With regards to supporting the rail at the centre I could do this when the Z range is limited, as above. It would make it take slightly longer to change between the two set-ups though.
Thanks for the help. I'll have another look for what steel RHS I can get hold of and modify the drawing accordingly.
I've found some 160x80mm steel box section. There's 5mm, 6.3 and 8mm wall thickness available. I think the 5mm should be ok. No idea how much it costs or if I can buy less than a 7.5 meter length....
(page 7 - I live very near to them but I've never actually been)
If you are not stuck with 40cm, why not bring the gantry down a foot, then increase the separation on the pillow blocks so you can centre support the rail?
Here's one of my blade designs. This one was optimised for less Z axis travel but as you can see it's still quite a lot. The calculations show the root at an even steeper angle, and hence need a good Z travel. I agree this blade won't need 400mm, but I really don't want to be faffing trying to squeeze the blade into the available space!
The blade there is a 0.7m blade I made for a smaller with turbine. Plywood isn't so good...
Do you think the 160x80x5mm box section will be sufficient?
I've edited the drawing to include holes to mount the bearings further down when I want only 75mm travel:
The thing floating around is a support for the middle of the rail. I've designed it in two parts since that means I can fix it on without removing the bearings from the rails.
I've not put the box section in yet. It's just occured to me that mounting the bearings to box section sturdily is going to be a lot more difficult! Would fixing the bearings to just one side be ok, or should I put a spacer inside the box section and use a long bolt?
Having now seen it fit so well on the mill I think you would be better for off building a VMC, but optimised for wood, 400mm z axis on linear rails bolted to a column would be be no problem. The other way to deal with the large Z axis you need is to fit a 4th axis and then rotate the blade to the tool, I've seen furniture machinces work like this.
Are you going to be making a lot of these blades? if not it seems like you are building the machine to make a part but limiting other useage (hope that makes sense)
nice work so far, is that your workshop?
4th axis...yes! I had that in mind. It's one reason I want a large Z travel to be able to fit a 4th axis, either directly to the Z axis or onto the base.
Here's my latest plan for the Z-axis:
I've changed it so that the rails move and the bearing are stationary. This significantly reduces the weight / cost. The supports in the middle of the rail limit the travel to 75mm, so I'd remove them when I need the full travel. I guess I'll mount the stepper motor on the top of the slide - shame about the added moving mass there.
The aluminium plates in that drawing are 15mm. I'm thinking I could make the bigger one 20mm thick, to better resist torsion, then *if necessary* add side pieces like in the previous design.
So, do you think I should go ahead with this design, or spend another whole day designing :lol:?
Have you considered to make the bed rails adjustable at each corner? this way you could keep the 'Z' shorter and do the machining in stages? It would make t machine very flexible for different uses.Spacers or a wind up/ down mechanism could be done fairly easily.If the nagging gets really bad......Get a bigger shed:naughty:
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