Introduction: Double Mirror Right Angle Drilling Guide

Picture of Double Mirror Right Angle Drilling Guide

Drilling a straight hole can be difficult because you can only see one side of the bit at a time.  Without a lot of practice, many of the holes end up perpendicular in one plane and not so perpendicular in the other.  Drilling with a conventional guide (2 blocks at 90°) works in some applications, but when using short bits there's not enough room.  This is quick, cheap & easy drilling guide will help you bore accurate holes even with small bits.  Using two small mirrors, it works similar to a dressing room mirror to help you view the bit from all angles.  When all the bits are parallel, start drilling.  It's that easy.    

Step 1: What You Need

Picture of What You Need

Basically what you need to make the guide is 2 wood blocks, 2 mirrors and a means of sticking them together.  In my case, I used double stick carpet tape.  If you don't have 2 small mirrors, you will also need a glass cutting kit & a straight edge.  

Step 2: Making the Drill Guide

Picture of Making the Drill Guide

I happened to have a couple 3/4" thick scraps already glued together from a previous box joint project which was convenient.  But starting from scratch, you'll want to cut your pieces 2 1/2" x 4 3/4" and 3 1/4" x 4 3/4" if using 3/4" material.  If you have precut mirrors, you'll want to cut your boards to match your mirrors.  I like the 3/4" board because it gives the guide a bit more weight and stands nicely.  The measurements aren't exact so use the odds & ends you have lying around.  Even if you've burned some holes in 'em like I did, they'll still work just fine.  Attach the 2 wood pieces together at 90° with glue and a couple screws.

I wasn't able to take pics while cutting the mirrors, but it's very easy on thin glass.  Simply dip the cutter wheel in oil and then run it along a straight edge lined up on your mark.  If it makes a scratchy "fingers on the chalkboard" sound, you doing great.  Light pressure is all it takes to score the mirror which can then be snapped off.  When breaking it, I like to support one side of the glass on my workbench top with the scoreline even with the edge of the bench.  This makes it easy to break the piece by deflecting the other side downward.  It is always a good idea to wear leather gloves & eye protection when cutting glass and mirror.  Remember that one mirror needs to be slightly narrower to accommodate the width of the other mirror (i.e. 2 1/2" wide and 2 3/8" wide if using 1/8" mirror).

Once your glue has dried and your mirrors are cut, attach the mirrors using double stick carpet tape or an adhesive. 

Step 3: Using the Double Mirror Drill Guide

Picture of Using the Double Mirror Drill Guide

To use the guide simply place it behind the bit and bring all four bits you see into alignment with each other.  In the first picture it is obvious that my bit is not close to 90° in any direction because the bits are not parallel in the mirrors.  In the second picture, you can see I am much closer to 90° although still not perfectly aligned.  Snapping this picture proved to be a bit "testy" but you get the idea.  

The beauty of this simple guide is that you can make adjustments as you drill to keep the bit at 90° to the surface.  While not as precise as a drill press, it is quite accurate when drilling pieces too big for the press.  The other advantage is that the guide is out of the way of the drill allowing the use of any size bit whether large or small.  

I hope this little drill guide will be useful to you.  I look forward to your comments & suggestions!


BeeTrap (author)2015-07-15

Great idea, thanks. I will definitely be making one. I have a drill press and a drill guide jig, but you can't always take those with you or they are cumbersome just to drill one hole. This will make up for all of that and my unsteady hand. Thanks again!

walter.warren1 (author)2015-02-06

Nice idea. My drill has a level bubble, but only for one axis.

alcurb (author)2014-10-27

Very clever tool for drilling vertically and true

sadiablo (author)2013-01-05

excellent idea. Will definitely be making one of these. A couple of vertical lines in the center of each mirror might also help as a reference.

sk8er6 (author)sadiablo2013-12-11

Question, wouldn't you need only 1 line on account of the reflections, or no?

sk8er6 (author)2013-12-11

10,000 THANK YOUS!

Stone_UFO (author)2013-03-16

awesome idea

Dardaro (author)2013-02-19

great idea i dont have a drill press, and this is very cheap and easy,i do have two mirrors for an old cardboard periscope project to make it

wannalearntoo (author)2013-01-26

Yours is a brilliant solution to misaligned drilling!!   Even though my drill has a water mark for vertical and horizontal drilling I was never able to do it right until now. I am forever grateful. Any more ideas?

kentdvm (author)wannalearntoo2013-01-26

Thanks! It does work remarkably well. Glad you could use it!

jtharkness (author)2013-01-05

What a great idea, and so simple! But you thought of it, and my hats off to you. Thanks, I will definitely make this, and perhaps also use it with my drill press since even there it is hard to see all perspectives for precise drilling.

voxelman (author)2013-01-04

This will also help with positioning the work piece under a drill on a drill press. I'd like to think of a way to suspend it spring loaded perhaps from the drill press head so that it doesn't have to be positioned each time.

