Instructables
Picture of Make a working lock and key
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In this instructable I'm going to run through the process of making a working 5-lever mortice lock and key. Steps 1 & 2 are an overview of 3D printing requirements and how the mortice lock works, with steps 3-7 showing you the construction of the lock, and the final piece demonstrated on page 8. For the purposes of this I will leave out the making of the decoration, though it can certainly be 3D printed also, but feel free to contact me if you want to know how to do it.

Step 1: Planning a 3D Print

Firstly, I'm going to run through the basics you need to keep in mind when preparing a model for 3D printing. If you have already used 3D printers, then feel free to skip on to the next page, or take a quick look at the bold writing to double check the basic rules.

There are several types of 3D printer available, and depending on what one you're using will affect the way you make your model. For example, a printer using photopolymerization uses light to harden a liquid resin in layers, so when completed the model is simply pulled from the liquid, allowing for all types of undercuts/ interlinking items. However, Thermal Extrusion printers heat plastic and print each layer on top of the previous, meaning that it has to create supports to reach any undercuts in the model. As a result, the supports need to be cleared away before the part is ready, so interior or interlinking details are not really viable. For the purposes of this instructable I am going to assume the model is being printed using Thermal Extrusion as it is by far the most common form of 3D printing. Another important aspect of the printer to keep in mind is the type of material you will be printing in, as it will limit the thickness and minimum level of detail it can print.

So, for thermal extrusion here is what you need to keep in mind.

1. The digital model you send to the printer will be in STL format (Stereo-lithography). This is basically a 3D placement of the paths of the surfaces on your model. However, if your model has any intersecting details it will have difficulty understanding what is meant to be an exterior or an interior surface, and can easily print the wrong thing. Avoid intersecting surfaces. While it can be time consuming to find ways to connect geometry together, especially if detailed, it is necessary. Booleans are a great tool for combing/subtracting objects, but be careful with these. Multiple boolean operations to one object can cause unexpected results. If using booleans, try to compile all objects to be cut into one object before cutting. If in doubt of any problems on your model then run an STL check before exporting. Most 3D programs have the ability to do this.

2. Don't try to send multiple objects in one STL file. As tempting as it is to just export everything together and rush through the printing setup it can easily cause problems, as well as leaving no room for manoeuvring objects in the print setup. One of the main problems here is that any models touching against each other will have a layer of support built between them, regardless of whether or not there is space in the 3D file for it, which can cause parts of your model to be lost. Individual STLs of objects also makes it easier to detect and replace faulty pieces.

3. Thermal extrusion builds up in layers, whose thickness depends on the quality and speed of the printer. This means that any vertical detail will have layered ridges, much like a stack of paper (though often rougher as the layers will be thicker than a single sheet of paper on most machines). While flat surfaces shouldn't have a problem printing vertically, it can become an issue when printing curves. Try to limit curves to being printed horizontally. While it takes up more space on the printer bed to lie everything flat, it will reduce the number of layers and thereby the roughness of the object. Think about how you place your models.

4. When making objects to fit inside another, don't make them flush. While 3D printing is highly accurate, there is a small amount of bleed in the plastics as they cool, and the ridges of the layers will provide grip to the sides. Trying to insert an object into an exact sized hole will be nearly impossible and require filing/sanding in order to fit. Allow a small gap (~0.5mm, depending on the quality of the printer) around the edges to ensure the piece will fit smoothly.

Phew. Ok, now that the boring part is over, let's take a look at what we're going to be making!
 
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glomscient5 months ago

I am going to try to make this, but I will use my medium of choice: hand tools and brass! This should be fun! (first I will have to get the right brass bits. I will probably use copper, as well.)

You can always use a sand cast from the 3d parts

Also, what would I need to view the files? I won't be printing them, but it would be nice to use as blueprints.

MattRickS (author)  glomscient5 months ago

That sounds amazing, I'd love to see a few pictures when you get it done. As for viewing the files, ideally if you had a 3d program like 3ds max or maya (you could download a trial), or Houdini (which you can get for free, it just restricts renders which you wouldn't need). In any of those you'd just need to go to File > Import and bring in the objects that way.

Otherwise I'm sure there are basic viewer programs out there. I can't remember whether the files were .stl or .obj, but a quick google search turned up these which look pretty good:
http://sourceforge.net/projects/stlviewer/

http://sourceforge.net/projects/objmodelviewer/

Let me know how it goes and if you need anything else to complete it!


