92 replies to this topic

[Pablo]

Chassis prep 101: I didn't really find any serious burrs on the edges so I just gently:

- ran a small fine file to all edges top and bottom, followed by 400 grit

- spun a round file in all the holes - bite bars, bushing uprights, and body mounts

- wet sanded flat parts of both tops and bottoms with 400 grit wet/dry

 

 

Not sure if I'm going to use the stock bite bars yet, so I left them alone for now.

 

I sanded the motor brace also, just to ensure it's fairly flat and has fresh new metal for solder.

Yes, it's overkill, but I have lots of time...  

[Bill from NH]

We wondered where you were hiding the past couple of days!

[Pablo]

Not hiding, just prepping cars for The Dungeon in 2017

 

First thing I did on the center section was check the tilt.

I need "some" - the rules I'm building for are no fronts, no min. front clearance, and .032" min. clearance rear.

Mine, out of the bag, was angled very slightly down. Tongue Tweaker fixed it easily - I held the wings tight on the block and they stayed flat.

Then I checked it on my flattest block - it was plenty flat enough, nothing to correct.

 

 

Pan section needed some minor hand tweaking to get flat, no problemo.

 

 

I found doing one half first with the other half off the block, then the other half, then all together, makes it simpler.

When I get to the point of questioning which is flatter - the chassis or the block - I know I'm done. 

[Pablo]

Before I examine the stock bite bars, I was curious about something -

now that I have a flat two-part chassis, will straight pieces of (.039" front/.047" rear) wires pass through the holes freely?

 

 

Yup. They went right through absolutely perfect.

While my test wires were in there, I noted the design of the pan movement limiters.

Fore and aft limits are perfectly equal, and left to right amounts are slightly more rear than front.

Very precise, obviously designed that way and the further I go, the more I like what I see. 

[JK Products]

 

[Cheater]

You are learning. 

He had a good teacher... LOL!

[MSwiss]

Greg,

How many posts does Pablo have to make in this thread, for you to upgrade him to tome status?

[JK Products]

See, I want him to stop for fear of giving away too many of our secrets!

[Cheater]

How many posts does Pablo have to make in this thread, for you to upgrade him to tome status?

He's already got his own subforum.

When he's done this thread will almost certainly be moved to Tech How-Tos & Tutorials.

[Pablo]

Jaroslav Recek obviously understands what makes a slot car handle. 
 
Bill of NH suggested the forward bite bar could be assigned double-duty as a front axle - I checked it - he is right. Would take some clever technique, but it's totally doable. Just for those who are challenged with front wheel mandates...
 
Another tuning design feature I noted is the pan crossover (which makes the chassis a two-piece vs a three-piece) does not interact with the center section. In other words, you have the advantage of the pans being connected, without the disadvantage of friction with the center section when the body moves.
 
In a situation where you actually wanted that friction, you can add some Lexan strips under the crossover and get it.

[Pablo]

Bite bars - here is what I found. The bends and curves that form the attachment end(s) make it practically impossible to lay it on a block and expect it to be flat. I tried to make them so, and couldn't. By no means is this a problem, and I'm sure you can just use them as is and do fine.
 
I set about to see if I could improve on them. My first thought was, small pieces of square tubing soldered to the pans rear, and .050" keepers outside of simple straight pieces of wire, front. The rear would be a piece of cake since it's basically the same way the Cheetah chassis bite bars are managed. The front would require some work - .050" keepers would be too sloppy over .039" wire, so I'd have to drill out some .063" brass tube to .039" and shim them up to make the keepers fit nice.
 

 
Wait a minute, hold the phone - about that time, I started to really understand the way the stock bite bar keeper bends work. They just need to be tweaked properly. All the small parts and tools got put away – all I need is a pair of pliers. My stock bite bars are done.  
 

 
Here is my method. The convoluted bends look complicated, but I finally realized they are very simple, and only perform one single basic function - keep the bite bar from falling out. They are well designed to do that, and I doubt it can be improved from that standpoint. The problem is, not only are they doing the basic job, they can also prevent the bite bar from being an "independent thinker." In other words, they are influencing the bite bar due to (unwanted) interaction with the chassis surfaces. So, I think all we need to do is ensure the bar is straight where it passes through the chassis holes, and prevent the curved/bent section from touching the chassis.
 
First, let the bent areas lay off the block while you ensure the main part is straight. Notice the light coming under mine – not good – easy to fix
 

 
Now tweak the bent portion upward the way you want it oriented on your chassis. Just enough to ensure all of it ends up elevated off the chassis about 10 thou. Like this:
 

 
Now the bite bars are laying exactly as they would without the keeper bends, and everything is still flat. Plus you still have the capability of rapid removal as designed. 

