Hi Ray, I was just thinking I needed to do an update. I've had company. Some snow bird friends are on their way back up North and stopped here for a week. Beyond that distraction, I've had a terrible case of "You can't get there that way". I put the bearing holder together for the Thompson screw and mounted the table. There was a hard spot when I turned the screw. Same spot every turn. It didn't matter how I adjusted the nut in the saddle, it wouldn't turn freely. So I took the table off the saddle and turned the screw. The free end scribed a circle nearly an inch and a half in diameter. I played with the bearing block for a while, but the inescapable conclusion was that something is bent. Hours messing with the screw, surface plate, and indicators and I'm pretty sure that most of the bend is where the bearing surface meets the threaded part of the screw, but there is also distortion in the threaded part. It was an Ebay screw and I would have sent it back, but I made some modifications to the nut and the undriven end bearing surfaces. The seller didn't fall all over himself to replace it, and I don't blame him. I should have checked it before doing modifications. I know better.
So much for the Thompson screw. It goes in the resource drawer. I have a 1605 import screw on the Y-axis and some other things. I am okay with the performance. The problem is the integral mounting flange. The nut will fit in the recess I cut for the Thompson nut, but the table will not go on with the big flange sticking up. That flange was most of the reason why I got the Thompson. So with the Thompson out of the running, I can either buy a screw and nut from Roton, or do something about the import nut.
I'm cheap, so I attacked a spare (and short) 1605 screw from the drawer. The nut is hard. Way hard. It eats carbide without flinching. I don't have any ceramic or diamond inserts, so I attacked it with the grinder. My coarse wheel is #60, but it ground the nut faster than I expected. I put a plug in the grease port of the nut to keep out at least some of the grit. I now have a nut that will fit in the saddle without rubbing on the table. The present screw is nowhere near long enough, but at least I know that the nut can be fit without excessive grinding time. The ground down nut feels like it digested at least some grit. I'm going to take it apart and see if I can clean it out and put it back together, If I cant get it back together, I'll have to grind down the nut that comes with a longer screw. I'll pump the next nut full of grease before grinding it. That should keep the grit out better.
Now I need to order a 400mm 1605 screw with machined ends and nut. But that will have to wait because I'm going to California and Washington next week.