Parallels
Setting up
Before placing the vice on the bed of the machine, clean the bed as well as the base of the vice. Any swarf will introduce errors — when the vice is clamped up tight, the swarf will mark the bed and the base. Any marks already present should be lightly stoned to remove any raised areas.
When the vice most suitable for the job is placed in position on the bed of the machine it needs to be trued with a dial test indicator (DTI) mounted in a collet or drill chuck.
The lever type is best suited to this, although a plunger type can be set up to do the same. Zero the DTI and wind the table of the machine so that the DTI moves along the fixed jaw of the vice or along a parallel clamped in the vice. Take note of any movement registering on the DTI. If there is movement, loosen one of the bolts clamping the vice to the bed and move the vice slightly to reduce the error. Clamp up the bolt and recheck. Continue until the error is reduced, ideally to zero. The greater the distance you move the DTI over, the more accurate the setting will be.
As one definition has it, ‘parallels’ are pieces of steel-bar stock accurately machined so that the opposing sides are parallel to each other. They are used to raise a workpiece to give clearance under the component for the drill not to damage the machine table or the base of the vice. Parallels can be bought in sets or you can make your own as you require them, but always make them in matched pairs.
You can never have too many parallels. They come in varying heights and widths, and can be stacked as required, although you never seem to have the perfect set for any particular set-up. Typically, the parallels you buy will be hardened, making them wear-resistant and very good for industrial use. Non-hardened parallels are generally one for the garage engineer and have the added advantage that if you do clip one with a cutter or drill, it is far less likely to damage the cutter or drill.
A very good idea is to make a set of parallels that are a good fit in the machine bed slots. These can be used to aid setting a component and give a good solid backstop.
This relies on the bed T-slots being in good condition.
Screw jacks
Screw jacks come in many different sizes and can be very elaborate or simple in construction. They support your set-up, stopping the component tipping when you are machining, or allowing support for another clamp to be added to the set-up.
V-block
When a round bar is held in a vice, there are only two points of contact. Any machining is likely to result in the bar tipping over, but this can be overcome by using a suitably sized V-block. This immediately gives three points of contact to apply friction and restrain any movement of the round bar. Don’t forget, a good set-up is rigid and stable.
Next issue, we’ll look at cutters and cutting speeds.