Braiding a 1/32nd CNC Routed Track

[HO RacePro]

I have ordered a custom 1/32nd scale slot track from a CNC job shop. I am only having them rout the slots and cutout the pieces. I have not yet decided if I am going to install braid or just copper tape.

If I use braid I'll need to cut the braid reliefs (gains). At the moment I am considering using a 5/8" diameter straight router bit to cut the reliefs 0.015 inches deep. The router bit would travel down the centerline of the 1/8" slot, leaving a relief 1/4" wide and 0.015" deep on either side.

The braid I intend to install is 3/16" wide and 0.020" deep. This should leave at least a 0.005" "reveal" -- the top of the braid should be at least 0.005" higher than the surface of the track. The glue line should add a few thousandths to the reveal. The reveal will permit standard HO cars to run on the track as well as my 1/32nd's.

I could use a 1/4" braid instead of 3/16", but I like the idea of leaving 1/16" of clearance of the braid versus the slot, just to allow for tolerances in braid width and installation inaccuracy. The narrower braid will still have loads of conductivity for the size of my track.

I will make a special guide for the router. It will have a pin that runs in the adjacent slot to provide the correct centerline spacing. An adjustable trailing pin will guide the router square versus the track radius. The location of that pin will be adjusted radially to compensate for the different curve radii, so everything ends up true and square.

I'll be testing out the whole setup on scrap MDF sheet before I attempt working on the actual track. The mortality rate of beautiful theories is tragically high once they encounter reality. I expect to be schooled by the testing. That's what usually happens.

What to use for glue is an issue. I have heard that there is a 3M tape product that folks have been using successfully to adhere braid to MDF. I'd love to hear from folks who have used it and learn from any wisdom they can pass on.

Ed Bianchi

[MrFlippant]

It would appear that you've given a lot of thought to your plan, so I expect you will move forward as specified. However, I caution against any "reveal" of the braid. For longevity, it's best for the braid to be lower than the track surface. I expect you're doing this for your HO cars, and I don't see a way to do both. That said, as a home track, it's probably not that big of a deal.

For the tape, I've not heard of any issues other than printing the slot and rebate first. Only those who taped directly to raw MDF had problems, which should have been expected, TBH.

[HO RacePro]

Can anyone tell me the name or the product number of that 3M tape?

Ed Bianchi

[chrisguyw]

Post removed

[Wicker Bill]

Bits that cut the braid recess are readily available. They have a guide shank that follows the slot so the only tool needed is a router.

[HO RacePro]

Can you point me towards one of those braid recess router bits? I've looked for them without any luck.

Ed Bianchi

[RichD]

With 1/32nd tracks the braid should be flush with or just slightly below the track surface or the guide flags of de-sloting cars will eventually chew up the braid. It used to be the common practice to use contact cement to stick down the braid, but that is a messy operation that goes better if there is more than one person doing the job. The fumes from the contact cement are dangerous as well. We switched over to using 3M double sided tape to stick down the braid and have had excellent results with that. The gains should be painted before the tape is laid down, it does not stick well to bare MDF. The source for the bit for routing the gains would be Slot Car Corner that also stocks the braid and 3M tape. Slot Car Corner also sells braid that is taped to save you a step. In order to make the gains the correct depth you will have to experiment with some scrap MDF. It is also a good idea to get a roller to smooth out the braid. There is a link to a track braiding article in the braid products section of the SCC site, that is not working. If you contact SCC you might be able to get a copy of the article.

[HO RacePro]

I have checked out the Slot Car Corner site. They list two braid relief router bits for sale -- one for 3/16" wide braid and the other for 1/4". Problem is the 3/16" bit is out of stock. When will it be available again? Doesn't say.

But while trolling the internet I came across an article where someone created their own braid relief router bit by drilling a hole into the end of an ordinary bit and inserting a 1/8" diameter rod, made from a slotcar axle. Apparently the body of the bit, which mounts the carbide blades, was not so hard that it couldn't be drilled. Interesting.

I have also discovered that there are "flush trimming router bits" that are drilled and tapped at the bottom for a small screw. That screw typically holds a small ball bearing that spaces the cutter blades versus the work. It has occurred to my devious mind that the tapped hole could be the right size to accept a 1/8" diameter pilot shaft. Possibly drilled out to size. TBD.

And of course I can't just leave my fantasizing there. There are such things as needle bearings designed for a 1/8" shaft that have a 1/4" outside diameter and a 1/4" length. While I am cutting into the end of a router bit could I drill it out to 1/4" ID by 1/2" deep? That would allow me to fit two of those needle bearings inside and have a free-spinning 1/8" diameter pilot shaft. I'd have to gin up some kind of a seal to keep the bearings from loading up with sawdust.

