Z-axis design - help sizing materials please!

[routercnc]

Hi Jonathan,

Great project you have there, interesting stuff.

There's no easy way to commit to an own design, and you'll no doubt end up tweaking whatever you make anyway. Making these CNC machines is a mix of previous experience, guesswork, copying parts of existing designs, understanding forces, making calculations, and fabrication skill. You've obviously thought about the problem, the risks, and the compromises, so it's probably time to give it a go.

My concern on drilling the hardened rails is that I don't know if they are stress relieved as part of the hardening process. If not then drilling a hole may allow the stresses contained inside to distort the rail. The bearings won't help you to 'make it straight again' between the span. But I'm really interested in a second opinion on this as well. I'm going to post this question seperately to put it to a wider audience.

[Jonathan]

There's no easy way to commit to an own design, and you'll no doubt end up tweaking whatever you make anyway. Making these CNC machines is a mix of previous experience, guesswork, copying parts of existing designs, understanding forces, making calculations, and fabrication skill. You've obviously thought about the problem, the risks, and the compromises, so it's probably time to give it a go.

Yes I tend to agree. I think I'll wait a bit to see the what the conclusion is on drilling these rails first. Is there any loss in buying the rails and open bearings and if the drilling doesn't work still using the open bearings unsupported?

If I do go down this route which bearings are a better bet...the adjustable or fixed ones?

I could always support the rails underneath without actually fixing them (hmm loctite!?). That would at least stop them deflecting in one direction.