[5Carbides]

I am confused as to why I am getting inconsistent lines when surfacing my spoil board with a 2" cutter (1" step over) after tramming to .004" difference over 6" inches. The existence of the lines is not so much the greatest concern (should it be at .004"?), but the inconsistency of the lines is what I do not understand. Why would I get lines is some areas but not consistently across the spoil board?




I trammed my Joe's Hybrid CNC using a tramming squaring from SST with two dial indicators. With the gantry near centered on the x and y axis, the front to back measurement is about .004" different and the left-to-right is about .0005" different. Both of those measurements are across 6" from dial indicator to dial indicator. The dial indicators are measuring against a 1/4"x20"x20" piece of glass that has been made parallel to the x and y axis prior to the measurements/adjustments above. Example: https://cdn.thingiverse.com/assets/8...132807_200.jpg (not my image, but that is the technique I used)

[awerby]

Is this the first series of surfacing cuts or the second? If it's the initial surfacing pass, the unevenness is probably happening because your bed wasn't flat.

[5Carbides]

2 full passes using the same pattern (front to back). Taking 1/32" off the first pass. And not changing the Z depth for the second pass (aka it stayed at z-0.0032 without re-zeroing Z).

[routalot]

What happens if you do the skimming cut across the spoilboard?The only time i have found this kind of issue was with a badly built machine that had some flex in the rails and it dug in a touch going one way and lifted a bit going the other way.Changing direction may just help with this operation,but could in itself,be highlighting a flaw that needs further investigation.

[machinehop5]

...non precision machine...well oiled . sunburned wood chucker...ing chucking saw dust anymore questions?

[ger21]

Does the machine use V rollers on angle iron? If it is, it could be variation in the angle iron.

[5Carbides]

It does use V rollers on angle iron. I did a feel test of the top angle iron and was not able to make a connection between unevenness of the angle iron with marks on the spoil board.That said, yes this was my #2 suspect.

Do folks have a process for addressing variations in angle iron/v-bearing setups? Other than replacing them with linear bearings. :-) (want to, but cannot justify the effort or financial expense yet)



I did recheck the tramming after the surfacing passes to confirm the Z axis had not lost its true (it did not).

[ger21]

Replace the angle with the proper guide rails for the V rollers.
https://www.pbclinear.com/Products/C...-Bearing-Wheel

[5Carbides]

Follow-up
- Did multiple surfacing passes sweeping across the the X axis (instead of Y).
- Started with a depth of .032". Still have lines, though they seem more consistent across the table than surfacing by sweeping the Y axis.
- Performed a second pass (same sweeping pattern) at .005". Lines seem consistent with first X sweeping pass.
- Performed a third (same sweeping pattern) at .002". Lines seem consistent with first X sweeping pass.


Results after all three passes:

[routalot]

Doesn't look too bad to me and if you seek further improvement,maybe re-tram and try another fine skim in the same direction.It isn't likely to get too much better without a bit of upgrading.Alternatively use a smaller diameter tool for skimming the spoilboard as this will reduce the height of any steps.

[pippin88]

Rails / gantry are not straight / flat.