DIY Audio Projects Forum

How to drill a hole.
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Author:  M. Gregg [ 21 May 2016, 10:27 ]
Post subject:  How to drill a hole.

Yes how to drill a hole,

A newbies guide for fun!

Remember PPE goggles!<<<if they are scratched forget anything else your going to fail sad but true!

If you have protective film on aluminium don't remove it and mark out on the protective film!

Pedestal drills are great but not everyone has one do they.

Just a few tips on how to drill a hole.

1 Remember you will see 1mm difference in alignment but guess what you can see 0.5 mm as well so when you mark out you need to work with a sharp tip indelible pen and measure three times then mark. eg Pic.

2 Mark out and take your time. If you are using aluminium checker plate mark and drill on the flat side.

3 Now here is the rub, after marking out centre punch the holes "BUT" double check each time before you centre punch because once you have centre punched the metal if its a mistake you will forget and drill it then its scrap. Another way to ensure no mistakes is put a circle around each centre punch mark you intend to drill.

4 Drill all holes with 2mm or 3mm max first then follow with the drill size for the hole required. If you don't do this the holes will all be out of position. Its important on thicker material to keep the drill at 90 degrees to the metal because the run out from front to back can throw the finished hole out by at least a couple of mm. And then it looks pants! This is very very important on checker plate!

Invest in a hand countersink tool if you intend to build a lot of projects.
Something like this and you can de-bur every hole easily without a file and produce a clean product.

I like hole saws for large holes you must lubricate the cutter and hole or it will rip the aluminium slow and careful is the order of the day others use stepped cutters. You can get hole punches but they are expensive.

NB after all the drilling is complete you can remove most indelible pen from metal with nail varnish remover!

M. Gregg

Author:  M. Gregg [ 21 May 2016, 12:08 ]
Post subject:  Re: How to drill a hole.

If you are drilling plastic,

Cover the area with masking tape keep each strip butted up against the next Don't overlap it and all the same applies as for metal however in this case to remove the mark-out just remove the tape.

The problem with plastic is with large holes the plastic can be ripped so you have to judge how large you can go and then use a dremel or file to enlarge the hole. Don't just drill the hole and try to centre it with a file its not going to work, you still need a perfectly marked and drilled hole to start with!

M. Gregg

Author:  M. Gregg [ 21 May 2016, 12:18 ]
Post subject:  Re: How to drill a hole.

When filing,

Again mark out accurately then file to the waste side of the line test what you are fitting in the hole then slowly take off equal amounts of the pen mark along one edge then retest for fit. Continue removing equal amounts from the pen mark on each side and keep testing for fit.

Pretty straight forward.

M. Gregg

Author:  M. Gregg [ 21 May 2016, 12:25 ]
Post subject:  Re: How to drill a hole.

The best centre punch I use is,

An automatic centre punch from RS. However it depends on how much you want to spend!
I wouldn't be without it I have 3 collected over the years.

So the most important thing to this is, MARK OUT accurately / Centre punch on the mark /pilot hole with small drill sets the accuracy of the finished project.

We spend to much time trying to get it done right, if only we did it right to start with, we would probably spend less time trying. :xfingers:

Another point to remember is if one hole is up by 1mm and the next is down by 1mm the inaccuracy is 2mm that's a long way out.
If your out 0.5mm up and the other is 0.5mm down its out by 1mm so 0.5mm is what you want or less.
Take your time so you can look at it and feel all is OK with the world.
If it was an example of lean manufacturing each hole drilled is adding value the last hole adds the most value if it scraps the product you have lost all that time and effort. Just for fun :D

M. Gregg

Author:  M. Gregg [ 22 May 2016, 03:37 ]
Post subject:  Re: How to drill a hole.

The dreaded square hole.

To make a square hole.

Mark out the square you intend to cut out.
Then mark the centre of the square by drawing a line from each corner of the square (so you have a cross in the middle)
Now you can go two ways:

Either put a centre punch mark in the middle and put a cutter through the centre (just smaller than the square) then file to the square.


Measure a saw blade and mark in from the edge of the square enough room to drill a hole so you can get the saw blade through in the four corners.
Don't miss the part of using the centre punch and small drill pilot hole, the reason is because you don't want the drill for the saw blade to cut beyond the square you are cutting out. If the drill runs off you will have spoilt the job even before you have started.
Do this on each corner then you can rotate the blade at each corner.
Cut out as much as you can and file to the line.

If you are lucky and have a coping saw like this: ... SUVQCSM%3A
then the holes in the corners can be smaller however not everyone wants to buy loads of tools for what might be a one off project and although I have had these tools in the past, I get away with a small hacksaw most of the time. Normally because I cant be bothered to find it. LOL :)

As a side note never hold your work piece with naked vice jaws they will mark the work piece.
If I am drilling lots of holes I get better results clamping the job on a piece of wood/board putting it on the floor stand over it and drill downward from above. YMMV.

You can get square hole punches for thin sheet metal but they are very expensive and not cost effective (Just my opinion) its not a one size fits all scenario.

