Using a Tungsten Round this year

[DerbyNut]

Hi everyone,

I have normally used cubes of tungsten weight in the back bottom of my car everu year and done well. This year I was thinking of using a tugsten round that is only .33 inches thick and 1.125 inches diameter I found online weighing 3.5 oz. Rather than inserting it from the bottom, would it still be okay to drill a hole on the top of the car in the read? I cant my axles in the rear by drilling them at an angle in the block. So the axles go downward towards the center of the block. So I think I would have mroe room in wood on top of the axles. i will have to go through some blocks of wood trying this probably.

But my main question is if I cut the block thin and insert this from the top, will I still get good performance as I would inserting from the bottom? I don't want to chance it hanging down too far and don't want the axles to be in the way.

Also, could I possible glue the tungsten round in using something like rubber glue? I would like to be able to pop it out after a race and use it in another car but I don't want to tear up the car it was in.

Thanks!

[DerbyNut]

Well, I've been reading more and unless I put the weight in from the bottom or in the middle of the car, I don't want it up too high. I hate to cut my axles cause it will be harder to align the read wheels which will be canted. I think I will have to stick with using cubes. I use the 1/4 inch cubes and form them as part of the car in the back and a little weight in front of the axles. I then normally use a plate to fine tune the weight close to 5 oz. and use small screws in the bottom to get it right on 5.0 oz. I use screws so I can easily remove one or two if needed in case the district scales read different. Or add a screw!

Does anyone know how to cut into the car in front of the axles for the cubes to fit nice? I always seem to butcher the car a little too much! I use a big drill bit and drill a series of holes acrodd. Then I use my dremel with a drum and sand it smooth. I just didn't know if there is a better way.

Thanks!

[FatSebastian]

But my main question is if I cut the block thin and insert this from the top, will I still get good performance as I would inserting from the bottom?

We have built bodies using this weight in the past, and most designs that I've seen place the weight on top in a recessed hole drilled out from the top with a Forstner bit or spade bit. Mounting this weight from the bottom with sufficient clearance would require that the entire weight be forward of the rear axle line so the axles have a place to go, or else the axles will need to be shortened. The first situation results in an uncompetitive CoM location, while the second greatly complicates construction and alignment.

Also, could I possible glue the tungsten round in using something like rubber glue?

We've successfully made cars with a removable disk before. Rubber cement is something that we never tried, but white PVA glue (aka Elmer's) is usually recommended where a semi-permanent hold is desired. It also helps if the hole in the wood is relatively tight so that not much glue is required; a Forstner bit works will for this. For thin bodies, the round must be removed with care to prevent breakage; a hole or two drilled through the bottom in advance provides a pathway for a punch to knock the weight out.

I see just now that you are reconsidering use of the round understanding that it will not be as competitive as cubes. IMO, use of the round is to promote ease of construction, than than obtain ultimate performance (although they can be very fast).

[FatSebastian]

Does anyone know how to cut into the car in front of the axles for the cubes to fit nice?

We use a scroll saw. First we drill a starter hole. We disconnect the blade from the upper arm of the saw, feed it through the starter hole, and then reconnect. We then cut (relatively) straight lines through the block to get a reasonably tight fit for the cubes. IMO an older scout can safely do this with adult supervision.

[DerbyNut]

So you cut all the way through for the cubes. Before I have left a little wood for them to sit on. I guess I could get thinner doing it your way. And that's what wood filler is used for on top!

Do you do this for both in front and behind the rear axles? I have normally used my band saw and cut a notch behind the rear axles and glue in cubes there. I leave a thin part of the top there as the notch. I use a little wood filler around them to smooth out the look. This way the cubes are in the way back.

[FatSebastian]

I guess I could get thinner doing it your way. And that's what wood filler is used for on top!

We assemble our cubes into rows in advance with CA glue using a homemade jig and insert them as a unit, minimizing their need for support. However, we have added various thin materials for support underneath, including thin wood veneer, cardstock, and even heavy paper. Some people like to use metallic tape, which also adds weight. (We have also used paintable materials on the top too as a covering in lieu of wood filler.)

Do you do this for both in front and behind the rear axles? I have normally used my band saw and cut a notch behind the rear axles and glue in cubes there.

We also use a bandsaw method for the back. We simply cut in from the rear of the car many times the depth of two rows of cubes, the result looking like a comb. We then simply knock out the teeth of the comb to create the space. We have used the scroll saw for clean up if necessary.

