Hi all, its that time again!
I've started sourcing parts for and designing build no.3. I'm trying to learn from past mistakes, and although I have much better woodworking equipment now, I'm going to go with a metal build. I want this to have the performance I've never achieved yet, and to be of high enough quality that it can be in my shop long term.....about 5-10 years. Its also practise for my future large metal build.
So....I've been working on a design as per the pics below. I'm switching back to a single stepper for the X axis instead of a second slave to reduce the width of the footprint because of liimited space, but also mainly because I don't see the need for two when one will work and leave me more flexibility for a rotary axis later.
I'm going with ballscrews for all axis. Its going to be mainly aluminium. I say mainly because I haven't decided if I need steel anywhere yet. The size of the aluminium is not definate yet, for example I dont know if the box section will end up having an 8mm, 10mm, or 12mm wall etc. I have to drop in to the supplier soon and figure out what he can order for me. I rang him today for the first time since my old aluminium supplier closed down. The new guy was pretty helpful.
I still dont have a welder so its going to be a bolt together construction. The aluminium angle used to join pieces in the pics is all 6mmx38mmx38mm. I'm wondering what people think about this....will it be strong enough....I have my doubts?
Supported rails for the X axis with open pillow blocks. Unsupported 20mm hardened steel rails, with closed pillow blocks for the gantry. The gantry rails I won on e-bay today from MarchantDice and they're 800mm (32"). Do you think this will be ok unsupported...I hope so...I already bought them?!! The X-Rails I'm going to go with about 1550mm (61").
The ballscrews I'm eyeing are 16mm single start 5tpi....thoughts?
I'm throwing around the aim of getting Gecko G203V's for this, but the cost is already going to be spread out until about Christmas, and they'll push it back a few months. I want to have a NEMA 42 for the X-Axis which would need the Geckos. I'm trying to decide between the 2974 oz/in and the 4036 oz/in:
http://www.anaheimautomation.com/man...ec%20Sheet.pdf
Otherwise I might go to the gecko G540 which would limit me to a NEMA 34 at 1700 oz/in which I think would be underpowered for the X axis.....thoughts?
For the Y Im also thinking either a 1700oz/in or a 2974oz/in. Z I'm not so sure....probably somewhere around the 1200/1300 oz/in mark.
The base is going to be supported from the angle on either side. i'm thinking either steel for this, or lengths of 12mmx150mm aluminium across the width....perhaps with angle bolted to the underside to give some more strength. Perhaps 1" or 2" tubing across to support the base? Its not very wide remember only 752mm.
I haven't finished the design. I think the Y axis stepper will be forward of the posts to the rear of the Z carriage back plate....does that make sense? I'm not entirely sure about this....I have my eye on a ballscrew auction on e-bay, but its only 875mm, which is going to be just a bit tight for my gantry....another 50mm would be just right....
The Z is my major hurdle I think. Can someone suggest the best type of rail setup for the up/down movement on the Z carriage to remove unwanted movement while not making the carriage wider than necessary? Ithink that for the Z a smaller ballscrew...maybe 10mm or 12mm would probably be best...ideas?
I haven't put legs onto it yet....I have to figure out the best place for them to not interfere with the movement of the X axis....
I would like a spindle on this....maybe 3Hp, and am currently investigating prices but damn! they are expensive! I came across this asian one: http://www.homeshopcnc.com/HFspindle.html any thoughts?
Thats it for now. I'll post design changes/updates as we go and as I'm arranging build materials.
Main areas of concern:
- Unsupported Y axis rails.....will they be ok for 752mm span?
- Pillow blocks for X axis and height of posts above them. Having never used pillow blocks before, will I have a lot of 'rocking' of the gantry?
- Type of metal pieces to span the base while maintaining ridgidity?
- 250mm long 12mmx150mm flats on either side of the X axis transferring movement from the screw....will these work out ok under high acceleration/decelleration ?
- How to design the Z axis movement, and type of rails to use?
Thanks in advance for any advice......