Making and using a screw head polisher
The screw head polisher, or frog tool, is based on an article in HJ Apr 88 by Eliot Isaacs FBHI
Some parts on a clock or watch have a highly polished flat face. An example of this is the top of some screws on English Dial clocks. When these faces need to be re-polished it is essential that the edges are sharp and crisp. There is nothing more distracting than rounded corners when it is obvious that they should be sharp!
If you try to polish the heads by most hand methods you will not get square edges. However using the Frog tool you will get a nice polished flat surface with square edges.
Fig 1. Frog tool
Making the tool
- Take a piece of mild steel 1.25" square by about .25" thick.
- Mark, from end to end, a line 5/8" from one side.
- At one end mark off 1/4" from the centre line. Draw a line from this point to the lower corner. Repeat this on the other side of the centre line.
- Saw and file to theses lines to make a wedge shaped piece of metal.
- Draw a line, parallel and, 1/4" from the short side.
- On the short end, drill and tap two 6BA holes 3/4" deep.
- Saw along the line and file flat both sides of the sawing.
- On the main body, Drill and tap a 4BA hole in the two corners on the long end.
- At the centre line on the short end, file a small vee.
- On the clamp, drill the tapped holes to provide a clearance for the 4BA screws.
- Using four 4BA bolts, assemble the tool as shown in fig. 1.
Using the tool.
First make yourself a selection of emery boards. I suggest use some flat pieces of wood 9" x 6" and fix the emery paper onto these using either a contact adhesive or double sided tape. The grades of emery needed will be, 220, 400 and 800 grits.
Locate the screw to be polished in the tool with the head downwards. Adjust the two rear screws until the head to be polished is laying dead flat. Using the course grit, hold the tool firmly on the emery board and push the tool away from yourself. After a couple of strokes, check the screw head. You will probably find that it is only touching one side, adjust the two rear screws accordingly. Repeat until the head is resting flat on the board. You can now polish the head using finer grades of emery until it is a mirror finish. The screw can then be either blued or left polished as required.
