Making Hardened Steel Blade Guides Homemade Machines & Jigs
It’s been two years since finishing my band saw, and although I have used it over that time, I believe it really should be used more often. Having a dedicated resaw band saw is a luxury, especially in a smaller workshop, and somewhat wasteful.
So, to make the saw more suitable for general use, I bought a new 3/8″ blade:
The problem with using a narrower blade is that the plastic blade guide blocks don’t work well, since there is not enough flat area behind the teeth. The UHMW plastic guides are perfect for the 3/4″ blade that was on the saw, but would wear out very quickly with the 3/8″ blade.
To solve this, I decided that I would make new blade guide blocks for the saw. The first thing that came to mind were sealed bearings, but I didn’t have enough of the size I would need to get it done. I would have to order new ones, and wait for them to come.
Before ordering the new bearings, I looked at other options: I briefly considered oil soaked hardwood, such as hard maple. Matthias Wandel has had excellent results with his.
I also thought about using sintered bronze, cut from a shaft bushing. I discarded this idea, figuring it would be too difficult to mount the pieces in the guides as they are. The idea was to do a temporary mounting of the new guide blocks to try out, then redo the upper and lower blade guides to accommodate the most suitable candidate.
Then I thought about steel guides, like the ones that came with my smaller band saw. I did some research online, and found that hardened steel guides are not as bad as most assume they are, and are actually perfectly acceptable.
Looking at the majority of lower cost to mid cost retail band saws, most have steel guide blocks.
Figuring it was worth a try, I looked around for some suitable steel. I found a long 3/8″ steel drill bit (shown in the picture above) that I’d had for a few years. Drill bits, even lower cost ones, are made from high carbon steel and can be heat treated.
Steel with a low carbon content (such as mild steel) cannot be hardened with the method described below. It does not have enough carbon. Mild steel can be ‘case hardened’, where the outer layer of the part is enriched with carbon. There is a fairly widespread misconception that quenching in used motor oil will do this. If any carbon is absorbed, it’s not nearly enough to increase the hardness of the part.
I had removed the table corner to take the old blade off, so starting with the lower guide made sense. I’ve removed the UHMW blocks to make way for the new steel ones:
To cut the drill bit off as square as possible, I drilled a hole through a piece of wood and used that to guide my cutting disk.
A clean cut:
I discarded the end of the bit, as it was chewed up from chucking in the drill. The four pieces that came after are 1″ long.
I also kept the drilling end of the bit and used it like a regular one.
To completely flatten the ends, I put each in the drill and spun it against a strip of sanding belt:
The ‘business’ ends. Smoother is better to reduce friction against the blade.
Holding it out in the open and using a ‘map’ gas torch, I could not get it hot enough to harden. The steel is too thick and the heat source to small:
To concentrate the heat, I built a ‘furnace’ from fire brick. I stood the guide block up inside and lambasted it with the torch:
Eventually it reached the correct temperature (turns from bright red to bright orange / yellow) and I tipped the bricks to roll it out into the oil:
A test to see if the heat treatment was successful is to try to cut into it with a file. If the file digs in, it’s not fully hardened. In this case, the file just skated across the end of the new guide block:
The normal next step in the heat treatment process is to temper the steel: reheat it to a lower temperature to reduce the hardness, making it more flexible and less likely to break or chip. For these, I left them in the hardened state, and just cleaned the end with wet / dry sandpaper.
The lower set installed. These are about the thickness of a sheet of paper away from the blade:
The upper set:
I made a short video about these new guides:
Early impressions on these are extremely positive, after doing a fair amount of cutting. They are not noisy, and don’t let the blade twist as it goes around curves. Examining the blade after some difficult cuts, there are no signs of wear, and the guide blocks are still cold to the touch.
One issue with these is that they are probably not wide enough for my 3/4″ blades, so I’ll be on the lookout for some 3/8″ thick tool steel bar stock, 3/4″ wide (an old wrench, perhaps).
While I’m at it, I may as well make and try out hardened steel thrust bearings, to replace the sealed bearings. I see these about 1/4″ thick and 1/2″ high, with a ‘V’ groove for the blade to ride in. Should be interesting.