BearingGate: An engineering failure analysis
Some of our bearings in the Titan Extruder and Titan Aero have been failing due to a series of unfortunate events and we're really sorry about that. We have a solution to fix the problem on the way, and we'll be in a position to issue replacement parts in the next few weeks. Titan products shipping from now on will not be affected because we have a short term fix in place. If you have experienced a problem then please email us and we will get replacements parts out to you. Read on to find out the finer details on what happened.
Titan Extruders (including Titan Aero) had been out in the wild for some time before we started noticing a very odd complaint coming in from some customers. The plastic lids, which we had manufactured from tough, near-bulletproof polycarbonate plastic, were starting to crack. This seemed impossible, so as well as replacing the cracked lids we also asked customers to send them to us, for some serious investigation.
Our first suspicion was that our supplier had substituted the resin for something cheaper or not purged out the extruder properly - perhaps resulting in hydrolysis from moisture or some other material defect. We went through every batch from every moulding run, literally taking a hammer to them. No dice. Polycarbonate is as crack-resistant a material as ever (phew!).
When the culprit was found, it wasn’t what anyone expected. It turned out that the lubricant used on some of our bearings had a chemical composition perfect for chemically-degrading polycarbonate. To observe how thoroughly chemical breakdown occurred, we even left lids to soak in hot baths of lubricant, where they more or less disintegrated.
This was, to put it mildly, a problem. It only took a little bit of lubricant leaching from the bearing onto the lid for it to have a powerful crack inducing effect.
Luckily, as Sanjay explained on Reddit, only some of the bearings had been treated with this particular lubricant. We immediately changed the bearing lubricant used in Titan products, the lids stopped cracking, and everything looked to be in order.
However, it wasn’t long after that we received news that these bearings, with the new lubricant, were sometimes failing, effectively causing Titan products to cease functioning until the bearings were replaced. While we had been assured by suppliers that the new lubricant would have the same performance as the previous one (without all the lid-disintegration), this turned out not to be the case as bearings were seizing up and even rusting - a clear sign of inadequate lubrication.
The short-term solution
Finally, after several rounds of product testing, we believe we’ve reached a solution for the short-term future. We worked with IGUS to replace the problematic bearings with IGUS solid polymer bushings. The polymer they are made from has been formulated to have really low friction, eliminating the need for lubricant, so there will be no mess and no danger of cracking. In addition to not requiring lubricant and having low friction, IGUS polymers also have incredibly good wear properities, so we are confident that they will last for ages, requiring no maintenance. Lastly they’re much less prone to permanent damage from axial overtightening loads.
There are two downsides to this solution. The first is that these bearings need to be machined from bar stock as they were not a standard part, and the material is surprisingly difficult to machine, limiting production capacity and adding delays to stock. Additionally there is a slight increase in friction compared to a true bearing. For this reason we do not recommend the 'Slimline' motor with Titan products that use IGUS bushings, but instead a 'Compact but Powerful' motor. This will mean a slight increase in weight on the print-head, which is compensated for with the larger, higher torque motor being more reliable and easy to use on many printers.
Nonetheless, these two downsides mean that bushings aren't a perfect long-term solution for our needs.
The long term solution
The original bearings used on Titan products performed perfectly well - we have machines in our print farm that have been running almost non-stop for over a year, all using the original bearings with original lubricant. They also have less static friction than the IGUS bushings and so can run more smoothly and be used with 'Slimline' motors to save weight on the print head.
In order to switch back to bearings with the original, effective, lubricant we are changing the resin which the Titan lid is made from. We've decided to move away from polycarbonate to Tritan by Eastman. Tritan has exceptionally good chemical resistance to lubricants and has very comparable mechanical and thermal performance to polycarbonate. Making the switch will eliminate the risk of degradation and give us the freedom to use the optimum lubricant in our bearings to restore the original performance of Titan products.
Unfortunately we can't put this solution to work right away. We want to make sure that nothing like this happens again, so we're running several rounds of high-stress, long-term tests before going ahead with these changes in production.
How we’re going to make this right with our customers
Firstly, we would like to sincerely apologise to all those who have been inconvenienced by this series of unfortunate events, and thank you all for your patience and support. The unforeseen issue with the degradation of the polycarbonate, followed by the subsequently induced issue with poor lubrication of the bearings caught us off guard in both cases. The decision to change lubricant, which appeared to be a good, well thought out solution to the cracking problem backfired. Despite the assurances of our suppliers that the new lubricant would perform just as well as the old, the bearings began to fail.
We’re working as quickly as possible to get the long term solution of Tritan-Titan lids and optimally lubricated bearings in stock and ready to ship, but this will take some time to get both the bearings and lids in stock in enough quantity to replace faulty parts. In the short term we will be shipping out Titans with the new IGUS bearings and larger motors to customers buying from today onwards. Unfortunately we do not have the production capacity to send these new parts out to every customer who has previously experienced this issue.
However as soon as we have the new Tritan lids and optimally lubricated bearings we will begin to issue replacements to all those who are experiencing issues. This will be the easiest drop-in fix for our customers, requiring no change in motors. We stand by our product and support our customers - we are committed to making this right with our customers and are happy to issue replacements to all those who have been affected.
Will you be issuing a recall?
No. This failure is not dangerous, nor is it a certainty for all Titan products. We have Titans and Aeros in-house that have been printing for thousands of hours with no problems. The fault is with a single, small part which we will be replacing free of charge for any customers who require it.
Will this affect the Lulzbot Aerostruder?
No. Lulzbot have used their own bearings in developing the Aerostruder, so it should have no problems.
When will Titans without this fault start shipping?
23/01/2018. If your Titan product ships on or after this date, it will not be affected by the bearing fault as it will either ship with bushings or with the improved lids and bearings. It will be clear in the Website product description whether the product you're ordering will ship with IGUS bushings or improved bearings.
Does this affect the Titan Aqua?
No. Titan Aqua has a completely different axial load profile from the Titan Extruder and Titan Aero, and should not suffer any bearings failures.
How long will it be until Titans with the new bearings start shipping?
We're still running stress tests, and as such our expected lead time until these better bearings go out is approximately 5-8 weeks. It will be made clear in the online product description whether the product that you buy will be shipping with IGUS bushings or improved bearings.
How do I know if my bearing is faulty?
If it jams for no discernible reason, if it's broken or cracked, or if there's an accumulation of rust around the bearing, then it's faulty. This issue only affects Titan products shipped between February 2017 and January 2018. If your product was ordered outside of that window then you will not be affected.