Upside - down saber saw?

Look up walking beam saw - though building a bandsaw (or modifying the one you have to cut steel - mostly a speed issue and the correct blades) might be as easy, and would cut faster (but it's harder to pierce with.) If you don't need maximum throat depth, bandsaws get much easier, as you can bolt two wheels to a post, rather than trying to build a rigid C frame (much like a jumbo shrimp or military intelligence.)

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Interesting!

I guess they got replaced by the band saw.

Still looking for a 'worm transmission' after all these years.

Heh!

Thanks!

--Winston

You need a workpiece holddown. Howzbout a rubber inline skate wheel on a stick, held from above, parallel with the blade direction?

Prolly holddown. The machine tends to vibrate and it's passed off into the workpiece, plus the effects of the blade cutting.

Oh, GAWD, I'm glad I dumped my DISH contract! I watched one of the little videos they had and instantly remembered.

Will a dust/swarf-collecting vac help?

With a holddown/guide, eh?

Use a wire instead of a guide. Tension the upper end like a coping saw or scrollsaw.

Try a jackshaft - it's a lot more obtanium (and adjustable) way to slow things down for the home shop budget.

But McMaster will set you right up if you like - try "speed reducer" - $300-500, with a few outliers above that range. The right angle kind are worm gears. Page 1014-1015

Or these days, a VFD - you might easily get a 1-phase-in 3-phase-out VFD and 3-phase motor for less than a speed reducer, and have variable rather than fixed speed available. Just depends on how you care to go at the problem (and whether you have 3-phase handy, so you could just use a

3-in, 3-out version.)

"Ecnerwal" wrote ........

That's how I did it.

The wheels hang below the straight ladder frame, giving 13" of throat. The drive wheel axle mounting block with tracking screws is partly visible at the bottom. The sliding wheel is mounted in a U shaped frame that fits loosely within the side rails. Bolts through the frame take up the slack and adjust tracking. I had planned to mill down the axle mounting blocks as needed to remove twist but the welding came out good enough.

jsw

Nuh uh. Read on. De blade be floppy and binds in de cut.

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Floppy blade. The workpiece resisted all attempts to seat on the table, despite a considerable amount of clamping pressure provided by yours truly.

"It came back to me like the hot kiss on the end of a wet fist." Thank you Firesign Theatre

Some. Not enough, though. One chip trapped between the blade and the bearing and it is 'bye bye guide', I conjecture.

Yup. The guide bearings damp the wobbly oscillation of the end of the blade. The foot shown would have been quite inadequate to resist the 'workpiece hop' I saw, sans blade guides.

Food for thought.

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All mounted under the table? I wonder how they approached the 'blade wobble' issue on the saber saw.

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I find that my saber saw is about as much 'work' to use as is a plain hack saw, for steel. :) Nice cuts, though.

--Winston

Beauty!

--Winston

Picky bastid, aintcha?

Buy better blades?

Betty Jo Bialosky was a real knockout!

Prolly so.

Yup.

Nup. These were top-o-the-line Bosch blades in a nice Bosch saber saw.

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Heck I'd rather put a worm transmission on my existing saw then build a 12/18/24 TPI version of this delicious thing:

--Winston

That surprises the heck out of me.

Spiffylicious!

-- In the depth of winter, I finally learned that within me there lay an invincible summer. -- Albert Camus

Me too, since the same blade cuts through steel really nicely when the workpiece is clamped in a bench vise and the saw is guided by hand.

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Indeed.

--Winston

Are you absolutely sure it's not caused by vibration of the workpiece? If the piece is hopping, it could -induce- a waggle, oui?

-- In the depth of winter, I finally learned that within me there lay an invincible summer. -- Albert Camus

I haven't seen any high speed video, but you are probably right.

Probably the first stroke of the blade goes well then *any* contact of the blade to the workpiece on the return stroke induces movement in the handheld workpiece, which causes the largely undamped blade to 'violin', side to side.

Once this lateral oscillation of the blade starts, cutting just about ceases as the workpiece gets trapped by the displacement caused by the resonant standing wave in the blade. (It doesn't really matter if it is fundamental or harmonic resonance. A dynamically floppy blade is effectively wider than the kerf at most points along it's length.)

At that point, the workpiece spends much of it's time riding the blade.

So the guides dampen the oscillation of the blade at it's resonant frequency. The blade remains 'straight enough' laterally and therefore does not trap the workpiece.

The blade probably still oscillates laterally when it cuts a clamped workpiece and the saw is hand held. It does not approach resonance because the base pressure of the saw against the clamping device (vise, workbench) prevents the workpiece relative movement that causes blade lateral resonance.

A first - order test would be to clamp a workpiece in a vise and attempt to cut it with much less base force than usual. I suspect that the lowered mass coupling would cause the blade to enter resonance at some FPM and pressure settings, resulting in a bouncy ride for the user. BTDT (Queue SFX: "trombone gobble")

That is my story and I'm sticking to it.

My take-away: What if you made a 'virtual' top guide, immune to swarf? Several displacement sensors and electromagnets dynamically phase - cancel lateral acceleration of the blade, straightening it in real time.

--Winston

Question: Why would it be so bad upside down when it isn't right-side up? Could it be the addition of the table thickness? Pull the shoe and mount the beast to the new, thin table. Let me know how it works.

Ayup. I've felt that with the recip saw many times. The 12" blades are the worst.

OOH, fun, Daddy!

Drill the tip of the blade, run a guitar wire through it, and support it at the top. It should end your troubles. Use the beaded end on top so you can drop a holey piece on it for further cutting.

"base force"? Or run a ball bearing holddown right next to the blade, springloaded at the top. But if it's a positional resonance, that prolly wouldn't help. The original shoe is probably tuned to the zero point of some wave already, probably at midspeed on a variable.

All the way to the San Josie Sanitarium, eh?

Quick, cheap, and easy. You'll have it done in half an hour, wot? Hurry, the patent office closes at 4 on Fridays.

-- In the depth of winter, I finally learned that within me there lay an invincible summer. -- Albert Camus

I don't know what's going on here: maybe 15 years ago I mounted my sabre saw upside down under a table and it works fine. Yeah, I have to be careful about it grabbing, but it's not a big deal to hold the work tight against the table.

The saw & blade are nothing special: a 30 year old Craftsman saw and a no-name blade.

Just another case of mileages varying, I guess.

Bob

I dunno about the lateral blade flop you mention. Maybe you're using long blades?

When I had a bunch of rosettes [1] to cut out of sheet metal (I forget the ga., but way less than 16 ga. 24 ga. maybe?) I mounted my sabre saw shoe-up under a hobby-grade router table. Made a 16 ga. plug for the round router-bit opening with a slot to allow the blade to pass through.

Then made an angle-iron bridge across the table to which I attached a thing very like a sewing machine presser foot. The presser foot could be adjusted for work thickness so's to make a very light friction fit when the stock slid under it.

The vibration was a bit hard on the fingers but I cut out the rosettes without readjusting the foot more than once or twice.

[1] Rosettes at the center of the roses here: