Another take on MattyVee's outstanding belt tensioner. In my case no mater what I did my belt was rubbing on the right side of my pulley when facing the printer. My belt alignment is spot on on the 16t drive side so I was half way there... I decided to try to shift my pulley 1/2mm to the right and that didn't help, then at 3/4mm the belt slightly rubs on the left side of the pulley. I consider this to be a non fix but figured I'd share my take on the design here. I don't have MattyVee's design information so I based all of my dimensions on Prusa's R2 of idler pulley mount, see attached Pdf for dimensions. I also beefed the mount up a bit as I only had Prusa's spare 40mm M3 socket heads to work with and I have a tendency to over engineer things so to use this you'll need the following,
(2) M3 x 40mm socket head screws with Nylock nuts to hold the swing arm
(1) M3 x 30mm socket head screw with Nylock nut for adjustment
(2) M3 x 12 socket head screws with either Nylock or standard nuts
Print as is with no supports as I adjusted countersink to be printed without support.
Someone in a forum requested step files so I'm attaching those as well...
Note: this is for a 20T idler only...