Civil Engineering Reference
In-Depth Information
so the plunger will move through 20 holes and sit in the 21st hole. Not mov-
ing this extra hole is the biggest cause of scrap work when using the dividing
head. I have seen experienced toolmakers make this simple mistake.
Sectors
To use the sectors, set the plunger in the starting hole. Set the holes plus one
on the sector plates. Rotate the sector plate so the left sector is against the
side of the plunger pin. Machine the work as required at this point. Rotate the
plunger to the right until it is at the last hole on the sector plate (you may need
to wind the dividing head an extra turn or two first) and lock the dividing head.
Rotate the sector to the right until the left-hand sector is up against the pin.
Continue until all the work is done at each position required.
DIVIDING A 13-HOLE DIAMETER
As a practical example, we will work out the way to divide a 13-hole diameter. Why 13
divisions? I have had to do 13 divisions in industry, and it is a real example that illus-
trates a lot of the problems encountered.
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We will assume a dividing head of 40 to 1, which is what is most likely to be found
in the home workshop. One turn of the crank handle is 9 degrees.
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360 degrees divided by 13 divisions = 27.69230769230769 degrees per division, so
we have to turn the main crank three turns to get the 27 degrees which leaves 9
degrees that need dividing by 13 holes.
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13 times 26 degrees = 351 degrees. That leaves 9 degrees = 1 turn, so any division
plate that has a multiple of 13 holes will do to give us the odd fraction of the
movement required. So if you have a 26-hole plate, move 3 turns and 2 holes to
give the required movement. If you have a 39-hole circle, move 3 turns and 3
holes. If you have a 65-hole circle, move 3 turns and 5 holes and so on: 26, 39 and
65 are all multiples of 13.
Do not forget to add the extra hole to allow for the plunger so 2 becomes 3, 3 becomes
4 and 5 becomes 6.
Ideally dividing should be done in one go, without any interruptions. Dividing is not
difficult, it just requires care, absolute concentration and patience.
