Single Arm Scotch Mount or Barn Door Tracker – DIY Guide

Acknowledgments

I would like to thank Mark Christensen for spurring the idea to fruitage. I'd also like to thank Phil Harrington for the most concise design ideas on the web. Of course, the biggest thanks goes out to George Haig of Glasgow, Scotland who invented the device!

measurements for a diy scotch mount

Why Build it?

Considering I own a computerized LX200 and a motorized 4" refractor, why would I bother building a hand-cranked camera platform? Personally, I find the whole idea of a non-motorized way to shoot the sky very romantic. The fact that anyone can make one for about $10 is incredible to me. I had as much fun and satisfaction.

building it as an activity I've undertaken in astronomy. In an age where everything is computerized, I find this simplistic tool amazing!

Tools Used

  • Drill, Drill Index
  • Protractor
  • Black Magic Marker
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    Pliers
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    Hammer
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    Screwdriver, Phillips Head
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    File or Sandpaper
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    Circular or Hand Saw

Materials List 

Description Size (Imperial) Size (Metric) Quantity
Wood (4" or 6") x 13" x 5/4* (101.6 cm) x (330 cm) 2
Tee nut, 1/4-20 internal thread NA NA 2
Lock washer & nut 1/4"-20 1 each
Circular Wood (opens a new browser window) for a handle. Should have a flat on it. 2 1/2" or 3" diameter 63.5 cm or 76 cm 1
Piano Hinge** (Match Board Width) 4" or 6" NA 1
Carriage Bolt 1/4"-20, 6" long NA 1
Cap Nut 1/4"-20 NA 1
Round Wood (Obtain from a hobby store. Used for puppet heads. 2-3/4" diameter ~70 cm 1
Wood Spacer- about the size of the Round Wood 1-2" square 1
Hangar Bolt (get a shorter length if you can.) 1/4"-20 x 2" 1
Rubber Plumbing adapter, 2" to 1 1/2". Made by Fernco®, part number P22U-139. NA NA 1
Wood 1-1/2" x 5" x 5/4" thick 38 cm x 127 cm x 32 cm thick 1
White Paint NA NA Not much
Construction Adhesive or Liquid Nails™ 1

Optional Hardware
Bicycle Spoke 1


* Wood thickness is optional. I used cedar 5/4" decking that I had left over from another project.
** Hinge may come with mounting screws. If it doesn't you will need to pick out the appropriate screws.


Design

  1. Cut your 2 blocks of wood pieces into 13" x 4" pieces. You can, however, make a 6" wide board and use a 4" hinge but you may give up some stability. (If using a 4" hinge, cut the board to be 4" wide, if 6" hinge, cut to 6" wide)

  2. Attach the piano hinge to edge of the board with screws and screwdriver. Drill clearance holes by marking the holes. The hinges should face each other. Click here for a picture.

  3. Bottom Board. CAREFULLY measure off 11.42 inches from the center of the hinge. This is the most critical part of the building process! Click here for a drawing (opens a new browser window). Drill a hole just big enough to allow the insertion of the T-Nut. Insert the T-Nut from the top side of the board and pound in with a hammer.

    Drill another hole in the very center of the board for another T-nut. This will allow you to hook up the Tripod to the tracker. Pound in the T-nut with a hammer.

  4. Handle. Cut out handle to be a round piece of wood, approximately 2-3/4" in diameter. If this is a difficult task there are a number of substitutes including a 12 sided handle (opens a new browser window). Drill a clearance hole in the middle to allow the carriage bolt to pass through.

    Paint the handle white. Use spray paint or any white house paint. I just dipped mine into a paint can and let it dry by hanging it off of a vice.

  5. Using the protractor, put tick marks on every thirty degrees (opens a new browser window) along the top edge. Then mark one of those tick marks from the center of the wheel to the edge. Starting on that line, make a mark on the edge all the way down. Make the 30-degree increments from the top only halfway. Every ninety degrees make marks from top to bottom.

  6. Camera Mount. Take wood spacer (from any scrap that you have) drill a hole in it to put the Hangar bolt into it and the Round Ball (opens a new browser window).

  7. Top Board. Use construction adhesive and mount the Rubber Plumbing adapter on the somewhere over where the tripod will be or near where the carriage bolt will hit the board (opens a new browser window).

  8. Insert the Carriage Bolt through the bottom of the handle and slide the Lock Washer on the opposite side of the carriage bolt head. Then thread on the Nut and tighten until the head of the carriage bolt sinks completely into the wood.

    Now insert the assemble wheel into the hole in the bottom board where the T-nut is. Thread it up till about 1/2" above the top surface of the board.

  9. Now thread on the Cap Head onto the end of the bolt. This allows a nice rounded surface to engage the top board!

    Optional Accessories


  10. Bicycle Spoke. The spoke serves a dual purpose. First, by drilling a hole near the edge of the board and centered, the spoke hangs down to act as a gage. The lines on the handle line up with the spoke thus giving you a reference as to where to stop turning.

    Second, it allows you to hand a watch from it and thus the gage and watch are at the same point of view. This eliminates taking your eyes from going back and forth from the watch to the wheel.

Exposure Times

Scotch mount: Turn Frequency Compared to
Focal Length of Lens*** (opens a new browser window)

Lens Focal Length Turn Frequency
Wide Angle (i.e., 35mm or less) 180 degrees every 30 seconds
Normal (i.e., 40mm to 65mm) 90 degrees every 15 seconds
Telephoto (i.e. 70mm to 200mm) 30 degrees every 5 seconds


Notes:
- In general, 200mm is the longest practical focal length that can be used successfully with the original Scotch mount.
- A nice trick is to take a finder scope and lay it on the hinge to get a fairly accurate polar alignment.


Disclaimer

Workshop tools can cause injury if not used correctly. It is your responsibility to ensure that you use tools safely and in accordance with the manufacturer's instructions and wear protective gear where appropriate. You are also responsible for ensuring the safety of yourself and others when using this device. Implicit in making or using the device on this web page is that the author is absolved from any and all liability for any damage caused or injury sustained in the construction or use of this device howsoever caused.

I wish I didn't have to say that but lawsuits are not welcome...

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