Jump to content
Ultimaker Community of 3D Printing Experts
Sign in to follow this  
zmaster

Does the PLA crack easily?

Recommended Posts

I'm going to design a box which is composed by some parts screwed togheter.

I will use PLA and i have read that it is hard, which also means it is fragile.

I think that if i'll make the screw hole - the one where the the screw grips, don't know the correct english term - too tight then the PLA will crack.

Is it like so? Do you have some experience/suggestions?

Share this post


Link to post
Share on other sites
I'm going to design a box which is composed by some parts screwed togheter.

I will use PLA and i have read that it is hard, which also means it is fragile.

I think that if i'll make the screw hole - the one where the the screw grips, don't know the correct english term - too tight then the PLA will crack.

Is it like so? Do you have some experience/suggestions?

PLA is really tough material, far from brittle as you described, and can be used with screws easily... I routinely make objects that use standard tripod mount screws (1/4in and 3/8in), and I have not seen a failure. smaller/finer threads are a bit more delicate by nature (i.e. M3) and should not be over-tightened. self-cutting screws should also not over-tightened.

The most important thing about PLA is the heat generated from friction. cutting a thread means you need to go suuuuuper slow, clean out the debris frequently, and check the tool temperature with your finger tips: if it is uncomfortable to touch, it gets too hot for PLA, which gets soft at 80C, and you can't cut into soft plastics.

Share this post


Link to post
Share on other sites
The most important thing about PLA is the heat generated from friction. cutting a thread means you need to go suuuuuper slow, clean out the debris frequently, and check the tool temperature with your finger tips: if it is uncomfortable to touch, it gets too hot for PLA, which gets soft at 80C, and you can't cut into soft plastics.

I think you're talking about drilling the holes with a tool, right? I'm going to create them directly in the design and use self-cutting screws, so there should be no problem.

Thank you!

Share this post


Link to post
Share on other sites
I think you're talking about drilling the holes with a tool, right? I'm going to create them directly in the design and use self-cutting screws, so there should be no problem.

I had explicitly mentioned self-cutting screws for that reason... just keep in mind that small holes become much smaller during printing... on my UM, holes for self-tapping screws that are designed as 1-1.5mm are filled completely and need pilot drilling for self-tapping screws, while 3mm holes turn out to be almost 3mm... so 1-3mm is a difficult grey area.

Share this post


Link to post
Share on other sites

I routinely make parts with 3mm holes intended for a M3 screw. The holes are modelled at exactly 3mm diameter, but when I print them they are a snug fit for the M3 screw (which I measure an outside thread diameter of 2.90mm). The advantage of this is that you don't need a nut in most cases, and can simply thread the screw into the plastic. I have only used hex hand drivers to insert the screws, and I have never used a special 'self-cutting' screw, which is something I did not even know existed apart from 'self-tapping' screws used for sheet metal work. I have been using button head machine screws of the type that come with the Ultimaker, and they work well. If you don't want the threads to catch on the hole I generally use 4mm diameter which is a pretty good fit after printing.

For the brittleness of PLA, I haven't done any scientific tests, but I know from experience that when it breaks it does tend to 'snap' apart, where as ABS will kink but stay connected. I don't think ABS is necessarily any stronger than PLA, the point where they fail seems about the same, but PLA fails differently. In the case of a screw thread, I think PLA is better suited because it's not as soft.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×

Important Information

Welcome to the Ultimaker Community of 3D printing experts. Visit the following links to read more about our Terms of Use or our Privacy Policy. Thank you!