Quote Originally Posted by johnsattuk View Post
Picked up this harmonic drive some time ago for a 4th axis project, not yet got round tuit. 50 -1 with 25mm through and pre-loaded cross roller bearing on the output ring

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Yeah,
Harmonics with through capacity exist but are not fitted to the Chinese eBay 4th axis models under discussion here, nice thing to have in the parts drawer, please post some photos when you've completed a project with that,
Regards,
Nick.