Centre drills

[jordan1]

Centre drills, are they really an advantage.?

 

[PhillipM]

Err, if you want to spot a centre accurately, yes.

What 'advantage' are you looking for exactly?

 

[brightspark]

Centre drills, are they really an advantage.?

not so much an advantage but a must in a lathe the only advantage if u didnt need one would be time on changing it

 

[jordan1]

For pillar drill, just that there is a degree of bend/flex in smaller drills to pilot. Thought the centre drill would be better for this of course.

 

[mike 109444]

Go for the long series type cos when you centre with a standard length centre then remove from chuck you may find you have to release the table of your pillar drill to drop enough to get drill to slip into chuck thus loosing position from your centre drilling.

 

[julianthegypsy]

Go for the long series type cos when you centre with a standard length centre then remove from chuck you may find you have to release the table of your pillar drill to drop enough to get drill to slip into chuck thus loosing position from your centre drilling.

Now that's a good tip! One thing I don't know is how to choose between the different sizes. What's the difference?

 

[Pete.]

A stub drill is the proper tool - centre drills are for drilling centres. For your small flexible drills, use a punch mark to stop them wandering.

 

[mike 109444]

http://en.wikipedia.org/wiki/Drill_bit_sizes
near bottom of page.
You match the larger dia of the centre drill to the finished size hole you are drilling (within reason!) A centre drill is more ridged than a similar size twist drill because is does not have all that metal removed (the flutes on a twist drill) but because it does not have the flutes you should not drill beond the small amount of flute it does have cos there is nowhere for the swarf to go and so it will jam the centre drill. If you choose the right size say kust above the finish size of the hole then you can chamfer/deburr the finished hole when cutting the centre drill hole. Also can be used to form the lead in for a hole that is going to be tapped.
And remeber if you are into turning (as in lathe work) then don't throw out the broken centre drills as they are HSS you can make boring tools from them (even done this on a pillar drill (lots of chatter though!!)

 

[mike 109444]

On the subject of drills/centre drilling lookup point thinning / web thinning. Useful to know, saves multi drill swapping

 

[MrFluffy]

A stub drill is the proper tool - centre drills are for drilling centres. For your small flexible drills, use a punch mark to stop them wandering.

Strongly agree with this.
Centre drills produce a angle hole which differ to the one normally found on a drill bit and wont guide a drill as bit accurately as piloting with a stub drill.

Theyre made to drill a workpiece so it can be mounted between centres on a lathe or other machine, not to make a drill start straight. The different diameter's are to cater for the different requirements between centres, weight of the workpiece and how much depth/contact you need on the centre after etc.

 

[brightspark]

if theres only a few holes to drill with a pilot 1st acurately i just use my home made spring loaded center . center punch the job and put it in the vice . pull the centerdrill down on to the mark and that automaticaly centers the vice in place , clamp it down and put in pilot drill

 

[Lawnmowerboy]

But the angle of a stub drill is lesser than a conventional drill anyway

Have a spot drill in my doom for some reason. Crap pic I know done on webcam!

 

[julianthegypsy]

Reading wiki, it says you shouldn't use a centre drill before a carbide tipped drill. I need to drill lots of 7.5mm holes in stainless on my small capstan, now I'm confused!

 

[brightspark]

Reading wiki, it says you shouldn't use a centre drill before a carbide tipped drill. I need to drill lots of 7.5mm holes in stainless on my small capstan, now I'm confused!

using a carbide tipped drill after putting a center drill in 1st will probably make the tipped drill snatch and chip the tips why do u need a carbide drill on the stainless a good hss drill will cope at the right speed and a good constant feed using coolant

 

[MrFluffy]

To get things centred properly on my mill to a punch mark, I use a very thin drill (1-2mm) and bring it carefully to the punch mark. When you have it even slightly offcentre to the punch mark you can easily see the bit flex as it enters the centre pop as its so weak if its not bang on. Then back out, alter x or y until you see no deflection. Then out with it and in with a appropriately sized stub drill.
If you need it located any more accurate than that method, then a drill bit isnt the way to make the hole anyway.

 

[julianthegypsy]

using a carbide tipped drill after putting a center drill in 1st will probably make the tipped drill snatch and chip the tips why do u need a carbide drill on the stainless a good hss drill will cope at the right speed and a good constant feed using coolant

Someone suggested I use carbide! Changing speeds on my little capstan is difficult too, though it does have coolant.

 

[hareng]

Rarely use centre drills or anything similar on mills and lathe. I do accurate work or not at all!

Capstan, as long as centres ar on and running true just plough straight in, job done.
If it starts to skate or veer to one side before cutting just feed in a little, it can often be seen to come back smack on centre, just need to get the feel.

Centre punching first is just relying on eye sight and aligning that mark, could be well out.

 

[graffian]

You can generally use the carbide drill and nothing else, they don't need centering and they drill bang on size with a good finish. So no spot drill/centre drill, pilot drills and often you just use a carbide drill instead of drilling and reaming.
I centre for drilling on the mill with a spot drill.
But if your going to have to bevel the edge of the hole, centre drilling isn't adding any more ops?

 

[julianthegypsy]

I need to get my parting tool sorted, its leaving too much of a tit and deflecting the drill, the centre drill will cope with it but I'm not happy with it at all. I'd much rather go straight in and bevel afterwards if necessary, though to be honest I can bevel the pin that's going to fit in the hole with a tool on the cross slide far quicker instead.

 

[Lawnmowerboy]

Just get the centerheight bang on and it shouldn't leave much pip