Soft Jaws Vs. Back Bolt Fixture Plate

Soft Vise Jaw

Back Bolt Fixture Plate

Operation 1

Typically involves machining the most complex side of the part first in a vise for the 1st operation, 

The back bolt fixture plate reverses this process. Think of it like creating a 'picture frame' around your part from the excess stock material. Here's how it works:

The first operation begins on the simpler side of the part, but with a twist. 

Features like hold-down holes, locating posts, and the picture frame pocket are incorporated. 

This pocket becomes the 'frame' to hold the part during the second operation. 

Note that the picture frame pocket is machined 0.150 inches deep, while the hold-down screws are only 0.100 inches deep, leaving the part 0.050 inches above the hold-down screws. This allows the cutter to fully machine the profile without encountering the hold-down bolts.

Operation 2

Custom jaws are created to perfectly match the part's profile. 

These 'soft jaws' securely hold the part for the 2nd operation while the excess material used to hold the part in the first operation is machined away to finish the part.

The part is mounted to the back bolt fixture plate. This setup allows machinists to access and machine the complex side of the part with excellent stability and accuracy. This method also simplifies programming since the hold-down bolts are not in the machining area, allowing for more efficient toolpaths. When the part is finished, it is held only by the tabs. The part is then pushed out of the fixture, and any remaining tab material is sanded flush

Advantages

Soft jaws are a common and well-established method, often preferred for simpler parts or when minimizing material usage is critical.

Locates the part well

Parts are securely held to the back bolt fixture plate. Resulting in faster feed and speeds and more reliable finished part dimensions.

Lends itself to quick setups between jobs. If the back bolt fixture plate work offset is in the machine, all that is required is to move the hold-down bolt to the proper location, mount the part, load the fixture into the vise, and press cycle start.

One or multiple parts can be machined easily. There's no need to rebuild the fixture; simply modify the CNC program to accommodate the desired number of parts. If you decide to machine more parts at once, no fixture modifications are required

Disadvantages

Doesn't lend itself well to quick setups between jobs since you need to remove jaws and add a new jaw for the next job.

Vise pressure can deform your part, leading to inconsistent part quality.

Managing and storing the Jaw between job runs.

Soft jaws wear out or deform over repeated use.

Requires more material to machine the part.

More machine time per part.