Hi all,
I'm planning a new build and I think I have come up with a general idea of how the gantry will be, but was hoping to get some input on the rigidity of it all.
So first of all, some requirements:
- Ability to cut aluminium very well
- Ability to cut steel, slowly
- Ideally the ability to face mill, slowly is fine
- Working area of 600-700mm in X and Y, 200-300mm in Z
- ATC BT30 spindle
- Enough space for a Haimer 3D probe (About 100mm tall)
- Fixed bed with vertical clamping area
The general idea is a gantry supported by high-level linear guides, with a ballscrew on each side - Something like this:
https://www.youtube.com/watch?v=T2-jDdAwlE4
Starting with the spindle, I was considering one of these: https://www.ebay.co.uk/itm/113626455544 These are 100mm diameter, 400mm long and seem to weigh about 15-20kg from what I have found. I'd use something like this (https://www.ebay.co.uk/itm/113361541312) for the Z axis, mounting the spindle nose about 100mm higher than the bottom of the gantry at its highest position to give space for the Heimer probe.
Originally I was considering a 1m long 80x160mm heavy aluminium extrusion (https://www.zappautomation.co.uk/mc1...x160-7520.html) for the gantry, strengthened by adding a 20mm aluminium plate onto the front, top and back - The extrusion alone is 11kg and the plates would add about 20kg. The plate would also add a nice flat surface for the linear rails and is easily made using my drill press. A chunk of steel box-section is out of the question as I don't have the capabilities to mill it flat, and don't know anyone with a milling machine large enough to do a 1m span.
The next idea was to use a THK KR65 linear guide (https://tech.thk.com/en/products/pdfs/en_a02_122.pdf) - The 1m version (700-800 stroke) with a single block and a cover which is 36kg alone. I'd add a large (30-50mm thick) aluminium plate to the back which would be about 200-300mm tall (20-40kg), with an extra linear rail along the top for additional support.
Thick plates would mount the gantry to the Y axis rails, with the blocks spanning about 200mm in length for stability. These would be mounted on aluminium extrusion, strengthened with thick Aluminium plates as required. The rest of the frame can then be made with a mix of steel box section and aluminium profile, as it's not as critical as the gantry.
I was hoping to use some existing 180W servo motors for all axis (http://www.jmc-motor.com/product/980.html), with two motors on the Y axis. A partial (10kg?) counter-balance on the Z axis probably wouldn't be a bad idea due to the weight of the spindle. If power is an issue, I'd go for larger AC servo motors.
So I suppose the main questions are:
- Will my plan for the gantry be rigid ? Is a large pre-made linear guide like the THK KR65 ever going to be enough, even with strengthening plates ?
- Will my gantry be too heavy for its own good ?
- Is (fast) aluminium milling realistic for this: a) Strength / span of gantry ? b) Type of spindle ?
- Is (slow) steel milling realistic for this: a) Strength / span of gantry ? b) Type of spindle ?
Thanks,
-Andrew.