[DonnyBahama]

For all you DIY machine builders out there - I won’t be making this any time soon but I do hope to have a Sketchup model to post in the near future.

The simple explanation is this: Think of a scroll saw, then turn the arm 90 degrees counter-clockwise. Beef up the bow/blade arms and replace the scroll saw blade with a segment of a bandsaw blade. Change the movement mechanism from the bow/arm pivoting from a fixed point, to one that travels linearly up and down.

Hopefully that description is enough for you to imagine basically what I’m talking about. The bow in this design would be beefed up significantly, of course, and attached to a sturdy beam which would travel vertically between two heavy duty drawer glides. The glides would be heavily braced to prevent deflection in the X and Z axes.

The (vertical) distance between the two arms would determine the resaw capacity and the (X axis) length of the arms would determine the throat. The throat would have to be limited since the longer the blade arms are, the more it’s going to deflect. Depending on how deep the throat can be before deflection, this might be less useful for curved/freehand cuts and more of a resawing machine.

Of course, the blade would be just a section of a regular bandsaw blade so a single bandsaw blades would provide several blades for this machine. One big uncertainty is the impact of bidirectional movement/cutting on a bandsaw blade - but it seems likely that there’s no one out there who could speak to that so it would just take some testing.

Thoughts? Comments?

 

[Loren]

Look at walking beam saws for ideas.

 

[helpertoo]

My bandsaw has a 132" blade and a 9.5 HP engine (gas)

 

[Foghorn]

My bandsaw has a 132" blade and a 9.5 HP engine (gas)

Tim??

 

[Sylvain]

Do you mean something like the saw shown in this video from about 1'19" ?

 

[Sylvain]

Have also a look here:

New Frame Saw / Scroll Saw

www.bob-easton.com

Note that for a good visibility and to be able to use the full length of the blade, the upper blade holder should be longer than on Bob Easton version.

 

[Sylvain]

Or maybe you think about something like this

 

[DonnyBahama]

I guess I’m not describing it very well; none of those links look anything like what I’m thinking about. (Plus, they’re all manually and/or treadle powered. My design is meant to be electric.)

My design is much smaller. maybe twice as big as an electric scroll saw but not much bigger than that. Definitely smaller than a floor-standing bandsaw. And more or less similar in design to an electric scroll saw only the blade would be about 18” long and it would literally be a cutout section of a bandsaw blade.

Picture an “F” - there’s a vertical portion and 2 horizontal sections, right? My design would put one of those horizontal sections below the table and the other one above the table. Those 2 sections would be about 18” apart with a piece of a bandsaw blade between them. The whole thing - the whole “F” - will travel up and down. The drive mechanism - below the table - would have a linkage similar to what old locomotive train engines had, only instead of an arm driving the wheels, I’d have a wheel driving the arm — and the arm would be the vertical section of the “F” with the linkage (driven by an electric motor) attached to the bottom of the F to make it go up and down.

Hopefully that all makes sense. Maybe reread my first description combined with this one and see if it’s clear. I don’t think you’ll find a “You mean like this?” video because I’m pretty sure nothing like this has ever been done before. (Possibly because it just won’t work!)

 

[Phil32]

It sounds like the capacity of the saw would be limited by the dimensions of the "F."

 

[Lazyman]

Sounds like you are basically just making a scroll saw that can take larger blades. One challenge may be making it run fast enough. Band saws may run at 1000 fpm and a reciprocating saw approaching even half that speed is going to need to be pretty heavy and counter balanced to prevent it from walking across the room. Perhaps using 1/8 or maybe 1/4 inch BS blades will allow it to run at a much slower speed. That brings up another issue. Band saws work by clearing the saw dust out the bottom. The tooth geometry is designed to make that efficient and you pick TPI and gullet sizes based upon how thick your piece is. By reciprocating the blade, only a few of the bottom teeth may exit and clear dust. If the piece you are cutting is thicker than the stroke of the blade, (the TPI of the blade plays a role here too) it may not clear the sawdust effective and bog down. I suspect that the stroke of a typical scroll saw is about the same as the maximum thickness you can easily cut with one.

Just thinking out loud about reasons why this may not have been done before.