Of course a pedestal drill makes life a lot easier if you have a workshop, but for the DIY guy with perhaps a workmate bench or even nothing at all the above is the way to go. You can do all the above with a wooden stool as long as you are careful and take your time. If the pilot holes are out forget the rest it won't be any good and you will be forever trying to make a silk purse out of a sows ear.

For an oblong hole put the cutter through twice if you need to then join the holes up and file to the line. Triangle is the same as the square either three holes or one cutter and file.
Remember it doesn't even matter if it takes you hours to mark out it will pay dividends in the long run.

Things like valve sockets don't try and be clever and drill the screw holes, drill the main hole then put the socket in place and mark the screw holes.
But it pays dividends at the initial mark up to put a line through the centre punch mark in the middle extending out to give you orientation for the small screw holes for the base. I.e. vertical or horizontal fitting.
Most people already know all this.

Clamping a work piece.

There are many ways of clamping a work piece:
G clamps, vice, workmate, pieces of aluminium angle screwed to a wooden board.
Or my favourite use the panel mounting holes with wood screws and washers to hold it on a board and drill.

If you are working at home not in a workshop invest in a children's plastic table cloth and put it on the floor before you start work.
Then all the mess is in one place and easy to tidy up!

M. Gregg

Author:  M. Gregg [ 22 May 2016, 06:24 ]
Post subject:  Re: How to drill a hole.

TOP tip,

If you mark and work on the back of the panel if you centre punch by accident it wont show!

An automatic centre punch is operated by hand pressure and the power of the strike is adjustable so you can centre punch plastic or metal !

A coping saw can be used with an Abrafile blade great for thin aluminium: ... ei0uuiM%3A

The hand countersinking tool was shown me many years ago by a friend. I thought what's the point I can use a countersink on my drilling machine. Its not until you use one that you realise how brilliant they are!

So for an average set up you require:

A small metal square like this: ... -zQ1pfM%3A

I don't use the adjustable ones they are OK but not reliable for perfect 90 deg.

Some hole cutters I have two I use mostly for the 9 pin signal tube sockets and the 8 pin power tubes. I use hole saws.

A sharp point indelible pen. And a pencil for wood.

Small flat, round and square files.

Plastic 12 inch ruler.

A selection of drills.

A drilling machine.

A saw of your choice, could even be a jig saw.

The patience to try and mark out accurately.

M. Gregg

Author:  gofar99 [ 22 May 2016, 14:24 ]
Post subject:  Re: How to drill a hole.

There is another inexpensice goodie I find useful. It is a layout template. You can find them in crafts stores and fabric shops. They come in lots of sizes from about 2 inches wide and 12 long to about 12 inches wide and 36 inches long. They are marked off in uniform grids. Either 0.1inch or 1/8 inch. Some have holes at various spots as well. It will let you layout the design without having to measure each spacing. The ones I use most are the 2X12 with 1/10 inch spaces and the 8x24 inch one with 1/4 inch markings.

A Dremel tool is very handy for DIY.

Another tool I find quite useful...but at first seemed unnecessary is a table (belt) sander. It is amazing how often it gets used to clean up edges on projects. Super on smoothing out the edge of a pcb you just cut.

Good listening

Author:  M. Gregg [ 31 May 2016, 07:25 ]
Post subject:  Re: How to drill a hole.

Just thought,

I would show another example of holes drilled by hand using the above methods.
So there you go now you can make decent vent hole grids in work pieces.
6mm holes after 2mm or 2.5mm pilot holes. Hand de-burr with hand countersink tool.

M. Gregg

Author:  M. Gregg [ 03 Jun 2016, 02:58 ]
Post subject:  Re: How to drill a hole.

Here is a consideration when drilling a hole.

OK first thing is basic electromagnetism. :|

You must always pass a supply and return wire/cable through the Same hole.
The reason is simple around any conductor you get magnetic fields which produce eddy currents in the metal around the hole.
The eddy currents are cancelled out because they are in the opposite direction around the return cable.

If you pass the supply through one hole and the return through another you cause eddy currents to flow in the surrounding material.
OK this is a concern in ferrous metals however its not good practice in aluminium either.

A few things to consider both in design and installation.
Consider signal corruption with anode cables passed through chassis. (type of material etc).
In the bottom picture the magnetic circuit is broken with non ferrous material.

So this is something to be aware of especially for the run of mains/heater cable etc the more current the more of a problem it becomes. The problem with signal cables is the interference with a signal running through a chassis or ground plane and eddy currents working like a transformer within the chassis.

I have seen newbies drill single holes for transformer wires to try and make it look neat with a row of single holes perfectly in line with each supply and return for HT/heater/mains etc all with each supply and return running in its own hole looks nice but its wrong!

You can use two holes for supply and return if you slot them (so basically they become one hole )like this:

M. Gregg

Author:  Geek [ 03 Jun 2016, 04:20 ]
Post subject:  Re: How to drill a hole.

Excellent point!

This is a concern especially for wires carrying high current AC, like heater wiring. Even rectified and basic filtered DC before regulation.


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