Pocket dimensions - slightly undersized every time

Hey team!

Just have a little question - I’ve looked around and can’t seem to find an answer so thought I’d extend the query to the forum :slight_smile:

I’ve got a weird little issue with pockets. In easel, if I import an SVG in order to create pockets in a 2D environment (I make guitars), the pocket dimensions always seem to finish off justtttt undersize. When I do pocket cuts in MeshCam (what I do all my 3D carving with) they come out absolutely perfect, and if I’m using Easel the spacing between pockets is also perfect, so I know it’s not a calibration issue with my machine. I’ve confirmed the dimensions of the pockets in Easel to be correct. I’ve measured my bit diameters (high end bits) and they’re all exactly to spec, and I’m always confirming I’ve selected the correct bit in Easel that I’m actually using.

So far the only thing I can possibly think off that within the pocket tool path there is a slight ‘stock to leave’ offset, but thus far I haven’t been able to find anything of the sort. I’d really love to use easel for all of the 2D pocket machining, as it’s just much simpler to set up - and then I don’t have to worry about creating an entire 3D model in Rhino, just the 3D carves, which would save significant time!!

Anyway, a weird little Q I hope someone has an answer for :slight_smile:

Thanks in advance!

You’ve already done what most of us would suggest, and you have good instincts.

It might be helpful if you can give a measurement of how far off your pocket is.

Other than that, I suggest you model a 1" X 2" rectangle in Easel, cut “on path” with your bit, and when your done measure the rectangle with calipers. Measure the width, length and the two diagonals and share the results.

You might try modeling the same rectangle as an SVG to import and repeat the process.

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I’m having a similar issue. Pockets are 1mm under size. Most other measurements are spot on.
I did one more step and confirmed that the generated gcode was correct.
The only explanation for my machine is that the bit is moving sideways slightly. Looking down on the bit as it cuts, the bit rotates clockwise so there is a force pushing the bit to the left as it cuts through. If this force moves the bit, the effect will be to reduce the size of the pocket.

In my case, I’m using a 3018 so the only option to increase the rigidity is replace the machine so I just have to compensate in my designs. I have already checked all the bolts to make sure everything is secure and minimised the backlash as much as possible.
In your case, recheck that everything is secure, especially the motor mount.

A simple test is create a couple of lines at right angles. Set the depth to just under twice your depth per pass. Easel should make two passes to make each cut, once in each direction. If your machine is perfectly rigid, you will get a clean slot. If the cutting force is pushing the bit to the side, you will see a ridge in the slot down one side where the forward and backward passes failed to line up.

The usual “slow down and cut less” advice should minimise the problem. (Unless you have a 3018, then nothing really fixes it. )

I should make it clear that I love my 3018. Combined with Easel, I can do wonderful things.

Vectric allows you to choose whether you want to the router to do a conventional cut or a climb cut (running the router around the path the other way). This might make a difference for for your tolerance.

Another thing to try might be to rough cut the pocket a tiny bit small, and then do a finish pass to get the last of the material at the edge of the pocket.

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