 

[Sylvain]

If properly designed, it should work.
An 18" blade means 9" max sawing height minus the table thickness.
As Lazyman said, counter weights will be needed.:
When the F frame goes up, another piece should travel down (same weight and speed?) (and vice versa) to keep the center of gravity of the whole assembly at the same level.
A simple rotating counter weight would induce horizontal vibrations.
The lateral movement of the (then two) connecting rods must also be balanced although if equal they should more or less cancel each other.

If I am right, on low speed vertical milling saws (hydro powered) the log was moved by a ratchet mechanism when the blade was coming down; I guess no pressure on the blade moving back up.

 

[DonnyBahama]

Cool! You guys are getting it now!

It sounds like the capacity of the saw would be limited by the dimensions of the "F."

Yep. But as I said in my first post, this might be more of a resawing machine than a bandsaw. (I’m good with my inverted jigsaw for cutting curves, etc.) I’m thinking I could put more space between the 2 horizontal pieces to increase the resawing capacity.

Sounds like you are basically just making a scroll saw that can take larger blades. One challenge may be making it run fast enough. Band saws may run at 1000 fpm and a reciprocating saw approaching even half that speed is going to need to be pretty heavy and counter balanced to prevent it from walking across the room. Perhaps using 1/8 or maybe 1/4 inch BS blades will allow it to run at a much slower speed.

Speed… OK, that’s interesting. But just because a bandsaw runs at that speed, does it really /need/ to run that fast? Could I resaw with this machine if I just fed the workpiece slower? And doesn’t the fact that this blade is reciprocating mean that it only needs to run at half the speed? I get that it’s only cutting on the down stroke, but what if I mounted a second blade right next to the first, oriented so it cuts on the upstroke? Sure, the kerf would be wider, but I could get away with lower speed, couldn’t I?

That brings up another issue. Band saws work by clearing the saw dust out the bottom. The tooth geometry is designed to make that efficient and you pick TPI and gullet sizes based upon how thick your piece is. By reciprocating the blade, only a few of the bottom teeth may exit and clear dust. If the piece you are cutting is thicker than the stroke of the blade, (the TPI of the blade plays a role here too) it may not clear the sawdust effective and bog down. I suspect that the stroke of a typical scroll saw is about the same as the maximum thickness you can easily cut with one.

Interesting. Couldn’t I just increase the size of the “mouth” (where the blade passes through the table? Or maybe have a slot (not too wide but wide enough) just behind the blade?

Just thinking out loud about reasons why this may not have been done before.

Exactly the kind of feedback I was hoping for. Thank you!

If properly designed, it should work.
An 18" blade means 9" max sawing height minus the table thickness.

Not necessarily… I don’t necessarily need that much travel. A scroll saw doesn’t have much travel at all. If I can get by with 4” of travel, or even 3, then 18” of blade would give me 13-14” of sawing height. And if I’m OK with only 12”, I could have 5” of travel. No idea how much travel this thing would actually need. It’s something I’d have to play with.

As Lazyman said, counter weights will be needed.:
When the F frame goes up, another piece should travel down (same weight and speed?) (and vice versa) to keep the center of gravity of the whole assembly at the same level.

That‘s an interesting point and I’m sure you’re right - that would be /optimal/ - but I’m not sure it’s essential. I don’t see why the arm can’t just pump vertically without a counterweight. It’s not going to be all that heavy. But even if it does need a counterweight, I should be able to integrate that into the drive mechanism.

A simple rotating counter weight would induce horizontal vibrations.

Wait, so you’re saying I /can’t/ fix it at the drive mechanism? If necessary, I should, at the least, be able to put in a secondary arm (under the table), weighted to match the primary arm, driven by the same mechanism but going up when the main arm goes down and vice versa. I can see where this might be necessary, if only to make the motor’s job a lot easier. Great input! Thank you!

 

[DonnyBahama]

Perhaps using 1/8 or maybe 1/4 inch BS blades will allow it to run at a much slower speed.

How would that impact my machine’s ability to resaw?

 

[Lazyman]

If the you are only getting half the FPM in the down stroke that a band saw achieves, it will only be able to cut half as fast at most. The tooth can only cut so deep as it travels through the wood so it requires a fast steady stream of teeth moving through the cut. Since the blade will only really cutting on the down stroke, I suspect that you won't be able to advance the wood by much during the upstroke which seems like would result in a frustratingly slow cut when cutting more than about an inch or two thick piece. Not to mention what affect the fact that band saw blades are not designed to run backwards. Also, I do not see how mounting 2 blades side by side in the kerf would work. I would think that the opposing teeth would prevent the ones facing the other way from cutting at all. Some scroll and jig saw blades have teeth that face in opposite directions but they are not side by side.

