Blade Clamp for Black & Decker KS890E Scorpion Saw by merlin49152

Last crawled date: 3 years, 1 month ago

Hi guys;
I recently trashpicked a Black & Decker KS890E Scorpion Saw that had the same usual fault that these saws always seem to have - ie. the blade clamp was broken off. This seems to be a weak point in all reciprocating saws and is a particular problem with this model, with some users reporting that the blade clamp had sheared off after only relatively light work.
Replacement parts are available, but at a relatively high price - this particular part was listed at £12.99 (roughly $18 US), which is more money than I was prepared to spend on a trashpicked tool, so I set about designing a blade clamp that would be easy to print in one piece (for strength) and without supports (for ease of cleanup) and that would be safe a reliable in operation.
ATTACHMENT TO THE TOOL
As with the official part, this attaches to the reciprocating drive shaft with 2 bolts. I've designed this part to work with 20mm M3 bolts as they are the closest to the original that I was able to find here. The blade fits into a 1mm wide slot, shaped to accept the back of the blade and hold it securely. An M6 bolt passes through the mounting hole in the blade to hold it really securely and prevent it from falling out in use. An M6 hex nut fits into a recess on the other side of the clamp. As is usual with printed parts like this, the easiest way to fit the nut is to thread it onto the bolt and tighten it in order to pull it tight into the recess which should then hold it firmly in place, with the intention of allowing the blade to be changed without dismantling the saw.
PRINTING THE CLAMP
For best results, print supportless with the rear surface of the part on the print bed. As the clamp needs to be strong, I would recomment a relatively high amount of infill (I used 0.1mm layer height at 60% infill and it seems to be OK, but if it ever fails in use I may try increasing the infill but it seems to be very sturdy as it is)
I used PLA although ABS should work too (though in my experience, ABS tends to shrink a bit, making it less suitable for precision parts). This part is not subjected to high temperatures under normal workloads, although of course the blade will get hot in use and this may be enough to soften the material, though this has not been an issue for me yet as it doesn't get particularly heavy use in my shop - If you're using this sort of tool in a more heavy-use / commercial environment, then I'll wager that you're not using consumer-grade Black & Decker products anyway :)
If your printer is working nicely, the part should not require any cleaning up before fitting to the tool.
FITTING THE CLAMP

Press an M6 hex nut into the recess on one side of the clamp. The easiest way to do this is to push the M6 bolt into the clamp from the other
side and tighten so as to pull the nut tightly into the recess. You can then unscrew the bolt and the nut will stay firmly in place without the
need for glue.


Slide the clamp over the reciprocating shaft with the two small screw holes towards the front, and facing the top of the saw.


Use 2 M3 bolts to secure the clamp to the shaft - I've sized the holes on the part to be tight enough that an M3 bolt will self-tap a thread
into the part for a firm hold.


Push the back of the saw blade into the slot in the clamp until it hits the back stop. At this point the mounting hole in the saw blade will be
aligned with the M6 bolt hole.


Screw in the M6 bolt and tighten securely.

Reassemble the saw casing. If the M6 bolt you used has a suitably sized head, then you should be able to unscrew it via the oddly-shaped hole
in the side of the casing, in order to replace the saw blade without dismantling the tool.
SAFETY
The big question that many people will have is the most obvious one - Is it safe to hold a powered saw blade with a 3D-printed clamp? Well I guess that depends on the level of use and abuse that the tool gets subjected to, but consider that the clamp totally wraps around the reciprocating shaft, and the screws pass through two sections of the clamp and the shaft, and that the blade itself has a 6mm steel bolt passing through it, so it's pretty hard to imagine the blade breaking loose from the clamp (Less likely than in the original part design) and even if, in the worst-case scenario, the clamp totally shattered / snapped / melted etc, the whole thing is enclosed within the body of the saw so it would ne next to impossible for the blade or any part of the clamp to break loose and fly away from the tool.
If I didn't think that this part was safe to use, then I wouldn't be uploading it here (and certainly wouldn't be using it on my own saw), but as with all things, you use this at your own risk :)
CONCLUSION
When I first printed this part, I wasn't sure how well it would hold up in use, so I conducted a few tests before attempting to do any real work with it. First of all, I cut through a heavy-duty cardboard tube, of the kind that rolls of carpet come on. This had around 7mm thick walls and the saw cut it without any issues. Next up was an offcut of laminate flooring (8mm thick MDF) and again it cut perfectly well. The final test was a scrap of 18mm thick chipboard ("particle board" in the US), and again it went through like a dose of salts. After these tests, I dismantled the saw to check that everything was still rigid and undamaged and found that to be the case. Since then, I've cut through several lengths of 2x4 as well as laminated chipboard and sheets of 12mm plywood, again without any issues or loosening of the clamp or its mounting hardware. I've not tried cutting plastic or metal with it though, as I don't have the right blades for these materials, but with the correct blade fitted, I don't see any reason why it shouldn't work. At this point I became confident enough in the design to upload it here.