DOB Mount

I decided to make a DOB mount for my telescope because it was easy to built with minimum requirement of any special tools. This mount was made popular by John Dobson and since known by his name.

Following are the build details of my DOB for 6″ telescope. This DOB is based on the plan given on Stellafane. You can make your own DOB design as you wish and I suggest to look for more designs from internet.

  1. Get 3/4 inch thickness plywood. Get marine ply if cost is not a concern.
  2. Cut two disks of 15 inch diameter for mount and rocker base.
  3. Cut two rectangle boards of 8×20 inch size for the rocker box sides
  4. Cut two rectangle of 12×8 inch and two rectangles of 12×9.5 inch for tube box. The 200 mm telescope tube will fit inside of it.
  5. For Latitude bearings, cut a 14 inch dia disk and then cut it in half to use each on both the sides of tube box.
  6. I fortunately got some already laminated plywood panels in scarp. You may also try to get it from scrap furniture vendor. It will help to save a good amount of cost.
  1. Drill 10mm hold at the center of both the bottom disks of 15 inch dia.
  2. Set three, 2″ plastic bush at 120 degree apart on one of the bottom disk. This will become base of our DOB mount.
  1. For latitude bearing, I had the ply 14″ dia round cut on band-saw from a workshop. It should be carefully cut all the way round. I could have cut it myself using my jig saw but band saw gave fine, straight and clean cut result.
  2. Also have the same curve of 14″ dia cut on the two side boards to set the bearings in it.
  • latitude bearing being cut round and cut in half on a band-saw
  • side boards cut should match the curve of latitude bearing
  1. If you were not able to get the ply cut round, you can use roti making patla/chakla which come in around 12-14 inch size (pic shown below is the patla available at D-Mart). Buy a good quality, solid wood, clean edge patla. You can buy 2 patla if you want full round latitude bearings at both sides. Just make sure both the patla’s are exactly matching with each other.
  1. Clamp both the side boards together and use a half round file to clean and match the curves on both the boards. It is required because there will be some unevenness even after cutting the curves on band-saw.
  1. On latitude bearing surface, glue straight piece of laminate (called sun-mica by some) using the Fevicol glue. Get the textured laminate since it will move smoothly on the Teflon surface which we will be discussing later.
  2. Secure it using masking tape. Let it dry for 24-48 hours
  3. Remove the masking tapes and use a hand-plane to clear the protruding edges of the laminate
  • after cleaning the edges using hand-plane
  1. Now start working on the tube holder box.
  2. Use the two cut rectangle of 12×8 inch and two rectangles of 12×9.5 inch (see #4 above)
  3. Clean and straighten the edges using a hand-plane.
  4. Arrange all 4 panels making them into a box
  5. Drill 4 mm size six holes on the sides of each 12×9.5 inch board. (Note: All 4 mm holes are pass through holes in this design. They will not have screws tighten in themselves)
  6. Drill 3 mm size of corresponding holes in to the 12×8 inch board to tighten the screws
  7. Use 1.5 inch long screws to tighten these boards together to make a box. We use screws so we can open the board to set and balance the optical tube.
Attaching Latitude bearings on the sides of Tube Box

This is a very critical step! Both the bearings should be fixed in the right place on the box and should be aligned with each other so when you move the scope, there is NO lateral motion.

