A Temporary Fix?

Recently, I blogged about learning to knurl reliably on my lathe (link). In that post, I mentioned that the first problem to solve was a stripped bolt - here's the photo again for reference:

This bolt controls and locks the rotation of part of the lathe called the "compound." It's not clear from that photo, but that's a very specific style of bolt called a T-bolt. It is used when you can't reach the head of the bolt when tightening the nut - the "T" shape keeps it from rotating. When I discovered the stripped bolt, I got the lathe going again by using a regular bolt, and holding it by the end of the thread with needle nose pliers as I tightened it. Then I ordered a replacement set of bolts (two required) from Little Machine Shop.

Sadly, the bolts they sent (on the right below) differed from the remaining original (left) in almost every detail. There are so many variants of my Chinese lathe, it's impossible to stock replacement parts for all of them.

Worse yet, now I have a project that needs my compound to rotate and lock reliably! So, I took that original bolt and tried to match it up locally, with zero success. Even Fastenal, the store that is all about odd fasteners, didn't have anything in stock.

I decided to make a "temporary" replacement to get my lathe back into service. I started with a likely piece of aluminum, and reduced the thickness of a bit of one end:

When done, I had some stock that exactly matched the bolt head in thickness.

Then I marked the stock for the width of the bolt head, clamped it in the un-vise, and cut it:

More cutting, milling, drilling and tapping, and I had two rectangular nuts the right size:

Since all the hardware on this lathe is metric, I kept to the plan and tapped them metric, 6 mm. I bought some 6 mm bolts and nuts from Home Depot, in metric class 8.8. Even a cursory look at the bolt aisle at Depot or Lowes will teach you that the cheap bolts are ungraded, and the American bolts can be had in Grade 5 or 8 also. Grade 5 is good, grade 8 is used on airplanes and high-stress applications. Metric 8.8 is equivalent to our grade 5, which makes it much better than the original T-bolt. That one was grade CCJ ("Cheap Chinese Junk").

I cut the heads off the bolts, and affixed the threaded remainder permanently with Loctite Red. A little time on the belt sander to round the corners, and I had two reasonable copies of the original:

It all seems to work fine. Easy to adjust, and positive to lock:

So, we'll see if this is really "temporary." I may be dead of extreme old age before I feel the need to replace those again!