spinner safety clips

I've hade some safety clips made up by D.Faulkner Springs, very pleased with the result but drilling the adapter hubs is proving very difficult, I'm using 4mm cobalt drills, I've managed 3 hubs (2 holes in each) but the 4th is proving impossible, the adapters and wheels are from Vintage Wheels US, the adapters are forged steel, any ideas anyone what drill would do the job.
I'd suggest finding someone with a rigid drill press, and throwing them a few dollars (pounds). It'd save you a LOT of trouble.
Sounds like you have some work hardening on the adapter, and the material has become very tough.
When I have had a problem like this I usually get an appropriate sized drill for my masonry impact drill.....stay with me here I know it sounds crazy....Get the drill sharpened with a green wheel used on carbides, it will go right thru that material. These drills are cheap and come with carbide inserts on the tip, they are designed to absorb shock and pretty sturdy.
The smallest size I have seen is .125 or 1/8" but there is also a .156 size and .187 sizing, not exactly what you have but you may find metric sizing on your side of the pond.
Aside from taking the adapter off and going to a machine shop that is probably your easiest way out.
Go slow and I would bet it goes right thru.
You're drilling the holes in the adapters by hand on the bench? With a hand drill? That's going to be tough route to go.

As suggested above, best to use a proper drill press and a carbide drill. If you don't have access to a drill press, then at least use a good electric hand drill with a carbide drill (and a steady hand). Some cutting oil may be helpful too, to get a bite in the piece.

Good luck!
I have a bench pillar drill which I could use but as they are on the car I'm a bit reluctant to go that far.

I've tried using a new solid carbide drill with and without hammer action, no effect and as I'm drilling downwards I've got my full body weight on it so the pressure is quite substantial although probably not as much as the pillar drill.

I think Phil is correct and it's work hardening that's causing the problem as I've been able to drill other holes as shown in the pic.


I might have omitted it but don't use the hammer function on the drill, just sharpen it to work as a standard drill, this will take a green wheel. The carbide inserts are pretty tough and a regular carbide drill I believe will be too brittle for what you need to do.
Since you posted a photo where can I get some of those neat little clips you are using?