What center drill to buy ?

[nsigr]

Hello

This is my second topic in this forum and as you see I am a total newbie...
Yesterday I was trying to drill a 5mm steel plate with my Einhel BT-BD 501 and I noticed that my drill wobbles a little.
I know that the pillar drill I have is not a very professional tool so I don't expect to much.

After a small research on the web I saw a few youtube videos from people who uses center drills to start their holes.
Is a center drill a good idea to make a straight hole and what center drill diameter I should buy ? I saw a few from 1mm to 8mm on ebay.

Thank you
Nikos

PS. I think that a General Metalworking section should be created to this forum

 

[Harbo]

I don't know if there are any set down rules but I would use a 2 or 3mm?
It's really just to form a starter hole - the centre drills are much shorter and have thicker shanks so more stable.

Rod

 

[nsigr]

Thanks Rod

I will get one and try it. Hope to have better results.

 

[chipmunk]

A centre drill will help but have you tried centre-punching your holes?

It's a lower tech method of correcting drill wander in metal but it'll also save you having to swap from centre drill to twist drill and should achieve the same end-result. Use either a manual or automatic centre punch - both work well.

Having said that I often use centre drills on the (wood) lathe because centre punching dead centre in round metal stock isn't always easy.

As far as sizes, the countersink on centre-drills is much steeper than the end of twist drills and so your aim should really be to just create a start for the drill. A reasonable guide might be to choose the diameter of the centre drill tip to the slightly larger than the size of the twist drill chisel tip which doesn't really cut - as with a pilot hole. The problem with centre drills is that they often require quite a bit of force to cut in larger sizes - certainly more than twist drills IMHO.

HTH
Jon

 

[jasonB]

If you want to form a starting dimple by drilling then forget using a centre drill and buy a spotting drill. These are ground with a sharper "point" so won't skid on the surface like a centre drill and being that they don't have the small dia pilot are a lot more durable.

The only time I now use a centre drill is when I intend to use the tailstock centre for support.

The spotting drills also come with a 90 or 118 degree point so a standard twist drill sits better in the dimple. one about 4-5mm will be OK or 3mm if doing a lot of fine work.

If punching then the prefered method is dot punch first and then inspect the punch mark, if its slightly of you can "pull" it into place by slightly tilting the punch and hitting again. Once you are happy with the position then use the centre punch to form your starting dimple.

J

 

[nanscombe]

Yes, I remember using a centre punch for starting holes during metal work lessons at school.

The manual one, where you just place it on the mark and hit it with a hammer, or the automatic type that has a spring in it and works by pushing down on it.

Either should allow you to start drilling in the proper spot.