strange behavior

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strange behavior

Postby antonfat » Mon May 13, 2024 5:51 am

hi I have a problem. Although the axes have no play, milling a 10 mm cylinder gives the result 9.85, while with a 5 mm cylinder the result is 4.95. What could it depend on?
Sorry for my English unfortunately I use Google Translate.
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Re: strange behavior

Postby Doncis » Mon May 13, 2024 1:13 pm

It depends on machine rigidity, spindle bearings rigidity, tool deflection, axis calibration, tool runout etc. When cutting forces kicks in, strange things happens.
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Re: strange behavior

Postby antonfat » Mon May 13, 2024 6:41 pm

Hi Doncis, thank you for your kind reply. Yet I worked with very light passes precisely so as not to have conflicting forces. I have recirculating screws on all axes, on the spindle I have a concentricity error of 1 cent. An error like this seems a little exaggerated to me.
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Re: strange behavior

Postby Doncis » Tue May 14, 2024 8:15 am

Please check spindle bearing preload, spindle bearing rigidity, tool holder assembly balance. If balance not very good, at, high rpm virtual tool runout may enlarge lot.
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Re: strange behavior

Postby ger21 » Tue May 14, 2024 11:23 am

Try cutting slower. Even the most rigid machines will have more play than you think. Small holes are the most difficult things to cut accurately.
Gerry
UCCNC 2022 Screenset - http://www.thecncwoodworker.com/2022.html
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Re: strange behavior

Postby antonfat » Tue May 14, 2024 6:28 pm

Hi ger21. I forgot to say that the test was carried out on ergal aluminum material, carbide cutter, Z displacements of 0.15 mm, lateral displacement 0.5 mm, for the speeds I respected the parameters recommended by the tool manufacturer.
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Re: strange behavior

Postby gerius25 » Sat May 25, 2024 4:33 pm

antonfat wrote:hi I have a problem. Although the axes have no play, milling a 10 mm cylinder gives the result 9.85, while with a 5 mm cylinder the result is 4.95. What could it depend on?
Sorry for my English unfortunately I use Google Translate.


The issue you're facing could be due to deflection or tool wear. When milling larger diameters, the cutting forces are higher, causing more deflection of the tool or workpiece. This leads to an undersized part. Tool wear also increases with larger cuts, creating a similar effect over time.

To troubleshoot, check your tool holders, tool overhang, depth of cut, and feed rates. You may need to take lighter cuts, use shorter stickout lengths, or switch to a larger tool for the 10mm cylinder.
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