Bang for Buck Tradeoff: Which modifications to go with?

[Vitamin K]

So, I apologize if this has been hashed out already. If so, links to previous discussions are welcome.

Basically, I'm trying to decide how to focus my efforts, the next time car-building time comes around (that would be now, if my son has his way). However, money, time and my dear wife's patience are in limited quantity, so I have to decide what factors give the highest payoff. This is sortakinda what I'm thinking, in order of priority.

- Axle prep and alignment: Chuck the pre-drilled slots (local rules don't forbid this), drill new holes with drill press. Raise a wheel. Polish axles if burrs are present. Obtain and use an axle press. Obtain and use a rail-rider tool to bend one of the front axles for RR. Optional: Obtain alignment tool for axle hole drilling...how important is this?

- Weight Distribution: Cut pine down to 'surfboard' size, attach hollow balsawood carved body for looks. Find appropriate COM and add tungsten or lead to bring weight up to 5oz. Note: Undecided between lead and tungsten, primarily due to the cost of the latter. Gonna be building at least three cars, here.

- Wheel Prep: Obtain wheel mandrel and fine grit sandpaper. Polish out any burrs from exterior of wheel. Polish hubs. Coat with massive amounts of graphite.

These seem to be the best "bang for buck" options that I can think of here. Are there any other things that would offer good payoff for the time spent doing them? I think attempting to cant the axles is probably going to be too difficult without dropping 50 bucks on a 'Block' or Silver Bullet tool.

Thoughts?

[FatSebastian]

So, I apologize if this has been hashed out already. If so, links to previous discussions are welcome.

Rather than point you to a long list of links, I might suggest that you get Troy Thorne's Building the Fastest Pinewood Derby Car to help you with focusing your priorities.

These seem to be the best "bang for buck" options that I can think of here. [...] Thoughts?

Axle prep and alignment: If you must use slots, "fill then drill" if allowed. Drill canted holes if allowed and if you have the ability, but you don't have to go all out by your second season if the wife has you on a budget. Burrs will be present on BSA axles out of the box. You don't need a Pro-Axle Press or Rail-Rider tool just to bend an axle; worst case, just put it in a spare wheel and give it a little tweak (then discard the wheel). Use a Micromesh polishing kit for the axles. Align to ride the rail!

Weight Distribution: Tungsten is preferred of course, but if you're going to have a taller body anyway then lead is definitely cheaper and more flexible. FWIW, we won most of our Scout races using lead.

Wheel Prep: Refer to Troy's book. Use a concentricity gauge to pick the wheels with the least run-out. There is probably no need to work the treads at all, and definitely no need to coat them "with massive amounts of graphite". The bores should at least be inspected for debris, and preferably polished then "burnished" with graphite.

[sporty]

see my builder tip video and pictures for drilling cant. you can do it with a drill press and a good #44 drill bit and a 7 inch long piece of drill rod.

Thats the best bang for your buck ! because if you have a drill press already. then the only investment is drill rod. 5/64th or 3/32 or light cant 1/16th drill rod. for under $4.00. you can do canting just as good or equal to a costly tool.

The only exception, is I love the pro body jig, for drilling my starter wholes.

[bracketracer]

I would suggest, if it is allowed under your rules, that if you build a RR car that you might shave off 1/16" or so on the body where the DFW mounts and provide adequate clearance for the front of the DFW where it comes close to the body with the bent axle. You want to shave off the 1/16 to keep the rear wheel on the DFW side from touching the rail. In this case, rubbin' ain't racin'!

I just started using angled drilled holes instead of the slots. I like the results! Don't forget to make yourself a notch in the body so you can add graphite to the wheels without removing them. I didn't know about that until I tried to re-lube the wheels!

[Vitamin K]

see my builder tip video and pictures for drilling cant. you can do it with a drill press and a good #44 drill bit and a 7 inch long piece of drill rod.

Thats the best bang for your buck ! because if you have a drill press already. then the only investment is drill rod. 5/64th or 3/32 or light cant 1/16th drill rod. for under $4.00. you can do canting just as good or equal to a costly tool.

The only exception, is I love the pro body jig, for drilling my starter wholes.

Thanks! I'll give it a look. If it's not too hard or expensive, I'll go for it.

I would suggest, if it is allowed under your rules, that if you build a RR car that you might shave off 1/16" or so on the body where the DFW mounts and provide adequate clearance for the front of the DFW where it comes close to the body with the bent axle. You want to shave off the 1/16 to keep the rear wheel on the DFW side from touching the rail. In this case, rubbin' ain't racin'!

I just started using angled drilled holes instead of the slots. I like the results! Don't forget to make yourself a notch in the body so you can add graphite to the wheels without removing them. I didn't know about that until I tried to re-lube the wheels!

Oh right, forgot about the narrowed front end for RR. (I've never built a RR car before).

Nice thing about having a balsawood top, is that I can just narrow the 'surfboard' part of the car and not worry about the actual body design that's carved in balsa.

[pgosselin]

Vitamin K,

I think you have about the right priority. This is how I would approach it.

1. Axle prep

2. Wheel prep--I would put a greater emphasis on polishing the bore than anything else.

3. Alignment--get those back wheels tracking straight--search for Sporty's skid test.

4. Weight placement--it depends on the level of competition in your district. We had a lead-filled car that took 2nd place at a regional race last year. I'm just now starting to unlock the speed benefits of tungsten. Lead will definitely keep your investment down while you tinker.

5. Once you get good at those, try drilling negative cant on your back wheels and a positive one on your DFW. Canted holes are a lot easier than bending nails.

