5 Tips for Holding Small Parts on a Vacuum Table

Vacuum tables or vacuum chucks can be used to hold sheet materials and small flat workpieces during the CNC machining process.

So, if you’ve been reading this blog, or cruising through our website, then I’m fairly sure you’re aware that we make an extremely capable CNC vacuum table. It’s the must have fixture for many industries – rapid prototyping, signage, front panels, etc. Where the vacuum table can truly shine is holding very small parts.

I once ran a demonstration for a prospective customer that showed that you can cut an entire 12” x 18” sheet of 0.020” thick aluminum into 6mm discs without having any of them fly off the vacuum table. See video below as an example. You can see that the last cut on the perimeter of these small parts goes through the sheet material exposing our VacuCard paper that sits between the sheet stock and the vacuum table – serving as a sacrificial layer that allows you to cut through the workpiece but not into the top of your vacuum table.

With all of this being said, vacuum tables are an excellent workholding solution, but they require a certain approach to get the most out of them.

1) Vacuum Table with Regular or Dense Hole Pattern?

Vacuum table tops in both regular and dense hole pattern to hold very small parts even after they are milled free from the sheet material.
Vacuum Table Tops can be ordered in the standard hole size (right) or in the dense hole pattern (left) which is designed to hold particularly small parts without having them fling off the table when they’re milled free of the sheet material.

The first defining feature of our vacuum tables is the density of the vacuum holes. We have two patterns, regular and dense. The regular pattern is well suited to most of our applications, but when you get down to parts smaller than a square inch, or a more difficult to cut material, a dense hole table is a good choice. The key to the dense hole plate is having more than twice as many holes as a standard plate, thus allowing better suction on smaller parts.

2) Use Vacuum Table Paper

Vacuum table paper called VacuCard is used as a sacrificial layer that allows you to cut completely through the stock without damaging the surface of your vacuum table.
Vacuum table paper known as VacuCard is air permeable but thick enough to allow you to mill through the workpiece without milling into the surface of the vacuum table.

The next step may seem like a no-brainer, but it’s especially important for very small parts. Once a piece of our vacuum table paper (known as VacuCard or VacuFlow) has been cut into, it becomes ineffective for smaller parts. Cuts in the paper allow a path for air to leak by, as well as leave a raised edge that prevents the material from sitting flat on the table.

3) Vacuum Table Strategy

Vacuum table strategy employs both tabbing and onion skinning methods to reduce cutting force so that the part stays fixed to the vacuum table.
Vacuum table strategy includes both onion skinning and tabbing methods to limit cutting force so that the workpiece stays on the vacuum table.

One of the single most important methods of holding small pieces on the vacuum table is your strategy. If you are a little too gung-ho and try to take out a small piece in one pass, you’ll likely have cutting forces too high for the vacuum to overcome. I always recommend two methods; Onion Skinning or Tabbing. Either one works quite well, simply leave a small amount of material at the bottom of your piece to take out at the end of the operation. This will greatly reduce cutting forces and prevent unnecessary scrapping of parts.

4) Tools for Use with a Vacuum Table

Vacuum table tool selection is made based on the required cut but the smaller the better because smaller tools reduce cutting force.
Vacuum Table tool selection obviously is made based on the required process or cut, but in general, the smaller the better … and consider downcut tools for finish cuts.

Use a carefully picked tool in conjunction with step 3 to increase your likelihood of success. My weapon of choice is typically an end mill that is a third the diameter of my original tool, combined with a high RPM and moderate feed rate. With such a small tool, your cutting forces reduce even further to prevent movement of the material. For very stubborn pieces, consider using a down-cutting end mill for finish cuts. Downcut tools push the material down while milling, instead of pulling up, which helps small pieces stay-put.

5) Mill Recessed Areas in Vacuum Table Sacrificial Layer

Vacuum table sacrificial layer like this MagicBoard allows for cavities to be milled to hold parts that are not completely flat or to add side support for flat parts.
Vacuum table sacrificial layer that can be milled with recessed areas so that your part is held in place by vacuum suction as well as physical support on the sides of the workpiece.

So, your part just isn’t holding, you’ve done everything you could, but it’s not happening. Don’t worry. There’s hope. First, to get the part to a state where it will hold on the vacuum table – you may need to leave some material, but that’s OK.  Next, get yourself some MagicBoard, or a porous aluminum. Both have excellent machinability, rigidity, and the ability to let vacuum flow through them. Take either of these materials and mill a cavity into it to retain your part. Now you have physical support on the sides to prevent part movement, which allows you to cut very small parts, very quickly.

