Making a multiprofile Drill bit

[N. Thornton]

OK will try that one, ta. Diamond disc has been completely rubbish at grinding them.

Regards, NT

[Capitol]

news:...

I've just checked, the last lot of spade bits I bought in the £ shop have a

7mm shaft. Get grinding!! LOL

Regards Capitol

[Ian Stirling]

Don't use diamond disks for steels. You end up with lightly carbonised steel, and no diamonds.

[geoff]

In message , Capitol writes

Grinding with a 7mm shaft?

ooer missus

[Capitol]

Interestingly enough, the type of countersinking drill bit ( spade version) that you are looking for was common about 40 years ago. They were very popular for boatbuilding in wood. I still have a couple of these which have survived, but I've only seen very low grade bent steel versions in recent years. As an afterthought, if you want to construct a spade type drill from a 6mm rod, then you may well find that a sacrificial 6mm allen key is a good starting point. This will probably be hard enough for 40 holes in softwood if you don't overheat the steel.

Hope this helps

Regards Capitol

[Capitol]

Bloody optimist!

Capitol

[Tony Williams]

Would it be easier with two drillbits?

No1 is a standard 6mm drillbit, pointy end ground for wood, and with a depth stop. That gets you the main hole, swarf pumped out, and ready as the guide hole for drillbit No2.

No2 is a length of 6mm bar, drilled at the front with a 3.5mm drillbit brazed in. At the back end of the 6mm bar have a combined countersinker (or recessor) and end-end depth stop.

No2 *might* be made from a cheap spade bit, right size for the countersink, but running backwards, with the 3.5mm bit brazed into the end of the drive shaft.

[N. Thornton]

Ah, that would explain a lot. Maybe I'll try an old grit disc then.

Cheers, NT

[Rod Hewitt]

[e-mail] (N. Thornton) wrote in news: [e-mail]:

I don't suppose that something like the drill bit supplied with this:

would help?

[N. Thornton]

Well well, I've got it done, and it saves lots of time. What worked was an old metal grinding grit disc. The diamond just didnt work on steel, and it turned out the grit disc I'd used before was a stone one, and almost useless on steel.

Job done!

Regards, NT

[Pete C]

Did it work out OK grinding a drill bit to a profile, how did you do it in the end? I was going to suggest using a new metal grinding disk :^)

cheers, Pete.

[N. Thornton]

Yes, I was just using the wrong grinding discs! With a grit metal cutting disc it went fine. I use cutting discs as the thin edge is needed in the flutes, plus the amount of side force on the disc is only slight.

Re your questions, they appear to be answered by what you quoted, so I guess I must be misunderstanding something. I used a drill to turn the bit and an angle grinder to grind it. Ran the drill backwards so it was the blunt edge of the flutes that hit the disc.

It turns out the bit doesnt perform as well as a factory job, for 2 reasons:

1. The flutes are shallow in the thinner section
2. the angle of the very short tapered section is by no means ideal
3. there is no recessing on the outer edge of the flute section of the smaller diameter section. but it works fine, and far faster than swapping bits over all the time.

Thanks for all your help!

Regards, NT