Center Line Scriber by Hugh McDonald
Center Line Scriber

By Hugh Mcdonald
Gooseberry Hill, Western Australia

Presented by Jock Dempsey
March 27, 2002
Hugh McDonald is best known as the inventer of the McDonald Rolling Mill. Hugh also has a great imagination and manages to come up with an original twist on all his work.

This demo is no different. The idea demonstrated here is one that my father also came up with a couple years ago. My father, a great inventor with many patents, rarely has his inventions duplicated.

This is our 130th iForge demo.


Center Line Scriber and examples. Click for detail image.
Hot slitting for twisted basket decoration needs accurate centre line setting out. I dreamed up this little marking gage in church last Sunday and came home and made it in less than an hour. It has two small sealed ball bearings, ex photocopier salvage, mounted on a piece of 1"x1/4" steel with a scriber centrally between them. The scriber is ground from a broken piece of 1/8" HS drill bit and cuts a track easily followed by a sharp chisel. It will scribe a true centre line on any steel up to 1" wide by twisting it sideways as it is pulled along and the bearings prevents the thing from jamming as these instruments tend to do when fitted with the usual pegs. The Photo should be self explanatory and shows the gadget sitting on two pieces of steel with scribed centre lines.

Hugh McDonald. 2 March 2002

McDonald Center Line Scriber
Hugh's comment that it is self explanitory may be true for some but not all.

The critical thing about this device is the accuracy of the hole locations. The rollers must be equal distance from the center. If the tool is accurate then the scribed line will be accurate.

The rollers are spaced farther apart than the width of the work and the bar turned to make both wheels contact. This means the tool fits a wide range of sizes. If you want it to work on larger stock you can drill extra sets of holes and move the rollers.
My Father's invention using this principle is a bit different and used for centering work on machine tools like a milling machine.

Comments Questions?
That's elegant! How was your father's different Guru?
It chucks in the machine spindle.

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