[sporty]

Rounds.

our cars were only 1/4 thick. we removed the whole amount of material for the whole, using a drill and then scroll saw to remove the rest. We jsut epoxied the round in, most of the time, had to shorten the axles some. We never liked doing this, so we stopped using the rounds.

A car drop or hard hit at the finish line, left the shorter axles with ease of more damage to alignment in the rear and easier for them to rotate or move even with them being glued in.


The cubes worked better for us and just used a scroll saw fro the rear, removing all the meterial but two 1/16th end piecies and the forward whole just after the axle area on the rear, just used a dirll to drill out a whole and again inserted a scroll saw to remove the rest.

A exacto knife came in handy for trimming, if the fit was just a tad to small.

The cars we did were 1/4 thick, so the cubes were flush at the bottom and the top of the wood.

Sporty

[DerbyNut]

That's what I'm going to do with cubes this year. Our cars will be the same thickness at 1/4 inches and I'll use a scroll saw as well which I already have. I like what FatSebastian said as far as gluing the cubes together with CA first to make it one piece. This way I can mark the size and cut.

I was trying to picture how you do it in the back without having any wood on the top or bottom. But then I thought that you are not going the whole width of the block with the cubes. So I assume you have a little wood on each side to glue to along with in front of the cubes which is the wood behind the axles.

What kind of glue to you use to glue them in? Epoxy? That's what I have used in the passed. I never wanted the cubes to come out on a hard stop or flip of the car.

Thanks!

[FatSebastian]

So I assume you have a little wood on each side to glue to along with in front of the cubes which is the wood behind the axles.

Yes, approximately 1/8" on each side of the plank, leaving room for rows six (1/4") cubes wide. Technically a row of seven cubes can barely fit across the back of the plank with no wood on each side - tricky! We've tried it both ways, but for a kid's car it is nicer having the extra wood on the sides for fitting the cubes.

What kind of glue to you use to glue them in? Epoxy?

Epoxy works. We also like CA glue as no mixing is required and it adds no appreciable weight. Granted, it is not as strong as epoxy, so we used CA glue only when we are already shielding the weights with something supportive like wood veneer or cardstock. (The shielding material in turn is usually secured with carpenter's glue or similar.)

[Scubersteve]

Technically a row of seven cubes can barely fit across the back of the plank with no wood on each side - tricky! We've tried it both ways, but for a kid's car it is nicer having the extra wood on the sides for fitting the cubes.

True, but it's easier to cut for two rows of seven. IMO

[sporty]

scroll down to the 3rd to last post on this page. for cut out.
for cubes
http://www.derbytalk.com/viewtopic.php? ... &start=120" target="_blank


i use 5min epoxy, i have used ca, however sometimes it does break off, I have seen it happen to others in races also or dropping it.

sporty

[whodathunkit]

scroll down to the 3rd to last post on this page. for cut out.
for cubes
http://www.derbytalk.com/viewtopic.php? ... &start=120" target="_blank

Sporty.. them are some nice looking cars.
Did Andy.. cut them out for you?

I wounder if the heat from laser helped take some moisture out of the block.
Ah' why even ask I know it did and that he cut them out.

I really like the car he has posted on here with the tungsten round on it.
you all know his Laser cut extreme modified car.
http://www.derbytalk.com/viewtopic.php?f=19&t=5012" target="_blank
If you'll scroll down in the post:
He also has some car photos with the upper half of the tungsten round covered.

hope this comes out right?? will see.
whoda.

[sporty]

Yes andy cut them out for me.

But somewhere on that topic in that secetion is cars that I cut out also, close to that.

But I did not have the time to find it and jsut went with what was closeest.


Sporty

[whodathunkit]

jsut went with what was closeest.

So did I Sporty.. So did I.

Have you had any luck useing the Tungsten Rounds that are ply able
and can be drilled or cut? Seems I've seen some.. some where
that could be drilled into.
Tundra-Tungsten composite? I think it's what they call it.

What about the Slotted Tungsten Round that has a cut out in it?
one could use it and place it just so.. that the axels woulden't have to
be cut down.

Here is what i'm getting at Guy's.
http://www.derbymonkeygarage.com/produc ... 447-9.html" target="_blank

[pwrd by tungsten]

With a tungsten round always dril through the bottom when the block is unshaped. then cut the body out. when the car is finished place a board of the proper thickness under the car and allow the weight to drop on the board and then glue in place. You might allow a sliver more if your rules are very tight.

Elmers glue works very well. However for scout cars we epoxy the weight in place due to the poor track conditions.