Sharpening countersinks.

[David ColwillParticipant @davidcolwill19261]

I have two identical Dormer 25mm countersinks. They are 10mm shank and are both very badly worn, with deep gouges in them. I did manage to complete the job using the less worn of the two but in reality they are both pretty useless.

The pictures below show one of the countersinks before sharpening. They say a picture never lies but this is clearly not true as it was very deeply gouged and this doesn't really show up.

I know you can send them away to be resharpened but I can't see myself ever getting round to sending them off.

So in the interim I ordered some off ebay. The 25mm cost about £10.00 and is an import one. It arrived the other day and does cut quite well.

Back to the Dormer ones. Looking at them I wondered if they could be sharpened in my reliance style swing drill grinder.

Firstly I needed to hold them in it, so I made up a piece of 20mm dia bar with a 10mm reamed hole and a grubscrew. After mounting the countersink with the cutting edge arranged vertically (by eye). I experimented with how far out to have it projecting. On my jig ( I believe they are all slightly different ) it seemed to be about 55mm to the point. My jig is mounted on a piece of steel and I use it on the surface grinder which allows me accurate control of infeed. I clamped up an improvised guard and gingerly had a go. I indexed it round by eye which seemed to work OK but could be improved.

So it all looked very promising BUT…. The relief angle is far from perfect and at the center is completely wrong. I'm not sure what is happening but am reasonably pleased with the result given that I spent less than an hour messing around with them. As I said the center doesn't cut but the last picture shows a piece of 25mm with a 10mm hole and it cut that sufficiently well for me to call it a success.

Obviously if you do have a go at this be very careful as the cutting edges of a countersink can be quite long and in my case the grinding was done on the side of the wheel, which isn't particularly safe.

Regards.

David.

[David ColwillParticipant @davidcolwill19261]

[Raymond Sanderson 2Participant @raymondsanderson2]

David these are very much like sharpening drill bits.
here's a video I found might help. I do notice this is a very rough set up and he is unsteady but gives you plenty to go on.

[John ReeseParticipant @johnreese12848]

On single flute countersinks I use a die grinder or Dremel with a small stone. I frind the rake face (inside the single flute. I use a stone small enough that I can maintain the correct rake.

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