Tuesday, November 24, 2020

Jigsaw Blade Clamp Repair (U-Shank to T-Shank Conversion)

Jigsaw blades are available in two major styles: U-shank and T-shank.  Unfortunately, I was unaware of this fact when I bought my first jigsaw at a garage sale for $5.  I mistakenly bought a package of T-shank blades for it when it really took U-shank.

Not wanting to admit that I wasted $12 on the wrong blades for a $5 jigsaw, I decided to use them anyways because the package said, "Fits all jigsaws".  The blades did not fit properly and would slip out during use.  I still insisted they were supposed to work, so I tightened the blade clamp harder... too hard it seemed, since I'd cracked it right down the middle.

To better illustrate the problem, here are some poorly drawn diagrams:

Simply put, those blades did not fit all jigsaws.  The U-shank, shown in blue, would've fit perfectly in the slot.  The roll pin going all the way though both sides of the blade clamp should've been a dead giveaway that this was the style to buy, since it would key right into the cutout in the end of the shank.  The T-shank style is narrower for the most part, but has the same width as the U-shank at its "T", giving the illusion that they were interchangeable.  The other giveaway was that when inserting the T-shank into the clamp, the roll pin was in the way.  I had to pull it out slightly to fit the shank in, and even then, the shank didn't go all the way in, the "T" portion barely hanging on the edge.  (The roll pin served 2 purposes: to key in the U-shank, and to hold the blade clamp onto the end of the jigsaw's arbor).  All this being said, how was I supposed to know any of this prior to just buying a blade and trying it? The jigsaw itself had no indication of what style of blade it accepted, and really..... okay maybe I'm trying too hard to cover up the fact that I was just too excited to use the jigsaw that I didn't bother doing any research prior to purchasing the blades.  My solution to all this madness was to create a new blade clamp that would key in the T-shank style.  

Here is a photo of the jigsaw with the clamp removed:

Here's another illustration showing the original U-shank vs. what I had in mind for holding the T-shank.  This posed two major design challenges:  Firstly, it's a part with a rectangular bore through the middle.  By itself, this wouldn't have been a problem since I could've just drilled a hole and filed it square.  The real trick here was that it's a rectangular bore - with rectangular features on the inside wall.  Using conventional machining techniques, this would seem nearly impossible, that is if I was to make it out of one piece (sinker EDM comes to mind when calling for this kind of feature, otherwise some combination of broaches which I also don't have).  There was also the idea of filing the rectangular bore, and then inserting small screws through the side with the ends filed most of the way down to create the rectangular features, but don't tell anybody I realized this when I was already 90% done.

I decided my best bet was to machine the blade clamp from two pieces, and weld them together.  Here are the blueprints I came up with:

Here are those two pieces after machining, prior to welding.  I had to use some small endmills (1/8" and 3/16") to make those features.

This is how they fit together. Note the size comparison with the original blade clamp.  Mine had to be bigger to fit the longer T-shank style, but also thicker because I wanted more thread so it wouldn't strip or crack like last time.

After welding, the final step was to drill and tap the screw hole, and drill the roll pin hole.  Since I'm not using the roll pin to key the blade shank, I only needed this hole to go through one side of the blade clamp (for holding onto the jigsaw arbor).  I threaded the hole for an M6 set screw.  This would be stronger than the original M4 socket head, but also allow me to utilize the same 3mm hex wrench that the jigsaw came holstered with.

All done and ready to go!  Note the purplish color from the welding heat.  At the same time, I also tried salvaging the original blade clamp by welding it back together, but the part was so thin, that the whole side just melted off.  I decided to scrap it.

Be on the lookout to see the blade clamp in action at the end of my new vise repair video!

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