What to look for when Purchasing a Bandsaw
What to look for when Purchasing a Band Saw
There are basically two types of of band saws, two or three wheel. When buying a saw for the first time, the three wheel saw appears to be the best bet. I gives heaps of throat (distance of cut between the down traveling cutting side and the upward return side of the blade) for cutting larger widths of wood.Disadvantages of the three-wheel Band saw
The three wheel saw has some disadvantages. With three wheels the blade has to change direction three times in one revolution thus increasing wear and causing premature breaking of the blade due to work hardening. The wheels are much smaller and this makes the blade turn in a tighter circle and again this causes premature blade breaking due to metal fatigue. The smaller diameter wheels provide less contact area for drive and slippage can occur during heavy cutting. Lastly because of the smaller wheels the flywheel effect is lost and there is no self run-on, again causing the saw to stall easily.
Advantages of a 2-wheel Bandsaw
The 2 wheel saw has the opposite effect of above, the blade only changes direction twice and blade life is 1/3 longer than a 3-wheel model. Larger wheels produce the flywheel effect and provide more drive surface area. As a rule of thumb the longer a band saw runs on after it is switched of the better it is, it has keep-going ability. However take note that some larger band saws have a break to stop the blade when it has been shut down. Remember the down side to the 2-wheel saw is that it has much less throat. The first piece of valuable advice here is look to the 2-wheel bandsaws as your best buying option.
MotorsThe main reason a woodturner buys a bandsaw is to cut round turning blanks and rip down billets from logs. Ripping especially requires horsepower (kilowatts for you young fellas). A saw with less than a 1hp (750 watts) is going to struggle with green hard wood blanks. I have re-powered my small Taiwanese saw with a one horse motor and it is still barely adequate. Second bit of advice look for more than 1hp if possible. Some band saws have a series of pulleys to allow different ratios. This can increase the power of the saw but this is at the expense of cutting speed. I am unable to recommend a cutting speed but the speed suggested by the manufacturer for cutting aluminum is about right for hardwood.
This is the distance from the saw table upwards to the top guide when it is fully extended and this determines the size of the blank that can be cut. Six inches (150mm) would be the bare minimum for a woodturner. However with motors of less than 1hp cutting 6" blanks may not be within the capability of the saw.
Blade Guides and Rollers
This is a really important part of the saw. There are two reactions to cutting. There is rearward movement of the blade as a reaction the foreword movement of the wood during cutting. If the blade was allowed to move too far rearward it would fall off the driving wheels. The sideways movement of the blade is a reaction to cutting around a circle forcing the blade to try and twist, uncontrolled blades have a habit of not cutting very straight. Each movement is counter-acted with guides and ball bearing races, above and below the cutting area. Backward blade movement is usually countered with a ball bearing that allows the saw blade to rub on it and the bearing rotates to prevent friction. The smaller this bearing is the faster it rotates and the quicker it wears out.
The twisting forces are countered with guides. These can be either solid thrust plates or ball bearings. More expensive saws are usually fitted with ball bearings but either method is acceptable. For a saw to behave correctly these guides must be firm with no end play in any direction and be adjusted correctly. These settings will be discussed at length in a later episode.
The average woodturner is usually either ripping down or cutting circles for turning blanks. It is my experience to suggest that course cutting blades are probably the best. Band saw blades are still classed in imperial measure. Teeth are classified in teeth per inch (TPI) or points per inch (PPI), see diagram for clarification. TPI is the most common method here in NZ. As a rule of thumb 3TPI is really good for woodturners. It will handle green wood and carry away the sawdust without excessive clogging. There is also a type of blade that has recently hit the market called "Extra-set". As the name suggests this blade has comes with much more set on the teeth than average and allows for tighter circles to be cut and really good sawdust clearing. Most band saw blade suppliers will know of this and will be able to supply Extra-set in 3TPI, I can really recommend this blade.
CHECKLIST: Buying a Band saw
To summarize let’s look at the requirements for your new band saw.
- A 2-wheel saw is your best bet
- Look for a saw fitted with at least a 1 hp motor.
- Anything less than 6" (150mm) in cutting height is not going to be adequate.
- Guides and rollers should be firm and have no play.
- 3TPI in Extra-set will be a good blade for a woodturner.