[Pablo]

Both tongue surfaces faced as usual with a Magnehone.

 

I'm not going to reinforce the tongue – JK says it's a stronger chassis, and my meaty fingers verify that. Whether due to the thickness, or different material, I don't know.

 

 

Bunky, the gap between the pan finger and wing tip you called a flaw and fixed with a shim?  Well, I call it something else.  

[Pablo]

I checked the upright holes for accuracy and to see what size wheels will give me .032" clearance.

 

Looks like the JK C43 was designed for about .063" clearance using about .720" wheels. It's accurate enough so no drilling/filing/etc. is needed, and I'll probably race it with about .685" wheels.

 

Found a pair of VBX un-shielded ball bearings – after a lighter fluid bath they will be soldered in... tomorrow... 

 

[glueside]

Pablo gets it!!!

[Koford fan]

I notice you have taped in middle on your bite bars. Any reason for it? Just test? How it looking without?

Great work so far.

[Pablo]

The bearing holes are precise enough, I didn't feel the need to jig it up before soldering home the BBs. Simply taped it down with axle center elevated .2975". This will make it (mathematically) clear .032" with .659" wheels or .062" with .720".
 

 

 
Slick 7 brace fits perfectly.
 

[Pablo]

I notice you have taped in middle on your bite bars. Any reason for it?

 
Good question, Tom, thanks. I simply wanted the bent end of the bar to sit high for the photo just to make my point clear about keeping it up off the chassis.
 
Without the tape, it doesn't sit so high. Doesn't have to – just enough so it isn't hindering the bar from doing whatever it wants.

[JK Products]

The force is strong with this one.  

[Pablo]

Centerline permanently marked at the rear.
 

 
I've been using a different technique than the usual sales receipt to set gear mesh on JK chassis lately. I like to end up with a 10 thou spacer inboard of the spur, so I tack the motor in with a 20 thou to the hilt.
Then the 20 thou is removed and 10 thou goes in. So far it's worked perfect every time.
 
Gears on my car will be 72 pitch 15/40. Hawk 7 motor has been broken-in and wire connectors tinned. You can see my tack solder blob on the lower forward edge


 
I took the time to find the left/right balance point of the motor (at the angle it ends up in of course).

Previous chassis versions didn't always have the motor sitting in the perfect spot, so I'd compensate for it.
The C43 does. Laying flush with the gear side right in its nest, it's in perfect balance left/right.

Also, the space between the endbell side and chassis on the C11 was really tight - the C43 fixes that.
 

 
Motor is in its happy place, now it's time to install some bracing...

[Pablo]

I was planning to install a S7-389 motor brace up front but the bite bar won't allow it. The standard JK brace and gear side attachment point will be plenty strong enough.
 

 
I'm done acid soldering so center section/motor, etc., got a warm soapy bath scrubbing.
 

 
Soon you will see why I titled my thread with the word "sexy"...

[Koford fan]

Nice work, Pablo. I like it.

[Pablo]

Thanks, Tom. 
 
The rest of the assembly was easy, no problems, nothing special other than the usual "Wolcott Ranch" race car attention to detail:
 
- pan doesn't need nursing to attach it - drop it over the center section, insert bite bars with a click, done. Brilliant design.
 
- Parma flag blueprinted, all rotating surfaces faced, Koford aluminum drilled nut and two 10 thou bronze spacers for tuning (one top one below to start), Slick 7 wires, TQ clips, Prime braid, Koford axle.
 
- spur gear balance tested using the BBs on the car – screw was the heavy point – tried a few different screws until I found the one that made it happy.
 

 
The wheels I'll be using are .680" OD Alpha Wonder rubber on carbon fiber hubs and are .800" wide. I used a single thin spacer between spur and BB, a couple thin spacers between spur and (left) wheel, and two 20 thou spacers on the right side. Look close and you can see my marks aligned.
 

 
My opinion is, the C43 has raised the bar in many ways and it's probably the easiest flexi chassis to make race ready of any I've ever built.

I give it three thumbs up (that's the max Cheater Wells allows). 

[Pablo]

My "sexy" chassis is dressed with a skin from ralphthorneracing.com

 

 

[Zippity]

Paul,
 
Are you going to install a SS or brass floating pin tube in the front? 

[Bill from NH]

What happens to those chassis skins when you solder motors in and out of a chassis? Years ago we made chassis skins using 3M colored plastic tape, but we never skinned the motorbox.