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UM2 PTFE fit in stainless steel part

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Hi guys,

currently I'm in a project to update my beloved UMO with a (chinese) UM2 head. Decided to go this cheaper way as it is just a proof of concept for a dual nozzle setup with some specialities... :-) Dont want to machine and play around on original parts in several iterations and destroy money...


So here's the question:
How tight should the PTFE part fit in the stainless steel part?

A bit loose so it turns freely or tight so it cant....?

Any hints appreciated...


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A point in between. If goes tootight it will deform when tightening the steel to the heater block (avoid using the spring and print an fixed height spacer). If it leaks remember that cleaning the steel coupler threads is very important or the burn material won’t allow the ptfe to contact the hotend making a gap that will add tons of blops, burn particles or even a big leak

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Thanks for the info and the hint. I will take care and give them a try.

Before re-machining (cheap chinese had inner diameter of 2.8mm) they were very tight so that they were moving with the steel part when screwing it in or out. Now, due to the ER Collets, they were squeezed a bit (had to re-drill the inner diameter) and they sit more on the loose side. Unfortunately I need the springs to realize my dual setup idea.

I will give them a try and when POC done, order original ones from UM...

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