Carriage Lock

Carriage Lock Designs

Personal Experience

After getting comfortable with the basics of turning on the lathe, I wanted to start getting serious about precision. Well, in my world getting serious about precision meant actually measuring what I was doing and trying to hit a target number reasonably close. I’d try for .001″ match, sometimes hitting it but usually getting within  +/-.005″, which still wasn’t too horrible. But as I started working on accuracy and precision, I started running into some serious issues when trying certain operations.

During facing, I’d get domed or concave surfaces. Sometimes the tool would just dig in and stall out the machine on a seemingly light cut (.001-.010″). After doing some research and reading a few things it sounded like I needed a carriage lock. Up until this time I was using the leadscrew engagement as a lock for the carriage. While I had read this was fine and dandy, it wasn’t until I experienced these problems that I actually looked at the play that was still happening on the carriage. I grabbed the carriage and moved it around with the lead screw locked. I was amazed I could still move it in several directions, sometimes up to 1/4″! Now that explains the dig in and doming I was having. If the tool started to dig in with enough force, it could just lift the saddle up and pull the tool far enough into the work to stall it, or going the other way it could push the tool out enough if the cutting pressure was high so that my facing cut could be .020″ different in the center than the edge.

This was very frustrating and after doing some research I learned of all the things that contributed to this problem.

1.) Saddle plates – These were sloppy. This is where the majority of the play came from. They’re tricky to adjust properly as it involved taking the saddle off the ways to get good access to the adjusting screws. Also the plates themselves are rough and a bit uneven.

2.) Gib Adjustment – The compound and cross slide gibs had loosened a bit since my initial tune up, and their slops combined added up to almost as much as the Saddle plate slop.

After tweaking these 2 items, the play was reduced dramatically. However, there was still noticeable movement on the carriage no matter how much I fiddled with the plates and gibs. After doing some more research, it sounded like a carriage lock was exactly what I was looking for.

Doing a search for a Carriage lock lead to an array of possibilities. Buying one was an option: had one for sale here. But after doing some more research, it looked like lots of people had come up with various carriage locks and made them themselves. This sounded like a good project to work on as a starter project. Here are some of the design’s I looked at:

After reading these sites and several others, I opted to roll my own version of the center locking type (gadgetbuilder’s). The reasons were:

  1. Two points of contact with the saddle, which would help limit rocking
  2. No modification to the lathe itself. I could use the existing follow rest holes for the mounting point.
  3. Simple parts, 1 custom top bar, 1 custom T nut to fit into the slot in the ways, and 1 screw/washer.

Lesson’s learned while creating the carriage lock:

  1. Pay attention to corners with a radius when measuring. The H in the saddle had pretty large radius’d corners. My initial measurements were between the edge of the gap, not the back where the radius was. This caused me to have to go back to the mill a few times to refit the T bar across the follow rest holes.
  2. If you’re using existing holes, measure their depth. When machining the top T Bar, I milled out a counter sink for the socket head cap screws. I wanted to use the existing screws from my follow rest. What I found however was that I had milled the sink too deep, and the screws bottomed out before tightening the T bar down. I ended up solving this with two washers stacked in the counter sink under the SHC. It would have been much better to just adjust the measurements from the start.

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