Designing a fixture with Multi-Rail RM system
If in doubt, you can always order your fixture design from OK-VISE. For the key customers we do some designs for free.
Below are basic principles to help our customers, should you wish to design fixtures it themselves.
Main rules for fixturing
- Allow enough access to all sides of a workpiece, on which machining operations are performed
- Guarantee reliable holding of a workpiece
- Prevent bending and vibrations of the fixture and the workpiece
- Pursuit easy loading and offloading of a workpiece
Calculating maximum size of a workpiece
You can easily calculate the size of workpiece(s) that you can clamp using multirail.
Simply choose ther base rail RM-100 ..RM-700, the clamp module(s) and stop modules.
Then, check the length of the chosen clamp and stopper modules in dimensions drawings ("dim") and you have maximum workpiece size S
Machining force vs. clamping force & friction
The picture below illustrates machining and clamping forces in the fixture.
Clamping force F created by OK-VISE clamp are indicated with the yellow arrows. In each stopper, a force that is equal the clamping force is created. Red arrows indicate forces that are applied to a workpiece while machining.
When the fixture is working with friction closure principle, friction between the jaw and the workpiece creates a holding force that resists machining forces.
Forces created by the weight of a workpiece are not presented on the diagram.
In the example below, a workpiece with a size of 300x300x900 mm is being clamped using two SRM-152 Multi-Rail sets (based on RM-500 Multi-Rail). In this example, Multi-Rail sets are installed on a sub-plate.
Estimation of how much force the fixture can resist in direction X:
Using 4 tons (40 kN) clamping power in two standard clamps with smooth jaws, where the coefficient of friction is low (µ = 0.15), the maximum allowed force X is:
4 * F * µ = 24 kN = 2.4 tons
Using 4 tons (40 kN) clamping power in two clamps and a stopper*, where coefficient of friction is high (µ = 0.8), the maximum allowed force X is:
X = 4* F* µ = 128 kN = 12.5 tons
* Grip jaw against the steel, the gripper leaves marks on the workpiece surface.
Please note that estimates above are rough.
If in the example above a workpiece is made of steel and its weight is approx. 600 kg, a coefficient of friction against the Multi-Rail base and workpiece is even higher.
Additionally, the force, which generates sliding movement of a workpiece in the fixture, and such constraints as bending or vibration of the fixture can be calculated as well.