictor of quality.)

[rpcarpe]

Might try wheels on the new lathe this year instead of the hand Derby Worx version. Will re-post when I see more of the wheels from the recent builds.

As promised, here are some observations on wheels. (not in any particular order)
- Black wheels cut/shape more easily than colored wheel sets.
- 2009 black wheels easily deform due to heat/pressure on a full lathe if you don't use a light touch. Hand lathe (derbyworx) still trues up the tread rather nicely
- Fairly consistent size for tread, not nearly as bad as 1999 wheels
- Cub opened the box, out came 1999 wheels! WHAT??
- Used new bore polish along with axle polish, much faster. Thank you John at [no advertising for this vendor] for re-explaining it to me.

Sorry, no time for setting up runout with dial indicator. Plus, battery op dial indicator died.
Hope this helps.

[knotthed]

Quadad,

Bought maybe 5 or 6 kits last year, picked out 4 number 7's as they were listed as a good wheel on some chart somewhere and I put the rest of the wheels in a box.

Bought maybe 10 kits this year and sorted the wheels by rotating them on wheel shaver to visually check runout. Mold numbers did not matter. There were some that were visually horrendous, so I went back and looked at last years wheels and overall the quality of last years wheels were much better.

I was shocked at how much radial and axial runout combined some of this years wheels had.

Note: our rules do not allow using the wheel shaver to shave or true them, so my son and I did the next best option - sort thru the wheels. Nothing like inspecting quality into the process!

Regarding the mold numbers - does anyone know if there is just one mold?

I suspect given the volume of parts, there may be multiple molds with the same mold numbers on the wheels. The mold numbers on the wheel would only serve to troubleshoot the mold as far as I know or as my best guess.

Does anyone know who the OEM for the wheels is?

[rpcarpe]

I think someone on this forum had some input on the new wheels. Maybe they know the OEM.

Has anyone tested the colored wheels? I noted they didn't cut as quickly on the lathe, but I haven't checked runout on them.

[mebetree]

I didn't "test" the colored wheels but I did use them on both of my son's car this year.

I would say they feel a little bit harder. We don't use lathes (banned) but do hand sand them while on a mandrel and they took longer to get right than the black wheels. One wheel had a weird problem where the outer edge got all rough and messed up when lightly sanding it almost as if there were air bubbles that got ripped open while sanding.

But I didn't do any testing of colored wheels vs black.