Need technical advice: building electrical frame-saw (3 blades)

[Bart van Weperen]

Hello to you all!

I’m in the process of making a “frame-saw”, a frame holding multiple saw-blades (3). I have managed to make a “hand opperated” version and it does work, verry slow but: it does do the job.

Now I want to make this saw power driven (electrical).
I’ve made a fixture for the frame, allowing it only to move up and down. (It’ll only saw going down)
I’ve measured the maximal movement of the frame (29 centimeters between highest and lowes point), I want to connect the upper part of the framesaw to a 30 cm diameter wheel using a piece of steel so that the frame will move 29 cm in all at each turn of that wheel.
I know that now I need an extra wheel (on one and the same axis -???-) so a “driving belt” can set the framesaw in motion.

Thus far no problems I couldn’t handle. Now to the part I realy know nothing about. I have an old electric motor but that has 8500 rpm: way toooo fast for this job. I’m thinking of having the frame move up and down no more than 50 times a minute. (I want to saw the wood, not burn it!)

Would it be possible to make some kind of gearbox for that motor so that it results in having a “drive-wheel” going at about 50 rpm? Or would it be possible to control the motors rpm by controlling the amount of power going into the motor, maybe using a kind of switch also used for controlling the brightness of lamps/ lightbulbs?
Or would it be better if I started looking for a different motor (less rpm’s)?
(As a last resort I could also use a bike, connected to the drive-wheel If only my wife would be willing to operate that….)

Thanks for all help on this, in advance!

 

(Since there's only room for 3 pics here, I'll post more in my own reply)

[Bart van Weperen]

more pics, as promissed....

[Bart van Weperen]

and even more pics!

[Mike Kolb]

Interesting set-up... although I'm trying to guess what a fellow could do with it?  There must be a good purpose for it's construction, but it's too early on a Sunday morning to think that hard.

Love the creativity, so what's the job will it be doing for you?

[Pierre-Antoine Roiron]

Considering that the motor is only 240W (did I misread?), some kind of gearbox really is needed to get enough torque to drive the 3 blades. You'll have to make some tries to get the right speed/torque. I'm sure you can get a gearbox from an industrial standard parts supplier, the same kind of people selling pulleys, belts,...

I have a doubt that the 6 little wheels can stand the feed force, leading to a big axial load and some canting. Maybe you should use 2 steel shafts and some sliding bronze sleeves or linear bearings instead. Both are available from the same suppliers you can buy your pulleys from. Or maybe I'm over evaluating the feed force.

[Bart van Weperen]

Thanks for the responses Mike and Pierre-Antoine!

The purpose of this saw is evident: it’s needed for sawing....
I have several planks ( 2,5 x 18 x 65 cm) and I want to use these as back- and sideboards, maybe also tops (my avatar shows a soundbox made from some of those planks, Fagus sylvatica L., family: Fagaceae common name: Beech)

The problem (my problem) is that I don’t have the means to re-saw these planks into thinner “slices”. A bandsaw that can do this job is far too expensive same as a circular-saw (and I’d also like going through life with my 10 fingers!).

In the past I had a factory re-saw some planks, but all they were willing to do was cut a plank in half and then thin them down to 3 mm. Meaning that 19 mm of good wood goes to waste. (In fact, none of the 20 or so woodsawing factories I contacted were willing/ able to saw one of my planks into more than 2 slices...)

So I started thinking... how do they saw a tree into planks? I found my answer by looking at pictures of (old) sawing mills (the wind powered ones, since we still have some of them here in Holland) They use big frame-saws. I try to “miniaturise” this, hoping I could double the quantity of usable material...
Constructing “the saw “ as such was easy and as shown on pic “zaag_werkt.jpg” it works. Disadvantage is that it takes a long time and a lot of sweat and thats why I would like for this saw to be power-driven.

And shouldn’t it turn out to be usable for sawing wood, then -dear Mike- I’d still end up with a verry elaborate cheese/ egg/ tomato cutter...

The setup shown in the pics is V.2 In V1 I used 2 steel shafts as descibed by Pierre-Antoine. I must have done something wrong becourse it had to much friction and thats why I choose the wheels. There still is room for more wheels on the back of the frame, and if needed even on the front...

Should I manage to get the saw running at say 50 motions per minute, then I still can prevent left-right movement by using 2 “drive wheels” (installed to the left and right “leg” of the frame) instead of only 1 (in the middle).

But: how to get this motor to drive the saw at a reasonable ratio???
From Pierre-Antoine’s reply I understant that the motor at hand maybe can do the job, if only I get the gears right... I keep on trying, and if I see, you’ll see!

Bart

[Pierre-Antoine Roiron]

I don't know if the motor can do it, you'll have to try. But if you want to try, decreasing the speed (increasing the torque) is a good start, using a gearbox which can be found as a standard at industrial suppliers. Decreasing the speed by, say, 200 using a screw/wheel system would be a good start : torque increased by 200 (minus friction) and speed around 40 strokes/min. I've seen that kind of machine in metal working shops, they run at 40/80 strokes/min.

I'm not an electrician, so you'll ave to get some man-of-the-art to figure out how to change the motor's speed. The way to do it depends on the motor's type.

[FRANK]

witch way to Carnegie Haul? Practice Man Practice, its a cool thingy mobobber you made there

[William F.Eden]

I think I would just keep looking for a friend with a bandsaw resaw.   But with all the equipment that our good freind Frank has  up there Iam sure he could cut them for you.Bill................

[Ned Knepp]

Something that strike's me is the frame looks way too long for the stroke length you will have. You will have a maximum stroke length of just under half the open blade length but the supporting frame is two or three times the length of the blades. I think it would be more stable if you shortened that to just over what you actually need. 

 

[Bart van Weperen]

-------- Update report ---------

Thanks to everyone advising me here!

Dear William, your idea/ advice is sound as such, but:… Any idea how much time (and money) it would take to ship “my wood” to Frank Ford??? Remember: I’m not living in one of the “Holland”’s in the USA or Canada, “my” Holland/ the Netherlands is that pinpoint on the globe, just right from the UK, and to the left of Germany…

Ned, I’ve had that same thought about the length of the frame. After some hard thinking I’m pretty sure I need this hight (???) and maybe should go even higher in order to install the motor. Thanks for the warning though!

Today I finished construcing this “saw” (Yes: pics will be posted) so now I “only” have to mount the motor…
When turning the drive-wheel by hand, it takes some power to get the frame going up, but down doesn’t take any power at all. Have to wait and see what will happen when I’m actiually sawing. Gravity will be my friend, I hope…

Modifications by now:
First I had a 7 cm wheel bolted to the 32 cm “drive wheel”, the weels moved, but far too fast. Now I’m using a 20 cm wheel attached to the 32 cm wheel and this is moving at a far better pace.
Also I use a dimmer-switch to further controll the speed… I’m not sure but I expect this to negatively influence the power of the motor and that could be a problem.

Tomorrow I’ll continue, I hope.