Hole Drilling Tips

[doitle]

Howdy. I recently started actually putting my builds into boxes and have run into a snag. Whenever I drill a hole I get lots of roughness around the hole and pits of twisted plastic that prevent jacks from screwing down tight and look nasty. I'm using my drill at it's highest speed and successively drilling the big holes ie pilot hole, larger, larger, working up to the target size. It seems like as I start to get into the bigger bits they always just chew the hell out of the enclosure. Are there any tips or things for preventing this? I'm just using the cheapo plastic enclosures from radioshack so I figured they'd be pretty easy to cut nicely. Since it's plastic and all.

[John Lyons]

For metal and plastic you want to use the lowest speed.
Also, if you are not using sharp bits then do yourself a favor and
get a new set.
You can also get a hand reamer and or a countersinking bit to
remove the burr around the edges. Although I think it's just the
speed...seems like you are using plastic boxes as well....

John

[doitle]

Slowest speed for plastic eh? Hmm... I'll try that next time I guess. How I wish I had a drill press... I am not entirely sure how slow speed hand drilling will go but maybe I'll be pleasently suprised. Also the bits are brand new but have a very very large threading on them and so I think that might be part of the problem too. the 1/2" bit is just gigantic.

[jacobyjd]

definitely slow your drill down as much as possible.

Also, for metal, I add a drop of vegetable oil on the spot I'm planning to drill. the bit cuts MUCH better that way.

Also, I have a small set of fine, round files--3 sizes, each smaller than the type of hole they're meant for. That helps deburr the holes.

I use a hand drill for everything--with a decent hand drill, you should be able to vary the speed by how far you pull the trigger back. Mine also has a gearing switch for lo or hi speed.

[Ripdivot]

Use a punch to get your holes started straight. Then drill a hole large enough to get a uni-bit started (usually 1/8"). From there the uni-bit should do a nice job. A uni-bit is a stepped drill bit. Google it and you will understand.

[doitle]

Yeah a stepped bit was what I was hoping to buy but Lowes didn't have any. My drill is speed controllable by the trigger but I fear that at low speeds the bit will just catch and either wrench the part out of my vice or wrench the drill out of my hands I think the files might be a good idea as well to try to clean up around the hole once it is finally drilled.

[newperson]

using a larger bit size by hand or machine after your hole is drilled is a good way of getting rid of the bad edges.  you just have to hit it a small amount.

[ErikMiller]

Harbor Freight sells step bits by the set for less than you'd pay for a single Unibit, and they work just as well.

Step bits do have a greater tendency to grab the piece, so clamp it down if you can. But they do a great job of making smooth-edged holes.

[Taylor]

Harbor Freight sells step bits by the set for less than you'd pay for a single Unibit, and they work just as well.

Step bits do have a greater tendency to grab the piece, so clamp it down if you can. But they do a great job of making smooth-edged holes.

Yeah, I bought the step bit set from HF and it's great. Seems the same quality as the unibit I bought from Small Bear, but for the same price you get 3 different bits. Step bits are the best; I will never go back to switching different bits in for every hole size - and they do a great job of deburring holes.

[WhenBoredomPeaks]

My smallest drill's diameter is 5mm, is it small enough to start the drilling with it, (the step-by-step thing) or i should get a smaller one?



+ Is it really important to use a 10mm drill for the 10mm jacks or i can use a 11mm drill for it?

[doitle]

Hmm... I will definitely look into those step bits from HF. They look like they might be nicer. I guess before acquiring any more bits or drilling enclosures I'd better get going repairing the chuck on my drill. I got it because the battery didn't work and I managed to repair some spot welds on the NiCad cells but now the chuck is completely seized up.

[R.G.]

I've spent a fair chunk of the last couple of years of reading time learning all I could about machining. Here are a few observations based on that.

Clean, sharply cut holes, edges, surfaces, etc. requires rigidity in the clamping of the part being cut, the cutting tool, and the cutting tool holder. Accordingly, it is incredibly difficult to drill clean holes in metal or plastic (and wood, for that matter, if not using a pilot bit) by hand. I would say impossible, but then someone might have the skills. I can't, and I've tried for decades. Holes drilled with a hand-held drill will always be out of round and rough.

If you want clean(er) holes, get a drill press. Harbor freight, under $75 will do it. Hand held drills are for when you need a hole and aren't too fussy about exactly what size or exactly where.

Plastic requires different drills to do a clean job. Plastics, and to some extent copper and brass need a much smaller rake angle on the cutting edge of the drill bit. The sudden grabbing you feel as the bit goes through the back is the feel of the cutting edge digging in and grabbing too much plastic. This is because as the drill breaks through, the center is then cutting air, and the amount of the cutting edge still cutting gets smaller and smaller. Since most folks aren't adept enough to reduce cutting pressure, the outer edges of the drill bit get 100% of the pressure forcing the bit into the material, and the outer edges hog in, taking a really deep bite, and then stalling. You prevent this by using a fine grinding stone and flattening the leading edge of the drill bit *evenly* and *on both sides*. The bit is then cutting with no rake, and can't dig it. But it takes a lot more pressure to drill the hole up to the there.

Drilling a clean, round hole requires that the drill bit be dead sharp and absolutely symmetrical. Commercial bits may or may not be symmetrical, depending on quality.

Machinists would never expect a drill bit to produce a clean, accurate sized hole. To get a clean, accurate hole, they will bore the hole on a lathe, or drill to about 0.005" undersize, then ream the hole to the correct size with a precision reamer.

