Jigsaw blade bending while cutting a circular window - solve

[edgeau]

Hi all. This post is to save someone else time as I have solved it.
First the problem. My design calls for port hole type windows. Rather than mess up my walls I have been experimenting on scrap ply from packing crates - just as well! I have half a dozen rotten failures on the way to success. It is easy to draw a circle but not so easy to follow the line perfectly but I saw a great idea for a circle jig on Pinterest. Here is what I built.

Trouble was the after a quarter of the circle the blade would bend in towards the center. I checked the base was perpendicular to the stroke of the blade, used new blades, and it is a new jigsaw.
After much frustration the solution was really simple, move the pivot point 1mm!
You see I had lined it up very carefully with the teeth of the blade. Once I set it to line up with the centre of the blade everything started working smoothly! If you look carefully at the photograph you will see one hole for the pivot screw on the line and another just off it at a different radius.

[Pmullen503]

Using the orbital motion (if your saw has it) will also help. When using a circle jig it's important to set the toe in to make sure the BACK edge of the blade isn't rubbing the sides of the saw kerf and throwing off the cut. Even free hand, trying to cut too small a radius with a blade that is too wide for the kerf it cuts will cause the blade to tilt. Orbital helps, in effect by making the kerf a little wider in curved cuts.

[noseoil]

A router with a straight-cut bit & a compass arm works really well also. Just need to be careful when starting & finishing the cut. I've never really cared for a jig saw for precision work, always a bit of run-out when using them. Good tip about moving the center, thanks.

[swoody126]

implementation of the mechanical pivot point is a good move for many who have this issue

it keeps the human error of trying to push a jig/sabre saw SIDEWAYS to get back in/on line when one drifts slightly

the friction area of the blade warms up and only requires slight pressure to cause the resuting bend

it isn't the machine's or the blade's fault that this occurs, just the inexperience of the operator

the WISE OPERATOR analizes the issue and implements the necessary intervention

WELL DUNN

your post WILL help others

sw

[mgb4tim]

x2 for the router and a straight bit. skip over a small spot, maybe 3/16" across from where you started, and stop just shy of making the complete circle. The arm is attached to the part that is getting cut out. So, until you're used this process, the router may run wild on you when the inner piece is free. Use your jigsaw to cut the remaining and sand the nibs left behind.

A router with a straight-cut bit & a compass arm works really well also. Just need to be careful when starting & finishing the cut. I've never really cared for a jig saw for precision work, always a bit of run-out when using them. Good tip about moving the center, thanks.

[H.A.]

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[OPPOSABLETOE]

Router compass is a precise way to go.

Another option; you can rout out a trough not quite through the thickness of the piece. Then cut through the remaining with jigsaw using the trough as a guide. Then clean it up with a flush trim bit or sanding.

[edgeau]

That is actually a really smart solution. You would get a good reliable finish with the trim bit. Assuming the extra kerf of the straight router bit over the jigsaw blade is acceptable to your application. In my case the inside of the circle is all waste so it would work well.

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