Component materials and design

Hi Guys, this is my first post here while I wait for my Mini to arrive

I’ve been circling this printer for a while, and finally submitted to the inevitable! My first task for the printer is to help me make parts for a computer racing simulator. I made one nine years ago, complete with home made pedals and a ‘gearbox’, but it was all made from metal and wood and is a leviathan - although I’m proud to say it all worked well.

Now I can see that using 3D printed parts, I can make a better, more compact and probably more reliable version. As a traditional engineer, I am used to cutting bits of metal until I get to where I want to be, now I know that I have to change that philosophy. However I did know the strengths and weaknesses of the traditional techniques, but am totally new to this, so would appreciate your help in understanding where I should be using the 3D printer and where I should not be. Also, tips on design techniques to avoid breakage and poor function would be good.

I am pretty competent with Solidworks, so will be using that to design the parts, and so can incorporate strengthening webs, lightening holes (although more probably in this case media saving holes is more accurate) and bevels and blends to avoid stress raisers

Before any of that though is to know the materials I need. I can finish machine parts on my mill and lathe, so accuracy of parts is not strictly necessary, and cosmetic appearance is not too important either. However toughness, resilience and strength are key so any advice on what material would be the best to use is very welcome.

I throw it out to you guys, hope you can teach me some things!

Cheers

Les

Well if you’re machining metal, you’re ahead of the game from a durability of materials perspective. Plastic is still plastic. You’ll probably want to use the 3D printer for rapid prototyping for fitment and functionality.

When choosing a filament it boils down to a few charateristics:

  • Ease of printing
  • Rigidity
  • Heat resistance
  • Durability

I’m a fan of ABS for strength and durability, but it can be finicky to print. PETG and PLA are good filaments for getting started…easier to print. PLA has a lower melting point so it can deform if left in hot places (like a car on a hot day), and there are challenges to printing on the LB machines.

Good luck with the machine, I hope others in the community can chime in to help your selection or understanding of the various materials.

Congrats on the new Mini. I originally got a Mini just to make prototypes and ended up using it for production parts. Personally for strength, heat resistance, and good finish and accuracy, I’ve had very good luck with Colorfabb XT and HT. XT is rigid and a little stronger than HT, whereas HT has a little more heat resistance and is a little more flexible. Both are a more advanced print so you may want to start with something like Colorfabb nGen, which has good heat resistance and it very easy to print. It is more brittle than XT and HT, and is more like a PLA but stronger and is a great filament to start out with. I even use nGen for some production parts that have lower heat and strength requirements. Best of luck with your new Mini.

The best tip i can give is to really flesh out your designs and geometry in Solidworks. i’d say 60-70% of a strong part can be made/broke with good or bad geometry. Then comes infill. Depending on the stress and forces increasing infill can increase strength. Next comes layer direction. This is akin to which way the grain is facing on wood. Depending on forces sometimes the weak spot in inbetween layers. Sometimes this can be overcome by also using glue or using acetone fumes to melt ABS/HIPS into a solid “Blob”, therefore hiding the layers and increasing strength. Next comes choice of filament or material.

My experience with nGen is less than stellar. It is brittle, and when i have used it a few times with brass inserts and set screws I’ve had it crack on me. I don’t think nGen is a filament i will use in the future despite low fumes compared to HIPS/ABS. I find PLA to be a nice filament that i hope to work with more in the future despite it’s somewhat sticky nature. I’ve heard good things about the HTPLA stuff.

Thanks guys, some good food for thought. I’ll have a play and see how I get on using those ideas.

One point I saw on a set of recommendations was that when using stuff like ABS, it is good to put a chamfer on the bottom of the part where the initial layer is laid down, in order to help in removing the part from the bed. This seems to go against other advice where you put an extra layer outside (a raft?) in order to improve print quality, can anyone comment?

I have to convert parts from solidworks files somehow, if I struggle I’ll be over to the software forum!

Les

Make sure when researching that the PEI surface is kept in mind. Most printers use a glass print bed which requires some additive or surface to increase ABS adhesion and prevent warping… blue painter’s tape, ABS slurry are common recommendations, but again aren’t necessary on the PEI.