You can clean the burs up easily enough. There are deburring tools made especially for this, and a hand countersink or larger drill bit can sometimes do an adequate job of cleaning burrs off the edges of holes.

Don't get discouraged - you're trying to get results that the pros wouldn't try with that set of tools.

[Taylor]

I think an important thing to consider here is what one's standards are for a good hole. I have a drill press, but unless I'm doing a bunch of boxes at once, I use a hand drill for enclosures. I find that the holes I make are perfectly adequate for my needs (those being a hole big enough to fit the part but not so big as to leave a visible gap). I've never had an issue with misshapen holes, or a need for more size precision, or rough edges.

RG, perhaps you can elaborate on why we would need precision like that? And yes, I'm not just talking about building things for ourselves, but to sell.

[R.G.]

RG, perhaps you can elaborate on why we would need precision like that? And yes, I'm not just talking about building things for ourselves, but to sell.

I don't think you do. I need clean, precise holes sometimes, which is why I went out and learned that stuff; but when I need it, the precision is not for drilling jack and pot mounting holes.

I was just answering the poster's question.

[lvs]

For drilling a large hole through plastic I first make a small one of about 3-4 mm and then use a wood drill (which has a point protruding in the middle) of the wanted diameter. The point of the wood drill sinks into the pre-drilled hole and prevents running away. But, with a wood drill there's also a lot of friction that can make the plastic melt under too much pressure or speed, and when it starts sticking to the drill, it might burst. But I succeeded in drilling a plate made of a hard, breakable kind of plastic.

A very thin material which will probably deform with the "last bite" of a large metal drill, I try to clamp between two small pieces of wood if the location of the hole permits it, and drill through the wood and material together. It's difficult here to make a hole precisely where it's wanted, but at least the corned beef can comes out unwrinkled and with a clean hole.

Far from professional tips, I admit.

[John Lyons]

The smallest size on my step bit is 5mm as well.
I always start with a 1/16" bit and work up size by size until
I to roughly 5mm. Then I use the step bit until I get close to the size.
If you start with a 5mm bit you will never get an accurately placed hole
as the bit will skate around a bit (pun) untill it digs in finally...

The step bit size will often be a little larger than what I am aiming for.
What I do is drill the size smaller with the step bit and then use a reamer to
get the exact size I need. I count the number of reamer rotations to get the
right size I need. Then memorize them. 

John

[Ibanezfoo]

Hmm... I will definitely look into those step bits from HF. They look like they might be nicer. I guess before acquiring any more bits or drilling enclosures I'd better get going repairing the chuck on my drill. I got it because the battery didn't work and I managed to repair some spot welds on the NiCad cells but now the chuck is completely seized up.

Careful with those bits from Harbor Freight.  If you drill any steal with them I have read in various places that they dull extremely fast.  I wanted to get one too but the reviews aren't so great.  If your're just doing plastic and aluminum I'm sure it will be fine though.  If you are looking for a decent drill press though, Harbor Freight has some decent ones for very cheap.  I picked up a benchtop 8" and a big floor standing drill press and they have served me quite well.  The chuck on the small one was nicer than the chuck on the big one but you can swap them out with a better Jacobs or whatever you want.  No run out though.

I just drill my stuff slowly with older HSS bits I'd had forever.  A little bit of oil when drilling metal.  Any rough stuff around the edges and I just grind it off with a dremel.

[Taylor]

I don't think you do. I need clean, precise holes sometimes, which is why I went out and learned that stuff; but when I need it, the precision is not for drilling jack and pot mounting holes.

I was just answering the poster's question.

Well, just for clarity, I didn't mean any accusatory or hostile tone with that question. I suddenly started thinking, "Have I been sending out stuff with bad holes and not realizing it?" I just wanted to make sure there wasn't something I was missing.

[R.G.]

Well, just for clarity, I didn't mean any accusatory or hostile tone with that question. I suddenly started thinking, "Have I been sending out stuff with bad holes and not realizing it?" I just wanted to make sure there wasn't something I was missing.

No problem, no offense taken - it didn't sound hostile at all. I probably hit the "precision" more than was needed.

As a somewhat interesting aside, there is a trick for drilling a square or triangular hole with a space bit in a hand-held drill. Neat trick but it's such a special purpose thing I didn't bother to put it in long term storage.

[head_spaz]

I like step drills for convenience, but I've bought three different sets from from Harbor Freight, and they all
have massive runout, causing high vibration. I always get three lobed - triangled holes whenever use them.
(and yes, I use a drill press)

So I've gone back to the previous methods that always gave me good results.

A good tapered reamer is one of my most essential tools.
You can correct a multitude of sins with this baby.
It makes jagged holes ROUND, and offers more sizes than any stepped drill set.
At only $4.50... it's hard to live without.



Then there is the Center Drill... which is my very favorite drill for making ROUND holes. These are IDEAL
for drilling enclosures. Beautimous results every single time!
No need to buy a whole set when just a few bits and a good tapered reamer will produce any size you want.



Next we have the Split-Point drill, which is ideal for drilling thinner materials. These work especially well on
stainless steel..
Split-points drill their own pilot hole and have a shallower cutting angle which practically eliminates bit bite.
These work best in a drill press because they require more feed pressure.



For better results when using standard twist drills, make your pilot hole the same size as the ROOT of the
larger bit. The root is the cross-section of the bit between the flutes. To determine the root, just measure
across the chisel point.
Ideally, when using twist drills, your holes should be drilled in only two steps. Pilot, and To-Size.
I usually drill my holes slightly undersize, and then ream them to the final dimension.