ETX-80 BEARING MOD FOR RA/AZ AXIS
Last updated: 16 February 2012
Sent: Monday, February 13, 2012 20:27:30 From: Mark Stewart (firstname.lastname@example.org) Pictures referenced are found here: http://s906.photobucket.com/albums/ac263/mstew57/ETX80%20Bearing%20Mod/ The instruction here are not the best. I did not think to take pictures until I was half done and I did not write this until months after I did it. If I can find a cheap (or free) base I will take a video of how to do it. Materials List should be less than $30 2 1 1/4" sch 40 pipe coupler 1 1 1/4" to 3/4" sch 40 pipe bushing 2 20mm ID x 42mm OD x 12mm Ball Bearing 1 20mm ID x 35mm OD x 2mm Needle Roller Thrust Bearing 2 20mm ID x 35mm OD x 1mm Thrust Washers 1 25mm ID x 42mm OD x 1mm Thrust Washer 1 1/4" x 2" galvanized pipe nipple 3 Allen Head grub Screws (can be any convient size and thread) 1 14mm ID x 20MM OD x 22mm Bronze sleeve Bearing 1 5/16 x 3" course thread bolt Electrical Tape Hot melt glue Tools Used Utility knife (box cutter) hacksaw (used a sawsall but hand saw will work) belt sander drill tap sized for grup screws drill bit sized for tap A cheap rotary stone may be nice for cleaning up in hard to reach places and flat sanding disc for drill may be needed. Disassembly: Remove by prying the cover on the bottom of the base. Remove lever used to tighten EA clutch Unscrew the bolt take it all the way out You may have to hold the bottom clutch nut from turning. Unscrew the castle style plastic nut Seperate the top from the bottom Remove the 3 screws holding the upper clutch and remove Mark the worm gear for up The upper section was tackled first. The tube from the base has to be cut off. I cut it off the thickness of the bearing (12mm), plus the thickness of the thrust bearing assembly (1mm+1mm+2mm=4mm, for a total of 16mm (see pic 1). It not really critical that it is exact as it can be adjusted later. I took the upper clutch part (mine was yellow and has the 3 screws that attaches it to the base) and sanded down the "fins" on it so the 1.25" coupler would fit over it. The assembly if formed by the coupler being cut off to fit 12mm above the cut off base tube previously cut when all the down on the upper clutch part (see pic 2). The 1 1/4" to 3/4" sch 40 pipe bushing fits over the upper clutch part and the top of it is sanded to fit even with the tube previously cut. It will mean cutting off some of the top of the upper clutch part to be even with the base tube. You can cut and sand until the parts fit as shown with 12mm left for the bearing to fit in after the pipe coupler sits down on the base of the upper clutch. (see pic 3 and pic4) I glued mine in place but you can put the small screws up through the bottom of the yellow upper clutch into the pipe coupler (see pic 5) but be sure they are slightly counter sunk because the gear slides along here when the clutch is loose. Test your assembly by sliding a 20mm ID x 35mm OD x 1mm Thrust Washers onto the upper part ot the base (metal stem) (see pic 6), then the thrust bearing (see pic 7), then a final washer. Take your clutch assembly with bearing in place and slide over the upper base stem against the thrust bearing washer. Put the ra gear against the clutch assembly and see how the gears mesh. You can sand the inside of where the roller bearing sitswith a disc sander than fits in a drill, or add 1mm washers for spacers. I had to add a washer for my worm gear to be centered in the worm (see pic8). Now drill holes for grub screws at 60 degree intervals around the clutch assembly as shown and tap. I made sure I drilled through both the pipe couple and pipe bushing to allow for extra threads but it really isn't that important (see pic 4). The grub screws attach the clutch assembly to the base tube, replacing the small screws originally used. Just don't over tighten as you could crush the tube and they don't have to be real tight anyway. Here is how the assembly looks without the worm gear in place (see pic21) Next is the lower bearing. The fins in the base where the plastic castle nut was were cut off and sanded smooth (see pic9 and pic10). A pipe coupler was sanded with a taper to fit in the area. It was cut to be about 16mm tall (see pic11 and pic13). The clutch fingers are dropped in (see pic12). Then the thrust bearing with washer on top (see pic14 and pic15). The roller bearing is placed on top of this (see pic 16). Now the shaft has to be extended. Tap the center of the upper part of the base stem to fit the 1/4" pipe nipple (see pic17). Put the white clutch disc that the clutch fingers press against on the base, place the worm gear with your up marks up, make sure your thrust bearing and washers are in place, along with the upper clutch/bearing assembly, and slide the lower base over the upper base stem. Mark the pipe nipple even with the bottom of the bearing. Slide the bottom off and cut the pipe nipple a little shorter than your mark (see pic18). Take the Bronze sleeve bushing and sand it to fit the clutch nut (see pic19 and pic20). it is going to take the place of the original plastic clutch nut and the roller bearing will ride on this. Now assemble the bottom base back onto the upper base. Slide the bronze bushing over the pipe nipple and inside the roller bearing. Mine was just a little tight against the pipe nipple so I sanded the pipe nipple a little but left not too much as it needs to be a little tight. If you sand it too much you will need to glue it to the pipe nipple shaft for the clutch to work properly. Take the bolt and drop it in the hole in the upper base and screw the round clutch with the holes in it onto the bolt. Tighten the bolt to slide the bronze bushing in. When the clutch starts to work (the bottom base starts to not turn freely) stop. Unscrew the bolt a couple of turns and mark the bottom of the bolt (see pic20). Cut the bolt off at your mark. Now reassemble but don't tighten the bolt enough to engage the clutch yet. Rotate the base and make sure it tracks level with the upper base. Mine did not so I straitened it out and then used hot melt glue to glue the lower bearing's pipe coupler to the bottom base. As I rotated the botom section the space between the bottom and top was not even but the closer spot was always in the same place. In other words the bottom base was not parellel to the upper part (it came this way from the factory), so i took the opportunity to fix this issue. It made the gotos better as a result. Reassemble and adjust the clutch bolt so the clutch lever will both engage the clutch when tight but be free when loose. The clutch always has a little drag but I leave mine engaged all the time and only use the motors for moving the unit. if you leave the gear off when assembling you can see how free the unit now opperates (see pic21). The base and forks are still flexible but the tracking is much improved. The scope will now operate in polar mode. The whole operation is easier than it sounds and took an afternoon once the parts were selected and sourced. How the clutch works now; the bolt is turned, the bronze bushing keeps the round holed nut from turning which leads to the bolt tightening. The tightening bolt pulls the round nut aganst the roller bearing. The roller bearing presses against the thrust bearing which the pushes up against the clutch fingers. The roller bearing must be left to slide up and down in the pipe coupler retainer and not glued in place although the upper bearing can be glued in place if desired. I used tape on mine to make it easier to assemble and disassemble. __________________ Mark
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