I recently started printing a robot project with my Form 2 printer using grey resin but owing to the final usage of the parts I decided to use tough resin, the objects in question form the tracks are are composed of two elements linked with 4mm dowel pins. The grey resin track links linked together with an interference fit between the dowel pins and links as designed, but when printed using tough this tight fit changed to a running fit. I was wondering if any other users had experienced this variation in dimensional tolerance between grey and tough resin and whether anybody has any suggestions as to a scaling factor I need to use.
As a general observation I believe the grey resin prints with extremely high accuracy and a series of lathe gears I printed fitted straight onto the lathe and were cutting stainless steel at the maximum feed rate with no fettling.
I don’t think we have exact data on this, but the general purpose resins are probably a bit more accurate because they are more rigid in the green state. This means there is less deformation during the printing process. Increasing support density is one way to address this. Orientation can also have an affect. We are also always working to optimize the printing process and support structure generation to improve this and are specifically working on accuracy now.
I’d love to see a video of the printed gears running in the lathe. Sounds like a fun project.
Thanks for your response to my question, I have been reducing critical fits by 0…1mm at a time, 0.1mm considerably improves the fit tightness. Would you suggest printing dimensionally accurate portions as vertically as possible to avoid sag?
I have We Transferred the videos of the lathe gears to Elaine Rutledge (Formlabs UK) and she will forward them to you. This is something we did a month ago and I had forgotten about it as I am currently designing a series of tracked robots and that had taken all my focus. We can design and print gears in Modulus or Diametral Pitch systems up to a maximum of about 140mm diameter
Theoretically the smallest dimensional change it should be possible to print is 50micron or 2 thousandth of an inch or 0.050mm. As your mod is 0.2mm 200microns this should be possible with tough resin which has a minimum layer thickness 50 micron. If you are printing with grey resin the minimum layer thickness is 25microns or 0.025mm.
This assumes there is a direct relationship between minimum layer thickness and smallest printable feature.
I have been prototyping with the clear resin and having good luck with it. I got a sample of the tough and found it more elastic but lacked the memory and would be too slow to return to original shape after being bent. I suppose it has it’s purpose on parts that are sensitive to cracking but so far the clear parts have been in the field for a couple of months now and holding up well.
The tough resin sample I got started to crumble within 2 weeks but probably because they used IPA to clean it.
For tolerances the parts I printed have been within .001" and the threads I put on some of them work smoothly.
Honestly I think the clear is a better choice unless your part really needs to bend and don’t expect it to just spring back.
Thanks for you email about your experiences with clear and tough resin. I started using tough because the grey was shattering when I tried to hammer dowel pins into it at temps below 8 degrees Celsius.
I was particularly interested i n your comments on the elasticity and memory characteristics of tough resin.
You also seem to be able to get accurate feature reproduction 0.001", 25 micron is great.
I will have to try clear resin but I seem to be experiencing problems with supply, I have been waiting now for over a month to have a defective cartridge replaced and almost 2 months to get a supply from a German supplier, I presume because of supply chain issues.
I’m having the same problems of definition and precision using the tough resin.
See en closed image of COMB printed in the same conditions (angle position & supports) with printing parameters according to the resin .025 vs .05.
Hoping thet FORLAB will progress in the chemical composition of the tough resin…
