Evening all, I'm just getting on my feet with CNC and have been unable to bottom this issue in finished parts. Its always in the Y axis furthest from the origin and always the this stepped effect in the wall. I've tried adjusting the current limits on the blackbox and the issue persists. I've calibrated all my axis and they seem as accurate as I can measure any suggestions what to try next? Any help or feedback would be greatly appreciated
Can you please give us some more info - what aluminium alloy is that? What are your speeds, feedrate, depth of cut? What type of toolpath are you using and what type/size of bit. What machine do you have, and are you working in a corner of the machine bed or in the middle? Alex.
Of course, Alloy 1050 Spindle at 21000 rpm Feed rate 550mm/min Depth of cut is 0.2mm DOC Contour strategy / tool path in fusion 360 6mm single flute up cut end mill Part is positioned in the middle of the bed machine is a custom build using openbuilds extrusion profiles
Your main problem is the alloy you are using. Aluminium Alloy - Commercial Alloy - 1050A H14 Sheet That alloy has poor machinability. I use 6082 T6, 6061 is good too. I haven't tried it but 70xx series alloys (aerospace spec) should be good too. I use 12.5 K rpm, 500 mm / min with a 6 mm two flute bit, so you could certainly increase your feedrate, but you need to use a coolant - isopropyl alcohol or meths works well. Your depth of cut is fine - I use 0.2~0.5 mm for contour toolpaths. I suspect your problem may be caused by tool deflection - you didn't say what size your machine is, but our hobby machines do have rigidity issues - working in the corner of a machine helps, as will leaving some stock for a finishing path - full depth taking the last 0.2 mm. Alex.
I realize the 1050 isn't the best alloy choice but its very common in the UK and actually cuts well with a single flute end mill I do use WD40 as a lubricant and have used a finishing contour also of 0.5mm Im not sure I agree the tool is deflecting to this degree, the visible steps are easily in the measure of 2-4mm and I have seen it in other materials too. EDIT - The reason I dont believe the tool has deflected is because it only does it in one axis and in one direction. Always the Y+ direction or end of the job. The machine has a working envelope of 300 x 400mm I was considering adjusting the pulsewidth milliseconds as I've seen other threads suggesting this could be a contributing factor? Any thoughts on this? Could adjusting the current limit too high cause an issue?
Maybe use your existing cutting techniques for the roughing cut, but leave 0.2 mm to do a full depth finishing pass. I use 0.8mm for my DOC, 900mm/min for speed and about 16000-18000 rpms with a 6.35mm two flute endmill and my finish is shiny and smooth, but I use a full depth finishing pass.
You can get 6082 T6 (plate not sheet, and usually only down to 4 mm thickness) from suppliers in the UK such as Aluminium Warehouse. UK's First Online Metal Supplier - Aluminium Warehouse It machines well with the speed and feedrate I mentioned - pic shows single contour toolpath using a two flute straight bit - actually a very cheap router bit. Ie; no finishing toolpath. Alex.
Thanks Alex, I have seen the prices at aluminium warehouse but the shipping is extortionate and I’m cheap Thanks for all the help guys I really appreciate it. I ran some more tests this morning. I tried tracing the first pass with a pencil in the spindle and it came out perfect against the CAD drawing I made. So tried to run the part again in aluminium and now I feel like a complete idiot! I saw the bloody bed move So I’ll improve the bed fastening and try it again.
