Doing Pockets

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Doing Pockets

Postby jdonaldson » Sun Jun 09, 2019 7:51 pm

I never have understood ( sure it has to do with the bit sizes ) how to machine a
pocket in a fixed size when indexing off the bottom left hand corner. They always
end up out of center so I typically just make my blank larger and the cut it to size
after cutting the pocket. I have a customer that wants me to do the following should
be a very simple job. I would like to use a 1/2 end mill to remove most of the material
and finish off with a 1/8 end mill. forgot to mention the preview looks correct but the
actual job will be offset

I need a recess CNCed into the top for a lazy-susan. Overall size of top is 18 5/16”x16 5/16. Recess is 16 5/16x 14 3/8” and 3/32” deep. Material is mesquite.

Thanks

John
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Re: Doing Pockets

Postby Adrian » Sun Jun 09, 2019 8:57 pm

Sounds like you've got a problem with your machine, control software or XY setting method. There's no reason why the pockets should be out of centre looking at your file as far as I can see.
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Re: Doing Pockets

Postby highpockets » Sun Jun 09, 2019 9:18 pm

Several factors to consider.
Is your material cut to the exact size?
Are you setting XY zero exactly in the corner?

As Adrian points out, the toolpath will cut the pocket as designed, unless there's a mechanical issue.

I generally don't like to have a finished size to start with. I much prefer to have some extra material to run a final cutout toolpath.
John
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Re: Doing Pockets

Postby TReischl » Mon Jun 10, 2019 1:12 am

I regularly work with cut to size parts because I put them in a vise. It is much faster to cut parts to size on a table saw/radial arm saw. Just finished up all the blocks for a Foredom bit/tools case I am building, IIRC there are 22 blocks in the case, half of them have pockets in them. The rest have various size holes for the bits.

When I do NOT use cut to size parts is when the piece needs radiused corners. Well, sometimes I will put them on using the disc sander. . . . but only small ones.

This sounds like a setting XY zero problem.

I use a .5 sq aluminum bar to do it. Put a .5 dowel pin in the collet. Then bump the dowel pin up against the .5 "feeler" gage. If I am on the lower left and doing X then I enter -.75 into the DRO. Y is -.75. Where does the .75 come from? The half inch bar and half of the dowel pin.
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Re: Doing Pockets

Postby jdonaldson » Mon Jun 10, 2019 6:33 pm

Thanks all for your replies, I have just been living with this since most of the time
I just trim based of the pocket but, I guess it's time to really figure it out

John
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