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How to dissemble Dec Head .

Steps to Remove the Dec gear and bearing assembly from the Dec housing.  Click on any of the pictures to see a larger view. This mod also requires that you extend the DEC from the RA assembly by about 1.5 to 2 inches.  See step 14 about this adapter. Please read all instruction through at least twice before considering this modification of the Dec Assembly.  It is pretty easy, but please heed the warning about the shims under the worm gear.  ALSO IT IS ABSOLUTELY IMPERATIVE THAT YOU REALIGN THE RA WORM GEAR MESH AFTER DOING THIS MODIFICATION. YOU MUST DO THIS IN ALL 4 QUADRANTS.  THIS IS BECAUSE THE 2 INCH EXTENSION WILL CHANGE THE WORM GEAR MESH, DUE TO FLEX.  IF YOU DO THE ALIGNMENT OF THE RA AND DEC WORM GEAR MESH CORRECTLY, THERE SHOULD BE NO DAMAGE TO THE BEARING, OR GEARS BY THIS MODIFICATION. 
YOU DO THIS MODIFACTION OF THE DEC ASSEMBLY AT YOUR OWN RISK.  THERE IS NO MANUFACTURE TO GET YOU OUT OF TROUBLE ANYMORE. 

  1. Remove Dec assembly from the RA assembly.

  2. Remove the black cover plate on the top of the Dec assembly Figure 1.


    Figure 1 Click on picture for larger view

  3. Remove the motor. The Motor is screws should required a 7/64 hex wrench, I had to use a ball headed 7/64" Hex on the screw closest to the wall.


    Figure 2

  4. Back the 2 screws in indicated by the blue arrows away from the worm assembly to give room to remove the worm assembly.


    Figure 3

  5. You are going to have to have the Dec assembly supported so that the Gear and Worm assembly is in a horizontal plane.  I did this with a 5 gallon plastic bucket and a couple of short 2/4's from Home Depot (See Fig 4).  Make sure you do not have the 2/4 under the gearbox.


    Figure 4

  6. Remove the Worm assembly, by removing the screws pointed to by the RED arrows noting the left and right shims. Mark shims as to left and right. My Dec assembly had 2 shims on each side. They were all different thicknesses. It is important that you replace them the same way they are assembled from Mountain Instruments.


    Figure 5. Notice that the shims could be one or two, or more on each side.

  7. Remove the black cup from the bottom of the Dec assembly by removing the 4 screws.

     
    Figure 6 - Black cup removed with it's screws.

    Figure 7 - The end of the assembly with cup removed.

  8. Remove the 1/4-20 cap screw and washers at the bottom where the black cup was. You will have to hold the Dec Gear, as it will rotate with this screw and washer.  Note that the washer has a curved top, this has to go back towards the bearing when reassembling.


    Figure 8

  9. Replace the 1/4-20 cap screw with a longer 1/4-20 cap screw with out the washers. Screw the screw in about a 1/2 inch.


    Figure 9

  10. The 1/4-20 long screw sticking out will be used to remove the Dec gear and clutch assembly. The shaft and Dec gear will come out of the top and  bottom bearing. Do this by holding the whole assembly above a carpeted floor. Gently bump the 1/4 -20 cap screw against a carpeted or padded floor, to pop the whole assembly up and out of the casting. Note: The top gear assembly is greasy. I put down plastic on my table top to do this work on. Use Jet-Lube MP-50 Grease to replace the Grease. This is available at Grainger.  Make sure you protect the bottom of the shaft, and the race where the assembly goes back into the bearing.

  11. Here is what the removed gear assembly looks like.


    Figure 10

    Figure 11

  12. This is a picture of the casting with the gear assembly removed.


    Figure 12

  13. The four screws in the casting can be removed (see blue arrows in figure 12 above), and the top part will come off the bottom part of the casting. I removed the top part and rotated it 180 degrees. (I first tried 90 degrees, but I could not get the mount to balance on both sides with it at 90 degrees.) After removing the 4 screws, the parts might be hard to get apart, or might be easy as mine was.  It they are hard, do not bang on the bearing assembly, to get them apart. Screw out the four screws part way only, and use a block of wood that will cover all four screws, and tap lightly until the 2 sections come apart.  When reassembling, go around in a circle threading the screws in a couple of turns, to pull the 2 sections back together evenly.

  14. Reassemble with the reverse order. You use the original 1/4-20 cap screw and washers to pull the gear and bearing assemble back into the casting.  Note: these washers have a beveled side. This side goes against the bearing when reassembling the assembly. See Figure 7 above. and Figure 11 below. Do not pull this in so tight as to make the DEC harder to rotate.  You do not want to preload the bearing.  Just snug with a tiny bit of locktite will do the job. You need to follow the instruction in the manual for replacing and adjusting the worm gear.  One tip: You need to adjust the worm gear at all 4 quadrants of the Dec main gear. You can use a 3/8" drill and put that into the gearbox side of the Oldham coupler and use a variable speed drill and rotate this slowly to get to each quadrant.


    Figure 13

      IT IS ABSOLUTELY IMPERATIVE THAT YOU REALIGN THE RA WORM GEAR MESH AFTER DOING THIS MODIFICATION. YOU MUST DO THIS IN ALL 4 QUADRANTS.  THIS IS BECAUSE THE 2 INCH EXTENSION WILL CHANGE THE WORM GEAR MESH, DUE TO FLEXTURE. IF YOU DO THE ALIGNMENT OF THE RA AND DEC WORM GEAR MESH CORRECTLY, THERE SHOULD BE NO DAMAGE TO THE BEARING, OR GEARS BY THIS MODIFICATION. 

  15. Here are several pictures of my Dec assembly remounted with my telescopes, showing the amount of rotation I picked up.  I have about 140 degrees to the west (right) side, and 150 degrees to the East (left) side for total of 290 degrees rotation. Not bad for 3 hours work.  Note: I had already extended the Dec axis out 2 Inches, with a RA Extension adapter.


    Figure 14

    Figure 15

    The Dec Head is shown only rotated 90 degrees in the above 2 pictures, New pictures will be posted soon of the Dec head rotated 180 degrees.

  16. If you decide to do this mode, Remember that the shims and their placement are very important, probably the most important part of doing this mod.

    After using the mount about a year, I put the DEC Head back to it's original position as it really did not add to giving me more rotation before the limits.

    I am leaving this up, so that one will know how to dissemble the DEC assembly.


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