In an example below, I set up a vise on the Fixture Plate and it is properly trammed with no further effort. That means the three locator pins have to be positioned relative to one another with sufficient tolerance for that to happen. You have to consider two things. First is the cost of the material is significant. Second is the accuracy is not that easy to attain, particularly for a plate that will be larger than the travels of your machine. Unless you’re an exceptional machinist, you probably won’t be able to build a plate larger than your machine’s travels that is also accurate enough. Aluminum is a great material for many purposes, but I prefer steel for Fixture Plates. The one exception is where weight is a problem. This is more likely an issue for rotary axis tombstones than for Fixture Plates. To use the three pins, place the vise on the Fixture Plate and slide it up against the two side pins. This locates the vise on the X-axis and ensures it is square (trammed) to the Fixture Plate. For more on machining big parts see this article: [ Tips for Parts That are Too Big for Your CNC Machine ] Fixture Plate G-Code Programming

If you’re like me, you considered building your own Fixture Plate. Seems pretty straightforward, right? I will lay out what you need to know to build a fixture plate, but before doing that, let’s talk about whether it’s worth it. Here’s another advantage of Fixture Plates–they make machining parts that are too big for your machine’s travel easier. Well, you could indicate the work offset from the vises (or fixtures) each time. That wastes the potential of the modular fixturing setup though. The hole grid on a Tosa Tool Fixture Plate alternates smooth (dowel pin) and threaded holes. The threaded holes take 1/2-13 bolts, and the dowel pin holes are 0.5005″ in diameter and finished smooth. The cast and anodized aluminum body of the dowel maker comes drilled to make 1 inch (25.4 mm) dia. dowel and includes both 1 inch (25.4 mm) and 15/16 (23.8 mm)inch steel guide bushings. The range of blade adjustment lets you make dowel as much as 1/16 inch (1.6 mm) undersize (frequently an advantage when you want it slightly undersize for a sliding fit) so Veritas includes a 1/16 inch (1.6 mm) undersize guide bushing because the additional cost is minimal.Now, having made sure the Fixture Plate is in the right place, you can see where the T-Slot Nuts are. Use a tool such as a drift to reach through the Fixture Plate holes and align the T-Slot Nuts with the proper holes. to cut precise tenons on parts such as chair spindles as shown in Photo B. It was immediately apparent that it would We can bolt fixtures onto the mill table just fine with T-Slots. So why use a fixture plate at all? Installing the Tosa Tool Fixture plate took a grand total of about 20 minutes. Making sure it was set up correctly was easy to do using their key system. With T-Slots, the T-Slot nuts slide. A fixture can thus be located anywhere. That sounds great except that the fixtures can be anywhere. With a Fixture Plate, your fixtures can’t be located anywhere. They have to go into the grid of available holes. In other words, with a Fixture Plate, fixtures are always at a well-defined location.

Aluminum Fixture Plates are available from some other vendors, and they are considerably cheaper. So why use steel? There are a number of reasons: Let’s go a little more in-depth with a particular feature plate. I received a plate from Dan Bye of Tosa Tool for review purposes and installed it on my Tormach PCNC 1100 CNC Mill. Yes, journalists get free product a lot of time, but I’ll tell you the straight 411 about a product anyway. My CNCCookbook business is far more important to me than any review, so I’m not afraid to be critical if need be. With a fixture plate, you measure the location once, and so long as you always install the fixture in the same holes, you won’t need to measure again. Aluminum and your table’s cast iron will suffer galvanic corrosion together. Hard anodizing the aluminum will help a ton to reduce that.

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Once clamped in place, the dowel pin holes are drilled undersized them reamed to size. Their position is not super-critical, but we should still spot drill and use screw machine-length twist drills. Secure Workholding devices such as fixtures and vises to the machine’s table using bolts and T-Slot nuts:

We can set up a work offset on the machine for the left corner of the fixed jaw, and the g-code will also know exactly where to find the vise and can assume that corner is part zero. Now if we design parts with that in mind, we save all sorts of time. This is a problem for things like machinist’s vises, where we want the jaws to be parallel to the X-axis travel of the machine. In fact, operators spend time aligning vises with that travel, a process called tramming the vise. But with a fixture plate, the vise can be accurately installed and square, so you skip the tramming step. More time saved! My Tosa Fixture Plate arrived in a nice wooden crate. No cardboard here! It’s a precision component, so I appreciate the extra protection afforded by the crate. The Thermal Expansion of aluminum is also higher than for steel. We’re looking to Fixture Plates for accuracy and repeatability, but if temperatures change much, aluminum will make that a problem. Especially when we consider the large size of a Fixture Plate, which can magnify the issue. There’s a grid of threaded holes there. They’re protected from chips by set screws that you remove when you’re ready to use a particular hole.The Tosa Tool Fixture Plates are well made and have some premium features found on much more expensive plates and not available from the other inexpensive vendors. Here are my favorites: If we make one hole perform both functions, we reduce the tolerance and repeatability with which we can perform the Location function. Imagine dropping a dowel pin down two bores. One is half or even 1/3 as long as the other. Remember, we’re talking 1/2″ diameters in bores that are 3/4 to maybe 0.8″ deep. There’s a chamfer at the top and bottom so we have even less length available. Which bore is going to hold the pin more accurately vertical and in position?