Intro: Metal Cutting Saw From Wood
This saw can be built in a single evening, and if you have to buy EVERYTHING will cost around $80. My total cost was $28 for the sheet of plywood. Everything else I had on hand. I've used it to cut through 1.5" Aluminum Bar Stock, 1/4" 2x3 angle, and 1/8 2" Pipe. It will pretty much cut anything eventually. And it's automatic, just start the cut, and keep an eye on it to stop it when finished.
Tools You Need:
1. Wood Saw (I used a miter saw, and a table saw, but you could do the whole thing with just a hand saw.
2. Drill Press (You could make this without it, but it is WAY WAY easier to be precise with one).
3. Carpenter's Square
3. Basic Hand Tools
Materials you need:
1. A Reciprocating Saw. If you sign up for their coupons, you can get this one: http://www.harborfreight.com/6-amp-reciprocating-saw-with-rotating-handle-65570.html for $20. This one is what I used and is perfect because it's easy to mount once you take off the handle.
2. Some Plywood (3/4" although 1/2" will work).
3. A light dimmer switch (optional).
4. A wood working vice like this: http://store.cbtoolgroup.com/jorgensen-woodworking-vise--4-12-p4302.aspx?utm_medium=cse&utm_source=googlebase I used an 8" vice I had.
5. Some 1/4" 2" bolts with nuts and washers for attaching the vice.
6. 4' or so of 2x4.
8. Some zip ties.
9. Some heavy stuff for weight (I used an old motorcycle starter, and an adjustable pulley).
10. Some High Quality Large Hose Clamps (6" or more).
11. One 8" Or Longer 5/8" Bolt (with only the end threaded) or a 5/8" rod / shaft. (A 5/8" hardwood dowel will work too)..
Step 1: Remove "Extras" From Reciprocating Saw.
Most reciprocating saws have a lot of extra plastic and stuff that isn't structurally important. To make the finished product more compact, you can trim all this off. If you buy the harbor freight saw I recommend once you take the handle portion off, you are left with a nice compact little saw that is easy to mount.
Step 2: Make the Base and Top Cover
The next step is to make a base that is wide enough for your vice, and your reciprocating saw to sit side by side, separated by a 2x4, with a 2x4 on each end as well (see picture). You'll also want to make sure you put some extra space between the reciprocating saw and the boards on either side (3/8" is more then enough).
Cut yorr 2x4's so they are about 4" Longer then your reciprocating saw. Your base plate should be the same length.
Then, lay everything out as show below. Figure out how wide and long your base plate needs to be, and cut it out. (I used some high quality, ply wood (not osb) for this for higher accuracy, however, my first one used 1/2" OSB, and it worked ok too.)
Now, cut your Top Cover. It should be wide enough to cover the 2x4's on either side of the vice, but not the reciprocating saw.
Step 3: Trim 2x4's, Drill Holes, and Attach Vice to Top Cover
The vice and bolts that hold it will likely get in the way of the 2x4's on either side of it, you'll need to trim these to fit. For me, 1" was about perfect. Now, measure carefully and drill holes to attache the vice securely to the top cover. Then, set it aside.
Now, take one trimmed 2x4 and the full length 2x4 and drill 5/8" holes approx 1-1/2" from the bottom and back of the boards. I used a twist bit instead of a spade bit because the more precise the holes are, the more precise your saw will be, so measure twice, drill a pilot hole, and then drill carefully...
Step 4: Assemble the Base
Ok, quick lesson about glue. Wood glue is usually WAY stronger then nails or screws. Because of the reciprocating action, I suspect one of these put together with nails would eventually become very loose (and less accurate). So, go ahead and glue it. THEN put screws in as well. The screws are solely clamps to hold the pieces tightly together while the glue dries. When the glue is dry, it won't come apart without splitting the wood. To prevent splitting the wood, I drilled pilot holes, and counter sunk the screws on top. I used A LOT of screws because I wanted it to glue really well and be VERY strong.
Now put the top cover on, and glue and fasten with screws.
