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Jim Koepke
09-19-2010, 3:47 PM
For some reason, when I woke this morning I was wondering if I could get heart burn from something I was dreaming I ate.

That reminded me of the Morey Amsterdam story about dreaming he was eating a 5 pound marshmallow and waking up to find his pillow missing.

So on to another thought that came to me while using my router plane yesterday. While advancing the blade it came to me to find out how many threads per inch were on the adjusting screw since this relates to how much the blade is being advanced. Checked out to be 18 tpi. Doing a little math this turns out to be a repeater at 0.0555555555 inches for a full turn of the adjusting nut. That means turning 1/8 of a rotation would advance the blade about 0.007 inches.

Many of us have used threads for measurements in the past, even if we don't realize it. Those fancy micrometers with the horse shoe on one end has a precision screw thread cut at 40 tpi. That is why they read out 0.025 inches per full revolution of the handle.

Anyway, out of curiosity since I often use screw threads and nuts to make my "hillbilly" micrometers when the real deal is not handy or the item to be measured can not be accessed with the real deal, here is something that was just done on a spread sheet to get close.

161904

Notice that these numbers are rounded to the nearest 1/10,000.

jtk

Mitchell Andrus
09-19-2010, 6:32 PM
Notice that these numbers are rounded to the nearest 1/10,000.



1/10,000. That's close enough given that we're eyeballing 1/4, 1/8, 1/16 of a turn.
.

Jim Koepke
09-19-2010, 7:01 PM
1/10,000. That's close enough given that we're eyeballing 1/4, 1/8, 1/16 of a turn.
.

I will sometimes put marks on my round adjusters for such things.

Also will work with minutes and such. 5 minutes on the clock face is 1/12 of a turn or 30. 1 minute is 1/60 a turn or 6. I was thinking of extending the spread sheet out to include those numbers.

jtk

Jerry Bruette
09-19-2010, 9:36 PM
Using thread pitch is a good way to determine the distance of linear movement. I use this method when setting impellar clearance on centrifical pumps.

You just have to remember to take out the backlash in the threads before you start counting turns.

Jerry