Nigel,

A couple of possibilities;

The end of a new piece of silver steel is often hard and either needs to be heated and slowly cooled or the first 10mm cut off with a hacksaw before machining. You might already know that because you say that your larger centre drills are fine?

I once bought a couple of duff small centre drills that wouldn't cut – so are yours ok? You could check by using one on something like aluminium or brass – just to check it cuts ok.

Yep, very often, small centre drills are run too slow and they struggle – so you could as you suggest look at the speed. Lubrication helps but a quick dip with a centre drill shouldn't need that much – i.e., a quick squirt of oil of coolant if you have it.

Phil H

A few more possibilities:

• Small centre drills are rather weak and you're heavy handed. (I break them fairly often.)
• The centre drill is too cheap…
• The tailstock is off-centre. Drilling off centre causing it to bore, cutting on one side rather than drilling. Usually fairly obvious when the tip first makes contact, but the other give away is the drill cutting an over-sized hole.
• It's one of those days. (I bored a cylinder exactly 0.1mm too big this afternoon.)

Dave

One of the first things I was shown when I started my toolmaker apprenticeship was how to shorten the end of a centre drill. The old hands would not use one straight out of the box. I still do it to this day 56 years later on all sizes up to BS4. Try it, only a small amount is needed to miss the end of the centre,

Nigel

How about a different approach.

• Turn a 60 degree male centre on the end of the silversteel.
• Grip a piece of brass in your lathe tailstock drill chuck.
• Centre drill the brass using the lathe headstock chuck.
• Blob of grease in the brass centre hole before turning the pinion.

Keep checking the loading of this bearing arrgt as the silver steel will expand as it heats up.

Hope this helps

Regards

Derek

I've found some generic centre drills have overlong and fragile pilots. If you're cute with a bench grinder or patient with a hand stone you can reduce the length, as said above. When I tried paying a bit more for a good brand, I got shorter, more robust pilots that worked better. I still use the cheap ones as well, but don't put hard pressure on them in strong materials.

Nigel

Any kind of pip after facing will push a small centre drill off centre and snap the pilot.

Emgee

Good result, Nigel

MichaelG.

There is no need to use a fixed steady to drill a long protruding shaft. Hold in the collet with a minimum amount sticking out, face and then drill. You can then pull out what length you need and bring up the tailstock.

Neil's comment about spot drills doing a better job should say at making a dimple to start a drill, you could think he is saying they do a better job at producing a recess for a ctr.

I am glad others have noticed that some of the "Colonial" centre drills are dire. If you put a colonial against a good brand, the differences are striking. Buy cheap and buy twice!

Martin

I have not read all the posts, and someone may have mentioned this, is the end that you are drilling flat ie notit in the middle, with a small Slocombe bit even an almost invisible bump can push the tip sideways and break it. After you break the tip, DON,T throw it away, it's good HSS, makes good cutting tool for boring bars .

Ian S C

Edited By Ian S C on 25/05/2019 12:35:44