I Charlie,

I wrote the original stiffness v5 sheet that you mentioned in the first post a few years ago, plus later posted a v7 which may be of interest.

I've tried to replicate your results but cannot match them (don't know all the dimensions etc that you used). So I'll just make some general comments.

The 13um in Z is bending due to the spindle weight applied to the centre of the gantry. This seems fine to me.

The 30um in X sounds like you've only noted the 'tool deflection' number which is only the bit due to twisting. There will be a bit more overall deflection due to X bending to give you a final total deflection in X. This is starting to sound a bit high (30-40um is 0.03 - 0.04mm) for aluminium. However, this is at maximum extension so you can reduce this problem as you've stated by raising the job in Z.

Biggest thing to point out though is that you haven't run the analysis on the gantry sides (plates) in the Y direction. Depending on your exact numbers this is likely to be similar or greater than the X deflection and because it is just bending (you can ignore Y torsion) and there is no work-around in terms of raising the job in Z etc. This is because all the tool forces in Y go through the ballnut and this is at a fixed height above the X axis bearings. This is why Jazz keeps pointing you to the raised X axis designs for aluminium since this offset between ballnut and X axis bearings is basically zero. You are then free to beef up the bed/raised X axis sides to react this force.

I have a machine broadly similar to your posts so far and it will cut aluminium but I you can tell from the sound it makes and machine vibration that it is approaching the limit. If I was cutting aluminium more regularly then this machine would not do. For the occasional piece it is OK.

Finally, feel free to experiment with the spreadsheet but do just use it to get a feel for general comparisons and where to place effort and material. As a like-for-like comparison of different gauge, sections, and dimensions it will give you direction, but don't expect to get the quoted deflections out as there too many simplifications. So long as you use it as just another way of investigating the design (along with reviewing the build logs and the invaluable subjective opinions of experienced builders) then you will be OK.

Good luck with it and welcome.