Idler, Motor Bracket Threaded rod help

Hi
I am building the Mendel90 and busy with adding the Threaded rod through the Idler Bracket and Motor bracket.
Instruction says add one Brass M8 Nut to the threaded rod and insert into the Bracket. Is it correct that only ONE nut per threaded rod ?
Will it not be too loose etc for the threaded rod. I see older versions had two nuts and a spring ?

Also why a Brass Nut and not a steel nut ?

Thanks for awesome forum.
Vaughan

Hi,

Yes, just one nut.

The idler and X motor brackets rest on the single nut (you need to remove the single layer membrane in the bracket if you are using self-printed parts).

The looseness of the fit is a mechanism to prevent Z-wobble. The rods are permitted to move a little in X and Y and the nut follows this motion but the bracket remains stable due to to slight oversizing of the nut cavity.

Brass on steel is a commonly used combination. I have seen it referred to as "self lubricating" which is probably incorrect as you still need to lubricate the rods. Apparently it smooths the motion somewhat.

Regards,
Neil Darlow

Edited 1 time(s). Last edit at 04/09/2015 03:49AM by neildarlow.

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

Hi Neil,

Thanks for the reply, I understand now. Was worried I was missing something. I could imagine that the brass is softer so it moves better over the steel thread.

Can not wait to get my Mendel90 up and running.

Thanks

Brass on steel has less friction that steel on steel and if there is any wear it will be the brass nut. If the steel thread wears it would affect accuracy because it might wear unevenly, whereas any wear on the nut has the same effect all the way up.

Springs aren't needed unless you want to print upside down as gravity holds the axis down normally.

The nut trap should be a tight fit, not loose. Any wobbly in the rod is allowed for by the flexible couplings.

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