  1. Lat bearings will be set on the sides of 12×8 inch panel
  2. Clamp both the lat bearings matching their curvatures (very Important!).
  3. Stick masking tape on 2 locations as a marker to align both the bearings for fixing it to side panel.
  4. Draw a circle on both the lat bearings and mark positions for 3 screws each.
  5. Drill three, 4 mm hole on the marked locations of lat bearing.
  6. Position the Lat bearings at 45 degree on both the side panels by matching the edges of their masking tape markers. Make sure to align everything correctly! you may need to remove and put the masking tape several times for correct marking and alignment.
  7. Once satisfied, drill 3 mm corresponding holes on the panel sides through the 4 mm lat bearings holes.
  8. Use screws to attach the bearings to the box as shown in the below images.
  9. Before screwing, place a pieces of nylon/rubber washer on each of the screws.
  10. Nylon/Rubber washer will create a small 3-4 mm distance between the lat bearings and tube box and help prevent touching of tube box with the side panels of the rocker box while movement of the telescope tube. They will also help in the minor angle adjustment of lat bearings with the rocker box.
  • Masking tape for alignment
  • draw circle to mark positions of 3 screws
  • lat bearing fixed by aligning the markers
  • nylon/rubber washers on the screws
  • It will help to create a small distance between the bearing and tube box
  1. Once lat bearings are attached to box, we can attach the side panels to the another piece of 15″ round disk or rocker base which will rotate on the base disk.
  2. Check the end to distance between the lat bearings. Both the side boards should be set at this distance between each other so that lat bearings can sit comfortably on the curves of side boards. This distance would be 11.25″ in our case but you better re-measure it correctly for your DOB.
  3. Fix the side boards on the round disk at measured distance. I screwed the side boards on my DOB by drilling holes from the bottom side.
  4. I made 2 templates from wooden strips to make sure the correct distance between the side boards at top
  5. Place the tube box carefully on the curves of side board to ensure it is fitting correctly.
  • measuring the correct distance
  • fixed from bottom
  • testing if bearings fit correctly on the sides
  • nailed template to ensure correct distance at top.
Attaching Teflon strips
  1. To have the lat bearings move smoothly, I used 4 piece of Teflon strips and attach them in the curves of side boards using the masking tape. You may use thin double sided tape as well. Though Teflon is notorious for not sticking to anything, I found it stick well with the masking tape.
  2. Once you do this and place the lat bearing over side board curves, you can feel the smooth movement of tube box. There is no alternative of Teflon for this purpose.
  3. Check IndiaMart site to find Teflon sheet dealers in your city.
  4. If for any reason you can not get Teflon sheet, Try using plumbing Teflon tape. You can put several tight layers of it on a piece of small plastic to use instead of Teflon sheet.
  1. We also need to attach Teflon to the bottom of the rocker disk so it can rotate smoothly.
  2. Cut long strips of Teflon sheet to attach to the bottom side of rocker base as shown below.
  3. Since I had thin Teflon strips, I used 3 plastic lugs, set them 120 degrees apart and screw Teflon sheets over them. Screws were countersink so they pose no problem of touching of rubbing the base board. If you have thicker piece of Teflon, you can directly screw it on the board. Just make sure to counter sink the screws on each piece.
  1. To provide side support to lat bearings, I used 5×5 inch mica board (used to make electrical panel board).
  2. Attached it the way as shown in the images below. Also pasted piece of Teflon sheet on each for resistance free smooth motion of lat bearings.
Final Assembly

You will have following items shown in the below image for final assembly. Two small pieces of plywood under the tube box are for the front support of rocker box.

All DOB parts for assembly
  1. Connect side boards to rocker base
  2. Attache rocker base and mount base using a 10mm thick, 3″ long stainless steel bolt. I used stainless still to prevent any rusting.
  3. I also placed an around 8 mm long piece of hose pipe over the bolt to prevent any lateral movement of the bolt during the use.
  4. Place the mount base over the rocker base and tighten the nut. I used a nylon nut which will not come out loose and tightness can be adjust between both the boards for smooth motion.
  • nylon nut
  1. Once the assembly is done, orient the mount correctly and check again for the smooth motion of lat bearings.
  2. If all goes well, attach the front boards on side boards as shown. They will give stability to the rocker box assembly.
Our DOB Mount is ready!
  1. Below are the pics of completed DOB mount.
  2. For finishing, I nailed 3 mm wooden beats on exposed ply of side boards and lat bearings (slightly long on each side as stoppers for lat bearings)
  3. To hide screw heads, I used stainless steel screw caps. They have also increased the aesthetics of the mount.
  4. I also plan to use wood polish on the exposed wood and ply surface in future.

You can see the smoothness of this mount in the video below.

Go back to Assembly

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