Workholding is the generic term for any device used to firmly hold your workpiece while machining it.
Although machine shops tend to focus more on other components of the machining process, such as the machine itself or the cutting tools, the importance of proper workholding should not be underestimated.
If put in place properly, workholding devices will allow the machine to work at its full potential, allowing you to produce quality parts efficiently.
On the contrary, if underestimated it can lead to failure.
In milling operations, for example, failures often occur due to the work being pushed out of its position by the force of the cutting tool or the workpiece flexed because not properly supported, both consequences of improper workholding.
Although the shop will generally provide all toolholding and workholding tools, it is important to have an understanding of what devices you should have and how they work.
Our goal in this article is to give you an overview of the main workholding devices that you’ll need when working on a milling machine. We’ll talk about workholding devices for turning centers in the next post.
All of the workpieces or the workholding tools installed on the milling table are held in position with the help of the table T-slots. It is fundamental to keep the slots clean from chips and any other debris.
Although they are strong and simple to use, one of their biggest disadvantages is that it’s hard to get your vise or other Workholding fixture back onto the table in exactly the same place and orientation. This can result in extra work every time a machine needs to be set up with new workholding for a new job.
Depending on what you will be attaching to the T-slots, you will have to use T-slot nuts and combine them with other fasteners that fit the nuts
Clamps are the simplest tools available to secure anything to t T-slot. There is a wide array of clamps available depending on the sice and shape of the workpiece or workholding tool.
This clamping kit is the most commonly used in machine shops:
Other common types of clamps used are the following:
Fixtures plates, also called tooling plates, are plates that are installed on top of a T-Slot table to provide a new way to position and secure Workholding. They typically feature a grid of holes that alternate threaded holes for fasteners and precision dowel pins for positioning.
The grid makes workholding positioning significantly easier and repeatable. Tooling Plates are typically made of either Cast Iron or Aluminum, though there are steel ones available too. They can be purchased or made from scratch.
The most basic type of workholding in milling is the Machinist Vise. Both jaws have great parallelism and perpendicularity, along with great strength, so they’re ideal for gripping stock and not letting go.
Here are some of the best models available on the market:
Other types of vises, such as the sine vise, are often used in job shops to work on parts that need to be machined at an angle. Here’s an example of a precision sine vise.
Parallels are often used with vises to hold the work at a height off the bottom of the vise, giving clearance for side milling and through-hole drilling.
Unlike parallels, jaw plates are positioned in the outboard position of the vise jaws and are generally used to clamp larger plates.
Vee blocks are generally used when the workpiece has a cylindrical shape, such as bars. Their design allows them to quickly and accurately locate the Y-axis center.
Vee blocks are also considered a useful solution to hold bars vertically or to secure other holding devices such as collet chucks.
Table slotted angle plates are used in setups when the workpiece being machine needs to be held at a true 90 degrees angle to the table.
These plates are heavy and available in a wide array of sizes.
When angle plates are used, the work is generally clamped or bolted to the plate.
The devices presented above are just some of the solutions that machinists can use to secure the work on the machine. Experienced toolmakers often come up with customized solutions, aka “fixtures”, that will help them to better hold the workpiece while it’s being cut. Here’s an example of how to machine a customized vise fixture plate.
If machined correctly, fixtures will be extremely helpful to machine particular parts, reduce setup times and eventually increase the profit.
The possibilities, in this case, are endless and depend mostly on the skills of the machinist.
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