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Clearance for 3D printing

I've been doing a lot of work in SolidWorks recently in order to master clearances when designing moving parts. I noted my observations below:

Friction Fit

Clearances for friction fitting parts became an area of learning for me when I was designing my woodworking box joint jig. I printed fingers and reference cubes of various dimension that are supposed to be a set. They are small pieces and they can be easily lost in the woodshop so I designed and built a holder. These are all of the components and then the next picture shows them fitted together:

I've found that a .35 clearance on all sides allows for parts to be held together, come apart easily and not fall apart if jiggled around.

A clearance of .40 allows pieces to sit in place but will fall out if turned upside down. It's important to know this clearance too because sometimes you want a looser fit.

Sliding Dove Tail

The sliding dovetail is something that I wanted to use in a woodworking jig for making segmented squares.

I did a series of tests to figure out what sort of tolerances are appropriate for a sliding dovetail. I print sections of parts to see how they fit together. It allows me to iterate quickly.

For good sliding action/ if some sort of lubricant is being used then .25 gap is appropriate

For firmer slide, .20mm

Low Profile Sliding Dovetail

The low profile sliding dovetail is essentially the same as above but I wanted to see if I could compress the design down to a few mm and see if it could still print and function with a decent amount of strength.

When designing something like this: 1) The tail part(male) influences the socket part(female)

2) If "tail" is 2.25mm tall, then the female slot must be .25 SMALLER. So this one would be 2.00mm.

When the pieces slide together....they slide beautifully with that .25 clearance.

One of the other things that I wanted to discover is how thin is too thin to have a decently rigid part? 2mm worked well. I would feel comfortable using a 2mm base for my router jig project. Really the 4mm overall thickness more than sufficiently strong.

Rotating Print In Place Pieces

I didn't have a particular project in mind when I started exploring this but I have always been intrigued by print in place parts. It's really quite amazing if you think about it. Many people make little trinkets and toys with this design methodology but I think its a very powerful technique.

The questions I'm trying to answer:

When designing in SolidWorks, what sort of clearance do I need to design into my part? What is clearance gives the right amount of friction for various applications?

To do this I designed a set of rotating print in place cylinders with various clearances: .20mm, .25mm, .30mm, .35mm, and .40mm

This print is actually a reference tool when designing. I keep this close by so that I can feel it when I am designing.

Observations: .20 comes off my printer pretty much fused at the bottom. At first I thought that it wouldn't rotate at all but after a hard twist it actually broke free and rotates very nicely. With a little lubrication of some sort this would be a very useful mechanism with very little play between the moving parts.

The problem with this clearance is that the force that is required to actually get the part unstuck for the first time is actually kind of a lot. As a part of a bigger project I'd be hesitant to use this clearance because you risk breaking your print trying to get this thing to rotate. It does print in place and it is a very stable design with little play.

If this is incorporated into a design with a low infill, then I don't think this is the best configuration. Again, its because of the force that is required to break it free for the first time. For larger parts with more infill and some design intent then I think this clearance would be okay.

.25 and .30 could be broken free by hand .35 and .40 worked right off the best and rotate super freely. There is some "play" to it and should only be used if your part can't allow for this. For example, if you want something that truly spins effortlessly, then somewhere in the realm of .35 and .40 is good.

Print in Place Ball and Socket Joints

The tolerance for a part like this is .40

The tolerance for a print in place ball and socket is .40mm

If the tolerance is too small then the pieces will fuse together and because its spherical there is a lot more surface area for potential fusing.

I designed and printed this 4 times to dial it in.

When the clearance is too small, when you're trying to break the part free for the first time, it requires a lot of force and the part could fail before the fused parts break free.

I WAS using low infill so this was a factor. Also lack of fillets in my earlier designs caused part failure too. The key take away is that the gap needs to be 0.4mm for it to print properly, break free and swivel with the right amount of friction.

Threaded Container Lid

Container with threaded lid:

I built this container in Solidworks from instructions by Conor Walsh. The threads on this project are pretty big however, they work extremely well and that's what we're aiming for.

My first time printing this model my Layer Height was set too high (.28), and I had supports. The print was pretty bad. Especially the threads.

The second time(shown in the gif) I printed I went back to my default layer height (.16) but still had supports on. The print was good but it took a lot of clean up.

The third print will be tested with no supports but I also tested a super fast printing profile. It was FAST but the quality was pretty bad. I printed without supports and the threads DID work but its not something that would last long. I usually only change one variable at a time but this time I wanted to see ow much of a time reduction I could get.

What I learned from the 3rd print:

No supports are necessary for monstrous threads like the one in this design.

The superfast profile is good for a quick print to see the form of a design.

4th Print:

I used super quality. It took super long too...but turned out great.

So honestly, dynamic or super quality are the way to go. Just depending on how much time you have. As I am writing this I am realizing that this is pretty obvious BUT sometimes you have to learn from experience. There's a time and place for each profile just depending on the quality you expect, how much clean up you want to do and how much time you're willing to let your print run.

Treaded Rod and Nut

This is another one of those exploratory techniques. I don't actually need this for a project at the moment but as a maker, it is something that needs to be mastered. Threaded Rod: I created a rod with a .25inch (6.35mm) diameter. The 1/4 20 thread was "cut" into the rod using these settings:

It printed just fine:

The Nut: When designing I incorporated a clearance of .2 and it ended up being far too loose. So instead of .25inch (6.35mm) I did 6.55mm. Version 2: I did no clearance and went straight 6.35mm to match the diameter of the rod. This was still too loose.

Version 3:

Much better. Decreased the "clearance" to 6.15mm so it is undersized by 0.2mm and it was pretty good.

Version 4: Just to be sure I did a print with where I undersized the nut by .3mm. So the diameter of the nut is 6.05mm.

This tolerance works nicely. I designed a set of knurled nuts and bolts. The bolt was 10mm and the die was used. The nut was 9.7mm and the tap feature was used and it honestly works perfectly.

The picture shown above is was a test of the clearance to print a nut and bolt. I've since designed and printed dozens of threads and bolts. The key thing I was testing here was screwing mechanics. It definitely works. Note to makers: Print Orientation for printing threads must be considered for the strength of the piece.

Printing Supports is also something that must be considered to ensure the integrity of the threads.

Regarding the strength, the image I have above with the .25inch (6.35mm) diameter rod and the 1/4 20 thread . It works but wont be strong for most applications.

You CAN make a pretty strong thread. For example, a 10mm bolt shaft with a 24/3 thread pattern is really quite strong.

Note to makers:

Set your rod diameter, cut the "Inch Die" your threads into the rod.

For the nut: Set the diameter of the circle 0.3mm SMALLER than the rod diameter and use "Inch Tap" to create the threads in the nut!

Once you start getting into monster threads like a 10mm bolt shaft with a 24/3 thread then the clearance is actually different. I did a 7.5 circle for the nut, and a 10mm circle for rod.

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