Intro: 6 Tips for Cutting Curves on a Bandsaw
Cutting complex parts with tight curves safely and accurately on a bandsaw can be challenging, but is fairly easy with some practice, a properly tuned-up bandsaw, and a couple special tips and tricks... enjoy!
What you need:
- A bandsaw
- A thin blade (1/4" recommended)
- Drawing of your cut lines (printed if necessary)
- Supplies for transferring the drawings to your material (see step 2 for methods)
- The material you are cutting into parts (I was using 1" plywood)
Step 1: Tip 1 - Set Up Your Bandsaw
Tuning-up a bandsaw is a process that involves changing the blade properly, centering the blade on the crown of the wheels, setting the guides and thrust bearings, tensioning the blade, and squaring the table. The difference between a well set up bandsaw and a poorly tuned bandsaw is huge. The photo above shows two cuts - one is a relatively clean and smooth cut, one is irregular and burned - you can guess which one was tuned properly and which was not. Believe me - it is worth the time to go through this process!
This Instructable won't cover the tune-up, so I highly recommend watching How to set up a Band Saw video with master woodworker Michael C. Fortune (via Fine Woodworking Magazine) to see exactly how to do this.
Step 2: Tip 2 - How to Transfer Cut Lines on to Your Material....
If you are making up the shapes as you go, just draw directly onto your material with a pencil. If your shapes need to be accurate to your plans, you'll need to print them full scale and transfer them onto your material.
** For parts larger than 8.5x11, FedEx/Kinkos does black and white prints (up to 36" wide) for a very reasonable price.
There are several transfer methods to choose from:
1 - PENCIL / GRAPHITE TRANSFER
With a soft pencil, on the backside of the print out. Tape the print in place on the material and trace the lines with a ball point pen. The pressure from the metal pen tip will press the graphite from the pencil onto your material, leaving visible lines when you remove the print-out.
2 - SPRAY ADHESIVE
In a well ventilated area (spray booth or outside), flip the print-outs over and spray a thin coat of spray adhesive (sometimes called spray mount) onto the back of the paper. Wait about 10 seconds for the adhesive to tack, place the paper, and firmly press the back until it is stuck on. After cutting on the bandsaw, the paper should come off pretty easily. I recommend a mild adhesive for paper, as some of them are really strong. Also, don't breathe the over-spray... it is pretty nasty stuff!
3 - VINYL STICKER PRINT-OUT
If you are lucky enough to have access to a vinyl printer, this works great! I printed out the parts at Pier 9 on the Epson (up to 49" wide!), cut them into smaller sections to make it easier to apply, peel, stick, and you're ready to cut.
Step 3: TIP 3 - Cut Big Sheets Into Managable Sections
It can be really difficult to maneuver a large and/or heavy part on the bandsaw, especially if the bandsaw has a small bed or a narrow throat (the distance between the exposed blade and the vertical column of the body of the machine). Using a jigsaw, I cut the sheet into about 5 parts, considering the throat limitations of the saw in our shop, which has a 15" throat depth.
Step 4: Tip 4 - Relief Cuts for Tight Curves
This is one of the most helpful things you can do to prevent the blade from binding as you make a tight radius cut!
Make a straight cut up to the line in the waste part of your material, and back it straight out. Do this everywhere that looks like it could make the blade bind. Now as you cut down the line, the waste material will not get in the way and cause your blade to drift off the line. I would do this for any curve smaller than a 2" radius, the more, the better.
Step 5: Tip 5 - Cut on the Outside of Your Line
The thickness of the blade is roughly 1/16", called the blade "kerf". This is what the machine turns into sawdust. Ideally the kerf is removed from the waste material, not the part you are keeping. For more accurately cut parts, direct the blade to the waste material side of your line and try to preserve the line as you cut, rather than cutting on the line.
Step 6: Tip 6 - Always Move the Cut Forward As You Turn the Material
When cutting curves, never turn the material unless you are also pushing forward as you make the cut. If your cut is drifting badly off the line, turn the saw off, back your material out after the blade has stopped moving, and start the cut over. Don't try to overcompensate by twisting the blade - it is flexible and can break or be pulled off the wheels.... Good luck and happy cutting!