Making a lathe test bar

Well there seems to be many trains of thought along this line. I can only tell you what worked for me.

Number ONE! Get it level. With a good level, your 6" torpedo won't do it this time, spend a few bucks or borrow one. No Twist, no Cant. Full length check along and across the ways, as many directions as you can figure a way to check it. And make notes, gives you something to look at to see if you're making a difference, I tend to forget, notes and sketches are easy. Take your time, let it settle for a few days between leveling sessions, mine took 2 months to get & keep level. Cast iron doesn't move easy or fast.
I wouldn't cut that piece of rod. Just face it off & center drill both ends, that way you can check alignment at several points along the travel of the tail stock. After you face & center drill it mark it lengthways with something to align with a chuck jaw with something semi-permanent, that way it'll be semi-repeatable and you can move it (longer or shorter). You don't need to make any cuts on the rod, a couple of dial indicators (tenths if you've got them), one for a top reading, one for the front, set up on the Tool-post with a couple of Mag-bases. Just keep running the carriage back & forth and making adjustments on the Tailstock until it's Dead-Nuts. And remember vertical alignment will cut a taper as well as side to side.
I know it sounds like a pain but, I've got my tailstock to less than a tenth front to back all along it's 36" of travel, I'm still off a touch in height, I'll get that straight as soon as I can get the tailstock split & shimmed.
Before you start, be warned, this Rabbit hole goes deep, there's no sense stirring a pot of worms if you're happy with things as they are! Why spend months chasing 0.002" of taper along 3' of travel when most of your work is only 10 to 12" long?
 
Several things can cause taper.

  1. The bed can be warn, and thus will lead to differing amounts of taper depending on the position of the tailstock and carriage.
  2. The bed could have twist, bow, etc and that will lead to a taper.
  3. With unsupported work you can get tapper if the head stock isn't horizontally and vertically aligned to the bed. If the lathe is rigid enough, this can even cause issues with supported work, as the lathe will just make the work piece flex.
  4. You can get taper if the tailstock is offset.
  5. You can get taper if the tailstock ram isn't horizontally and vertically aligned to the bed.
  6. You can get taper if the tailstock ram doesn't lock down consistently and securely.
  7. Depending on how your tailstock is built, you can get taper when locking the tailstock down because the two parts of the tailstock shift in relation to each other.
  8. tool pressure can of course all cause taper.

#'s 5,6,7 are what will usually get you on smaller or cheaper lathes. #1 & #2 can get you on heavily used lathes, or larger lathes that haven't been properly "leveled".
 
Joeman77 said:
Well there seems to be many trains of thought along this line. I can only tell you what worked for me.

Number ONE! Get it level. With a good level, your 6" torpedo won't do it this time, spend a few bucks or borrow one. No Twist, no Cant. Full length check along and across the ways, as many directions as you can figure a way to check it. And make notes, gives you something to look at to see if you're making a difference, I tend to forget, notes and sketches are easy. Take your time, let it settle for a few days between leveling sessions, mine took 2 months to get & keep level. Cast iron doesn't move easy or fast.
I wouldn't cut that piece of rod. Just face it off & center drill both ends, that way you can check alignment at several points along the travel of the tail stock. After you face & center drill it mark it lengthways with something to align with a chuck jaw with something semi-permanent, that way it'll be semi-repeatable and you can move it (longer or shorter). You don't need to make any cuts on the rod, a couple of dial indicators (tenths if you've got them), one for a top reading, one for the front, set up on the Tool-post with a couple of Mag-bases. Just keep running the carriage back & forth and making adjustments on the Tailstock until it's Dead-Nuts. And remember vertical alignment will cut a taper as well as side to side.
I know it sounds like a pain but, I've got my tailstock to less than a tenth front to back all along it's 36" of travel, I'm still off a touch in height, I'll get that straight as soon as I can get the tailstock split & shimmed.
Before you start, be warned, this Rabbit hole goes deep, there's no sense stirring a pot of worms if you're happy with things as they are! Why spend months chasing 0.002" of taper along 3' of travel when most of your work is only 10 to 12" long?
Click to expand...
Thanks, Graham.

I'm getting quite an education.
Dan_S said:
Several things can cause taper.

  1. The bed can be warn, and thus will lead to differing amounts of taper depending on the position of the tailstock and carriage.
  2. The bed could have twist, bow, etc and that will lead to a taper.
  3. With unsupported work you can get tapper if the head stock isn't horizontally and vertically aligned to the bed. If the lathe is rigid enough, this can even cause issues with supported work, as the lathe will just make the work piece flex.
  4. You can get taper if the tailstock is offset.
  5. You can get taper if the tailstock ram isn't horizontally and vertically aligned to the bed.
  6. You can get taper if the tailstock ram doesn't lock down consistently and securely.
  7. Depending on how your tailstock is built, you can get taper when locking the tailstock down because the two parts of the tailstock shift in relation to each other.
  8. tool pressure can of course all cause taper.

