Sharpening drill bits

[fred]

As we work mostly in wood the necessity of sharpening drill bits seldom arises. However we are in the process of drilling and countersinking an 8.5mm hole in 200 pieces of 8mm flat mild steel so I had to dig out my old drill bit sharpener. Similar to this :

recommends an angle of 88 degrees for drilling hard materials and an overhang of 1.16"

This is a mad angle when set on the device. The bit approaches the grinding wheel nearly horizontal. W.T.F. This can surely not be correct. Existing angle on the bits is about 60 degrees. I just used a sharp bit I had to set up for sharpening.

Besides what's with this 1.16" overhang ? What's that about ?

Very rarely having to work with steel we are using an electric drill in a hefty drill stand. Reducing the drill speed electronically doesn't appear to be a satisfactory way of drilling these holes so we are reduced to using max speed and applying pressure to the point were the speed slows slightly. Not a good idea. We've burnt out one drill (Cheap Skill) already.

Any suggestions ?

[Nightjar]

Mild steel might be harder than wood, but it is not, in metal terms, a hard material. You want to set it for general purpose drilling.

It is how far the drill sticks out of the end of the jig. For GP drilling, they recommend half the drill diameter, which is 4.25mm.

Take them to a metal working workshop and get them drilled for you on a pillar drill. You are going to struggle with a hand drill in a drill press, particularly when you come to countersinking.

Colin Bignell

[tony sayer]

In article , Dave Plowman (News) scribeth thus

And don't forget some lubricant, makes a lot of difference;)...

[TheScullster]

"fred" wrote

If you are struggling at 8.5mm, try using a pilot hole - say 4mm. Also apply cutting fluid/coolant while drilling as the bits will soon overheat. The general included angle for a metal twist drill point is 118 degrees. Dormer are a good reference for all things drill Google "dormer drill information handbook" without quotes and select pdf fifth entry.

Phil

[dennis]

Given the price of drills and the fact that he is only drilling 200 holes I doubt if he needs to sharpen a drill.

8mm drills are only £5.50 for ten from toolstation.

However it really needs a pillar drill, even a cheap £35 one from lidl/aldi would be OK.

I hope he remembers the cutting fluid.

[Tim Lamb]

In message , fred writes

I would appreciate a copy of page 2 if you could kindly put it up.

As others have said, the job would be much simpler if you had access to a decent pillar drill. IMO 8.5mm is too large to drill in one go and you would be better to pre-drill at 5mm on full speed and follow with 8.5mm at low speed.

regards

[Nightjar]

If you have the time, it is cheaper than buying new and, if you know what you are doing, you will end up with something that cuts better. It was only below about 1 mm (we used down to No 80) that I would have replaced, rather than resharpened.

I would be very dubious about buying those. That is similar in cost to just one Dormer 8.5mm TiN coated jobber drill.

You have just knocked over £40 off the profit he expects to make from the job.

Often not practical on a pillar drill and certainly not essential for mild steel.

Colin Bignell

[Dave Plowman (News)]

The Lidl ones I use - coated in something - seem to be certainly as sharp as I could do. I'd be rather upset if I bought bits which weren't - you need very good skills to sharpen smaller ones especially.

Yes - but I 'upgraded' to a Lidl one. Much more powerful induction motor than my previous PP one for about the same price.