drill bits and taps

[Steven Ford]

The advice of more knowledgeable and experienced engineers will be welcome:

When drilling and tapping for M3 bolts I seem to make something of a habit of breaking the bits. Is this because I have a touch like a blacksmith, am performing the task incorrectly or am I buying cheap and nasty tools? Is there a secret to stressfree drilling and tapping? How can you tell a superior drill bit or tap from the other sort? Is there a particularly excellent brand?

As an aside - I found a supplier of SS M3x35 cap head bolts that will go all the way through from the drive case of a Tiger 1, the hull side and the armour fillet. www.stagonset.co.uk. Putting a bolt in from both sides seems to result in one or other protruding.

[Adrian Harris]

> Is this because I have a touch like a blacksmith, am performing the task incorrectly or am I buying cheap and nasty tools?

Could be any of the above. When hand tapping I usually do it as a series of cuts:

1/4 turn forwards, 1/4 turn forwards, 1/4 turn backwards - repeat as necessary. You have to do the backwards turn to free the swarf from the taps cutting edges so as to prevent it from jamming - and hence breaking.

> Is there a secret to stressfree drilling and tapping?

Get someone else to do it Are you using a cutting compound when tapping ? That's supposed to lessen the risks, though I must admit I haven't tried it yet.

> How can you tell a superior drill bit or tap from the other sort?

Price usually. I know this is a hobby but don't buy "hobby" taps or drills, especially Draper/Clarke type ones. If you have a look on http://www.mscjlindustrial.co.uk/cgi/insrhm you'll see just what sort of choice you have for drills and taps.

I switched from Draper to Dormer and these seem much more reliable. Go for the best you can afford. There are different drills and taps for different sorts of material, but it usually says in the description for which metals they are suited.

Adrian.

[leesellars]

Hello Chaps

Adrian is right for ali you must use a cutting compound I prefer a paste type. You just have to take your time.
Also use the correct size drill for tapping use of a Zeus book will help on this.
Try and keep clear of Budget drill bits and Dies. I get all of mine from J&L industrilal supplies.
Pay a bit extra. Stick to Middle of thier range top of thier range is for industrial use as Mark at Armortek will endorse.

Lee

[Derek Attree]

Hi Steven
For M3 tapping use a 2.5 drill and a cutting compound. Rocol works ok.
However I use lathe cutting oil myself. Illacut 30.
As has been said take it slow and forwards and back also get the tap square
to the job.

It will get easy to do when you have done a few and you get the feel.

Quality tools the way to go.

Derek

[Steve Stuart]

At work we use quality Ti Nitrile coated bits, they last much longer, keeping their edge well. Definitly worth the extra cost.
Also keep the speed right down, very slow and lots of steady pressure keeps progress going.
One of my best purchases is a Breast Drill, which makes drilling through sheet steel with small diameter bits relatively easy!
My Grand Father's Brace has been an extremely use full peice of kit, it is far more powerful when used with a screw driver bit and holder than an electric screw driver.
Steve

[Armortek]

At Armortek we avoid drilling and tapping small holes whenever possible. It is what you might call a "high risk operation". Even with the best tools and ideal conditions, you may still break tools. Small drills should rotate as fast as possible. The advice the guys have given on hand tapping is good. Life is easier if you use tapping compound on the drill also. Methylated spirit is an excellent tapping compound for aluminium. Light oil is good for steel.

Mark