[jipilabont]

I need help designing a strap driven nut that would stay fix but the leadscrew would translate trough the pulley driven by the strap.

[Jim Dawson]

Here is how I did one

Built a housing



and put roller bearings in it to fit the nut body



Machined the pulley and put 4 drive pin holes in it that fit the nut bolt pattern



And the way it fits together



and the ''exploded'' assembly, note the thrust bearings on each side of the nut/pulley assembly.



The preload on the thrust bearings is adjusted by these 4 set screws in the motor mount plate



And the assembled view. The little roller ''car'' keeps the lead screw from rotating in use.




I hope this gives you some ideas.

[vegipete]

Nicely done, Jim. I take it that the O.D. of the nut runs happily on the roller bearings. Did the nut body need any work to match the roller bearings?

[Jim Dawson]

Nicely done, Jim. I take it that the O.D. of the nut runs happily on the roller bearings. Did the nut body need any work to match the roller bearings?

Thank you !

Yes, the roller bearings are happy. I was lucky in that the OD of the nut was exactly the correct diameter to fit a standard roller bearing. I don't remember the exact dimension but it was around 60mm or so.

[jipilabont]

I already thanked you buti will do it again : you are an expert. I use your photos to figure out what to do and order bearings roller, stop and leadscrew.

[jipilabont]

Thank you !

Yes, the roller bearings are happy. I was lucky in that the OD of the nut was exactly the correct diameter to fit a standard roller bearing. I don't remember the exact dimension but it was around 60mm or so.

i usually speak french not sure to understand "run happy". Does this mean not a press fit nor a slack fitting but just inserted in freely and turn supported all the way?

[Jim Dawson]

i usually speak french not sure to understand "run happy". Does this mean not a press fit nor a slack fitting but just inserted in freely and turn supported all the way?

Yes, It is U.S. slang meaning a good fit and and working well.

[jipilabont]

So a 28mm nut would run happy in a bearing of 30mm. Or may be with shims?

[Jim Dawson]

So a 28mm nut would run happy in a bearing of 30mm. Or may be with shims?

No, you would want a 28mm bearing. The nut needs to fit the bearing with <0.025mm clearance. Should be a tight slip fit.

Metric Needle Bearing