Fixing a Jeweler’s Saw
© Brian Meek
V1.0, All Rights Reserved
Every jewelry studio has a few basic sawframes floating around, either rarely used deep throated saws, or orphans swept in with the tide. Once upon a time, these basic sawframes were made in Germany. Then production moved to areas of the far East. No matter where they were made, however, these generic sawframes always seem to share one fatal flaw: pot-metal thumbscrews used to clamp the sawblades. I’ve never understood why even the copies faithfully repeated that catastrophic flaw. As anyone who’s worked around a jewelry studio for any length of time knows, the potmetal screws never hold up. They fail in a variety of ways, the two most common being that the threads strip, or the thumbscrew portion simply shears off, leaving a dead sawframe with no way to clamp a blade. Over the years, I’ve seen a variety of different ways to fix the problem, from Lee Marshall’s custom machined ‘quick clamps’, (now discontinued, alas) to improvisations like soldering a brass washer into the slot of a matching screw, to create an impromptu thumbscrew. There are also ‘rebuild kits’ that will allow the sawless jeweler to replace his shredded potmetal thumbscrews with a brand new set of potmetal thumbscrews, just like the last ones, and a new set of clamps, for a mere $10 or so.
There is an easier way. The cost is a trip to the hardware store, and about $1. The result is a sawframe where the blade clamps are held by properly formed tempered steel screws that will be nearly impossible to strip or snap by hand.
A closeup of a stripped potmetal screw.
The procedure’s actually pretty simple. First, the clamps. If there’s a problem holding on to sawblades, it’s almost never the clamp pads. As long as they’re installed correctly, and there aren’t deep grooves on the inside surfaces, there’s not much to go wrong with them. If there are grooves on the inside faces, file the inside surface flat again. Problem solved. I’ve never seen a sawframe where the clamps needed to be replaced.
Those potmetal screws, on the other hand, just need to go. The way to do this is simple. Of all the ‘generic’ sawframes I’ve examined over the years, all but one had thumbscrews that were sized for 10-32 screws. (This is in the US. Elsewhere may be different.)
Various stripped potmetal screws, and the cap-screws and wingnuts to replace them.
Go to the hardware store. Buy two 1/2” long 10-32 socket head cap screws. (If you don’t know what any of this means, don’t worry, I’ll explain at the end.) Buy two 10-32 wing-nuts. Total cost should be under one dollar. If you have some small 10-32 screws laying around the shop, those will work too. Button head by preference. Whatever you use, make sure they’re decent quality, or the whole exercise will be moot.
Unscrew the thumbscrews from the sawframe. Screw your replacement screws into the threaded holes, starting on the outside of the wrong side of the sawframe. The idea is that instead of having a thumbscrew screwing into the sawframe, you have a new screw coming out. Thread the screw in as tightly as possible. A bit of threadlock wouldn’t hurt. Then put the blade clamp onto the screw, and put the washer from the original setup onto the screw after the clamp goes on, and screw on one of the wingnuts. Repeat this on the other clamp, and you’re done.
The cap screw threaded into the frame, and the wingnut and washer securing the clamp pad.
The clamp pad and washer were carried over from the original setup.
It’s just that simple. Now what happens is that the wingnuts replace the function of the thumbscrew, but they’re traveling on the hardened steel of your decent quality screws, rather than being potmetal disaster magnets. You may be wondering why we don’t thread a new steel thumbscrew into the saw, instead of doing a two-step like this. The answer is simple: if we just tried to use a new steel screw in the existing threaded holes in the sawframe, we’d be depending on the accuracy and quality of the threading job done by the original manufacturer, who has already proven themselves lacking in the quality department. Thus we do not trust or depend on them. No matter how bad a job of threading the original manufacturer did, it should hold up to threading in and locking a new steel screw just that once. After the screw is mounted, all the force and wear are applied to the new screw, which was purchased with quality in mind, rather than the uncertain quality of the threaded hole.
The sawframe with both thumbscrews replaced. Should take about 2 minutes.
A word about screws
If all that talk about 10-32 and cap screws sounded like Greek to you, here’s a quick explanation. In the US, screws are normally described by numbers referring to their diameter and number of threads per inch. With larger screws (above 1/4” diameter) the diameter is usually called out in fractions of an inch. With smaller screws, it’s usually a number. Smaller numbers are smaller screws. (It actually has to do with the screw’s diameter as described by an obscure wire gaging system, as I understand it.) For any practical purpose, they’re just number four, or number 10 screws, and they are the size they are. So a 4-40 screw would be a size four screw, with 40 teeth per inch, while the 10-32’s I’m talking about above are size 10 screws (and thus larger than the 4-40) with 32 teeth per inch. A fairly standard utility screw is ‘quarter twenty’, or 1/4-20. So the screw is 1/4” in diameter, with 20 threads per inch. Not all screws of a given size are the same. In the US, there are two systems, National Coarse, and National Fine. The National Fine pitch for a number 10 screw is 32 threads per inch (TPI) while the National Coarse pitch is 24 TPI, so it’s entirely possible to get a size 10 screw with 24 TPI instead of 32. It’ll look like it should fit, and it will, for about half a twist. Then it’ll bind up. Be aware of that complication. Both numbers matter.
There are other systems out there, most especially Metric. Standard Metric screws only have one pitch at any given size, so a 6mm screw, for example, will always have 1 thread per millimeter. That way you don’t have to spend time worrying about the various formats. The drawback is that the standard pitch is a compromise, and may not be optimal for any given application. For example: that one sawframe that I’ve seen that didn’t have 10-32 thumbscrews had 10-24 screws instead. They were still potmetal, but the extra thickness of the coarser threads meant that they were strong enough not to strip out the way the finer 32 TPI threads do on all the rest. That particular frame was a very old German one, and it’s survived all these years with its coarse thumbscrews intact, even though they’re potmetal. Having the ability to choose an appropriate thread-pitch is very useful. Being stuck with one ‘all purpose’ standard sometimes isn’t the best answer.
The easiest way to check a thread or hole is to get a couple of screws and nuts of known size and pitch, and see which one fits. There are thread gages, and various test plates for identifying mystery screws, but that rapidly becomes a very deep rabbit hole indeed.
When I spoke about socket cap screws and button heads, I was talking about the shape of the head of the screw. Socket cap screws are the ones you see in the pictures, with the sockets for hex wrenches. Those are standard machinist’s screws, and are usually of higher quality than generic hardware screws. Button head screws have a head that’s a smaller, low dome. These are available either in phillips head or socket cap head, to take either a phillips head screwdriver, or a hex wrench. The hex wrench version are harder to get, and the local hardware probably won’t have them, but they’re nicer to look at, and won’t stick out as far from the back of the sawframe. (Special order them from and industrial supplier, or specialty screw supplier.) Phillips head button-heads may well be available in the hardware store. Hex heads are preferred because it’s easier to crank them down tighter with the hex wrench than a phillips head screwdriver can manage without slipping. The size of the standard socket cap head won’t make any actual difference, using buttonheads just makes it look nice. My primary personal saw is done this way, and has been for 20 years. The backside of the screw hasn’t ever gotten in the way.