Autonopedia

A

The position of the first hole in a harrow bar is marked with a centre punch.

Each hole thereafter is marked from the previous one using the gauge or scriber made in Lesson 5.

Do not try to mark all the holes before starting to punch them.

B

The holes in light harrow frames are slotted and punched to the finished size and shape in one operation.

This is the special punch used for punching square holes in light harrow frames

It combines the action of a slot punch with that of a square drift.

C

Do not attempt to punch the hole right through from one side, but use the punch as described in Lesson 16.

As there is no upset, make sure that the slot is started exactly in the middle of the bar.

It is important to keep as much metal as possible either side of the hole.

D

Round holes in light bars are made with a combined punch, similar to that shown in B on above, but it is of round instead of square section, like this -

E

Heavy flat bars are first slot-punched and then the hole is opened out by upsetting.

This is being done here to the lower hole which is hot. The upper one is complete.

F

The hole is finished off with a special stubby drift, which is marked at threequarters of the thickness of bar.

It is driven in from each side in turn almost as far as the mark.

This is done on the flat of the anvil and not over a hole.

The use of the special drift prevents burrs forming on either edge of the hole.

G

Harrow tines must be a push fit in the holes.

The holes must be spaced exactly so that the harrow frame can be assembled correctly.

It is therefore essential to use a scriber to mark off each hole as the previous one is punched.