It’s never a good thing when customers are disappointed. So, imagine the disappointment when your brand new Jerrill.com nozzle arrives in the mail and this happens when you tighten it onto your Printrbot Ubis hot end.
At least one customers even had this happen after a few days of happy printing.
First and foremost, it is critical to get a new nozzle in the hands of the customers whose nozzle broke. After all, a nozzle just shouldn’t break like this. It’s a design flaw plain and simple. And as long as I’m selling these things, I’ll make it right. Don’t worry!
The next item on the agenda was to determine what went wrong. Time to cut open a few nozzles.
I compared a Printrbot 0.50 mm nozzle, a Makerbot 0.40 mm nozzle, and a Jerrill.com nozzle that failed QC.
It’s admittedly difficult to taper the dome of an acorn nut into a cone with a tiny flat, when you have no idea how much material is safe to remove and still have a structurally sound nozzle, and you couldn’t control it that well even if you did. Additionally, the spec for the acorn nut specifies a minimum tapped hole depth… not a maximum. Eventually, I hope that nozzle sales are so good that I can get some professionally machined nozzles, but it’s a little too early for that kind of tooling investment. So, this is what I have to work with.
My initial passes at a QC process have been to tighten a 1/4″-20 bolt into the nozzle using the #4 torque setting on my hand drill (whatever that means) which leaves the nozzle tightened on the bolt more than hand tight. Some nozzles bulge a little. A handful of others have broken like in the photo above. Both of these are tossed in the failed nozzle bin. If it passes those tests, it still has to survive repeated poking at the tip with a pin to make sure that there is enough material left on the flat for successful drilling and extrusion.
Even with the solid brass acorn nuts we’re using, there is not a lot of material left at the tip for strength. Printrbot seems to have the sturdiest design in their nozzle. Makerbot benefits from a male threaded nozzle where a threaded hot end can’t apply stress to the thinned brass in the tip of the nozzle.
This comparison, however, points to the bigger problem of ever smaller nozzle bores. It’s not slicer settings and filament types. It’s a limit on how deep the ever smaller drill bits can drill. For example, the 0.10 mm drill bits that I’m using (and admittedly breaking… a lot..) only have a drill depth of 0.50 mm! Unfortunately that doesn’t leave a lot of nozzle for strength, whether it be strength against a bolt in QC, a hot end, or just the pressure of extrusion at these diameters.
I’m interested in seeing some photos of other sacrificed and cutaway spare nozzles from other printers for design comparisons. At $10 to $20 each, it’s an investment that I’ll have to make over time. But it’ll be interesting to gather some industry best practices to inform future nozzle designs. In the meantime, happy printing!