Wondering Drill Bits

[ianmac]

Hi All,

I know this question has been raised a number of times and there are always some good replys however I stumbled across this on the weekend by accident and though i should let everyone know.

I always centre punch the job but some times the drill still wandered off centre for some reason.

Fix. Centre punch the job and run a file over the cenre punched area. do this until you notice that the area is flat again.

Although i have only been doing for for a week it has worked first time every time.

Let me know how you go!

[Tel]

Yep Ian, that's a point that's often overlooked - the crater raised around the pop mark by the punch can be anything but regular, AND in a random direction so it pays to flatten it out. The use of a centre drill is of great help as well

[paul]

Useful tip - cheers Ian!

[lancelot]

Hi Ianmac, I completely agree with Tel on this one... centre punches Have their place, but some times it is not in model engineering...I worked for many years in the Aircraft industry and the use of the centre punch was a NO NO, reason being possible cause of stress related cracks... the gear we used for preciision drilling of holes could very easily be made using the equiptment we model engineers already have at our disposal...slip bushes and the means of holding them plus an optical centre punch which is not all that difficult to make... the end result of using these tools is a hole drilled spot on in the correct place...

www.browntool.com/

I am sure this site will give you some idea of what I am on about...
All the best for now,
John.

[ianmac]

When it has to be dead on off to the mill we go.

First off i turned a piece of stainless into a taper from 3/8th round.

use that to align the job, fit centre drill and drill, then replace centre drill with drill bit.

Perfecto!

Is was only by chance that i filed down the centre punched surface. Now everything gets a lick of the file before before drilling.

Wish i was old enough to have spent some time in the grandfathers workshop the things that i could have picked up.

Ian

[engineeringtech]

This is a good thing to remember!

[ravensworth2674]

It's OK to file- or even better to mill a flat on a curved surface prior to even marking off but what if the centre drill or the drill itself is blunt?

I am doing a drilling operation on a Headstock Dividing Attachment on a Myford Super 7B and there is only one thing- apart from getting new drills and that is to sharpen them.
After all the Four Facet System avoids the centre drilling operation.

Another thought. perhaps

Norm

[ianmac]

I am not sure what you mean?

I would never want to drill with blunt drills. they really dont take much time to put a new surface on them. You find that they will wonder because you are applying extra force and trying to rub your way through. Center drills are only a few bucks.

Usually you find that if you are carefully you just need to give the relief a little lick on the grinder and then a rub with the side of the oil stone.

I find the smaller the drill the more finicky as i am sure anyone does

One Tight fisted penny pincher who will remain name less buys rubbish drills to save??? I have in the past just touched up brand new drills for him by giving them a bit more relief on the back of the cutting surface.

These drills were utilizing a new Chinese technology, they burn there way through timber so i ground a bit more relief and converted them to the old school method. ;D

Ian

[tcase]

I always use an optical punch (where I can), a major advantage is the the punch end is the same as the included angle of the drill tip and there is far less tendency to wander and it raises less burrs.
Where I have to use a normal centre punch I now follow up with a punch with a the same angle at the tip as the drill.

[ace]

I had the same problem sometime back and took advice from fellow engineers only to find that I still suffered drill wondering. I soon invested in a quality set of drills and 'hey presto' no more wondering drills. ;D

ace

[Deleted]

Talking of the need for quality drills, a couple of years ago I bought an 'Engineer's Drill Set' going up to 1/2" from Axminster Power Tools, a source from which I have bought many excellent items. However, the drills had obviously been ground by eye by child labour somewhere in darkest Asia. I found this out when the 7/16" drill I'd selected drilled 15 thou oversize! I've had to regrind the lot and usually revert to my Titan drills instead.
Caveat Emptor!

[ace]

I have over the past couple of years purchased 3 drill bit sets, 1mm to 10mm in 0.5mm increments and letter drills and number drills from Chronos. These have been expensive but money well spent and the sizes are clearly marked on each drill.

ace