iconoclast
Enlightened
- Joined
- Sep 11, 2007
- Messages
- 207
I hate to post yet another newbie lathe leveling question, but I'm frustratingly close to getting this thing level (that being my only real reference point for achieving straight/untwisted) yet I've got two problems I can't seem to find a solution for.
I have the machinist level that does 0.0005" per 10" span, and I have it calibrated so that turning it 180 degrees shows the same reading.
I have 1-2-3 blocks that boast parallel within 0.0001", flat within 0.0001" and square within 0.0001" and I'm using them to level based on the flats of the ways and not the tops of the V part of the ways.
I don't have the luxury of leveling screws, but if I have to hoist this thing up yet again to adjust the shims I'm going to seriously look for a way to attach some. Nevertheless, I have the thing shimmed such that along and across the ways are all level, according to the above mentioned equipment, at all four corners. Just for good measure (no pun intended) it also shows level (along and across) in the middle (roughly half way between the headstock and the tail).
So far so good. Then when it's time to tighten down the bolts, everything goes to $#!+.
Specifically, even slightly tightening any of the bolts make the rear (furthest from the operator) ways seemingly bow in the middle. That is, along the rear ways near the headstock the level says the tail is too high (two to three bubble lines), but along the rear ways near the tail the level says the head is too high (one to two bubble lines). Around that time placing the level across the ways in the middle will suggest the rear is too high (easily two bubble lines).
That bowing problem occurs even while keeping the head and tails mostly level across the ways, but that brings me to the second problem. The tailstock end has two bolts, one on the front side foot and one on the rear side foot. (The headstock has four of it's own.) The bolt on the front side of the tail will become tight with the bubble only moving one line towards the back. With my fingers I can "tighten" the rear tail bolt such that it moves the bubble three lines toward the (tightened down) front, and yet it still isn't what I'd quite call "finger tight". Presumably, I could shim the rear tail such that it's out of level when the bolts are loose but levels in when the bolts are tightened, but that seems just wrong somehow, and I don't know if that just compounds some other wacky twist that will cause other problems. (Not to mention any interaction with the rear-ways bowing problem mentioned above.)
I've searched the web, read through numerous accounts of lathe levelling and theories regarding the pros-and-cons of adding twist for straighter cut, dissection of the strengths and flaws of RDM, the physics of using lathes on ships, and torn out some more my hair. Yet the closest thing I could find to anything relevant was one old-time big-lathe installation manual that suggested that shimming the outside edge of head and tail equally on the front and back could help correct ways that bowed up in the middle (presumably equally front and back) and vice-versa (inside edge of head and tail for ways that bowed down in the middle).
Incidentally, for most of my newbie machinist questions thus far, a google search returns useful results from this cpf sub-forum more often than any one of the dedicated machinist sites. Who would've guessed? Anyway, that combined with the fact that I already have an account here means you all get first crack at helping me. Please?
I have the machinist level that does 0.0005" per 10" span, and I have it calibrated so that turning it 180 degrees shows the same reading.
I have 1-2-3 blocks that boast parallel within 0.0001", flat within 0.0001" and square within 0.0001" and I'm using them to level based on the flats of the ways and not the tops of the V part of the ways.
I don't have the luxury of leveling screws, but if I have to hoist this thing up yet again to adjust the shims I'm going to seriously look for a way to attach some. Nevertheless, I have the thing shimmed such that along and across the ways are all level, according to the above mentioned equipment, at all four corners. Just for good measure (no pun intended) it also shows level (along and across) in the middle (roughly half way between the headstock and the tail).
So far so good. Then when it's time to tighten down the bolts, everything goes to $#!+.
Specifically, even slightly tightening any of the bolts make the rear (furthest from the operator) ways seemingly bow in the middle. That is, along the rear ways near the headstock the level says the tail is too high (two to three bubble lines), but along the rear ways near the tail the level says the head is too high (one to two bubble lines). Around that time placing the level across the ways in the middle will suggest the rear is too high (easily two bubble lines).
That bowing problem occurs even while keeping the head and tails mostly level across the ways, but that brings me to the second problem. The tailstock end has two bolts, one on the front side foot and one on the rear side foot. (The headstock has four of it's own.) The bolt on the front side of the tail will become tight with the bubble only moving one line towards the back. With my fingers I can "tighten" the rear tail bolt such that it moves the bubble three lines toward the (tightened down) front, and yet it still isn't what I'd quite call "finger tight". Presumably, I could shim the rear tail such that it's out of level when the bolts are loose but levels in when the bolts are tightened, but that seems just wrong somehow, and I don't know if that just compounds some other wacky twist that will cause other problems. (Not to mention any interaction with the rear-ways bowing problem mentioned above.)
I've searched the web, read through numerous accounts of lathe levelling and theories regarding the pros-and-cons of adding twist for straighter cut, dissection of the strengths and flaws of RDM, the physics of using lathes on ships, and torn out some more my hair. Yet the closest thing I could find to anything relevant was one old-time big-lathe installation manual that suggested that shimming the outside edge of head and tail equally on the front and back could help correct ways that bowed up in the middle (presumably equally front and back) and vice-versa (inside edge of head and tail for ways that bowed down in the middle).
Incidentally, for most of my newbie machinist questions thus far, a google search returns useful results from this cpf sub-forum more often than any one of the dedicated machinist sites. Who would've guessed? Anyway, that combined with the fact that I already have an account here means you all get first crack at helping me. Please?
