DSG325 - Soft Jaws and alternative fixturing

what are the benefits of soft jaws?

allows you to old a part that you otherwise wouldn’t be able to

What are soft jaws?

• softer steel or aluminum

• sold as blanks with the intention of machining a pocket into them

what are hardened jaws?

• “default” jaws in vise

• precision ground

• durable

• not meant to be machined

what are the considerations for designing the pocket in the soft jaws?

1. support the bottom of the part

2. secure/squeeze the sides of the part

3. Judicious use of reliefs and extra clearance

   1. avoid over-constraining and point loading

What are some guidelines for supporting the bottom of part

• match level changes

• may require surfacing the soft jaws

• leave enough ‘breathing room’ between top of soft jaws and bottom of pad

what are a guideline for securing sides of part

• grip on faces that are parallel to the z axis (and each other)

what is a rule of thumb for locating faces

design parts with pairs of parallel faces or other locating surfaces even if they are not functional or immediately obvious in the operating orientation

what is the rule of thumb for adding reliefs

• avoid point loading

• maintain even pressure, greater grip power

• ensure part is located as excepted

What is G code

the “language” generated by the CAM software that makes the CNC machine move - wrt origin

what is a rule of thumb for designing datums into soft jaws

can design datums into soft jaws for accuracy and repeatability

how can stock become the fixture using tabbing

1. stock is oversized by enough that a silhouette can be slotted in

2. part is left hanging on by periodically spaced tabs

3. as last machining step, tabs are thinned down so that they can be broken off

what are the pros of tabbing

fewer setups required

• greater accuracy

• less pick and place / human intervention

• good for higher volume parts

fewer fixtures to keep track of

what are the cons to tabbing

remaining tabs have to be filed off - poorer surface finish in those areas

reduced rigidity

• reduced dimensional accuracy as part sags

• chattering/vibration - poor surface finish