Post by Roger on Aug 7, 2019 21:48:47 GMT
Apologies if the photos are the wrong size, I'm using a Photobucket account for these to keep them separate from my other uploads.
I thought I'd share some shots of the CNC conversion while I strip it for maintenance. The Z-axis has been a bit suspect for a while, with the odd clunk when it does the first move of the day. I'm also not happy with the backlash compensation with it as it is. The strip down is intended to check the leadscrew that operates the knee and to see if there's a problem with the slideway. It's had a pretty hard time so I expect it's pretty worn and needs some adjustment. What it really needs is shipping off to someone to regrind the ways, but I can't afford to be without it for a long period so that will have to wait until another time.
Anyway, here are a few shots to show some of the conversion details.
This is a top quality ground recirculating ball leadscrew which I had from the machines I still support. Alternate bolts go through the bellows retainer. I wish I had beefed up the casting, it's a bit thin where the nut is.
You can see the little tubes that return the ball bearings from one end of the bearing to the other.
At the moment I don't use the Linear scales. They were very expensive Newall types which I hope to use at a later stage. At the moment, the options for doing that are limited and I think I'm going to have to do my own thing with the electronics for that. Some sort of Fuzzy Logic seems favourite, but I need more time to sit down and work out a solution.
The AC Servos has a plain shaft but the THK leadscrews have a keyway.
I made the flexible couplings from aluminium.
The undriven end of the X-axis servo is supported by a bearing with an oil seal.
That just pulls off. the big sleeve is a mechanical end stop made from Grey PVC
I can't find the spanner to undo the nut on the end of the thrust bearings at the moment, but I can get the table off without it.
The large flange on the RH side of the thrust housing doesn't touch the cream coloured housing. Instead it bears on the outside of the thrust bearing pair. There are two angular contact bearings back to back which are supplied ground to give the correct preload if you clamp the outer races and inner races solidly in the housing and on the shaft. There's no adjustment.
You can see how little room there is under the X-axis. I had to search really hard to find a leadscrew with a small enough ballnut, most of them are round.
The Y-axis leadscrew thrust arrangement is the same.
Finally you can start to see the Z-axis drive arrangement. This was the biggest challenge of the conversion due to the limited space. I still need to get the Y-axis leadscrew out of the way so I can get to it.
The pulley is keyed onto the end of the leadscrew but it probably doesn't need to be. I tightened the flanged nut up tight and then spotted through for the M4 cap screws that hold the pulley on.
This is how it looks with the pulley and motor removed. The access on this side was where the handle for manually adjusting the knee went with a large cast iron boss. That was replaced with an aluminium plate and bracket to hold the motor.
The thrust bearing is on the knee, in the casting which had to be machined to suit. Here is the plate which clamps the outer races into the bearing pocket machined in the knee cross beam. The blue item is a filter to keep dirt out of the bellows which suck and blow each time they move.
You can see the bottom thrust bearing with the retainer removed. Machining this pocket was a challenge. I did it on a Bridgeport a friend has.
I'd like to remove the thrust bearings for inspection an greasing, but I still can't find that damned spanner! I'm beginning to wonder if I ever made one, but it's unlike me. I simply can't remember, it was done back in 2008 and a lot of water has passed under the bridge since then.
So I've used a piece of material that has a handy M10 hole in it to hold the body of the tool so I can add the two 5mm dowel holes. Here I'm clocking it to get it on the centre line of the chuck. I can spin the chuck right round and adjust the quick change tool post to get it at the right height.
Then it's just a matter of zeroing the DRO and winding the cross slide both sides of the tool to add the holes.
A similar idea was used to hold the tool so I can drill and ream the handle hole.
It fits really nicely, so I'm pleased about that. The same tool is used for all three axes.
The pins are just short lengths of Silver Steel.
More tomorrow when hopefully I'll find out what's causing the problem with the Z-axis.