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Registered Member #538
Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181
Just making a case for my amplifier (a gainclone) and I need to drill 10mm holes on bit over 1mm steel on my drill press. How the hell should I drill them, I've tried everything and everytime the drill bit starts going in this "pattern" and the hole ends up having three to eight "corners" (not circular).
I've tried drilling with low rpm, higher rpm, lowering the bit real slow and tried all kinds of drill bit increments and everytime it starts "oscillating" and the hole ends not circular. Gonna go buy a.. dunno the correct term but the cone shaped drill bit and see if it works out better with that.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
A simple solution with simple tools:
1. Mark the dead centre with a smart blow from a centre punch to stop drill bit from wandering, and secure the work in the vice.
2. Using plenty of oil, drill a small pilot hole, keeping bit cool.
3. Expand hole with progressively larger drill bits.
4. Finish hole to required dimensions with a conical tungsten-carbide reamer or diamond burr.
You should also check to see that your pillar drill does not have excessive run-out - off-axis wobble - which can come from worn bearings and so on.
Edit: Added afterthought: If you have only simple hand tools available, there is nothing wrong with using good old-fashioned methods, and enlarging your first hole to the desired size with rat's tail and half-round hand files.
Registered Member #1739
Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261
A good idea I tried on thick aluminium, but you can try it as well as it will just take more time for your case, but USE AT YOUR OWN RISK as hell knows how it will end up (ended up well for me however, even with aluminium being a more drill-locking metal, but who knows). The trick is - drill a smaller hole by sequencial usage of more and more thick drills (I used a single thick one as, again, had aluminium to deal with). Then - the spooky part - take a handleless rat's tail rasp which's thin end fits the hole you've just drilled and the thick one exceeds the target diameter - and lock it HARD in your hand drill. I mean lock it really hard and check the balance really carefully - I bet it's no fun of removing it from your forhead if anything goes wrong ;) Do not set the torque too high, just above the one at which it gets locked bad sometimes, and SLOWLY AND CAREFULLY start pushing the rasp through the hole. If you start to feel any harder vibrations, immediately stop the drill before taking the rasp out of the hole and recheck the balance.
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
Be careful with a step drill, some don't like thick steel, and tend to heat up semi-fast.
Start with a metal punch to put a small mark to center the bit, use lower RPM, higher torque, clamp your workpiece down, lots of cooling oil. Don't slam your drill bit into the workpiece if you have a drill press, go easy with the pressure so you don't snap the bit.
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How to drill big holes in sheet metal?