Paul

[Vitamin K]

I'm assuming that I need to make up my mind about whether or not to cant the wheels before I start to fine tune the alignment, no? I'm still pretty leery about my ability to accurately drill angled holes into a block, even with a jig on the drill press.

-K

Vitamin K,

I think you have about the right priority. This is how I would approach it.

1. Axle prep

2. Wheel prep--I would put a greater emphasis on polishing the bore than anything else.

3. Alignment--get those back wheels tracking straight--search for Sporty's skid test.

4. Weight placement--it depends on the level of competition in your district. We had a lead-filled car that took 2nd place at a regional race last year. I'm just now starting to unlock the speed benefits of tungsten. Lead will definitely keep your investment down while you tinker.

5. Once you get good at those, try drilling negative cant on your back wheels and a positive one on your DFW. Canted holes are a lot easier than bending nails.

Paul

[psycaz]

VitaminK,

I would start with drilling the axle holes. Take some scrap wood and practice that. Watch for the drill bit to wander as you start to drill into the wood. Find that sweet spot on how fast to drill down. How fast to set the drill press to. Practice drilling with the cant to get comfortable with it. Take a 1/4" plank of someting, mark it, and drill away. Do 10 holes per side. Put wheels and axles on each side and see how it sits.

It's not the area where you will see the most improvement in times, but the cost is so low, it's a cheap place to start. The Sunday papers here have coupons weekly for 40% an item at Michaels. If you have it there, pick up a piece of 1/4" bass wood. Cut some planks and have at it.

[pgosselin]

Drilling straight 1/16" deep pilot holes before you angle the block of wood for cant helps immensely to prevent the bit from wandering.

Paul

[Vitamin K]

Drilling straight 1/16" deep pilot holes before you angle the block of wood for can't helps immensely to prevent the bit from wandering.

Having a little trouble visualizing how this ends up looking. How deep would I make the pilot holes? Just far enough to break the surface a bit?

Still mulling the best possible way to jig up a setup for drilling on my dad's drill press. Will definitely need to practice with some scrap wood.

Oh, but I have another question about drilling canted axles holes: Once you've got your axle holes drilled, obviously you want to test the tracking to make sure you've got straight rear wheels. My question is: At what point of the build process do you do this? It would seem like a bummer to get your car sanded and painted and prettied up and then discover that it wasn't tracking straight. Would it be better to test the tracking with the 'rough' piece of wood and then remove the wheels to do the rest of the body work? Do I run the risk of stripping my axle holes with the wheel/axle removal? At what step in the process do you guys do the alignment tests?

[Stan Pope]

Drilling straight 1/16" deep pilot holes before you angle the block of wood for can't helps immensely to prevent the bit from wandering.

Having a little trouble visualizing how this ends up looking. How deep would I make the pilot holes? Just far enough to break the surface a bit?

1/16" deep!

At what step in the process do you guys do the alignment tests?

From Sporty's previous writings, test immediately after drilling the blank! Don't worry about stripping the holes, but do worry about damaging the axle heads!

WIth this method, perfectly straight axles are a "must." You need to be able to remove and reinsert axles with no change in alignment! Evaluate your ability to straighten BSA Axles sufficiently if you are required to use BSA Axles. My experience with the ProAxle Press is that it does a pretty good job of straightening, but might not be up to the necessary straightness in this application. You can test straightness by doing the "skid test", observing good results, then twisting one rear axle 90 degrees and repeating the skid test. If still good results, then you are "good to go." (I think I'd repeat this test on the other side as well, just to be safe.)

[Vitamin K]

Having a little trouble visualizing how this ends up looking. How deep would I make the pilot holes? Just far enough to break the surface a bit?

1/16" deep!

D'oh. For some reason my brain processed this as 1/16" in thickness. Sorry.

At what step in the process do you guys do the alignment tests?

From Sporty's previous writings, test immediately after drilling the blank! Don't worry about stripping the holes, but do worry about damaging the axle heads!

WIth this method, perfectly straight axles are a "must." You need to be able to remove and reinsert axles with no change in alignment! Evaluate your ability to straighten BSA Axles sufficiently if you are required to use BSA Axles. My experience with the ProAxle Press is that it does a pretty good job of straightening, but might not be up to the necessary straightness in this application. You can test straightness by doing the "skid test", observing good results, then twisting one rear axle 90 degrees and repeating the skid test. If still good results, then you are "good to go." (I think I'd repeat this test on the other side as well, just to be safe.)

What's the alternative to straightening with the axle press? Buying guaranteed-straight axles?

[Stan Pope]

What's the alternative to straightening with the axle press? Buying guaranteed-straight axles?

Hmmm ... I've heard that those whose rules allow (and maybe some others, as well) and who want high performance do so. Because "my crowd" is supposed to be limited to BSA axles, I haven't paid a lot of attention to purchased-finished alternatives.

[Vitamin K]

What's the alternative to straightening with the axle press? Buying guaranteed-straight axles?

Hmmm ... I've heard that those whose rules allow (and maybe some others, as well) and who want high performance do so. Because "my crowd" is supposed to be limited to BSA axles, I haven't paid a lot of attention to purchased-finished alternatives.

So....what's your preferred method then? Or do you have an entirely different approach that doesn't require axles to be so perfectly straight?

[FatSebastian]

What's the alternative to straightening with the axle press? Buying guaranteed-straight axles?

FWIW, in our experience, an axle press does not seem to make a bent axle perfectly straight, although it can make a bent nail much straighter.

I suppose one might be able to buy a bunch of nails and sort through to find the straightest ones. The alternative is to use stock that has been machined.