Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: greenene on July 15, 2017, 09:09:36 AM
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I cut mostly mdf and, especially with 1/2" holes, I find that the feed direction of the tool makes a difference in the finished diameter. I look for a tolerance of =+/- .002, but find that the difference can be as much as .010". My cutting method is usually a depth of cut of .090 with a .125 carbide single flute upcut router bit.
I'd like others to confirm this finding.
tony
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A climb cut deflects the tool away from the material making the hole smaller. Conventional cutting pulls the tool into the material making the hole larger. Tools, materials, and machines all deflect, and your machine likely has backlash too. Compensating for all that is what makes you a machinist
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Machine rigidity plays a large part in accuracy, especially related to cut direction.
The forces that occur when the machine changes direction are enough to cause tolerance issues.
With the spindle turned off, and no tool in the collet, grab the collet nut, and push and pull on it. If you can move it more than a few thousandths, then I'd recommend climb cutting if you need tight tolerances, and trial and error to get the results you are looking for.
Keep in mind that small holes may require lower feedrates to get more accuracy, as the quick back and forth motions can cause a machine to flex.
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I have also stumbled upon using a sharpened 1/4" spiral bit, the diameter is smaller on a sharpened bit. That was many years ago in the early days.