Step 5: Create Reciprocating Saw Hinge
To make this, I glued 3, 3 1/2" long 2x4 Pieces together, and then ran them through the table saw to get the perfect width, and to make sure they were square.. You should have something resembling a rectangular cube.
Then drill a 5/8" hole all the way through, approx 1" x 1" from the bottom and back of the 3 pieces.
Now, you are going to attach a temporary strip of wood (as in the picture below) to hold the saw. I used my prototype to cut a piece of 1/4" x 1-1/2" x 2/4" Channel which I used for the final version. This is very important, as the stiffer this piece is the more accurate your saw will be.
It is important that the hinge is STIFF. The reciprocating action looses a lot of it's effectiveness if the hinge has a lot of slop in it.
Step 6: Attach Saw, and Install Hinge.
Using the hose clamps, securley attach the saw to the strip of wood you attached to the hinge. Make sure the saw is fairly straight, so once installed the blade will be vertical.
Now put the hinge block in, and push the 5/8" bolt / dowel / rod through the hole in the outside 2x4, the hinge block, and the inside 2x4. It is ok if it's a tight fit, when the reciprocating saw is running, the vibrations will have no problem making it swing.
Step 7: Wire Light Dimmer
This tool will not work with the reciprocating saw at full speed. This will generate too much heat and the blades will burn up after a few cuts. So we need either a light dimmer, or some adjustable way to hold the trigger. While most large electric motors CANNOT be controlled with a dimmer switch, most power tools with variable speed can use a light dimmer (I opened up the trigger on my reciprocating saw and found a Triac just like a light dimmer uses). For my prototype I just put a zip tie around the trigger, and slowly tightened it until I got the speed I wanted.
Follow the instructions on the light dimmer, and just put the two wires that go to the reciprocating saw motor where the light would go.
Step 8: Making It Square
We need to get the thing square, what good is a saw if it can't cut square right? You'll want a brand new blade, or the strait-est used one you have.
First Horizontally: Remove the saw from the hinge, but leave the hinge in place. Put the square in the vice as shown below, and loosen the bolts on the vice. Move the vice around until things look perfect and then tighten the bolts again, you may need to remove the vice, and drill slightly larger holes to make it perfect.
Now vertically, re-install the saw and clamp the square in the vice as shown below. The vice has the two slider bars which you want the square to rest firmly against. Now, lift up slightly on the reciprocating saw blade (it is unplugged right?). This will remove the slop and show you the angle of the blade while it's cutting. So, now see if the blade is parallel to the square vertically. If not, loosen the hose clamps, and twist it a little till it is square. This takes some time, and when you tighten the hose clamps the saw will probably rotate just a hair, so you'll need to account for that. Take the extra time, and get this as perfect as possible. Trust me, it's worth the extra 5 minutes to get it perfect.
Step 9: First Cut - Slow Is the Name of the Game... Then Add Weight
Almost Done! Now you need to get something you can cut in half made of metal... Lift up the reciprocating saw, put the thing in the vice, let the reciprocating saw blade rest on it, and turn it on!! You really want it to go fairly slow. Top speed on the saw will smoke your blade in no time.
Once you have it going, experiment with adding weight. There are lots of ways to do this. On my prototype, I hung some odds and ends from a scrap piece of copper wire I had hooked to the end of the saw (not the blade, the saw), see video below.
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Later, I found a tapped hole on top of the saw, and made a dowel that screws in securely, I then stack small weights on the rod.
Step 10: Protect Your Awesome New Tool by Staining the Wood.
You want to protect your saw from all those nasty chemicals in your shop, so go get some stain and give it a few good coats. This will keep oil (which you will probably use when cutting steel) from damaging your awesome new tool.
Step 11: Tips for Better Results.
While the saw is running slow, you can move the blade with your fingers. If the cut doesn't quite look straight you can move the blade left or right and gently hold it there until it starts to take.
I found NOT using oil with aluminum cuts better. Otherwise the aluminum mixes with the oil and makes this paste that gets in the teeth and prevents it from doing any cutting. For steel, use some oil... Motor oil, Wd-40, whatever.