@BobKarnaugh Machined us a new topslide nut, this part replacement is normally $1100.
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Yes, he did as a matter of fact
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Just went out and tried to thread it in, seems to too large to even fit in. When layed against the acme threaded screw, matches nicely.
Hopefully I can get back from Paris early today to thead the part.
Well, does the tap go into the existing nut’s thread smoothly? The existing threaded nut’s gage pin diameter was about 0.391 if I recall correctly, while the new holes were drilled 0.406. Also, there is the practice slug with the 0.406 hole in it. I would be cautious in enlarging the hole much.
Doesn’t go in at all. Even the tapered part.
@BobKarnaugh and I played with the Acme tap this afternoon and it was interesting. The tap would not go into the old nut even though the dimensions seemed OK. To make a long story short, we decided to just cut threads in the practice part the Bob had made. The tap itself is interesting because it’s two taps in one - a starting tap followed by a finishing tap. Anyway, we cut the threads and the piece fit on the screw just fine. It’s nice and tight at the beginning and end of the screw but a bit loose in the middle (much better than the old piece). It seems that there is some wear on the screw. I’m not sure how much difference it will make. Now we need tap the real piece. It’s may be a bit tricky getting everything set up square.
The new threaded piece is on the Acme threaded rod that Tim brought in. You can see the tap in the background.
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The tap is a “looser” tolerance tap. So that maybe playing to the looseness.
Does the rust act as a lubricant or anti-backlash filler? 
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As Mike said above, and can be seen from closely inspecting the photos, the rod threading is more worn in the center region than the ends. The nuts, new and old, demonstrate notably more play when at the center of the rod than at the ends. While the center even looks to be less in diameter, it measures equal in diameter; it is the width of the threading that has been degraded through wear.
The question now is do we want to attempt replacing the worn acme thread rod with new? The rusty rod in the photo is not worn, only has superficial rust. It can be just fine with a rust clean off and oillng, I believe.
Also, the closs slide can be anticipated to have at least as much of the same issue as the topslide. Beyond that, the Bridgeport has a tremendous 50+ mils of backlash on the X axis, about 30 mills on the y axis. Determined by checking the travel of the wheels with the deck locked.
While we are at it, lets order a drum of anti backlash filler.
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Backlash on a lathe and mill are two separate games.
On the lathe, you are generally only working with forces away from the cutting tool. I would say away from the centerline, but some odd cases come up with the compound turned beyond 90. So roughly 98% of the time, you are only riding on the side of the backlash pushing towards the centerline. Short of retracting he toolbit to traverse without leaving a spring cut, or pulling out of a threading operation, how often do you actually use the back side of the thread? The biger issue is that forward of the wear, 20 thou on the dial might be 20.1 of travel, and behind the worst wear might be 19.9. And even that I don’t consider to be that significant.
It is easier to find examples where the gib and ways wear is a bigger issue.
I tapped the new part @BobKarnaugh made on the lathe.
Once I had it squared up (to within .001), it didn’t take but a few minutes or so to tap.
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So @BobKarnaugh ,@Chris_Wischkowsky & myself finished rebuilding the compound. We ended up replacing the lead screw as well. We machined the acme rod down to diameter to do a press fit.
The compound has minimal backlash now.
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Great work! The replacement parts these guys fabricated the manufacturer wanted about $2,000 because they are out of production spares!
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Well a few weeks ago during Bobs Lathe class, The press fit came loose. We tack welded together with the help of @malcolmputer. Unfortunately I believe someone locked the Gib set screw and the fusion welds broke.
So I prepped & did a full TIG weld around it. It’s not perfect but hopefully it will do.
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Welp, it ain’t coming loose again.
Thanks for cleaning up after me 
Now it will either give them feedback they are being silly, or more likely they will strip the threads out of the brass part.
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This would be awesome to have.
Wouldn’t this also mean you now have to use two feet to tig with? Left one on the positoner and the right one on the current?