Anthony,
Surely that is a fault with the operator not knowing the machines' limitations, not the machinery, especially breaking 3 sets of half nuts. I did make new ones for mine, but because they wore away, not broke. To me that smells of the wrong feed setting in the gear train, too fast.
I only ever broke one item on my machine, and I know that was my fault because I was cutting 2 TPI thru the gear train driven by the spindle, when I should have driven by the leadscrew. 4 TPI, as far as I can remember, is max when driving from the spindle.
I regularly parted off 3" brass bar with no problems at all, and normally took 1/4" roughing cuts in steel (1/2" off the diameter), so to me, my machine was plenty rigid enough for what I needed to do, and if I needed another lathe of that size, I would get one again.
But anyway, back to the topic heading.
I am trying to remember something from about 15 years back, and I think this is the rough design I used. The ladder top adds to the rigidity of the machine by helping to prevent twist and bending forces. I made a custom drip tray that sat between the lathe and stand top. When finished, the top had all weld joints dressed level and the whole lot was checked and adjusted for flatness. You only ever have to do this the once for your lathe, so it may as well be right.
I think the bottom part had two cross braces instead of the one I show.
Now a close up on the reverse selctor. I actually fitted the bronze bar (the same width as the slot in the gear), and set it up on the mill, picking up on the half moon that was already in the top piece and bored the bottom piece, so I had the correct sized full support hole. But the way you suggest, having just a bar sitting in the gear groove and giving support to the gear is a definite step in the right direction, and should improve things no end.
A very fuzzy picture here, but it shows enough of what I did. I turned up a pulley with a 1/4" full depth round bottomed groove in it (1/4" deep). This was the same diameter and central bore as the actuator knob, and they were swapped over. Then a little bracket and a bent handle were knocked up, pivotting towards the top of the handle, the bend was to allow the bottom part to not hit the apron so that the top half had enough movement to operate the linkage with a piece of 1/4" unhardened silver steel used in the knob groove to move the operating linkage in and out. It never failed to work and the crossfeed became a joy to use rather than a PITA. For a quickie guesstimation of sizes and lengths, I think I made the handle out of 1/2" stainless square bar.
I had a little trouble, when heavy cutting on back gear, the back gear would jump out of mesh. So if you look at the little ball on the end of the red line, it is pointing to a collar that stops the shafts moving side to side. I drilled a blind hole into it, I think 3/16", and fitted a ball and spring. Then on the small casting the little ball is also sitting on, I drilled a small detent into the face. Once all assembled, the back gear was put into its operating position and the collar then moved around the shaft until the ball went into the detent, the collar was then tightened up in that position. So whenever the back gear was used, the detent used to engage and stop the gear from coming out of mesh. Again, another little mod that worked perfectly.
This was just a mod because I was forever losing the tightening spanner for this nut. I got a ratchet spanner, machined up the top of the nut to fit it, and basically made it a fixture to the nut. Cut the unwanted end off and put a bit of heatshrink on it to stop pain when in white knuckle mode. A quick flick of the lever and it was ready to undo or do up. Nuff said.
I did do another mod to the tailstock, just before I sold the lathe, and it can be found here.
http://www.homemodelenginemachinist.com/index.php?topic=2114.0
Now this is a collection of bits around the saddle and apron. Top to bottom.
Fitted a 100 sized QCTP. This required the bottom of the toolpost turning so that it could fit on the limited size offered by the topslide, I also had to remove a bit of the casting top, just so that I didn't take too much off the toolpost.
Next comes all singing all dancing resettable dials, courtesy of Messrs Myford and their ML7 lathe. BTW, the Atlas 10" is very similar to the ML7, just 50% larger. I was at a show, and bought two of the dials for 17 squid each, and by tapping out the centre to Atlas size, they were fairly easily fitted, but did require new index plates making and fitting. I also did the anti backlash thrust washer jobbie on the topslide and cross slide at the same time. Much better than the tiny little bits that are on there as standard.
Then comes the saddle clamp handle, I don't think I need to go into details, only to say that I got a few brand new parts from a dealer when I made up a few extras of the underneath clamp plates. They are unobtainable new in real life, and he was willing to do a fair exchange.
Next comes the major bit that you can't see. The half nuts and holder are made from Mazak, and under normal conditions, I would expect a life of about two years out of them. They were over 20 squid for a new set, and very badly cast. By the time you got them to fit, they wobbled all over the place. So I made a copy of them out of a piece of gauge plate and some lumps of brass. I also fitted a basic gib set to them, so that play could be eliminated as they wore. I checked them after about 3 years use, and nothing needed doing and showed very little signs of wear. When I sold the machine, I gave the chappie two spare blocks I had made with the screw thread cut thru them, all he had to do was cut them in half, mill a little, and he would be ready for another long trouble free machining spell.
I had a stage in my workshop where I was repairing all sorts of odd things with weird threads. So I marked up the top of my drop in indicator with 16 markings, this helped me a lot during my single point screwcutting phase.
One thing I need to mention was the fitting of a reversible 1/2 HP motor and control box. This is a must if you are to do any metric screwcutting on this lathe.
I think that fitting the smaller motor really helped keep the machine from being damaged. If it didn't like what I was doing, it would slow down or stall before any mechanical damage came to it.
Over the years, I got to know it inside out and back to front, so very rarely would I ask it to do more than I knew what it was capable of, but it did everything I required at that time.
Loads of lube everywhere, and a clean up every now and again was all it required, and it became one of my most loved and accurate machines I ever owned, up until I got my new one sorted. Now that is a totally different story.
Bogs
