Problems with Setting Burr

[Londoner2015]

I recently bought 2 sizes of setting burrs. I've never used them before, as i'm new to setting stones.
For some reason, it just isn't drilling into the silver.
I am making a couple of pendants with foil backed stones, so i just need to drill the same shape into a large domed solid piece of silver, and it isn't drilling.
I tested my ball burr, and it eats into the metal, but it won't be the right shape.
I'm using oil to lubricate the burr. What am i doing wrong?
I'm so rubbish

[Goldsmith]

You should use a drill first before using the setting burr.

[Londoner2015]

I did. I already made the hole...

[BarryM]

I did. I already made the hole...

Possibly the hole is too small? The setting burr is not designed to drill out a small hole to full size, but to shape a hole that is already about 60% - 70% the diameter of the stone to be set ( at least that's how it has been explained to me, I am not a professional stone setter)


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[Londoner2015]

Ah ok. That could be the problem then. I will try making the hole bigger first. Thanks so much

[ps_bond]

Radial velocity vs linear velocity. Burrs cut fast at the outside edge, but as you get closer to the centre they cut less and less.

[Londoner2015]

Thanks Bond - Super Moderator! I need to make a bigger hole!