Epetty2011 months ago
Hi Matt, I am following your directions to make this lock in a 3d design class I am taking at my local community college. I have made the Key as well as the "Curtain" I am now trying to move onto the levers. I have the basic shape down but I do not understand how they all go together. I understand that the bottom of each lever needs to match the length of the notch on the key but how do you set this up to figure this out? If you could please elaborate a bit more on the steps to creating these levers correctly, that would be great! It is an awesome design and I hope I can pull it off! If I end up doing so I will post pictures of the actual 3d model printed on the 3d printer!! Thanks for all of the help!
Epetty20 Epetty2011 months ago
By the way I am using Solid Works any advice would be greatly appreciated!
MattRickS (author)  Epetty205 months ago

Apologies for such a late reply! Not sure how I missed this one. I'm sure you've long moved on by now, and hopefully got it working, but if not, I'll explain now:

To create the levers is quite simple, but my description was a bit confusing. You basically just need to position your keyshape where it would be inside the lock, and place a lever shape in it's "open" position over each pin (ie, rotated as though it has just been turned. Make sure it's pivoting around the pin that the levers would be attached to.). Then just taking one pin and lever at a time, create a cylinder shape that matches the length of the pin. This is representative of the path the pin takes as it's turning around inside the lock, so it's center needs to be the same as the key's. Then whatever is overlapping between the new cylinder 'path' and the lever just needs to be removed. This means that when the key is rotating on that path, the lever will be pushed up to that height, and seeing as you created it in the "open" position, it will open correctly.

I hope that explains it a bit better. Reference the image I had in that section for a visual aid, you'll see where the pivot of the lever is (shown by the coloured arrows) and the keys pivot is central to the cylindrical section of it. Notice how the curve created matches the path the keyshape will take while spinning.

MrNathann2 years ago
If anyone makes a working copy, I would love to see it.
MattRickS (author)  MrNathann2 years ago
I won't have access to a 3d printer for some time myself, but a number of people have gotten the STL files off me so hopefully we'll get to see their printed pieces. I'll certainly be trying it as soon as I can.
mangomango2 years ago
This is an absoutely fantastic design. if you could provide .STLs i can get this printed and assembled within the week
MattRickS (author)  mangomango2 years ago
I've finally gotten round to emailing them out to people, if you want to message me an email address I can send them on.
oldmicah2 years ago
As someone who is hopefully about to leap into 3d printing (has it shipped yet!!!) the 'Boring' part as you put is extremely valuable to me. Neat project overall, but I did want to let you know that while I sometimes skim the intro sections of instructables I always appreciate them. Many thanks!
tonys1232 years ago
It is creative. Love it.



www.smilebetter.jp
Love to see a printed model.
Great instructable!
MattRickS (author)  Greasetattoo2 years ago
As would I. Unfortunately I need to find the time to get back to my old college where the printer I used to use is to do that. I'll add it up once I get it printed, though it may be some time. Who knows, if I'm lucky enough to win a 3d printer it'd be up first thing.
sleepycat2 years ago
Beautiful design! :)
qli22 years ago
Impressive!! Well done.
kelseymh2 years ago
What an awesome project. I especially appreciate all of the discussion of practicalities for good 3D printing design.

Much of your Step 1 resonated with my own professional work. I'm part of a large software project which provides a simulation of particle physics in matter (particle detectors, radiation shielding, medical treatment planning, space physics, etc.). We provide tools to build 3D geometries (with different materials, surface properties, and so on), through which the simulated particles are tracked and interact.

The software can get very confused if volumes overlap, or if there are "non-existent" regions between volume elements. The CPU time can also go up tremendously if complex geometries aren't built with some thought to their structure. It was very interesting to learn that some of those same issues apply to 3D printing of "real objects"!
MattRickS (author)  kelseymh2 years ago
I'd assume they would be a much bigger problem for the sort of projects you'd be working on than they would for 3D printing. I overlooked a few of those mistakes when running things through a printer for people and generally you just get an odd line of support material running through your model. Seeing as they generally require some cleanup unless the printer is really good quality then it isn't too much hassle, just something to be aware of. That being said, I did once disintegrate a robot arm in a particularly bizarre print.

What you're doing sounds far more interesting however. I've some long term aspirations to be working in particle and fluid dynamics myself, though for a much less useful purpose (film and media).