Scary sounds in the shop
I remember one of my instructors saying something intriguing when I was in college learning about woodworking and furniture making. He said to always listen to a power tool or machine.
It struck me as weird, as the noise coming from these sorts of tools is generally loud and obnoxious even at the best of times, and I wondered what I’d be listening for. Back when I was learning about the different woodworking power tools and machines I didn’t know the intricacies of the sounds that were produced by these tools and therefore didn’t know when the sounds were slightly off.
It makes perfect sense now that I’m much more familiar with all the different power tools and machines used to create joints in woodworking. Whether it’s a table saw, belt sander, thickness planer or any other power tool or machine in the shop, you eventually get used to the specific volume and pitch they make and can tell the difference between a cutting edge that’s breezing through the material, or one that’s struggling even a little bit to make the cut it’s being asked to do. Even a loud and whiny router at first seems just screechy no matter the situation, but after using one for long enough, and paying attention to the sound it makes, the user can tell a lot by the sound it’s making.
No mistaking this sound
The other day I was routing a total of four handle openings in two bins that would become recycling containers in a cabinet I was making. I used four plunge cuts in each corner of the rectangular-shaped handle opening to remove the material in the corners, then made three or four passes at ever-deepening depths to remove the waste and create the opening. I was working with 1/2″ thick Baltic birch, which isn’t overly dense, especially when compared to many solid hardwoods I regularly use.
Things went smoothly with the first three openings, but the last one went sideways for some reason. I don’t think I was getting complacent, though it’s possible. The first 12 plunge cuts went off without a hitch, but as soon as I got partway through the first plunge cut in the final opening the router and bit let out a heck of a noise that scared me. Thankfully. I didn’t react, as that could have made matters worse. I released the plunge lever and brought the bit out of the material to see what happened. Fortunately the damage was minimal and the opening could be salvaged, but I still wanted to know why it happened, mainly because I still had to machine three more plunge cuts, and wanted to learn a bit more about these tricky power tools we call routers.
The router bit was being guided by a guide bushing on the base plate of the router. The bushing ran on the walls of the template I had clamped to the workpiece. The router couldn’t have moved inward to allow the bit to cut deeper into the workpiece. The bit itself must have flexed enough to cut close to 1/8″ further into the workpiece than it should have. To me, that’s a surprising amount of flex, especially considering the shank didn’t break.
I was using a small plunge router with a 1/4″ collet. The router bit was a 1/2″ diameter straight bit. A 1/2″ shank would make for a much stronger router bit, but I was plunge cutting fairly slowly (or so I thought) to not stress the bit too much. It’s impossible to say for sure, but I think a few factors came together to cause the loud noise as the bit aggressively cut through the 1/2″ plywood. In hindsight, the plunge rate I used was likely slightly too fast, but that wouldn’t have been enough to cause the bit to dig in like it did. The fact that the cutting diameter of the bit was 1/2″ and the shank was 1/4″ was definitely a factor. Shanks that are 1/4″ are much weaker than their 1/2″ counterparts. The reason I reached for my 1/4″ router was because all my other plunge routers were set up to do a few dedicated operations and I didn’t want to change them. On top of these reasons, there’s a chance that my router moved slightly during this plunge cut and immediately had to bite off more material than I safely could. Looking at the tearout makes me think the router moved in a climb-cutting direction when it was nearly through the plunge cut, causing noise and tearout.
As is usually the case, it was likely a combination of things that came together to cause the loud noise and some excess tearout to occur. Thankfully the workpiece ended up with a small amount of tearout that was easily concealed and I was totally fine, short of a scare. The worst-case scenario would have been the bit breaking while rotating at 20,000 RPM and bouncing around and hitting me in the face, as my head was lowered to have a closer look at the cut I was making.
When I was making the plunge cuts, I don’t remember any sounds coming from the router that would indicate I was pushing things too far, but that’s not to say they didn’t happen. This sound was a loud and violent one with (likely) no warning, but other workshop sounds are a clue as to what might happen if you keep pushing a tool beyond its capabilities. Listen to your tools and show them the respect they deserve. Not only will you be less likely to damage your workpiece, but you’re much less likely to get hurt.
A quick note about ear protection, and how it helps the user focus on the task at hand. When I’m operating a power tool or machine that makes a lot of noise (router, thickness planer, etc.) I always wear hearing protection. This obviously protects my hearing, but it also does something else I feel is equally important. When I’m being blasted with a loud sound I find it hard to concentrate on the operation I’m doing, and therefore more likely to rush an operation or not pay close attention to what’s happening. Ear protection allows me to relax and focus on the operation, while still being able to hear the tool and pay attention to how hard it’s working.
Plunge Cuts First
Once I had the template made, I clamped it in place. A guide bushing on the base of the router positioned the bit at each corner of the opening and then I made a plunge cut. A jigsaw was then used to remove most of the waste before I returned to the router to trim the rest of the opening.
Although you can’t see the template opening or the workpiece, this is the setup I was working with. I used a bit with a 1/4" shank with a 1/2" cutting diameter to make this cut. I used an oversized plywood base plate, as that’s just simply how my router was already set up. The guide bushing was fixed securely to the plywood base plate.
Close inspection of the tearout reveals the bit might have lurched backwards during the plunge operation, causing the bit to quickly (and loudly) climb cut a small amount of material. Thankfully I didn’t get hurt and a small roundover bit removed most of the visible tearout so the client will never know.