Recovering Alloy Wheels with Damaged Threads

Recovering Alloy Wheels with Damaged Threads - Printable Version

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Recovering Alloy Wheels with Damaged Threads - Nonfractal - 4th-Feb-20

Recovering Alloy Wheels with Damaged Threads.
A guide for those not familiar with cutting threads etc.
[attachment=5506]
Background
Set Screws ("Grub screws" to our new world colleagues)
Probably the smallest part of any slot car that can cause calamitous failure on track.
If your set screws fail, you may end up spinning a loose wheel off down the track never to be seen again. Angry

You may also lose all drive if a set screw in a crown gear fails.

The majority of set screws (slot.IT, Ninco, Policar) are the smaller variety requiring a 0.9mm hex wrench.
I've found that the smaller set screws are quite likely to fail after many wheel changes and prolonged use.
Overtightening these smaller set screws will probably strip the thread in the soft alloy used in slot car wheels.

Some manufacturers (NSR etc) use a bigger set screw commonly known as UNC 4-40 use a 1.3mm hex wrench
Quite how an Italian manufacturer ended up using imperial set screws is a bit of a mystery to me.

Tools. You will need :
A. 1/8 inch drill
B. Tap&die set containing a UNC 4-40 tap
[attachment=5507]
[attachment=5508]

Both of the above are available through various online tool shops and ebay sellers.

Fixing wheels.

Let's start with the easier of the two grub screw types.
1. When a small screw fails it is often possible to drill and re thread to the larger size.

Use the tap holder in the set to mount the drill.
The alloys used in slot car wheels are generally very soft so you will probably not need to use a power tool at all.
Run the drill into and through the existing hole.
[attachment=5512]
Fit the UNC 4-40 tap into the tap holder
Run the tap GENTLY into the hole
For each turn forward, turn half a turn back to clear the debris from the cutting.
[attachment=5510]
When you are finished, you should be able to run a UNC 4-40 set screw into the hole.
[attachment=5511]
Job done !

2. When a larger screw fails.
The best approach is to run the 1/8 drill into the failed thread and right out of the other side to create a new hole.
You may well need a power drill to do this but do be gentle.
Some slot manufacturers create 2 (or even three) set screw holes in their wheels.
NSR only create one so running the drill through to create a new hole is relatively simple.
Be aware that the rim often has a concave cut to allow the driver to access the set screw.
Allowing the drill to run right out to the far side if the rim will cut this concave for you.
Once you have cut the new hole, run the tap through it as above.

When performing the operations above , do not fear! The wheel is ruined and would be heading for the trash so the worst you can do is confirm that prognosis. Cool

When cutting small screws out to larger ones, you may find that there is not enough alloy on the collar side of the hole to retain the new thread. There is no work around for this.

Choosing set screws.
Is this even a subject ?

Cost ££££
Set screws can be bought from your slot car retailer in branded slot car zip lock bags.
Typically a bag of 10 for £2.50
Have to a look at online sellers not aiming at the slot car market and you will find these available in much larger quantities at much lower prices. You will find a bag of 50 screws for less than a fiver. Free delivery...Deal!
Always buy stainless steel screws. Far superior.
Don't buy pointed-end screws, these will cut into your axles.

My preference is the shiny steel set screws. The Matt black ones are much harder to find if you drop one on the floor. Bigsmile

Lengths
UNC4-40 screws are Available in various lengths. I Find that 1/8th inch is sufficient.
Screws that are too long will get in the way of your tyres and create a wobble because of the balance offset created.

I hope this short guide is useful. Comments welcome
I'm aware that there are many ways to skin a cat and the screws/threads I chose are not everyone's preference.
Remember this is not an engineers guide. It's a guide for non engineering slot heads!

AlanW
(NonFractal)

RE: Recovering Alloy Wheels with Damaged Threads - Gordon Steadman - 4th-Feb-20

Good post.

I've been drilling and tapping gears for some time as quite a few have suffered the ravages of time. Quite why I didn't think to attack the wheels in the same way, I'm not sure. I only have a few modern RTRs but they all seem to suffer apart from Thunderslot who use sensible size grub screws. I don't have any NSRs.

I will immediately go and make them usable again - thanks Thumbup

RE: Recovering Alloy Wheels with Damaged Threads - slotloco - 4th-Feb-20

Excellent article, very helpful with the number of pics. I am sure it will be very helpful for a lot of people. - We are "grubs" down-under too; at least in the shakey isle.

I too have wondered why NSR chose UNC4-40 instead of the slightly smaller M2.5 grub screw (M1.3 head)
The common size of the tool for tightening is one saving grace.

