drilling small(ish) holes

[twangman]

Hi all,
Spent the last few weeks messing around with the mill and lathe and learning the limitations of my capabilities – I’m having a problem drilling small diameter (2.5mm) holes in a flywheel for an Elmers standby engine, - the “hole” (from the rim to the hub) in the steel flywheel had snapped the drill just when the drill breaks through to the hub opening (I had to bate the bejaysus out of the snapped drill (BFH approach) but I’ve managed to recover the flywheel with a bit of re-working) then the same thing happened when I was drilling the crank disk – as soon a the drill met the hole where the crankshaft would go, the drill snapped.
So the question is, am I doing this the correct way by just drilling through from the periphery to the shaft opening or should I have something like a filler piece in the shaft hole or is there some method of breaking through that I’m missing here?,
I have found that working on these small scale engines requires some real attention to details and that I must stop dropping parts on the workshop floor – they’re bloody impossible to find .

Regards

John C.

 

[steamer]

Twangman,

Old trick I have seen posted here by others and I have used before.

Cause:
Whent the drill breaks through, it grabs the edge and pulls thru, that results in a broken drill

One cure:
Put a close fitting plug in the hole of the same material as the flywheel. Then drill the hole.
The plug will support the cutting lip as it goes through the hub bore, preventing the grab and the broken drill.

Then take the plug out. That should solve the problem.

Dave

 

[ksouers]

Hi John,
Well, 2.5 mm is pretty darn small! One thing with small drills is you really have to up the speed, crank the RPMs up as high as you can. Consult a cutting speed chart for the size drill you are using.
Here's one from LMS here in the US.

http://www.littlemachineshop.com/Reference/CuttingSpeeds.php

It has a calculator so you can input the size drill and material you are cutting and will give you the RPM to run.

You also need to keep chips clear. Pull the drill all the way out frequently and blow the chips out with an air hose. Keep track of how deep you are, as you get close to breaking through let up on the pressure and start pecking till you break through.

To do small holes properly you should be using what's called a sensitive drilling table or attachment. This allows you to only use finger pressure to advance the drill. You should always use a pecking motion, take your time, take it easy. Keep the hole and drill bit clean. Drilling small holes is easy if you have patience.

Once you have a few holes under your belt and you have the basics down, you'll find that they really go rather quickly.

 

[MadKad]

I have drilled titanium with 1mm and drill lots of things around that size not normaly more than 1.6mm, the first time I drilled titanium I went fru 10 1.4mm drill bits as i was drilling fast, I then relised that slow was the way to go for titanium.

Going at high RPM will help, and like steamer said with the plug idea, or placing a peace of the same steel but up behind the hole your making will do the same job.

Bringing the drill bit out and back in will clear any chips, also dont alow your drillbit to get to hot as that can make some problems, but thats hard at high RPM