2 gantries with a shared work area

Todd wrote:

I say this knowing nothing about Machinekits implementation of this if it even exists. But it may make the integration of duel gantries and their interaction with each other easier, on one computer with shared resources rather than two separate computers and trying to transmit position info between the two.

One place you may be able to save some cash and combine items. Rather than having 4 ball screw assemblies just for the gantry axis, use just 2 fixed screws (one on each side) with 2 nuts on each screw and rotate the nuts instead of the whole screw. It often makes more sense to rotate the nut rather than the screw on really long screws like you're going to have there anyway.

As far as the shared work area, you could always just not worry about predicting interference with soft limits and simply rely on hard limit switches to prevent crashes as they happen.

Hi I would love to do a rotating ballnut setup but don't have the skills or know where to start, my plan was to use 2020 ballscrews 2m long * 4 the cost is £640 + import tax I should be able to spin these to get 10m/min although considered better bearings so I can spin 50% faster for 15m/min.

Since I can't find 4m lengths of Hiwin's I was going to butt 2 together to get the travel.

I have also considered making 1 gantry R&P powered for the whole length and 1 gantry with 2m ballscrews. If I did this I would not use the shared area to work one part. I would not like to work 50% of a part R&P and the other 50% ballscrew I think it would be noticeable.

The advantage of this is I have 1 gantry for speed and 1 for aluminium and higher accuracy.

Really though 2 gantries working the one area is a lot cooler.

andypugh wrote:

I don't find rotating nuts to be that much harder than rotating screws. My lathe has rotating screws, but the mill has a roaring screw on Y but rotating nuts on X and Z.

I guess if you are looking to buy all off-the-shelf parts then rotating screws is easier, but if you have any machining capacity at all then it should not be so hard.

Couldn't you use a flange style ballscrew, machine a recess in the centre of a timing belt pulley to locate the flange and bolt them together? That would be an easy job on any lathe.

I'd also try and offset the joins in the linear rails on each side of the gantry by having unequal length rails. Make sure you tell your rail supplier you want to join them together so he gets nice clean cuts on the ends.

andypugh wrote:

Well, you also need some sort of thrust-bearing arrangement for the ball-nut to rotate inside too.
But there are lots of cheap car wheel-bearing sets in the right sort of size.

Yeh, that makes sense. I've got some trailer bearings somebody gave me. I might need this one day...but currently my rack and pinion drives are working nice on my machine but we are talking 21 m/min for plasma.... I'd love to see a sketch or cad drawing

Never mind, found one
www.nzbzd.com/Rotating-Ball-Screw-Nutxjfckbub



I think the dark bearing cup needs to be pressed into the gantry.
I've actually got some M30 x 2 threaded rod and matching half nuts that might nearly be big enough to machine some sort of tapered bearing mount out of

Andy thanks, there are some very good ideas on this thread
www.mycncuk.com/threads/3340-Rotating-Ballnut-design-ideas
The one on Page 13 is very nice and compact despite its supposed flaws.
You'd need to be careful with the maximum RPM of standard wheel bearings as a wheel rotates quite slowly. But then again plenty of lathes use tapered roller bearings!