I have done the odd wheel too - I used M2.5 as the boss on many wheels is so narrow these days, the hole for the larger UNC4-40 doesn't leave much meat on the inside of the boss
Alan - one thing I often read is just the opposite of what you wrote about stainless steel screws. A number of guys say "don't use stainless steel ones, they are too soft; use the black hardened steel ones"
Personally, ..... I use both.... haven't had a problem with either type - but I use torque wrenches - Slot.it and ScaleAuto.
Interested in your further thoughts on the subject.

ps, Good tip about not using pointy ended grubs, I have seen a couple of people come unstuck there.
Cup End also grip better than pointy end due to the larger surface area of contact.

RE: Recovering Alloy Wheels with Damaged Threads - BAracer - 5th-Feb-20

If my memory serves me right, there are facilities to fix my R-Series scaleauto rear wheels with 2 grub screws. I was going to do that when I got a moment...

...once I buy myself a torque driver.

Any reason not to use 2 screws?

RE: Recovering Alloy Wheels with Damaged Threads - Gordon Steadman - 5th-Feb-20

(5th-Feb-20, 09:22 AM)BourneAgainRacer Wrote: If my memory serves me right, there are facilities to fix my R-Series scaleauto rear wheels with 2 grub screws. I was going to do that when I got a moment...

...once I buy myself a torque driver.

Any reason not to use 2 screws?

Better balance I would have thought! I usually do it with the gears for that reason plus security.

RE: Recovering Alloy Wheels with Damaged Threads - Nonfractal - 5th-Feb-20

(4th-Feb-20, 04:15 PM)Gordon Steadman Wrote: Good post.

..but they all seem to suffer apart from Thunderslot who use sensible size grub screws. I don't have any NSRs.

Gordon,
The designer behind ThunderSlot is the same as the earlier NSRs,
If you see "NSR by GM" on an NSR chassis it will have been designed by Giovanni Montiglio.

Thunderslot will have a presence the UKSlot Fest
I'll ask Giovanni about set screw sizes.
Why bigger? That's obvious
Why Imperial UNC4-40 , that's a mystery.

RE: Recovering Alloy Wheels with Damaged Threads - Gordon Steadman - 5th-Feb-20

(5th-Feb-20, 11:25 AM)Nonfractal Wrote:
(4th-Feb-20, 04:15 PM)Gordon Steadman Wrote: Good post.

..but they all seem to suffer apart from Thunderslot who use sensible size grub screws. I don't have any NSRs.
Gordon,
The designer behind ThunderSlot is the same as the earlier NSRs,
If you see "NSR by GM" on an NSR chassis it will have been designed by Giovanni Montiglio.

Thunderslot will have a presence the UKSlot Fest
I'll ask Giovanni about set screw sizes.
Why bigger? That's obvious
Why Imperial UNC4-40 , that's a mystery.

But isn't that the same thread as the classic gears from yesteryear? I like it as most of my cars are retro and I only have to use one size of grub screw.

Very sensible choice in my opinion Bigsmile

RE: Recovering Alloy Wheels with Damaged Threads - slotloco - 5th-Feb-20

Actually Gordon

you probably just solved the mystery.
That may well be the reason Salvatore went with 4-40

Salvatore was a top steel chassis racer - at the same time as Ernie Mossetti or MR Slotcars.
Ernie once told me that Salvatore won his world title using a car Ernie built - I cannot confirm or deny...

Alan - will be interesting to hear what Giovanni can tell you.

RE: Recovering Alloy Wheels with Damaged Threads - Nonfractal - 6th-Feb-20

(5th-Feb-20, 09:22 AM)BourneAgainRacer Wrote: Any reason not to use 2 screws?

There might be a very good reason not to use 2 set screws in a slot car wheel.
I've been looking up "bearing location" in larger scale engineering.
Most bearings have only one set screw and are often located with a corresponding flat spot on the shaft.

Some bearings use two, but these are never 180 degrees separated
90 degree or sometimes 120 degree is used.

This must be related to the pressure between the shaft and the inner face of the bearning.
Maybe set screws at 180 degrees apart would work against each other.

If you use two screws at 180 degrees apart, maybe if one comes loose, the other does not compensate, so maybe you're doubling the chance of failure instead of halving it...

AlanW

RE: Recovering Alloy Wheels with Damaged Threads - BAracer - 6th-Feb-20

Yes...it would end up just being two points of contact opposite each other. One gets loose, they both get loose.

I'll save that second fixing point for when I strip the first!