Hi Had a quick surf on the forum, but nothing obvious came up. (new) Openbuilds X32 controller with a (slightly smaller) Lead 1010 machine. Calibrates perfectly (200 steps per mm) on X & Y using the software. Bit size is correct (1/4 comes out at 6.25mm, so very close). A 20mm x 20mm pocket in Vectric produces the correct G-Code (openbuilds grbl mm post proc) but only a 19.3mm box when cut. No obvious play in the machine. Puzzled! Anybody any pointers? thanks in advance James
Hi Peter - yes nearly same error in both, I think Y is 19.5mm or so. Code spaced for readability. Vectric was set to a 1/4" bit at 6.25mm. 6.875mm+(6.25mm/2) = 10.00mm. thanks! Code below: Code: T1 G17 G21 G90 G0 Z20.320 G0 X0.000 Y0.000 M3 S15000 G4 P1.8 G0 X-1.875 Y-1.875 Z5.080 G1 Z-1.500 F254.0 G1 X1.875 F1100.0 G1 Y1.875 G1 X-1.875 G1 Y-1.875 G1 X-4.375 Y-4.375 G1 X4.375 G1 Y4.375 G1 X-4.375 G1 Y-4.375 G1 X-6.875 Y-6.875 G1 X6.875 G1 Y6.875 G1 X-6.875 G1 Y-6.875 G0 Z5.080 M5 G0 Z20.320 G0 X0.000 Y0.000 M2
If you actually entered a bit size of 1/4" into Vectric (and you say the actual bit diameter is close to 6.25mm), then that is why it undercuts. That's why it's important to accurately measure a bits size before "camming".
apologies if not clear in the post, the bit is a 1/4" but measures & cuts as 6.25mm which was entered into Vectric. Either way 2x0.1mm does not add up to 0.7mm
Please re-check your calibration - the pdf in the link below explains the theory, the video describes the calibration wizard in Openbuilds Control - that makes it easier by doing the sums for you, but calibrate over the longest distance you can accurately measure. Conventional milling and climb milling produce slightly different results because of tool deflection, so please do experiment with both The material you are cutting can also have an effect - very soft materials (like mdf) can be pushed away from the bit instead of cutting. For most accurate results it's always better to leave a small amount of stock for a full depth finishing pass (separate toolpath with most cam/controller set ups). Calibrating your cnc Alex.
the only think I can think of is that its skipping steps under load? tbh this is a 1.5mm deep cut at 1100mm/min in ply, so shouldn't be hardwork?
thanks Alex, will check again tonight. Tried a 1/8" bit first, and switched to a (nominal) 1/4" bit to rule out deflection issues.
If it's a profile or pocket cut and still lines up when it's gone all the way round you are not skipping steps - once you have missed a step you don't get it back again Alex.
Our official number is 199.1 - its a rolled screw, precisely 200 is theoretical, but unlikely to be correct. Was there a change in error rate between bit sizes? Same percentage of error, or same error? If the error is still the same millimeters out - its machine calibration/tramming/something in the motion setup. If you cut a pocket twice the size, then we expect the error to double up as well
Right. I understand the story now.... TLDR; the test piece was bending just a little bit So this started with issues with mach3 controller being weird, so replaced with X32. All good. The new test piece of scrap wood was long and fairly thin, with it appears enough to account for a 1/2mm of accuracy when not screwed down in the middle too (doh!). The 199.1 steps/mm is spot on (i'd changed it). Oddly a 5mm slot still comes out at 4.7mm or so, but as a 192mm oval comes out at 192mm, I think thats more to do with bit deflection and wood compression. Thanks Peter and Alex for your help. Really appreciated. I think that's probably why people come (back) to OpenBuilds, good products and good customer support!
