The Large mill from scratch project

[dberndt]

Figured it was about time to start a thread about the build I'm going to be starting soon. The model is getting into shape and alot of the motion hardware is already purchased. A set of 1.3M nr55 thk rails as well as a set iko lrwx45 rails and some 18" hsr25s for the Z axis.

Heres the first pic.



Not sure how to inline images hosted on picasa. Oh well, click the link i guess. Hmmm, maybe i just figured it out.

[digits]

Looks interesting and very solid

I like the way that nothing overhangs or cantilevers too much - keeping the centre of gravity of the table over the base at all times seems like a very smart move to me

What are the dimensions of that thing - from the dimensions of the rails, it sound massive - looking forward to pics of it in the metal!

Good luck

[dberndt]

Its roughly 2Mx2.3Mx1.7M and about 5000lbs. It may need to go on a bit of a diet.

[aspenelm]

just a couple of observations, it doesnt look like the table surface is large enough to cover the total work area, maybe thats what you want. Also, I would imagine it would be very difficult to get the split in the bridge to be nicely aligned or machined for the z axis. It looks like you have a z slide on each side of the split. why dont you make the bridge continuous, and place z axis on one side of the bridge. just my opinion.

[dberndt]

The bridge is split so that the spindle load is centered. Its alot harder to support the head as rigidly when its cantileavered out from its supports. The table is not as big as it could be made but this is by design. I've left the table about 2" narrow of what it could be to allow room for way covers, hard stops, other good stuff like that. Theres only ~35mm between the end of the carriage/yoke/whatever you want to call it and the braces/gantry columns. It still leaves about 600mm/23" of travel in that direction. Which I'm reasonably happy with.

[digits]

Originally Posted by dberndt The bridge is split so that the spindle load is centered. Its alot harder to support the head as rigidly when its cantileavered out from its supports. The table is not as big as it could be made but this is by design. I've left the table about 2" narrow of what it could be to allow room for way covers, hard stops, other good stuff like that. Theres only ~35mm between the end of the carriage/yoke/whatever you want to call it and the braces/gantry columns. It still leaves about 600mm/23" of travel in that direction. Which I'm reasonably happy with.

Have you seen the DSG designs from Mori Seiki? They have some IMHO beautiful designs with a split bridge for the same reasons - they put the rails on the bit joining the halves and run a screw on either side though - which might make all the alignment a bit easier, and also puts the Z-drive axis right through the spindle's axis.

This doesn't seem to be Netscape friendly, but it is a nice presentation:
http://www.moriseiki.co.jp/english/p...dcg/index.html

[arie kabaalstra]

Very intresting design, i like it, maybe you could build the Bridge behind the Z-motor as well, providing ridgidity, and better alignement..
You might even consider running a third guiderail at the back of the spindle assembly creating a triangular support this way..

[damae]

That's one sturdy-looking machine! Is this for a business, or is it DIY for the joy of it?

5000lbs sounds about right for a machine of those dimensions. You could increase the mass (and ability to absorb vibration) for little cost by casting polymer concrete inside the large columns. Also, you might think about designing some forklift pockets into the base of the frame, to make rigging that much easier.

Please, keep posting and show us how this progresses!

[dberndt]

This machine is just for the fun of building it. I dont really have a plan as to what to do with it when its built. Build another machine I guess, maybe a cnc lathe.

I've spent the last few days tweaking the drawings and figuring out the drive system. Leaning towards a low inertia 750w sureservo system from automation direct. I've been crunching the numbers and it looks like with the appropriate reduction I should be able to get around 500ipm rapids and lots of torque for cutting. I modelled it with a 500lb cutting force from the side of the cutter, that should be plenty high I imagine. Though I have no real imperical data about what the sideloads whilest endmilling might actually be. Very dependant on cutter/rpm/feed I would imagine.

I got a very nice ballscrew off ebay the other day, unfortunately it tore through its packaging in shipping and bashed off something. The threaded end is toast and will have to be re-machined. Its bigger than any machines I have access to so I will have to farm that work out.

Hopefully the plans for the bottom part of the frame will be done sometime in the next week or so and I can send them out for quote. Need the weldments normalized and ground.

[dberndt]

The other day I saw a post that had a good link to a dealer of machine levelling feet that were made of rubber or something similar and had a leveling screw/nut. I think it was here but maybe not, anyone have the link. I have to find them again and get the specs so I can figure out how to size the holes for the feet.