[boydage]

I have an old tested and tried machine. I am building a new Z Axis for it to carry a spindle that is 12kg instead of the 6kg 2.2 baby I smoked a few weeks ago. The machine itself is pretty heavy, the gantry is 6mm alloy plate screwed down onto a 300mm x 80mm LVL timber beam. Its great.

The Z axis. I am going to go for a 300mm travel and have kept the SBR20 rails at 600mm length to keep good space between the linear guides.

My question is the back plate, and the plate I will screw the spindle onto (in green on the pic). Thinking I will just use 10mm x 200mm 6061 extrusion. Is that too light in duty?

The only other option is to go 16mm 5083 that will not be as flat as the 6061 so once I have machined it flat will only probably be 15mm. Still 50% more in size.

Open to thoughts on what I should use here. I am quite confident the 10mm 6061 will be very rigid - but will it be enough? We only want to do things once huh. The diagram attached is a build drawing. I am wanting a good rigid machine to cut alloy. The spindle is a 4.5kw aircooled beast of a thing..... I think I am in love with it. But thats another story.

[peteeng]

Hi - I think the 10mm will not be rigid enough. It will need to be thick and have side webs as well. 4.5kW is a big beast. Peter

[NIC 77]

Flat plates bend easily....and things in a cantilever configuration also bend easily....both things are working against you (and most people, it's not personal ) on your Z axis.

Reinforced nicely, your 10mm plate will be far stiffer than your 16mm plate without reinforcement.

I see you have some space on the plate on either side of your spindle.

You could choose to use either steel or aluminum for your reinforcements. Steel is much stiffer, and less expensive, but if you are looking at stiffness to weight ratio, you can actually sometimes do better with aluminum because you can make the geometries larger for the same weight. Not that saving a little bit of weight will be all that important on this.

You could start with something like bolting some 2" x 3" x 1/2" angle onto both plates. Obviously the 3" side would be perpendicular to the plates, and for the back plate, the angle would go either under the bearings or on the other side.

For the Z plate that the spindle is bolted to, you could even do a box structure around the spindle if you want to go nuts about it. Have you got any of that 10mm plate left over?

How does the spindle bolt onto the plate? This will determine if the actual spindle housing is adding to the rigidity of your Z axis, which it might be.

Personally, I'd stick with the 10mm thick and modify it on this machine. Also your gantry risers don't look like they have any reinforcement, I'd do those too.

[boydage]

Good words thanks. It took me a wee while to draw up some sides and cut them out today. The longest time was drilling the side edges of the back plate and tapping a thread into them so I could screw the sides on. Decided to use SS hex pan type screws because they look COOOOOL when there are a lot of them. Kind of like a rivet gusset on an aircraft ha

I cut the back plate out today. And was a tad nervous when I screwed the linear blocks on as I was retrofitting it to the gantry. I measured the distance between the original rails ummm maybe 7 times. It fit, it moved, stoked.

Now its as rigid as a rigid thing. I am about 50% assembled - I will post a pic. Especially when its got the big spindle hanging off the front. B

[boydage]

Ok. I finished my Z axis I thought I had a pic but I dont - must get one up its awesome.

I did manufacture it to the letter. All the holes line up - absolutely stoked. It was like I had bought the parts in a shop. I will admit this is the first time I have drawn something like this up in CAD and actually made it for myself instead of bits and pieces here and there.

I did find there is a 0.5mm slope on the side of my spindle. Working that out, it appears the gantry is approx 2mm lower on one side, proven by actually measuring it. It was mentioned I need to beef up the sides. I am going to do that. I am thinking I will just buy some 20 or 25mm plate and cut it out of that. What is there now is just a 10mm plate 5083. I reckon it would be good to balance it and make the sides a bit artsy fartsy too. You know, kind of a spacy looking design. I am also going to make the sides longer in length. I will lose some travel but that will be better I reckon.

Thoughts? A different way? What is on there is a bit springy now given the new spindle and Z has added about 8kg. The gantry itself is SOLID and would hold a couple of ton.

[peteeng]

sorry empty file - try again can you do a jpg vs a pdf? Peter

[boydage]

Oh - the empty PDF - how about this?

I thought about it in bed last night. Yep, while I slept ha. Need to sort. Its funny, I started with the bed, then a new control box and full rewire. Then a Z. Not much longer and I will be welding some 200 x 100 x 6mm box section. I do like my massive gantry though.

[peteeng]

Hi BD _ now you have to match the columns to the gantry. No value in having them L shaped and they need to be thicker....or webbed. Peter

[boydage]

You know what I did all those years ago? I weighed it. And I worked out the COG. And built the L shapes to get it in the centre. Not to mention the fact I could get two pieces out of what I had bought ha.

Hey so what do you think? Something like some 25mm 6061? I was unsure also what you meant by webbed? Do you mean like a box subframe?

[peteeng]

Like these maybe -
https://www.youtube.com/watch?v=LiQaFeTy_eU