Help with Circles

[chrislewis425]

All - I have my mill up and running and am having a strange problem. My initial project has holes of two diameters (9.5 and 22 mm) and neither are coming out round. They are fine on the Fusion drawing, but in execution are not correct.

Also having some strange results on size. I've measured my Freud Carbide #73-762 up spiral bit (sold as 1/8") and found it to be .1125" instead of .125". I edited the tool menu to create a bit this size and the "not round" holes are also too small in diameter. I've also tired selecting a .125" tool and the holes get smaller.

I created a 100 mm x 100 mm square and cut that out (with tool selected at .1125") and it is indeed 100 mm x 100 mm. So I'm back to the circles.

Belts are tight, I have the stiffening kit, running the Dewalt 611 router, the accessory control box, and the Freud solid carbide bit. Cutting in 6mm hardboard at 2mm max step for each pass. Using roughing and final passes. 762 mm/min feed rate.

I'm a newb at CNC, so maybe this is obvious and I am just missing it. Any help is appreciated.

Thank you,

Chris in Seattle

[mrbigj]

Mar 6, 2017 4:04:05 GMT chrislewis425 said:

All - I have my mill up and running and am having a strange problem. My initial project has holes of two diameters (9.5 and 22 mm) and neither are coming out round. They are fine on the Fusion drawing, but in execution are not correct.

Also having some strange results on size. I've measured my Freud Carbide #73-762 up spiral bit (sold as 1/8") and found it to be .1125" instead of .125". I edited the tool menu to create a bit this size and the "not round" holes are also too small in diameter. I've also tired selecting a .125" tool and the holes get smaller.

I created a 100 mm x 100 mm square and cut that out (with tool selected at .1125") and it is indeed 100 mm x 100 mm. So I'm back to the circles.

Belts are tight, I have the stiffening kit, running the Dewalt 611 router, the accessory control box, and the Freud solid carbide bit. Cutting in 6mm hardboard at 2mm max step for each pass. Using roughing and final passes. 762 mm/min feed rate.

I'm a newb at CNC, so maybe this is obvious and I am just missing it. Any help is appreciated.

Thank you,

Chris in Seattle

Chris,

I'm no expert, so take this with a grain of salt. I would try another piece of software and see if you get the same results. If you don't, it's something with the software. If you do, it's something with the hardware. That would at least give you a place to start. 

I'm still learning Fusion 360, so I don't use it. But you might try Easel or 123d Design or something like that.

J

[Derek the Admin]

Chris, apologies for the canned response I'm about to give you... but check out what I just wrote to another member about circles:


I would program a big square, perhaps 200mm. Cut it out of a cheap material like MDF instead of your nice walnut. Before you pull it off the machine, write on it how it was oriented with a sharpie or pen. Now pull it off and examine it. Is there a taper to the piece? Meaning when you view it from the side does it have a slant or is it straight? If it has a slant then the cutter is out of plumb. This most likely results from the gantry rail being tilted forward or back. This is solved by taking a square and measuring the gantry rail for perpendicularity to the bed. If it needs adjustment then loosen the tap hole bolts on the X rail just enough to rotate it into position. You can also view it from the side to make sure the edge of your square lines up with the spindle itself.

Next actually measure the square for squareness. If, for example, you put the square on the top right of your cut out piece (as it was oriented on the machine) and you had an air gap between your square tool and the 200mm square you cut out, then that means you would need to pull the right side of the gantry rail forward just a bit. There is a little adjustment there for this purpose.


And you are doing fine. The hole thing is really the torture test. Any out of plumb or out of square condition shows in smaller circles. I'm sure you've got a pretty good build there, but circles are pretty unforgiving. Also any flex just inherent to the machine can manifest in a circle, though I don't think your cutting settings are aggressive enough to make that the case.

Hope that helps.

[chrislewis425]

Well, if I can find a square that will align with the 1/2" bit length, I'll let you know!   

I'll try a longer bit and check the router square to the table, but this looks more like an X,Y problem. I have the Inventables Colt mount with a brass shim. A solid carbide bit will not flex and the machine seems pretty sturdy. Speed is slow and cuts are shallow, so I'm kind of stumped.

I was hoping the "cut a square test" would show a calibration problem, but no luck there.

I'll keep playing with settings and cutting more circles. I'll even try Easel again, but only export the code. It just did not seem as precise when I first tried it, so I put it aside.

Thanks,

Chris

[chrislewis425]

All - finally worked this out. Tried using Easel and still got out of round holes.

On to machine trouble shooting... Checked for flex and square - all ok. Checked for drive train lash and found the culprit. I thought I had set up the belts tightly enough, but after cutting the tie-wraps and retightening, circles came out round!

Onward and upward!

Chris in Seattle

[jkendall]

Mar 21, 2017 19:04:41 GMT chrislewis425 said:

All - finally worked this out. Tried using Easel and still got out of round holes.

On to machine trouble shooting... Checked for flex and square - all ok. Checked for drive train lash and found the culprit. I thought I had set up the belts tightly enough, but after cutting the tie-wraps and retightening, circles came out round!

Onward and upward!

Chris in Seattle

You just solved a mystery that just came up with a project I have in mind. I was doing a test cut and saw that the final product was coming out oblong. Not only that, the twists in the bit were getting loaded-up the deeper I got. Thanks for the thread and the info! Tight as a drum and I got a circle like the one below my finger.

[chrislewis425]

Glad to help. This is fun stuff - when it works...

Chris