Interesting. Couldn’t I just increase the size of the “mouth” (where the blade passes through the table? Or maybe have a slot (not too wide but wide enough) just behind the blade?

The problem is not the mouth on the table. The issue is that the amount of wood that is removed with a band saw blade is dependent upon the size of the gullets. As the blade moves downward, the gullets collect the sawdust and carry it downward. On a band saw, if you use a high TPI blade which naturally have smaller gullets to resaw for example, it will limit how fast you can cut because the gullets fill up near the top of the cut and bogs down the blade. With a reciprocating action, any teeth where the gullets do not exit the bottom of the cut will fill up with sawdust in the first few strokes and never empty also bogging down the saw. If the blade only has say 3 or 4 inches of travel, that is probably about the maximum thickness you will be able to cut. That is my theory based upon what I have read about how band saw blades work, anyway.

 

[Sylvain]

There is no minimum blade-speed for sawing. Paul Sellers has made a (hand) bow saw with a section of bandsaw blade.
Two man saws to cut logs have teeth to cut in the two directions. But then you would have to file new teeth.

here is how I see it.
It is a quick and dirty principle drawing. The relative scale of the piece is to be adapted of course.
One could try without the counter weight first.

I am not sure it would be much smaller than a bandsaw.

 

[sunnybob]

I've tried very hard to understand what youre thinking of, and to be honest, I think youre trying to reinvent the bandsaw.
This is like those "crafty life hacks" that plague facebook, where somoene puts a huge amount of engineering skill and effort into turning odds and ends into a tool that does the same job as something you can buy over the counter.
If this is just a hobby to keep your brain active, I totally understand, but apart from the brain power and mechanical skills required to build this contraption, once finished, exactly how much more useful will it be over a small table top bandsaw?
I cant visualise what work this will do that a bandsaw cant?

 

[DonnyBahama]

There is no minimum blade-speed for sawing. Paul Sellers has made a (hand) bow saw with a section of bandsaw blade.

Yeah, but have you seen how fast Paul Sellers’ arm moves?!
Good point, though. Thanks for making it.

here is how I see it.
It is a quick and dirty principle drawing. The relative scale of the piece is to be adapted of course.

You’re on the right track but that’s not really how I’m envisioning it. I’ll post a Sketchup drawing as soon as I have the time.

I am not sure it would be much smaller than a bandsaw.

The way I’m envisioning it, it definitely would be smaller than a bandsaw but reducing the size isn’t really the point.

exactly how much more useful will it be over a small table top bandsaw?
I cant visualise what work this will do that a bandsaw cant?

The point isn’t making it smaller than a bandsaw or giving it functionality that a bandsaw doesn’t have. The point is affordability. I think it will be not only cheaper than a comparable (i.e. resaw capacity) bandsaw, I think it will even be cheaper than a DIY version of a comparable bandsaw. Also less of a pain in the butt to change the blade.

 

[sunnybob]

Unless you have free access to materials and a machine shop, I fail to see how that can work out cheaper than a small bandsaw from a big box company.
Very often people with ideas dont count the cost of the pieces, let alone the petrol and shipping costs of getting them to the workshop.
Seriously, have you costed this project? And have you found the price of a small bandsaw?

Bandsaw blade changing isnt a pain once youve worked out how the thing is supposed to work. I can change the blade on my 14" bandsaw in a couple of minutes, but I dont change the blade unless it breaks, which can be as long as a year if I dont mistreat it too much 😃 and I do everything from bandsaw boxes to ripping 8" high hardwoods, and cutting thin plastic.

 

[kaerlighedsbamsen]

So, if I understand You right, you are talkung about a smaller, tabletop sized version of this?

(fantastic place btw) Or this:

(with a saw blade instead of a file)

I am all in for new ideas and could easily see that being made into a functional machine. So I´ll say make one!

Probably its largest ability over a bandsaw being the ability to easily saw inside holes etc. And perhaps allso have the option for several blades at once, making resawing a breze?

Let us know how it goes

 

[Sylvain]

"Probably its largest ability over a bandsaw being the ability to [...] saw inside holes "
This seems THE good reason to make one if one doesn't want to glue back two halves of a piece.

interesting article: https://en.wikipedia.org/wiki/Reciprocating_saw