Bent Axles vs. Canted Drilled Holes?

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sporty
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Re: Bent Axles vs. Canted Drilled Holes?

Post by sporty » Tue Jan 27, 2015 1:27 pm

Ngyoung.

I drill canted Too. Have for awhile. I even drill Railrider wit mild cant. To use less bend on my axle.

I try and stay two way thin king if I can.I don't always tho.



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Stan Pope
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Re: Bent Axles vs. Canted Drilled Holes?

Post by Stan Pope » Tue Jan 27, 2015 1:53 pm

Vitamin K wrote:
ngyoung wrote: It is also pretty easy for one of the wheels to get knocked out of alignment during racing. It is usually bad enough having just that one DFW to worry about being bumped.
... I had to grip the nail head fairly well with the pliers and it took an appreciable amount of torque to rotate the axle heads. However, I just don't see a lot of forces that act on a typical pinewood derby car that are going to cause the rear axle rotation to change. ...
The "lever arm" of an axle bent 2.5 degrees at 1/2" from the nail head is 0.022 inches. Given so little leverage, it seems that an impact capable of twisting the axle in the hole would as likely bend the axle. Such an impact would not care if the axle were originally bent or straight!

I think that this is testable, though. We could set up a car with no offside front wheel, exposing a rear axle to impact.

First phase:
1. Using bent axles, align the rears.
2. Station a PWD block lengthwise on a track flat just past where the flat begins positioned so that the offside rear wheel must strike the end of the block.
3. From the normal starting line, release the car and allow it's offside rear wheel to strike the block.
4. Check rear wheel / axle alignment without changing the alignment.

If the check shows a change in the alignment, then either the axle was twisted OR the axle was bent.

Repeat the above using progressively heavier blocks until a check shows a change in alignment or you run out of patience.

If alignment did change, then we could differentiate between the axle being twisted or bent by the impact.

Second phase:
1. Insert a straight axle in place of the offside rear axle.
2. Verify that the rear alignment is approximately as good as in the first phase above.
3. Station the heaviest PWD block above on a track flat just past where the flat begins positioned so that the offside rear wheel must strike the block.
4. From the normal starting line, release the car and allow it's offside rear wheel to strike the block.
5. Remove the straight axle and test it for straightness by rolling the shaft on a flat hard surface. If the axle resists rolling at any point, then it has been bent by the impact.

Whatcha think, folks? Would that answer the question?


Stan
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Re: Bent Axles vs. Canted Drilled Holes?

Post by davidwilkie » Thu Jan 29, 2015 2:04 pm

sporty wrote:Are we really helping david?
Yes, you all are...and I don't mind the debate -- sort of relish it actually.

We do have a drill press. Yes, these are Scout cars, each Scout building one per year. My two sons plus some of their friends, so I need a reasonably efficient method for multiple cars, though my two sons are willing to put in the extra time (the shop is in "our" house after all) so I can do one method for several cars and my sons can employ a more labor-intensive method.

But the original question really was intended to be which is better in the spirit of a faster car, taking into account probability of getting it right. We are reasonably skilled, but are not building cars year around and racing them outside of the annual scout race.

Also, the reason for all this pre-build research is that my boys typically do pretty well -- win or nearly win their "rank" and place at some level (get a trophy) in the whole pack -- but have yet to win the pack, despite coming pretty close...so they are looking for just a little bit more speed.

My gut sense is drill canted holes, test right after drilling (with thumb tack for front or using the 90-degre square method I saw somewhere) throw out and start over if not straight, and then do some final alignment testing near end accepting that BSA axles are not perfectly straight and might suffice for some very minor tuning. That's my gut sense. My other thought is do one son's car one way and the other's the other way (let them decide which) and see which works better!



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Re: Bent Axles vs. Canted Drilled Holes?

Post by Vitamin K » Thu Jan 29, 2015 2:27 pm

davidwilkie wrote: But the original question really was intended to be which is better in the spirit of a faster car, taking into account probability of getting it right. We are reasonably skilled, but are not building cars year around and racing them outside of the annual scout race.
I started a topic not too long ago, trying to determine if there was anything inherently faster in respect to drilled cant over bent axles, or was it just an ease-of-use issue? As best as I could determine, it really came down to ease of proper alignment.

So, I think the questions to ask are:

- Would I have an easier time drilling canted holes on the press, evaluating and (possibly) tossing bad blocks until I was satisfied, or would I have an easier time tuning alignment by rotating bent axles and watching for rear-end drift? (Presumably with wheel-isolating bias weights).

and

- Do I prefer to have my alignment set as the very first thing in my build process? Or would I rather it be the very last thing in my build process?

These aren't trick questions. Perfectly reasonable to come down on either side, IMO.
davidwilkie wrote: My gut sense is drill canted holes, test right after drilling (with thumb tack for front or using the 90-degre square method I saw somewhere) throw out and start over if not straight, and then do some final alignment testing near end accepting that BSA axles are not perfectly straight and might suffice for some very minor tuning. That's my gut sense. My other thought is do one son's car one way and the other's the other way (let them decide which) and see which works better!
Or..! Build your boys' cars one way, and build a daddy car a different way! That way if you beat them, you can gloat over both of them, and if they beat you, at least they beat you together. :mrgreen:



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