Also, has mirrored 1/8th inch acrylic that has adhesive on the back. A 12"x12" piece costs about $10.

anode505 (author)2013-01-04

pretty clever

pfred2 (author)2012-12-26

Too big for a drill press you say?

You'd be surprised how well that works.

kentdvm (author)pfred22012-12-26

That is sweet! Never seen one like that before but a great idea.

lime3D (author)kentdvm2013-01-03

Yep, Mag Drills have been around since the 1970's. We used them to drill holes in the middle of very large plates of steel.

RichardBronosky (author)lime3D2013-01-03

Every good cat-burglar movie has one of these. I just saw it in Bad Santa last week.

pfred2 (author)kentdvm2013-01-01

It isn't as compact or portable as your mirrors are though. But once it is setup it is easier to manually operate.

hcalitz (author)2013-01-03

After drilling far less than half of all 180 holes straight, I certainly appreciate your genius! :) Brilliant idea!

LarryB (author)2013-01-03

Great idea! Reflection might be clear enough to work even if you used a cut section of a CD-ROM. Easier to cut than glass and cheaper too. The hinge then could be DUCT tape for a really low cost model to leave in the toolbox.

kentdvm (author)LarryB2013-01-03

Excellent idea. CD's would certainly be more durable on the go if they are large enough to see. Give it a try and let us know. I like it!

Ludwig Von Mech (author)2013-01-03

Brilliant. Just Brilliant.

WPee (author)2013-01-03

Looks like more fun than a 'fun-house' full of mirrors...... Nice!

Ganhaar (author)2013-01-03

Every now and then you come across a simple but brilliant idea to a and wonder why you haven't heard of it before.

Edgar (author)2013-01-03

So THAT'S how even I, can make a decent 90º hole!
Good Job! :)
Went to my Blog post:

ptorelli (author)2013-01-03

Ingeniously simple solution!

Bettybstt (author)2013-01-03

This is an excellent instructable! Even though I have been doing cabinetry and some carpentry for the past 14 years, I still can't hold a drill straight up and down. I have tried using a try square as a guide, but this is SO much better! Thanks. Now, can you make a jig that will help me use a hammer?

BrianJewett (author)2013-01-03

Brilliant! Every wood and metal shop teacher should be showing this trick. This is one of those things that could have been done 100 years ago and Yet I've never seen this before.

nicholas1951 (author)2013-01-03

A simple and elegant solution to a persistent problem. My congratulations to you!

lasharela (author)2013-01-03


polymarkos (author)2013-01-03

That is damned smart. I've oft had trouble precisely aligned drilling, and spent plenty of time jiggling a workpiece and swearing. This thing makes me wonder why I didn't think of that! Any time you say 'why didn't I think of that' you really mean that it is pure GENIUS!

Manny B (author)2013-01-03

Cr@p! That's devilishly clever.

sarawelder (author)2013-01-03

This is a superb idea! FOr those of us wearing progressive lenses, getting things straight gets a lot harder. I will make this this week!

sconner1 (author)2013-01-03

Great tip for those who either don't have a drill press or have a piece that can't go on a press.

blindpig (author)2013-01-03

Really cool idea! I've drilled a lot of crooked holes,am sure gonna' add this to my bag of tricks....

Brooks.B.J (author)2013-01-03

Really neat idea, I love it! Thanks for posting it ;-)

driveitlikeustoleit (author)2013-01-03

You can take a small circular bubble level and glue it to the back of your drill. When the bubble is in the crosshairs you're straight up.

billbillt (author)2013-01-03

Very good idea!...

avengine (author)2013-01-03

simple and good idea, I like it.

badbad214 (author)2013-01-03

Nice. Stupid idea: If you trace a vertical line on each mirror at the same distance from the angle it should give you a good reference to align your drill...

silver912targa (author)2013-01-03

Good idea! And thanks for sharing it.

spremoneb (author)2013-01-03

Good point, in fact the angle between the mirrors is irrelevant as long the drill is paralel to both reflections. Geometrically speaking if the drill is parallel to both reflections than it is paralel to the intersection between two planes- the hinge axis. So hinged version is excellent idea. Only under one condition, both mirrors have to be perpendicular to the plane to be drilled, but whatever the opening of the mirrors they will always stand up right.

DavAnt (author)2013-01-03

now that's really clever!

lbrewer42 (author)2013-01-03


balisticsquirel (author)2012-12-29

Do the mirrors have to be exactly perpendicular? I'm thinking of thinning them up and putting a hinge between them - to create a compact fold-out tool to carry around.

kentdvm (author)balisticsquirel2012-12-29

Thanks. I don't think it matters and I like the idea of a folding mirror. Might have to one of those too.

rimar2000 (author)2012-12-26

¡Clever! This is lateral thinking.

My thoughts exactly, but I thought it was perpendicular thinking ;)

giocad (author)2012-12-27

very ingenious!

Blue Hawaii (author)2012-12-27

Really nice trick! I have some plexiglass mirror scraps that will be used to make mine! Thanks!!

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