Category: Tolerancing

Some 3d printers end up with rough top layers. One thing that you can check if this happens to you is the rate of filament flow. Filament flow is affected by a couple of things, the most common issues are:

  • Flow rate setting in slicer. I normally set my flow rate to 105% – 110% for the first few layers, then turn it down to 100%. If this is set too high then your printer is adding more filament than you might need, resulting in a rough surface.
  • Extruder calibration. Run a simple extruder calibration to double check that you are extruding the amount that you think you are. If you are overextruding, you might be causing problems for yourself.

Just like checking your oil and your tire pressure on your car every once in a while, you should run a quick check on the overall health of your printer from time to time, as well.

My preferred way to do this is to print a Benchy model. There are other torture tests, but once you know what you are looking for with this model, it can tell you a whole lot. It is not a diagnostic tool, in the sense that it will tell you what adjustments to make, but it does tell you if there is a problem so that you can do some additional investigation, if needed. Benchy features include, bridging, holes of all types and angles, retraction, fine details, etc.

I talk a lot about getting the most out of your 3d printer. But, how do you know if your 3d printer is capable of doing the job? Sure, if you are making a Christmas tree ornament, who cares if it’s an extra 0.5mm too thick? What if you are making a functional assembly? Or, what if you are building a prototype for a component that needs to fit inside of a housing? Is your machine capable?

One way to know for sure is to do a quick tolerance analysis. Rather than looking at the machine capabilities only, you can now design with certain tolerances in mind. Based on what you know about your machine variability, you can design components so that, even with the variability from your process, you can still make parts that will fit. Or, you can know if your machine is incapable of making the parts you need, in which case you need to come up with an alternative manufacturing process.

Supports can be tricky, at times. Make them too close and they fuse together with your print and are difficult to remove and leave a nasty surface finish. Make them too far from your print, and your print has nothing to build on. So, how close is close enough but not too close?

Run a tolerance test for your printer. You can find several parts to print that will help with this. Most are some type of widget that prints several different pieces with various gaps in between the parts. If your gap at .25mm is fused together on the tolerance test part, then your machine tolerance is about .25mm and you can’t expect it give you better accuracy than that. Going back to our supports, you can’t place supports closer than .25mm or they will fuse to the part.

To improve this, calibrate your machine.

When designing parts for 3d printing, make sure they will fit together. Sounds like common sense, but I hear of a lot of people trying to fit a 1/2″ pin inside a 1/2″ hole. Unless your intent is to get an interference fit, it won’t work.

From a design perspective, you need a small clearance fit for components to fit together. You can either make the hole larger or the pin smaller.

From a manufacturing perspective, your perfectly round pin that is exactly 1/2″ on your computer isn’t exactly round or exactly 1/2″. Depending on a lot of variables, it’s going to be slightly oversize or slightly undersize. How much will really depend on the process that you choose, the materials that you use, the environment that it’s in, the condition of the machine, etc. In addition to extra functionality like extra print heads, closer tolerance control is probably the biggest reason why a $10,000 3d printer costs so much compared to the little hobby printer that I have at home.

There are a couple of things that you can do to improve your tolerance. Maintain your equipment, get better equipment, level your bed, maintain your environment, buy good quality filament, etc. You should also run a tolerance test. You print a couple of parts that have gaps in the cad of varying sizes. If your 0.020″ gap is fused together, then that is your limit. It’s good to know your limit.