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Tutorial News

My astronomy project:
EQ6 Mount, dismantling / rebuilding


Contents:

  1. Introduction and Disassembling
  2. Internal gearbox alternatives
  3. Needed belt length, measurements
  4. New timing belt and pulleys has arrived
  5. Lids to worm gear adjusted
  6. Lathe of 60 teeth pulley
  7. Installing 60 teeth pulleys
  8. RA and DEC shaft shims
  9. Test installing timing belts and motors
  10. Installing RA timing belt and motor
  11. Installing DEC timing belt and RA shaft into chassis
  12. Testing and adjusting
  13. Power up and EQMOD gear ratio setup
  14. Hang up the telescope, balancing and calibrating parking point
  15. Fine adjusting RA and DEC worm gear play
  16. Drift align and auto guide calibration
  17. Setup EQMOD and PHD2
  18. During work

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!


8, Shaft shims:

To find out what thickness of the shims I need for the RA and DEC shaft I follow this to some part:

You should follow it too, not only my page with ideas.

RA shaft shims:

The function of the shim is to align the center of the worm gear to the center of the worm drive. To find out what thickness of the shaft's shim I need I have to do some measurements.

EQ6 Mount, RA and DEC shaft shims

I start with the RA shaft.
I do it in three steps. First I need to know the distance from the roller bearing's inner distance to the mount's chassis.


EQ6 Mount, RA and DEC shaft shims

I measure in both ends of the shaft and take the average value. All these figures I get I put in in an Excel sheet, you will find it below.


EQ6 Mount, RA and DEC shaft shims

I also need the worm drive shaft's diameter, it shall be almost exact 8 mm. It's divided by two in the excel sheet. These three steps will give me the average distance from worm gear shaft's center to the chassis.


EQ6 Mount, RA and DEC shaft shims

RA shaft, it's here the shim shall be installed later. The shaft's diameter is 40 mm.


EQ6 Mount, RA and DEC shaft shims

I test assembling the RA lid which holds the worm drive and cover the worm gear.


EQ6 Mount, RA and DEC shaft shims

Put on the worm gear without a shim, it's not so easy to do this, the RA shaft is grinded to a very high precision. Be careful to not scratch the surface on the shaft and slide the gear / roller bearing on gently.


EQ6 Mount, RA and DEC shaft shims

Now I measure the distance from top of the worm gear and down to the chassis. Hold the the tool straight, otherwise you introduce an error.


EQ6 Mount, RA and DEC shaft shims

You also need the thickness of the worm gear. If possible, try to get 0.05 mm in precision, maybe better with a digital tool.


EQ6 Mount, RA and DEC shaft shims

Assemble the stop for the adjusting of the worm drive's play against the worm gear.


EQ6 Mount, RA and DEC shaft shims

After I have done the calculation below I found that I need a 0.67 mm shim, I used one 0.5 mm and one 0.2 mm shim. Note that I use steel shims, I bought the dimension 40 x 50 mm, 0.1 mm, 0.2 mm and 0.5 mm thickness. I ordered them from England through Ebay, search for ScrewsCity (but wait until I have tested if it was a good idea to use steel shims). The original plastic shims didn't convince me, they are a bit elastic. If I need that I can put a plastic shim at the other end of the shaft where it doesn't introduce any error if it change its thickness.

I don't put on any grease yet, just testing that everything fit.


EQ6 Mount, RA and DEC shaft shims

I saw I got some dirt on the worm gear teeth, clean them with tooth brush.


EQ6 Mount, RA and DEC shaft shims

Checking that I got the correct distance after the shims was installed, perfect, the worm gear and the worm drive is on the same height. If you look at the worm gear you can see dark spots on the teeth. They are not in center because it has been installed with wrong distance, or it could be that the old plastic shims has been compressed and then thinner.


DEC shaft shims:

EQ6 Mount, RA and DEC shaft shims

Now I redo the same procedure for the DEC shaft. I noted that I must have at least one 0.5 mm shim already from the beginning, otherwise the worm gear will not reach and touch the roller bearing inner ring's surface.

I don't need to install the DEC shaft to do this measurement.


EQ6 Mount, RA and DEC shaft shims

Measure the distance, don't forget to subtract the 0.5 mm shim that was added temporary above.


EQ6 Mount, RA and DEC shaft shims

This is the excel sheet I had created as a help with the calculations. If you find it useful you can download it here:

Note, you download and use this file on your own risk, I don't take any responsible !


RA assembling and checking timing belt:

EQ6 Mount, RA and DEC shaft shims

Next thing to do is to check if I have the correct length of the timing belts. I start with RA timing belt. Tight the lid with the screws but only loose.


EQ6 Mount, RA and DEC shaft shims

The Allen screws that adjust the play between the worm gear and the worm drive.


EQ6 Mount, RA and DEC shaft shims

The are two of them, one on each side. They move the lid sideway which the worm drive is mounted on. I adjust them to get minimal play and then tight the lid's top screws.


EQ6 Mount, RA and DEC shaft shims

The timing belt, this is the end that shall connect to the stepper motor. This will be difficult because when the motor is installed it block the view and then you don't know what you are doing.


EQ6 Mount, RA and DEC shaft shims

View from another angle.


EQ6 Mount, RA and DEC shaft shims

I now see that I have to move the timing pulley on the worm drive shaft. To get clear from the chassis I need to make a bigger opening.


EQ6 Mount, RA and DEC shaft shims

The tension of the timing belt is adjusted by moving the stepper motor with its bracket. It was very difficult to measure how long length that was needed. It should also had been 5 mm shorter compare to what I ordered, but it came in sizes with 10 mm steps. As seen from the photo above I need to increase the length of the hole about 5 mm.


DEC assembling and timing belt check:

EQ6 Mount, RA and DEC shaft shims

I now check if I have a similar problem with the DEC timing belt.


EQ6 Mount, RA and DEC shaft shims

Not that big problem but still have to grind up the hole, about 3 mm.


EQ6 Mount, RA and DEC shaft shims

Checking with both motors in place if it's space enough around them. Maybe I have to cut one or two mm on the bracket that holds the DEC motor.


Machining work to do:

EQ6 Mount, RA and DEC shaft shims

The DEC timing belt opening that has to be widen to get more space for the timing belt. Note how I have polished the surface from paint and big scratches. It didn't look very nice from the beginning.


EQ6 Mount, RA and DEC shaft shims

The RA timing belt opening. This surface is very rough, I didn't have a lathe big enough to do machining on the surface.


EQ6 Mount, RA and DEC shaft shims

The mounting brackets for the motors that I also need to machining the holes and the edge, just a few mm. Note: I don't destroy anything, it can still be rebuilt with the original spur gears.

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To page IX, Installing timing belts and motors

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