Nonfractal
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Registration Date: 10th-Jun-19
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Recovering Alloy Wheels with Damaged Threads 8
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Recovering Alloy Wheels with Damaged Threads Tips & Tuning
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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)