The print surface of the Mini will be a sheet of PEI. Its perfect for adhesion of ABS as long as the auto-level process works. No need for any other coating to the print bed. Other keys to printing ABS on the PEI:

  • turn off the print fan for the initial 3-5mm of the print
  • use a brim (5-10mm) to help seal the bottom to the print surface.

While we’re on “best practices” and “vs. Internet”, don’t use a razor on the PEI bed surface… Get a good removal tool like an artist knife set (specifically, No 2 in that set). The wide thin blade will get under the print and allow you to separate the print from the bed by simply sliding the tool around the project perimeter. With the PEI, you want to make sure the bed is cooled to 50C and don’t lift up. Both tips helps increase the life of the PEI, and keeps it stuck to the glass bed.

Thanks for those tips, I’ll get one of those palette knives. Had to look up the difference between a brim and a raft, but now (slightly) wiser

On the cooling to 50 deg C, I assume you mean to 50 deg C and below, rather than actually at 50 deg C?

Cheers

No, he means 50C. You should remove while the bed is still warm, as close to the removal temperature as possible (varies a bit by material, but usually around 50C). It certainly won’t hurt if it is a little cooler (say between 40C and 50C), but you do NOT want it to cool down fully.

Allowing the bed to fully cool can cause some materials to bond to PEI too firmly, resulting in damage when trying to remove. In addition, materials that shrink a lot during cooling can “stretch” the PEI if they cool down fully while still adhered, and this will eventually lead to bubbles under the PEI because the adhesive fails.

The default scripts bring the bed to removal temp, move the bed forward, then turn the heater OFF. If you aren’t there to remove the print right away, that can lead to problems as described above. For that reason, many people modify the end scripts to hold the “removal temp” for a longer period. Personally, I updated all of mine to hold the temp for 2 hours – so that if I am busy, on the phone, etc., I have plenty of time to get the print removed before the bed heater turns OFF.

It really depends. For some things you add a raft if you are having problems with warping. Though if the warping gets really bad you may just have a failing heater pad. For some things adding a chamber might be worth while. Though having a flat thin tool to get under the corners is more important. Not sure what the default tools lulzbot ships with but last i saw they look wholly inadequate. For some items like ABS i’ve had them pop off by themselves as the temperature cools down.

One tip for exporting solidworks files to STL is if you are working with assemblies you need to change the export option to something like “export all as one file” or something along those lines. Otherwise your part will either export as separate files or you will get weird files that only print certain layers and have odd gaps and spaces in others.

You’re being too kind. :laughing: That “clam knife” that came with my mini is probably good for opening clams, but I found it beyond “wholly inadequate” for removing prints. Somewhere between useless and downright dangerous. :unamused:

I use one of these: https://www.amazon.com/gp/product/B0027ITF5O

Right, 50 degrees it is then!

A couple of knock on questions, concerning the use of the ABS filament (the one purchased from the Lulzbot site)

I have read conflicting info as to whether to use the Elmers disappearing glue stick first, is that something that would be beneficial? I also had someone tell me that ABS juice is good to get a good bond, but I’m not convinced that it wouldn’t affect the PEI layer

Cheers

Les

ABS is best printed on the bare PEI at 100-110c. Glue stick will not help, and acetone (part of abs juice) is NOT recommended or needed on PEI.

Clean the PEI with 99% isopropyl. If you do have any adhesion issues, wet sand it lightly with 2000 or 1500 grit, then clean with 99% isopropyl.

Glue stick is useful for some materials, like nylons or flexibles, to either help adherence or prevent a permanent bond (depending on the material). But bare, clean PEI is great for ABS.

Happy printing!

I’m sitting here mesmerised watching my Lulzbot Mini, that I unpacked just over an hour ago, print an actual ABS part I designed

No fuss, no problems, no head scratching, just the gradual emergence of my first ever home designed 3d part. I never believed it would, or even could be this easy!

I’m hooked

Les