Problem drilling small holes in aluminium

[reefphilic]

I've noticed that small drill bits(0.7mm to 1.3mm diameter) tends to wear out very fast when drilling metal compared to 3mm or above size.

I've to replace the 0.8mm (0.0314961 inch) drill bits after drilling only about 4 holes of about 4mm deep. I'm not even drilling stainless steel or titanium, just plain soft aluminium.

Is there any special drill bit that can last longer? How about special techniques? Should I use slow speed with high pressure? Slow speed with low pressure? High speed with high pressure or high speed with low pressure? Or does it make any differences?

 

[wasabe64]

Low speeds with AL, use a cutting fluid to prolong the life of the tool (WD-40 works well, TapMagic AL is better).

Clear away the chips from the tool often.

You are cutting over 4x the diameter of your drill in depth, be sure to back out the drill often to clear chips. While aluminum is a soft metal, it likes to load on the tooling and can interfere with proper cutting and build and trap heat. In most drilling work, it is recommended to completely back out the bit every time you travel 2x the diameter of the drill in depth.

 

[Lynx_Arc]

If you are drilling a lot of holes you may even want to cool off the aluminum now and then as heat can either temper or untemper your drill bits at times causing them to either become softer and bend more or harder and more brittle subject to breaking. Cutting fluid cools a lot better than wd40.

 

[robk]

I use cobalt drill bits, they last a lot longer than HSS or even carbide. They're not expensive, started using them when my HSS bits were wearing out drilling glass filled PCB's, but found they work well on AL also. Above - good advice on drilling a little, back off to cool and remove material from the bits.
Rob

 

[reefphilic]

Thanks for the advices. /ubbthreads/images/graemlins/smile.gif I'll get some cobalt drill bit and try it out.

One more question. If I back off and stop frequently so that the metal and drill bit don't have a chance to reach high temperature, can I do away with the cooling fiuld? Just wanted to reduce the mess created. Does the cooling fiuld serve any other purposes?

 

[jsmn4vu]

Using a cobalt bit on aluminum, you can get away with not using cutting fluid better than you can when using steel bits. WD-40 does a fair job for cutting aluminum, but I wouldn't use it for cutting steel.

The trick to not dulling a drill bit is to use enough pressure to keep the edges cutting, and not let them slide. With a tiny bit, that's not a lot of pressure. And always use the "pecking" technique as described earlier.

 

[reefphilic]

I do use the "pecking" techniques mentioned. But due to me worrying about breaking the tiny bits, I may have use too little pressure at times and causing the tip to slide. I will take note of that.

I just bought some Cobalt bits. Whoa! These things are expensive. Cost about ten times of those HSS drill bits of same size! The label stated that it is a solid carbide straight shank CB drill. Since it has a carbide body, is it susceptible to breakage due to bending(flexing)? I wish I have the space for a drill press. /ubbthreads/images/graemlins/frown.gif

 

[Anglepoise]

I presume you are using a drill press. Small drills do not do well hand fed.

I suspect you are not keeping the feed ( down pressure )high enough. These small bits need to cut and if you have too high a speed and not enough down pressure , they just spin and burn.
Kerosene as a lubricant is great for aluninium and will stop the formation of a 'false edge' that aluminum is famous for<g>.

 

[reefphilic]

I stay in an apartment so I don't have the space for a drill press. /ubbthreads/images/graemlins/icon23.gif I've to make do with a cordless drill. Hopes I don't break the carbide drill bits.

Yah, I suspected it might be the low pressure that caused premature wear out. Speed wise, I'm not too sure. How fast is considered too fast( a rough range will do)?

Another thing, what is a "false edge"?

Thanks. /ubbthreads/images/graemlins/smile.gif

 

[DLNoss]

Carbide bits, particularly that size, break really easily. HSS should work fine if you peck it. Usually peck at a depth at about equal to the drill diameter. If you don't cool it with something, the aluminum might be galling up on the tip. Not trying to be a know-it-all but this is the kind of stuff I do all day. MSC has some pretty good prices on small bits and stuff. www.mscdirect.com

 

[Anglepoise]

[ QUOTE ]
reefphilic said:



Another thing, what is a "false edge"?

Thanks. /ubbthreads/images/graemlins/smile.gif

[/ QUOTE ]

If one is drilling or lathing aluminum ,without any liquid lubricant, a build up of aluminum on the cutting edge forms. This is called a 'false edge' and can be responsible for the drill to cease to cut completely.

Lubricant, Kerosene is best, will limit this. Problem only happens with aluminum.

 

[PANZERWOLF]

i use a set of 0.3-1.6mm HSS drills
for aluminium and brass i don't use fluid, i just "peck" enough, use slow to medium slow speeds and watch the temperature of the piece
as for pressure, the pressure is right when you feel the bit getting "grip" (not easy with the small diameters), and when you produce nice and long spiralled borings (still don't forget to peck)
i don't experience any blunting with this methods

i once broke the .55 but could resharpen it with my dremel /ubbthreads/images/graemlins/grin.gif

dremel makes quite small drill presses btw, so if you lack space, you can still get one of these (they only fit dremel tools of course)

 

[eluminator]

Dremels turn too fast for me. I like slow speed. About the only power tool I use for drilling is a cordless screwdriver with a chuck. I think it turns about 100 rpm and that's just the way I like it.

I've drilled 1 inch holes in polycarbonate sheet with the screwdriver and a butterfly bit. It does a good job.

 

[jsmn4vu]

The variable-speed Dremels are nice, as are foot controllers.