Z Idler Tooth Idler

[claytoncarney]

First build. A bit confused here...

On page 48 of the manual. I assumed that the M5x30 BHCS was screwed directly into the plastic for retention. However, I found no bite on the printed part. I checked the STL and it indicates a screw hole 5.0mm diameter. I measure M5 at around 4.75mm diameter. I'm guessing then that this is not a dimensional accuracy issue.

The manual does not explicitly states screwing directly into plastic, as it does on other parts. On parts that are so indicated, the STL clearly shows bumps or printed in place threads.

I asked on Discord, but got no definite answer. My only guess is that the design is using belt tension to retain the tooth idler screw. Is that in fact the case???

 

[Sanity Agathion]

Hello, that should thread in normally, maybe not very tight but not fall out, tension keeps them in place. Did you print them yourself, from ABS or ASA? Maybe re-print them with a percent or two more flow.

 

[claytoncarney]

Printed in Polymaker ASA on a Prusa Mini with an ad hoc chamber (45-50°C). The hole is not large enough for a 5mm drill bit to pass, but the screw slides with little to no resistance.

 

[Sanity Agathion]

On page 48 of the manual. I assumed that the M5x30 BHCS was screwed directly into the plastic for retention. However, I found no bite on the printed part. I checked the STL and it indicates a screw hole 5.0mm diameter. I measure M5 at around 4.75mm diameter. I'm guessing then that this is not a dimensional accuracy issue.

Hello, just in case I checked the screw sizes, and according to DIN 912 and ISO 7380-1 norm for metric screws, the diameter should be between 4.82 and 5.0 mm. If your screws are 4.75, they are out of spec and you should probably replace those.

 

[claytoncarney]

I checked the specs also and yes these Formbot fasteners are out of spec. However, other stock I have (4.87 diameter) has only a very slight bite. Perhaps that's by design, I'm not sure. I can say that other components designated as threaded in plastic have definitive characteristics. The A and B Drives have printed in place threads. Components on the Stealthburner have nubs protruding inside the hole. They also explicitly state in the manual directly threaded in plastic (don't over tighten). Given that the idler STL specifies a 5.0mm diameter, it does not appear that even an in-spec screw would ever have much bite. Not really clear what the intention was here...