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What Can a Vacuum Chuck Hold

Although the power of a vacuum was first witnessed over 350 years ago, vacuum chuck technology is often overlooked in the manufacturing community. In this tutorial we’ll cover some basic limitations and to see if vacuum chuck workholding is right for your application.

To Vac or Not to Vac

In a machining environment a vise should always be the first choice in workholding due to the high mechanical clamping force. However, using a vise is not always an option for certain materials and shapes.  Some soft or thin materials can be damaged or bowed by a vise. Using a vacuum chuck also allows machining of 5 out of 6 full sides of a part – vises allow limited exposure of 3 sides. If using a vise causes any of these problems, then a vacuum chuck is absolutely an ideal workholding device. The rule of thumb in evaluating if vacuum chuck workholding is right for you is best remembered by the phrase “Short and Fat”.

Evaluating the Workpiece

“Short and Fat” conveys two ideas.  First, parts are best held when a large surface area (fat) is presented to the chuck surface.  A high vacuum is defined as 26″ – 30″ Hg and produces a holding force of 13 – 15 PSI.  For example, a 5″ x 5″ part being held by a vacuum chuck at 28″ Hg (or 14 PSI) has 350 lbs of downward holding force applied to it (5″ x  5″ = 25 sq in. 25 sq in x 14 PSI = 350 PSI). The more surface area a part has, the stronger the hold, the more aggressively material can be removed.

Vises have a theoretically infinite amount of pressure that can be applied to a workpiece whereas vacuum chucks rely on the atmospheric air pressure around us to press a workpiece downward against the chuck surface. Since this force has a limit of 14 pounds per square inch (14 PSI), any forces that might lift the part should be avoided. Rather, material removal should be focused on creating sideways forces, but sideways forces on tall parts can lead to unwanted lifting due to leverage. Short parts do not experience this unwanted leverage.

How tall is too tall? Plugging in a 25:1 ratio into a simple equation offers a good starting point. Divide a part’s surface area by 25 to find a safe part thickness (5″ x 5″ = 25 sq in. 25 sq in / 25 = 1″ tall part). Many other factors play into this equation such as material type, cutter style, feed rate, aggressiveness of cut, etc. so fine tuning to the exact application is encouraged.

“Short and Fat” reminds us of the ideal part shape, but trying to keep a part in place while cutting on it is a discussion for another tutorial.

Tags:  /  Comments: 2



October 13, 2011


Dear Sir,

I am Mechanical engineering final year student .I am doing a project on vacuum chucks in a solar manufacture industry.i have some doubts.In that industry they have to grind small calcium strips.present they using vacuum grinding but its not giving good results.i got a small idea that if hold those calcium strips on vacuum chucks in more quantity and apply grinding operation means the out put may be high.I need your suggestions regarding this.I am kindly requesting you to give your valuable suggestions.

Thanking you


November 28, 2011


The rule of thumb in vacuum workholding is the larger the part size, the better the results. If your strips are large enough, you might get better results. Also, grinding usually does not produce any lifting forces so you should be able to grind the parts as long as they are kept from moving sideways.

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