Testing CNC Machine Vise Holding Power

Let’s test some workholding methods – measuring clamping force, deflection, and torque wrench consistency!

Workholding is arguably the most difficult part being a machinist but it’s all good. We’re diving into the science behind force and pressure and understand how to approach and improve workholding techniques. Let’s explore how force varies between different people, tools, vises, AND how super glue holds up. Big shout out to Eric at Orange Vise for loaning us this awesome load cell that gives a digital read out of force!

Sometimes, holding on to a part can be the most difficult part of being a machinist. Diving right in, how much force can we apply using different wrenches? We tested three wrenches under two conditions – regular applied force(tightening the vise to a “normal” amount) and maximum force (tightening the vise as tight as possible).

  • Speed Vise Handle – 2,144 lbs MAX: Using our smaller speed vise handle, we hit an average force of 1,118 lbs of force. Applying as much force as possible with the speed vise, we hit a maximum average of 2,144 lbs.
  • Regular Vise Handle – 4,118 lbs MAX: Using a regular length vise handle, we hit slightly larger values (more length = more mechanical advantage). So with this wrench, we had an average force applied of 2,265 lbs and a maximum average of 4,118 lbs.
  • Torque Wrench: Because torque wrenches have variable values and lengths, the applied force here isn’t important. What IS important is how consistent those numbers are. We were able to get a reasonably consistent value each time, but there are many variables which can affect this value outside of the wrench itself.

How does the clamping depth of a part effect the holding strength?

We found that it took less force to loosen a part with more holding area – sounds backwards, right? Actually, no! Clamping pressure and clamping force are two very different things. Pressure is equal to force divided by area, meaning that a part held further into a vise has more area and consequently less clamping pressure. Now this doesn’t mean you should clamp on to a part with as little area as possible! Too much clamping force over too little area can cause the material to deform or break, causing the fixture to fail.

This budget torque wrench is our general use wrench for around the shop
High quality Gedore wrenches with a 16mm shank that accept most collet wrenches. These are often the type included with high-end toolholders like REGO-fix

Excel File

Related Videos & Resources:

Super Glue Fixturing for CNC Machining!
DIY Vise Fixture Plate Widget
Recommended Machine Shop Tools