I finally installed the hardened V rails on both the X rails as well as the upper AND lower Y rails on my PRT Alpha.
My rails were very worn, they have been ground to shape more than 6 times now (I lost count) and I was not looking forward to doing that again. It's not hard, just time consuming. This time I went ahead and ground them aggressively using string and a straight edge to get them flat on top. I also ground the sides to remove burrs and make them smooth on the side where the hardened rail would be installed. I didn't grind all of the V away, just enough to make sure it was FLAT and the rail cap would rest on the top edge.
For the X rails and upper Y rails it was pretty straight forward. I used T2 V rails from SuperiorBearing.com with 13/64" holes every 3". First I ground the rails, checked them, put the rail cap on and placed a spring clamp between EVERY set of holes all the way down and added a spring clamp on each end. I then used a 13/64" bit to drill the holes. I used M5 x .80 x 14mm button cap screws with nylon lock nuts and a washer on the mild steel side. That went well with the most tedious part being drilling. I repeated that process for the upper Y rails. I purchased a dozen 13/64" drill bits, I ended up using 6 of them for both X and upper Y rails.
For the lower Y rails the process was different. I clamped the rail caps in place with a combination of Bessey and regular clamps to make sure it was in position and would not move. I then used a self centering bit (like you'd use do drill hinges) and made a divit in every hole to help center the bit for the next step. I then drilled in the center of each hole with a 4.2mm bit all the way through. After that, I used a 5mm tap and tapped each hole. Then installed the same M5 x .80 x 14mm cap screw along with an M5 lock washer. That went reasonably well but be sure to buy at least 2 taps, there were 46 holes total and my first tap lasted for 44 of those.
All of the above was done AFTER making doubly/tripplely/quadrouplely SURE the rails were flat, smooth, spaced correctly and parallel. To give you an idea, I spent as much time measuring positioning and double checking as I did drilling/tapping/bolting the rails in place. When you do the lower Y rails this way the entire rail is now PERMANENTLY in place as you have effectively screwed the entire rail to the gantry cross member 23 more times in addition to the bolts with T nuts.
If you have questions, let me know.
Photos:
1676 shows the X rail with the spring clamps and the end spring clamp
1677 shows the long X rail shot with spring clamps
1679 shows the transmission jack we used to handle gantry
1683 shows the clamps on the lower Y rail with some of the bolts already installed and the tap I was using.
/RB