In the process of grinding the jaws on my lathe, I tightened down one of the compound bolts…but it never got tight. Hmm. I looked at it carefully and noticed the nut and stud were both turning. Not good. I disassembled the compound and found one of the T bolts had broken. I pulled the bolts out and found one had sheared apart. It turns out that this wasn’t an original bolt. Someone had made it by welding a stud to a small plate.
As you can imagine, I need a replacement T bolt and you can’t just pick up a replacement part. Luckily, Gill offered the use of his lovely Monarch 10EE to make a new one. I ordered some 1″ 1144 steel to make the bolt and headed down to his house once the steel had arrived. I cut off a piece to use and mounted it to the lathe to being work which first involved facing the piece.
The T bolt uses a 7/16″ – 14 tpi thread. To cut the thread on the new bolt the diameter of the piece was brought down to the major diameter of the thread. behind the section to be threaded, the bolt was brought down to the minor diameter so that the tool would have a place to stop after making a pass to cut the threads. Without this area, the cutter would cut a V shaped groove into the part when the carriage stopped moving.
Cutting the threads required making several passes advancing the compound each time. After demoing how it worked, Gill turned the threading operation over to me. After a small error at the beginning of the first pass, cutting the threads went well. In the picture below you can see the results of the threading operation. In this pic, I’m about to reduce the diameter of the T, which explains the cutter.
Once I was happy with the part, it was parted off and rechucked to clean up the opposite side of the T bolt.
Here’s a pic of the new bolt fresh off the lathe compared to the original T bolt. The original T bolt has a kidney bean shaped head. So, there’s a little more work to do.
To shape the head, I painted the bottom of the bolt, held both bolts back to back, and scribed the correct shape on my new bolt. I set to work using a file to shape the bolt after putting it in my vise with Aluminum jaws in place. I used couple coarse files to remove most of the material and then finished the edges with some smooth files.
Here’s the final part compared to the original.
With the new bolt in place, it’s time to make chips again. I’ve added a green arrow to show where the bolt goes. They’re loosened and tightened to rotate the compound.
Making the T bolt I learned a couple things. First, 1144 steel machines very nicely on Gill’s lathe with carbide and on mine with HSS. I even got a good surface finish with a regular cutting tool profile. Second, you have to be quick when threading. Threading involves the carriage moving pretty quickly. When the tool exits the area you’re threading you’ve got to disengage the carriage feed before the tool hit the work piece. Third, quick change tool posts are wonderful. Being able to just drop the tool in place and go without setting the height is great. Finally, Gill’s lathe is very nice. Well, that last one was just reaffirmed.