Bertha

[SimonC]

Hey Jazz,

No worries about throwing a spanner - I really appreciate the advice!

1. Diagonal bracing makes perfect sense. Do you think triangular plates or more box section at a 45 degree angle would be better?

2. Ball screw alignment on X. I was planning to make oversized holes in the box section to allow for radial adjustment (ie. not threading into the steel but using a nut on the inside of the box section). I was thinking I'd put the gantry at one end, fix the bearing in place then move the gantry to the other end to fix that one. Do you think that would work? Do you also need adjustment in the axial direction somehow? I've actually got double fixed bearings for both X and Y (FK for X, BK for y) as I read somewhere that was better.

3. Ball screw alignment on Y. Here I was imagining I'd fix the double BK units to the 60x30 extrusion in the middle of the two 90x45s, then use oversize holes on the rails to do the same kind of thing as above, only this time allowing the rails to move slightly to make sure there's no binding. Does that make sense do you think?

4. Z axis rear plate. I'll scrap that in favour of some plates at the sides as you suggest.

5. Y axis belt protection / gantry style. Yeah, haha, funnily enough I'd had it the 'other' way around in all my designs up until the last revision. I changed after reading the thread where someone made a diagram showing the 'screw behind' approach wasn't as good. I get what you're saying though - it was definitely cleaner the other way around and kept everything out of the way. I'm kinda thinking I might switch it back.

6. Rear belt. I think I'll just put a board at the back to keep the chips away from this - seems easier than re-routing the belt.

Thanks again for your thoughts :-)

Cheers, Simon

[JAZZCNC]

Hey Jazz,

No worries about throwing a spanner - I really appreciate the advice!

1. Diagonal bracing makes perfect sense. Do you think triangular plates or more box section at a 45 degree angle would be better?

Either will work. just make sure you can triangulate the largest area you can. You really can't over do it but very easily can under do it.!!

2. Ball screw alignment on X. I was planning to make oversized holes in the box section to allow for radial adjustment (ie. not threading into the steel but using a nut on the inside of the box section). I was thinking I'd put the gantry at one end, fix the bearing in place then move the gantry to the other end to fix that one. Do you think that would work? Do you also need adjustment in the axial direction somehow? I've actually got double fixed bearings for both X and Y (FK for X, BK for y) as I read somewhere that was better.

Yes this will work fine. The Axial alignment needs to close but not super critical, the FK at each end will make it a bit trickier but you'll be fine. Regards if it's better or not then Yes but how much at this level is debatable and one I'm not getting into so don't anybody ask me too.!!

3. Ball screw alignment on Y. Here I was imagining I'd fix the double BK units to the 60x30 extrusion in the middle of the two 90x45s, then use oversize holes on the rails to do the same kind of thing as above, only this time allowing the rails to move slightly to make sure there's no binding. Does that make sense do you think?

You won't fasten those blocks to the Extrusion slots of 60x30 if that's what you plan on doing.?
I may be miss understanding here.??. . . . Regards the rails and over size holes for aligning ball screws then that's a bit of hard way to go about it and will be pain. . . . . Over size holes and shims on the ball-screw mounts would be easier.

The most common cause of bent ball-screws is not from ball-screw end alignment but the distance from Ball-nut mount to screw centre. If it's out then when it approaches the bearing blocks it bends the screws. It's a slow job setting screw alignment and ball-nut mounting but worth the effort so building in has much adjustment potential greatly helps.

I changed after reading the thread where someone made a diagram showing the 'screw behind' approach wasn't as good.

Well strictly speaking yes it's not the ideal but that depends on how far back and how it's done. The amount where talking here doesn't make a jot of difference and believe me if you built the machine your way and in the night I switched it without you noticing you wouldn't tell any difference, either in how it performed or quality of finish. Get silly about and then yes it show in cut quality and that's depending on what your cutting.