Hi,
I converted an Anilam Crusader M w/ the SEM motors and West Amp servo Amps. I think there are some similarities to the systems and a bunch others have done it as well. There's another thread on this forum of guy doing just what you did, I posted a few things for him in his conversion, so look for that when you get a chance.
The whine you hear is the 5kHz switching frequency of the old West Amp servo's. 5Khz is w/ in the audible range for our ears. New servo amps are higher, around 20kHz or more and quieter:-)
I have looked into the replacements for the servo amps. First off, a manual on the sem servo motors::
www.hhrobertsmachinery.com/Accessories/SEM/SEM-MT.pdf
The SEM servo's are 30amps peak, so a 30 amp peak drive would work. I like the copley 423. However, I have 2 brand new copley 422's that I want to use that are only 20Amps peak, but I bet they'll work great. I'm still using hte original West Amps and that whining is annoying...
West Amp went out of business and the 'story' is that many of the engineers went to Servo Dynamics and the Servo Dynamics SD1525-10 is a 15amp cont/25amp peak servo amp that looks a lot like the west amps and is a replacement.
One thing to watch out for is that the DC bus voltage is higher than 100Vdc, I believe, and many of the AMC or Copley amps only goto 80Vdc. I would measure the input power on your mill to verify, I think mine is near 120vdc, but I don't recall off hand. The copley 422 and 423 go to 180Vdc.
www.copleycontrols.com/Motion/pdf/412.pdf
I am currently using tach feedback to the original west amp servo's and closing the loop around the linear scales. It 'mostly' works and I get some 'movement' that can be called hunting/pecking/dither where the control system is hunting between two encoder spots. I was bent out of shape at first on this, but then when you think about the linear scale resolution is 0.0004", the hunting really isn't going to affect anything I'm doing. There are fixes for it, put a 2nd encoder (like you mentioned) on the servo and dual loop, or use single loop w/ an encoder on the motor only. Either would work.
I am using a 5i25/7i77. I just bought a 7i92 to try on a small lathe I'd like to retro-fit. You might consider going to a 7i92/7i77 setup with the PREEMPT kernal. I think it will take a smidge more work to setup, but that seems to be the future of linuxCNC as the RTAI kernal is not supported as well (I guess, not an expert in this). Either will work and will take time/learning to get going. I like the ethernet because you can string it a decent distance and should be 'ok'...
Lastly, John Thornton has converted a mill like yours and has info here:
gnipsel.com/linuxcnc/
I like these guys at Sector 67 for info:
code.google.com/archive/p/sector67-sandb...rojectSheetCake.wiki
Here's one where the guy used PICO systems and he has a schematic I found useful:
sites.google.com/site/bmklawt/home/emc2
(also, west amp servo manuals)
Good luck,
Mark