We’ll often get asked the question “why does my bandsaw blade not cut straight?”
If you’ve had a job come off the saw with a poor finish and wonky cut, you’re likely frustrated. Crooked cuts mean you’re going to have poor joins, which can throw the accuracy of a whole project out.
However, fear not.
There are some simple ways we can fix the problem of inaccurate, wonky cuts.
Having the incorrect TPI
Your problem very like could be that you have an incorrect number of teeth for the application.
You can't use the same TPI for every material size.
Too often, people try to use the same blade for every size of steel they cut. This is not possible! The size and shape of the material you are cutting impacts the number of teeth you need on your bandsaw blade. While a vari-pitch blade can help give you more flexibility in this area, it’s not going to mean you can use the same blade for everything.
Does this mean you should keep multiple different blades, so you can quickly get the right TPI no matter what job you’re doing?
Absolutely.
A handy rule of thumb is that you should aim to have 5-7 teeth in the cut at any one time.
Is my TPI too fine?
If you have more than 5-7 teeth in the cut, the gullets in the blade are going to become filled with swarf. This will cause the blade to lift in the cut, then crash back down, putting a shock load on the tooth.
Swarf build-up will cause the blade to deflect in the cut.
The build-up of swarf also causes the blade to deflect in the cut, which is what creates the inaccuracy.
Is my TPI too coarse?
If you have less than 5-7 teeth in the cut, there is too much strain on individual teeth. This results in fractures and microcracks which compromises the integrity of the blade. This can lead to wonky and inaccurate cuts.
Bandsaw Blade Tension
Having the correct bandsaw blade tension is also critical to achieving straighter cuts.
Mostly, blades are under-tensioned. Unless you have a very high-quality bandsaw machine, or your blade is too short, you’re going to struggle to over-tension your blade.
A tight bandsaw blade can't wander or flex in the cut, increasing accuracy.
When the blade is tight, it doesn’t have any room to wander or flex in the cut. This results in pressure being applied evenly across the blade. Because of this, the blade can’t deviate during the cut, resulting in straighter cuts.
We say that correct blade tension can solve up to 90% of your bandsaw blade problems.
An Example
For example, Mike might be doing all his cuts with a blade that has a TPI of 8/12.
This is fine, because he mostly cuts smaller RHS. However, if he gets a job where he needs to cut a larger piece of solid, this TPI is too small.
Excess swarf will build up in the cut, and the blade will be forced to deflect.
And if Mike hasn’t tensioned his blade enough, it will be an even more wonky cut.
Keeping things straight
I’d recommend you find out the correct TPI for each new job you’re doing. You can download a handy TPI chart that you can keep near the saw to help you quickly work it out.
I’d also recommend you check out our video about how to check your bandsaw blade tension.