Oh the endless annoyances of DIY slotcar engineering.

Ed Bianchi

[Wicker Bill]

Take the easy way out, call SCC, and ask when the bit will be back in stock.
Every bearing router bit I have has a shoulder under the cutting edge to act as a boss for the bearing to mount to, so that would have to be ground off to make them flush cutting on the bottom. You would need a rabbiting bit since they are ground to cut on the bottom as well as the side. Flush cut bits are ground to cut on the side of the bit.

[HO RacePro]

Do it the easy way Wicker Bill?

How little you know me!

Ed Bianchi

[Mike-]

HO -

Something to ponder...

You might think about making the braid "level" (or a coupla thousands below the surface) with the track surface, rather than ANYTHING above the surface.

Why -
Because as cars go around the corners, and the tails slid away from center, even for a split second, the tires will catch the braid, and eventually roll it over, leaving "lips" of braid sticking up. Then you will end up making some sort of tool or using your thumb nail to push the braid back into shape.
EVEN using steel braid and magnets. The cars WILL deslot eventually. As the cars slid across the track the tires, and or body parts will again...catch the braid and try to lift it.

Many if not most professional tracks that I've raced / run on put the braid level or even a little "below" the surface just for this reason. I've run on high end "pro" tracks with the braid as much as .02" below the track surface.

Granted, that I'm betting that you will be using mostly non-foam tires on your cars, so .02" below is overkill, but level to about .005" deep, is MUCH preferable to anything above.
This is from MANY (1962 to now) years of racing with "all sorts" of tire material.

The braid on my wood track is mostly level with the surface, except where the adhesive is a little thick and the braid is above the running surface. And YES...every not and again, I have two places that I need to "relevel" the braid where lips form and need to be pressed back down.

Mike

[RichD]

I can't recall how wide the braid on our tracks is, you could go crazy and use 1/4 inch wide braid for which the proper bit is in stock. Slot Car Corner is very good about answering calls and e-mails concerning any questions that you might have. Slot Car Corner does not just sell track braiding supplies they have assisted in building a number of tracks and should be able to tell you how deep the gains need to be.
With regards to making your own bit by drilling out a regular one I would expect that it would be difficult to drill out a properly hardened carbide bit, even if you used a lathe. MDF looks like it should be easy to route, but cheap bits quickly wear out while good quality carbide bits last a long time.

[HO RacePro]

I used to install braid on my tracks flush with the racing surface. But...

I learned that 'reveal' is essential if you are going to run HO cars with the traditional pin and hard pickups. And my customers want that ability. So I have been installing braid with reveal on all of my HO tracks for more than a decade. It has held up very nicely. I have never had any complaints.

I also run 1/32nd cars on my HO tracks -- every other lane. The reveal doesn't upset those cars at all. No damage to the braid or the cars. You'd never know the difference. This is a case where real-life experience invalidates theories.

Gerry Cullan owns one of my low-banked Slider oval tracks, and it has reveal. It is one of the most popular tracks in the HOCOC race rotation. After many years of service it remains in like-new condition. Tons of fun to race on.

As for ginning up my own braid relief router bit -- of course I would not try to drill into carbide. But most bits in the size range I need have carbide inserts held in a softer metal mount. That mounting material is what I would attempt to drill.

Below are photos of the homemade bit from a post I saw online. The poster admitted he had not fixtured the bit well for drilling. But I see this as a proof of concept. If Slot Car Corner doesn't come through for me I might try this.

Ed Bianchi

Untitled 1.jpg Untitled.jpg

[RichD]

That should drill OK, it would be best to use a lathe and to make the pin a press fit, rather than gluing it in place. I just checked the SCC site and the bit for 3/16th wide braid seems to be back in stock, but there is no picture of it.

[HO RacePro]

I heard back from Slot Car Corner yesterday. I learned that their special routing bit for 3/16" braid is out of production and will no longer be offered. That item will be removed from their website shortly.

So if I want to go the special router bit route I either need to install 1/4" braid, find an alternate source for the 3/16" bit, or gin up my own.

I will do some experimenting. I want to test out a couple of alternatives before I commit to one specific way to install power conductors on my new track.

Which new track, FYI, I am going to pick up today. The basic track sections have been CNC routed and cut out. Crossing my fingers no awful mistakes were made in my design or the finished pieces.

Ed Bianchi