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Maksdampf

Replace weak 2mm V2A Hex screw Heads with nickel plated 10.9 steel screws

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As many people have experienced UM2 uses very weak V2A screws. There are a number of design choices on the screws that make them especially unsuitable for high torque applications.  But high torque is required for example when the belt is tensioned by pressing down the Stepper motor and screwing it on very tight. On my UM2 it looks like some hexagon screw heads were already blown out from the factory assembly.

This is a cumulation of several unlucky design choices:

- M3: A M4 screw would have a bigger head which can handle higher torque. But as we know nema17 have M3 threads :(

- The hex head: An ASSY or TORX head would have been more durable

- Half round head DIN 7380: A half round head has only a 2mm hex, a M3 screw with DIN912 would have had 2.5mm which allows nearly 50% more torque.

- V2A: Stainless steel has a high ductility but very low hardness compared to steel. V2A screws are more expensive, but that does not make them the better screws. A galvanised 8.8 or 10.9 steel screw head is several times harder than a stainless steel screw.  Stainless steel is a good choice for constant weathering or seawater but completely unnecessary for indoor appliances. Against humidity zinc plating is more than enough and if the looks of zinc is not appreciated, nickel plating or black nickel plating is a very good alternative to stainless steel. Plated steel screws are magnetic too, which makes automated Assembly so much easier than with V2A screws.

In my last product design jobs we used black nickel plated 8.8 and 10.9 hardened steel screws with 2.5mm hex socket and even some screws with a custom designed head and with pre-applied screw adhesive.  I sourced them directly at a large chinese screw manufacturer and to our amazement letting manufature only 20K of one type was already cheaper than buying plain steel screws from a major german screw distributor - and of much higher quality and consistency. Apparently the manufacturer used a fresh Die just for our screw heads, which produced better tolerances and surface quality than what we could get at any german screw wholeseller.

I think better screws would be a good upgrade to the UM2 manufacturing line. Send me a pm and i can give you some sourcing suggestions for stronger screws.

Edited by Guest

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