How to Machine a T-bolt

T-slotted tables can be found throughout the workshop, on a variety of machines. In this Instructable, I’ll talk through the general process of making a T-bolt, which can be used to secure parts to these tables. A T-bolt is an excellent beginner machinist project. It is relatively simple but is also a good opportunity to practice plain turning, screw cutting and milling operations. In the end, you have something you can use for future projects!

The one created here is roughly 150 x 10 mm and is used to clamp a rear tool post to a Myford cross slide. I’ve omitted dimensions from this tutorial because everyone’s applications are different so you’ll want to machine a bolt that’s the right size for you.

• Steel bar
• Lathe
• Milling machine
• Hacksaw
• Workbench vice
• Collet block, or a way of indexing by 180 degrees in the milling machine

To keep the steel supported initially, you’ll want to use a centre in the tailstock. A live centre is easy to use for roughing applications. Start by chucking a piece of steel, facing it off and centre drilling the end. The live centre can be replaced with a half-centre as the bolt approaches its final size to allow room for the tool.

The T-bolt has a lower flange, which slides into the widest part of the T-slot. An optional second flange can be added to the bolt to provide extra strength. Machine the bar to a smaller diameter for the second flange to make it easier to insert into the T-slot (optional).

Screw-cut the thread to ensure it is straight and accurate. The thread can be screw-cut undersized and finished with a die, or screw-cut directly to size. Using the combination of screw-cutting and a die will produce a straight thread of the right size relatively easily. Even a die mounted in a tailstock die holder won't be perfectly straight. Nevertheless, if your lathe cannot screw cut, using a die is an option. The bolt can then be removed from the chuck and the excess material can be sawn off. Face the bolt to length.

An easy way to mill the parallel flats on the flanges of the T-bolt is using an ER collet fitted into a square collet block, which is then put into the milling machine. Mill the lower flange first, flipping the collet block to mill the other side.

The T-bolt should be a slightly loose fit in the T-slot to ensure that the bolt doesn’t jam in the slot due to swarf or other debris. Of course, making the bolt too loose reduces its strength and contact area with the T-slot, so this is a compromise. In the video, you can see that I left a small amount of wiggle room.

And that's it! It's simple to make large or small, long or short bolts - the method is similar. Please have a look at the embedded video for more detail on the process. Thanks for reading.