So, that’s pretty much it. With a lot of practice and a little patience, using these basic guidelines will find you well on the path to machining some very intricate parts on a very small scale. To learn more about DATRON vacuum tables and other workholding accessories feel free to download this brochure.

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Vacuum Tables for CNC Machining Centers and Milling Machines

Vacuum table for CNC milling machines features a vacuum chuck, an air permeable substrate and a vacuum pump.

Finding a method to secure parts on the table of a machining center has been a challenge since before CNC was invented in the 1940’s. For years, there has been a very keen interest in vacuum table or vacuum chuck technology for securing material. Traditional vacuum systems, however, have a lot of limitations that often disqualify the technology for part holding.

Limitations of the Traditional Vacuum Table:

  • Small parts don’t have enough surface area for the vacuum to hold them
  • Parts with through cuts cause the loss of vacuum suction
  • Parts that are not flat either can’t be held or require additional setup time – which is often too long, particularly in short run or low volume scenarios

Successful CNC Vacuum Table Design:

 

Vacuum table design is critical to its ability to hold very small parts securely during the high speed milling process on a CNC machining center
Vacuum table design consists of a the vacuum chuck, an air-permeable sacrificial layer and a powerful vacuum pump.

 

Fortunately, DATRON has developed a unique vacuum table that solves all these traditional vacuum table limitations. Here’s how each of the limitations mentioned above have been overcome.

Holding Small Parts with a Vacuum Table

One of the biggest limitations with traditional vacuum table technology is that parts are often too small or don’t have enough surface area for the vacuum to hold them securely on the table. This exact situation was presented to DATRON when a knife manufacturer contacted us with a requirement for both a high-speed machining center and efficient means of holding knife handles during the milling process. Adding to the challenge was the fact that the product line had many different sizes and shapes and was constantly changing.

 

Vacuum table for CNC machining centers made by DATRON allow for batch machining of many small parts from a single sheet of material.
Vacuum table with a batch of Harley knife handles milled from aluminum sheet material.

 

The vacuum table solution that we delivered was inspired by elements used on vacuum tables for much larger router-type table formats. These large scale systems use a permeable wood fiber board with a large flow vacuum to hold or secure large sheets for machining. Our smaller vacuum table, made from aluminum, features a dense grid of small holes in the top plate. A special thin permeable substrate sits on top to distribute the vacuum evenly and allows us to hold much smaller parts than the conventional or larger scale vacuum tables. In cases, where the parts are particularly small, we have a special version of the permeable substrate with a light tacky surface (kind of like the adhesive on a Post-It note) which is enough to secure the parts. The combination of our vacuum table design, the substrate material and a powerful vacuum pump – all developed to secure knife parts for one customer, has ultimately become an integral CNC accessory for many other customers and different applications in the years that followed.

 

Vacuum tables held aluminum sheet material during machining on a high speed milling machine to produce a batch of Harley Davidson knife handles.
Harley Davidson knife with handles made on DATRON milling machine equipped with vacuum table workholding.

Milling Through Holes on Parts Held with a Vacuum Table

Another common problem associated with conventional vacuum tables is that when you cut through sheet material, you get a loss of vacuum. If open holes allow too much loss of vacuum and the parts let go, often damaging the cutting tool, the machined part and even the CNC equipment. With DATRON vacuum tables, you can have up to a 40% open area and still hold your parts. This of course varies depending on the part, but typically, you have no problem with through holes or profile cuts. This allows for the flexibility and efficiency of cookie cutting each of part out without special tabs, screws or second operations to remove the parts from the sheet. In the case of the knife manufacturer, they would typically lay down a 24” x 36” sheet of 1/8” aluminum, start the machine, and within a couple of hours, they’d harvest over a 100 pieces of finished parts simply by sliding the permeable sheet off the vacuum table. The permeable substrate also allows you to cut completely through the material without machining into the vacuum table top. The swapping out of sheets was usually less than a minute, so almost no production time was lost due to new material change-overs.

 

Vacuum table holding small parts machined from sheet material using a high speed CNC milling machine.
Vacuum table holding small parts that have been milled free from a large sheet of material.

