Vacuum workholding is an excellent choice, and often times the only choice, for holding workpieces. Here are several quick tips to keep in mind when evaluating and/or using a vacuum workholding device.
- Vacuum Power has a Limit – The most powerful vacuum chucks have a limit of 13-14 pounds of downward holding force per square inch. This is because the air pressure around us is what actually squeezes the part down onto the chuck. A vacuum would have no effect in outer space since there is no air pressure.
- Use Small Cutters when Possible (if you’re not following tip #7) – Small cutters exert less torque, reducing side forces thereby reducing the chance of throwing a part off the chuck. So, instead of using a 1″ wide cut around a part, use a 1/4″ cut with four passes.
- Use Sharp Cutters – Sharp tooling reduces side load which also reduces the chances of throwing a part off the chuck.
- Don’t Use High Helix Endmills – Low helix, or even negative helix cutters will reduce or eliminate any chances of lifting a part off the chuck during aggressive machining.
- Use Common Sense – Holding a part that is 1 inch square and 4 inches tall is not going to work. Short and wide parts are the best candidates for vacuum workholding.
- Vacuum Workholding is Often a Secondary Choice – Yes, vises and clamps are the preferred method of holding a workpiece due to higher holding force, however certain part shapes and sizes may restrict their use. A vacuum chuck may be your only choice, but don’t expect to be able to machine a part as aggressively as when using a vise.
- Use Workstops Whenever Possible – Though vertical holding force may be high, side forces may easily shift a part sideways off the vacuum surface, especially when machining plastics with a low friction ratings (nylon, teflon, delrin). Adding pins, side rails or even cutting a shallow pocket for the part to sit in will greatly limit sideways movement.
- Flexible Workpieces Might be Problematic – Because the rigidity of the workpiece helps maintain a vacuum seal, very thin or very soft materials may be more likely to flex and lift off the vacuum chuck.