Cobalt HSS drill bits - gone blunt drilling stainless steel

[Robert Wilson]

A few (very few) are most ain't.
This is an example of one of the very few that are worth buying
http://www.axminster.co.uk/tormek-dbs-22-drill-bit-sharpener-950970

and here is an example of one of the many not worth buying
https://www.amazon.co.uk/Drill-Doctor-750X-Unit-3-Pin/dp/B000BKTA00

Ouch!

Perhaps for professional users who use bits all the time, but not for the likes of somewhat un-gifted amateurs such as myself!!


I can buy enough bits to last me for a number of years at those prices!!

Thanks for the info and advice.

 

[Norman_E]

Probably the cheapest drill grinding attachment that is any use is this type. https://www.ebay.co.uk/p/Draper-Drill-Grinding-Attachment-1180c-44351/1004322325?iid=161820867363
I will not normally touch Draper tools but this is in fact a copy, probably Chinese, of the American made General 825 attachment. These things are OK for sharpening drills from about 1/4 inch up, anything smaller is hard to set correctly. I have one of this pattern that I bought in the USA, and have sharpenned quite a few big drills with it.

 

[RichardS]

This used eBay one is exactly the same as mine: http://www.ebay.co.uk/itm/Electric-...161537?hash=item1c8eefc141:g:DxEAAOSwF3JZheo1

I'm not sure where you can still buy them new but it works well for any bit larger than about 4mm.

Richard

 

[Robert Wilson]

Probably the cheapest drill grinding attachment that is any use is this type. https://www.ebay.co.uk/p/Draper-Drill-Grinding-Attachment-1180c-44351/1004322325?iid=161820867363
I will not normally touch Draper tools but this is in fact a copy, probably Chinese, of the American made General 825 attachment. These things are OK for sharpening drills from about 1/4 inch up, anything smaller is hard to set correctly. I have one of this pattern that I bought in the USA, and have sharpenned quite a few big drills with it.

This used eBay one is exactly the same as mine: http://www.ebay.co.uk/itm/Electric-...161537?hash=item1c8eefc141:g:DxEAAOSwF3JZheo1

I'm not sure where you can still buy them new but it works well for any bit larger than about 4mm.

Richard

Great, plenty of choice, for a gizmo that doesn't need to be for high-precision jobs.

 

[Robert Wilson]

Update:-

I found a 7mm "reamer" in my "put it in their for a future task" drawer. Carefully reamed out the hardened 6mm holes, then drilled with my last remaining 8mm bit. I was very lucky, because I could even get at the holes from the reverse side as well.
Took it very slowly with plenty of oil and a lot of grunt and after a couple of hours had all six holes satisfactorily drilled.

So that's a tough job completed and I should soon have the rudder and skeg re-assembled after months of head-scratching, and a fair bit of trial and error.

Thanks one and all.

 

[skipmac]

For drilling SS and other metals I have much better luck with these than any cobalt, titanium or other special bits. These bits cut through SS like it was soft lead.

http://www.ebay.co.uk/itm/Norseman-...578837&hash=item210f834112:g:UEsAAOSwInxXOMmT

Also comes in metric sizes. Not cheap but this is definitely a case of you get what you pay for.

 

[Robert Wilson]

For drilling SS and other metals I have much better luck with these than any cobalt, titanium or other special bits. These bits cut through SS like it was soft lead.

http://www.ebay.co.uk/itm/Norseman-...578837&hash=item210f834112:g:UEsAAOSwInxXOMmT

Also comes in metric sizes. Not cheap but this is definitely a case of you get what you pay for.

Thanks, I'll bear them in mind for my next project, whatever that may be!

 

[PCUK]

Just sharpen them on the bench grinder with a fierce tip angle. Nothing special needed. Resharpen as required. Any old bit will do the trick if you resharpen regularly.

 

[William_H]

https://i1.wp.com/makezine.com/wp-content/uploads/2015/09/drill-sharpener2.gif?resize=620,222

That angle seen at the point is not so critical. The angle I refer to is the cutting angle. Look at a large drill bit from the side and you will see a sharp edge. (one on each side) Imagine this edge is like a wood plane carving into wood or a pen knife taking off a sliver of wood. You have the cutting angle determining the angle it cuts into the material shallow or steep. Perhaps not as critical as the fact that the edge wears away leaving a shoulder behind the cutting edge which may in fact be hitting the material first. So in sharpening you have to cut back the shoulder a bit to leave the cutting edge as the first to hit and carefully sharpen the cutting edge but trimming back the shoulder or metal behind the cutting edge.
The sharpening action with an oil stone is one of doing each cutting edge separately. With the bit in a vice vertical you attack the shoulder area at about 45 degrees rolling to a lesser angle as you move towards the cutting edge. The flat of the stone must be parallel to the cutting edge. A bit hard to explain. Start with larger bits that are not too blunt and use a magnifying glass to see just where you are grinding. give it a go. You can use a rotating grinding wheel but they take off so much material quickly and get the tip too hot that you loose track of the angles. good luck olewill