Duplicating House Keys

by nrp, published

Duplicating House Keys by nrp May 30, 2011

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Full writeup on my blog at: eclecti.cc/hardware/physical-keygen-duplicating-house-keys-on-a-3d-printer

It occurred to me recently that I had printed almost nothing actually useful on my RepRap 3D printer, aside from parts to improve on or build more RepRaps. I am rectifying that with this project. The goal here is to generate working house keys by inputing the key code of the lock into a parametric OpenSCAD model. Instead of having to explain to my landlord how I ended up with a wedge of plastic jammed in my front door, I ordered a box of (well) used locks and latches from eBay to experiment on. Luckily, the lot includes both Kwikset KW1 and Schlage SC1 locks, which are the two most commonly found in the US. I created an SC1 model to start with, but I’ll probably make a KW1 soon.

EDIT: I uploaded a KW1 model as well.

Designing the key model was actually pretty straightforward. I measured a key with a ruler and calipers and created an approximate model of it that is reasonably easy to print. I then got pin depth specifications and parametrically differenced them out of the model. To generate new keys, you can just edit the last line of the file and enter in the key code for your key. If the code isn’t written on the key, you can measure the height of each bit and compare to the numbers in the Root Depth column on the aforementioned pin depth site. Perhaps more nefariously, you could implement something like SNEAKEY to generate key codes without physically measuring the key.

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I finally have a working 3D printer and decided to print out a key to my house using your model. Worked perfectly.


So, infill solidity should be set to 1.0?


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Duplicating House Keys by nrp is licensed under the Creative Commons - Attribution license.

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You’ll of course need OpenSCAD to edit the .scad file and generate an STL to print out, unless your key just happens to be 33172 like the example STL posted below. If it is, you can unlock the doorknob currently sitting on my desk. As a small, precise object, this is a great test of how accurate your Skeinforge settings are. You may need to adjust some thicknesses or the built in pin depth fudge factor to get it working properly with your printer. The pictures above show the key being used on a disconnected lock cylinder, but I found it was also strong enough to turn a deadbolt. If your lock needs a lot of force to turn, you may need to cut a space into the key to use a torsion wrench with it.


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darco on Apr 17, 2014 said:

I finally have a working 3D printer and decided to print out a key to my house using your model. Worked perfectly.

tim1986 on Sep 30, 2011 said:

I tried to print one and it printed too sparse. What would you recommend as print settings(shells, solid layers, infill solidity)??


nrp on Sep 30, 2011 said:

I print it entirely solid with 1 extra shell.

michaelqpd on Jul 30, 2011 said:

I think you got the KW1 depth_inc = mm(.023) out by 0.001 mm should be .022. Going off some documention. Everything else seems good.

nrp on Jul 30, 2011 said:

I was going off of the numbers here: http://web.archive.org/web/200...

That shows a 0.023" increment in depth.

yanniknelson on Jun 6, 2011 said:

change your lock you've just given every one your house keys

rhmorrison on Jun 12, 2011 said:

No, only the doorknob currently sitting on his desk :-P

VeryWetPaint on May 31, 2011 said:

Rather than using the 3D printed key directly it could be used as a new duplication master. Unlike duplicated keys, a 3D printed one doesn't accumulate errors from previous generations.

Have you seen Daniel Bejar's visualization of key-duplication loss?

relet on May 31, 2011 said:

Or you could just attach that dremel to your Makerbot and mill your key.

hintss on May 30, 2011 said:

couldn't you burn the key if it got stuck in a lock?

nrp on May 31, 2011 said:

Yes, if you're not worried about arson. ;)

Your best bet is probably to take the lock apart and push the key back out the front with a small spudger.

Linkreincarnate on May 30, 2011 said:

Given that the script are parametric it should be trivial to make a bump key for most major locks. Just set every tooth to the maximum. (Or was it minimum?)

-soapy- on Jul 16, 2011 said:

A bumpkey will work as long as it is cut below the lowest lift in that particular lock.

So if you had a key with only #1
amp; #2 cuts (rare, but I've seen them) a bumpkey cut to #2.5 or #3 would work. One cut of a #3 depth would make life impossible for that bumpkey.

Best bet is to get a proper lock, really. US locks are generally rubbish, and the weak backsets supplied are a liability. Try and get yourself a UK British Standard lever lock. Not one in ten locksmiths in your area will have the first clue how to open it, and it will stop a crowbar or boot far be
tter than a tatty little locking knob handle or even a deadbolt. Plus it can't be bumped!

nrp on May 30, 2011 said:

Maximum bit depth, so minimum size of the key. I'm not sure it would work very well as a bump key. The plastic key is I think more inelastic than a normal brass key. Worth trying though.

Meskdavi on May 30, 2011 said:

Yet another reminder that security systems don't stop anyone just delay them. Cool idea though

-soapy- on Jul 17, 2011 said:

Hahaha. Security systems stop lots of people every day!

What you mean is that the average security system doesn't stop someone determined enough to put hours into it. Which is true. Most security systems can be broken with a bit of effort - that's what a good locksmith or pen tester will do.

However, if you want something impenetrable, you need to spe
nd a bit of money. And have a couple of guards and several layers. And even then, with enough time and resources, you still won't be safe! The CIA or whoever have an infinite resource to put against you, so without serious money to resist, you are stuck.

But to the average hacker/thief/locksmith?
Hardly the same thing.

When assessing security, always determine if there is a specific, targeted risk factor.

TheRuttmeister on May 30, 2011 said:


I was measuring my house key last night after a friend suggested I try and print one!

I gave up... glad to see you didnt.

MakerBlock on Jun 16, 2011 said:

TheRuttmeister: An easier way to duplicate a key might be to put it on a white piece of paper, photocopy and scan the copy or take a picture, scale to proper size, use Inkscape to convert to DXF, import into OpenSCAD, extrude, perhaps add some details, and print!