Intro: Precision Measurement With Solder
I purchased an inexpensive vise to use as a milling attachment for my mini- lathe and as expected, it was quite rough. To improve performance I began to fettle all surfaces, especially the sliding ones and found a need to measure a recess between the sliding jaw and it's keeper strip that rode along the vise bottom on machined ways. Shimming this area for a slip fit would be most beneficial when clamping up stock, otherwise the moveable jaw would possibly ride up and away from the work, giving poor results. The following is how I dealt with the issue.
Tools needed were very simple: a file and some round solder, although a solid core would work just as well as a fluxed. Also used was a dial veneer but a micrometer, or even a simple caliper would do the job of measurement. Should the diameter needed exceed that on hand, I would have twisted several lengths together to form what was required, but the size I had worked fine.
Upending the vise gives access to the aforementioned keeper strip that does two things: it prevents the moveable jaw from falling away, and, with the right amount of clearance, it keeps the jaw parallel with the stationary one. As received, it was a very sloppy fit with the jaw's bottom being well down and away from being true with the way surfaces, shimming would be the answer, but how much?
Cutting a short length of the round solder, I unscrewed the keeper, placed the solder on the jaw bottom and re-screwed the strip back in place, tightening until it was snug against the ways. Now properly called a “lead”, it will tell me all I need to know. As part of the fettling process, I hand ground the contact side of the keeper strip to assure intimate contact with the ways.
Removing the lead, I measured it's new thickness and looked through my drawer of steel washers for a pair of suitable thickness to give me just the right amount of slip. Luckily, I had two that were perfect for the job, and no grinding down or stacking up was needed, a very fortuitous find. I simply placed them on the jaw bottom and screwed on the keeper strip, job done.
Step 5: Final Inspection
Testing with a round steel rod confirmed that my efforts were fruitful; the jaws remained in parallel and undistorted under load.
Step 6: Parting Thoughts
The use of solder, or “leads” is an old machinist trick for making just such a job as this both precise and easy. In the Navy we would use this method for measuring shaft bearing wear on machinery that would otherwise be impossible to gauge accurately on round as well as flat surfaces, so it's one for the workshop notebook.