Holding Non-flat Parts with a Vacuum Table

But, not all materials are perfectly flat. Most machinists would never consider holding slightly warped material or objects like an aluminum extrusion with a protruding lip with a conventional vacuum system. However, the DATRON vacuum tables also accommodate a thicker version of the permeable substrate material that we call Magic Board. With a thickness of 1/8”, the Magic Board still allows for adequate vacuum suction while providing the flexibility to mill special pockets or contours into it that accommodate non-flat parts. Milling pockets or cavities in the material can also be a technique to secure or locate a nesting of preexisting parts. Additionally, the added thickness of this substrate also provides reduces the risk of cutting into the vacuum table when using cutting tools like drills or thread mills that need to penetrate through the work piece further than normal.

 

Vacuum table permeable substrate called Magic Board distributes vacuum flow evenly and allows for cutting through holes without damaging the top of the vacuum table.
Vacuum table diffuser (called Magic Board) – an air permeable sacrificial layer between material and vacuum chuck.

Reduce Setup Time with Vacuum Table Workholding

It is common with traditional vacuum table systems to spend a great deal of time setting up a job before getting started with the machining cycle. Dealing with cutting gasket material and having to place it correctly for your corresponding parts is often a very time consuming and tedious practice. In some cases, special custom tables need to be designed with supplementary screws, locating pins, guides, extra clamps, etc. to hold parts down properly or in the correct locations. In cases when a conventional vacuum table will not work, countless hours of applying double-sided tape is sometimes a method used to secure parts. This can create all sorts of issues such as coolant attacking the adhesive, glue getting on parts, or the tape simply letting go.

 

Vacuum table made for DATRON high speed CNC machines provides 24" x 26" of vacuum workholding.
Vacuum table called QuadraMate combines four 12″ x 18″ segments for 24″ x 36″ of vacuum workholding.

 

With the permeable substrate system, usually there is no setup involved. Quite often you simply load in the desired material, turn on the vacuum pump, and start machining right away. This saves many hours of setup time over a production week and reduces part rejection resulting from improper setups. The DATRON vacuum table is a revolutionary and unique design that reduces production time significantly in many applications. It also allows a greater flexibility and in some cases the capability to machine parts that otherwise were impossible. It often reduces part rejection rates and improves part quality. From small thin parts that cannot be mechanically mounted, to parts with free-form outside contours, the DATRON vacuum table offers unique machining advantages that provide a competitive edge.

Here’s a video showing how the DATRON vacuum table works:

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Workholding Tip for Milling Small, Thin Metal Parts

Workholding Tips for Milling Small Parts

Securing small, thin pieces of metal during the milling process can be a big challenge. There are several ways to do it, but which produces the most favorable results?

Mechanical fastening is one option, but it’s often ruled out when the part is so small that it simply does not have enough area to accommodate the fasteners. Using tabs can effectively secure the part during the milling process, but presents a secondary problem – removing the tabs without damaging the finished part. Another common practice is using adhesives such as double-sided tape. However, tape is inherently flexible and frequently allows the part to move during machining, thereby jeopardizing quality.

Workholding Tips for Milling Small Parts

DATRON has found that using hot glue can be a very effective technique. Here’s how it works:

  • Get a stick of high-bond glue like the ones found at a craft store for use in a hot glue gun.
  • Cut a piece that is wider than the part that you need to secure and about ¼ inch thick.
  • Place that piece of glue on a ridged sheet of aluminum material and heat it in a toaster oven set to 350 degrees.
  • Once the glue liquefies, remove the sheet of aluminum from the toaster wearing oven mitts or using tongs, and place the part you need to machine on the liquid glue. (If the part is very thin or light, you may need to press it down using a pencil before the glue sets.)
  • Within minutes, the glue will harden and effectively secure the thin metal piece to the aluminum sheet. You are now ready to place the aluminum sheet in a vice and begin milling your part.
  • Once you are done milling, reheat the aluminum sheet with your part it in the toaster oven and remove your part when the glue softens. You may find some residue on the finished part which can be removed with a product like Goo-gone. You can also remove the residue by reheating the part one last time and sandwiching it between paper towels.

While the hot glue method detailed above is reserved for extremely small parts, vacuum workholding can be used when milling somewhat larger flat parts or batch milling many parts from sheet material. DATRON vacuum tables are designed to secure flat workpieces from 0.001” to 0.250” within seconds. These vacuum tables feature airflow-optimized ports with recessed chambers to provide superior vacuum distribution. A low cost, gas-permeable substrate serves as a sacrificial vacuum diffuser, allowing the cutter to machine through the workpiece without cutting into the table.

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