Swingmill Blades — Re-Tipping, Sharpening Are Keys to Keep Sawmill Cutting
(Editor’ Note: This is the second in a series of articles about saw blades for swing blade portable sawmills, also known as ‘swingmills.’)
Circular saw blades for ‘swingmill’ portable sawmills perform similarly to those as stationary circle sawmills or portable double-bladed mills.
Most swingmill blades have between five and 10 teeth. The number of teeth depends on such factors as horsepower, speed of cut, depth of cut, finish quality and density of timber.
Tip Condition
When you chip a tooth or lose a tip on the blade, you usually can keep cutting until the end of the job or the end of the day. A new tooth may be welded on fairly cheaply, and it can be done according to your schedule; very few sawmill operators want to stop in the middle of a job.
You may lose a tooth when you hit a nail or stone or go too fast through a dead knot. The broken-off piece of the tooth will hit the tooth behind it, chipping a smaller piece off that tooth, too. Therefore, you will usually see two tips damaged in a row: the first one almost completely gone and the second one chipped as shown in Figure 1. One or two chipped teeth will not cause too much problem. You might just saw a bit slower, and it will be a bit harder to push. However, the boards will still be true and the finish will be fine, and you can finish a day’s work.
If you continue to use a blade for several days with an entire tip missing, there will be no tungsten left – nothing to protect the blade steel from damage. In this case the tooth seat begins to wear and bend back. In order to repair this, a saw shop would have to file down the raised bit and put more steel into the seat and build it back up again. It may cost an additional $20 to repair a seat. When you do need to get tooth seats fully built up again, expect to wait a couple extra days to get your blade back.
Diagnosing premature tip failure is straight forward. If the tooth is entirely gone, leaving a clean seat, it is likely that the saw doctor did not put enough heat into the soldering process. If there is a thin sliver of the tooth left, it is likely that the saw doctor used too much heat in the soldering process, creating a hairline fracture in the tooth.
Sharpening
Blades should be sharpened about every 400 board feet of sawn timber or sooner on gritty or sandy bark. Take the top off the log first (with all the grit in it), and then sharpen the blade once you start to get into clean timber.
Most swingblade sawmill manufacturers supply 12 volt sharpeners with their mills, included in the price of the mill. The sharpener shown in Figure 2 runs off the mill battery and sharpens the blade while it is still on the mill. It is fitted to a jig that sits on the blade against the collar.
A diamond wheel must be used to sharpen tungsten. Attached to the sharpener head, the wheel is swiveled up and down against the face of the tip by hand. Make sure the face is covered evenly so you match the hook angles. This jig can be adjusted to follow the hook angle (if not already set).
Each tip takes about 10 seconds to sharpen, so the whole blade takes about four or five minutes. For a full day of cutting, you might sharpen the blade three or four times; that’s a total sharpening time of 15-20 minutes per day, cutting 2,000 board feet. Some sawmillers prefer to work harder and longer and only sharpen once or twice a day.
Re-tipping
After a few weeks of cutting, the tips will get thinner as you sharpen them down. A tip can be used down to about one-fourth of its original thickness or about 3/64-inch thick. Assuming you do not hit any metal, a set of tips on a blade will last about 17,000 board feet of sawn timber. Fully re-tipping a blade will cost about $30-$70, depending on the saw shop.
When you take a blade in for re-tipping the first time, give the saw shop your manufacturer’s spec sheet. Swingmill blades are still fairly new, and many saw doctors have never repaired them before.
The manufacturer’s spec sheet will show the correct tooth size and width required and the hook and rake angles. Incorrect angles can lead to blade wandering, so it is important the saw shop has the specs.
When the blade comes back, compare it to the other one you have. Note how the blade performs on the mill and give the saw shop feedback. The saw doctor might not get it perfect the first time, and he will need to know what to change to get it just right. Once you gain confidence in a saw shop, you could recommend them to other mill owners.
Most manufacturers of swingblade portable sawmills sell re-tipping jigs. You also can get pre-shaped and pre-tinned tips (with solder and flux on them) from them, and you can weld them on yourself if you have a basic welding set.
You will need a jig or device that holds the blade and tip in place together as they are carefully aligned. The tip and seat are heated to just cherry red, and the two brought together to set and cool.
(Editor’s Note: Future articles in this series will focus on maintaining the plate and gullets and tension, blade adjustments, and maintenance and running costs.)