#'s 5,6,7 are what will usually get you on smaller or cheaper lathes. #1 & #2 can get you on heavily used lathes, or larger lathes that haven't been properly "leveled".
Click to expand...
Thanks, Dan.

Keep it coming, guys! I'm learning a lot!

Regards,
Terry
 
Dan_S said:
Several things can cause taper.

  1. The bed can be warn, and thus will lead to differing amounts of taper depending on the position of the tailstock and carriage.
  2. The bed could have twist, bow, etc and that will lead to a taper.
  3. With unsupported work you can get tapper if the head stock isn't horizontally and vertically aligned to the bed. If the lathe is rigid enough, this can even cause issues with supported work, as the lathe will just make the work piece flex.
  4. You can get taper if the tailstock is offset.
  5. You can get taper if the tailstock ram isn't horizontally and vertically aligned to the bed.
  6. You can get taper if the tailstock ram doesn't lock down consistently and securely.
  7. Depending on how your tailstock is built, you can get taper when locking the tailstock down because the two parts of the tailstock shift in relation to each other.
  8. tool pressure can of course all cause taper.

#'s 5,6,7 are what will usually get you on smaller or cheaper lathes. #1 & #2 can get you on heavily used lathes, or larger lathes that haven't been properly "leveled".
Click to expand...

And remember.
Everything moves, Benches, Cast iron, Concrete, even the very Earth under you feet!
 
Joe is right! Come to that maybe settle for a fifths indicator. If you get down to tenths, and start using levels of 4 arc-seconds sensitivity, (0.0002" in 10 "), you realize that everything is a bit squishy, and you can hardly ever measure the same thing twice and get the same reading. You can see a granite surface plate "deflect", and "level" even down to the concrete floor seems to move a bit.

The taper turning is effect is enough to be obvious. You can make the work turn parallel to the ways by adjusting so that the taper, over the lengths you mostly work, is too small to matter. It may get to be less than you are able cut and show it up in a measurement.
 
Joeman77 said:
Take your time, let it settle for a few days between leveling sessions, mine took 2 months to get & keep level. Cast iron doesn't move easy or fast.
Click to expand...
Joe - that is something I have wondered about. Suppose you have a lathe bed just plonked down on a bench, not necessarily level, or there is a bit of junk under one corner, or something. That iron is eventually going to settle a bit "twisted".

Can you measure any "bends or twists" coming out immediately? If it has "settled" into that state, and you take out the cause? Does it really take a couple of weeks relax out? Can you "force it" in any way?

I read that the guys who scrape on camel-back cast iron (semi-steel?) straight edges hang them up from one end and smack them with a mallet to make them "ring", to relieve internal stresses. Apparently done in a few minutes.

If a lathe bed has been set non-level, or worse, hard bolted down so that it "distorts over time", then making it level on the top will only work for a while, until some of the distortion works out. You have to level again, and again, approaching the desired end with ever lower forces, and doomed never to quite get there. Dang - but I can so dream up some dark stuff! :disspirited:
 
graham-xrf said:
Joe - that is something I have wondered about. Suppose you have a lathe bed just plonked down on a bench, not necessarily level, or there is a bit of junk under one corner, or something. That iron is eventually going to settle a bit "twisted".

Can you measure any "bends or twists" coming out immediately? If it has "settled" into that state, and you take out the cause? Does it really take a couple of weeks relax out? Can you "force it" in any way?

I read that the guys who scrape on camel-back cast iron (semi-steel?) straight edges hang them up from one end and smack them with a mallet to make them "ring", to relieve internal stresses. Apparently done in a few minutes.

If a lathe bed has been set non-level, or worse, hard bolted down so that it "distorts over time", then making it level on the top will only work for a while, until some of the distortion works out. You have to level again, and again, approaching the desired end with ever lower forces, and doomed never to quite get there. Dang - but I can so dream up some dark stuff! :disspirited:
Click to expand...
I'm not sure you can force cast iron to do anything fast without lots of heat & pressure, it moves slow and at it's own pace, usually a plus for us! I believe if it started out flat & true you can bring it back, except for wear or extenuating circumstances, it'll just take time.
Movement is always measurable, just not always the direction we want! And everything moves!
I don't know about ringing it back, anything is possible though. In the case of Camel-back straight edges I guess I always thought those things were about one step short of granite when it came to stability.
And sometimes dark is the stuff dreams are made of. Coal, Iron, Smoke & Fire!!
 
Please look at post #13 here:

www.hobby-machinist.com

Test bar

Hello. I recently-ish ordered a mt2 test bar, along with some other stuff. Unfortunately the test bar went out of stock before my order was packed. The company offers another test bar that is a combination mt2/mt3, and I told them they could send me that one instead. I had considered that one...
www.hobby-machinist.com www.hobby-machinist.com

Bob Korves gives an excellent approach.

Robert
 
Joeman77 said:
I'm not sure you can force cast iron to do anything fast without lots of heat & pressure, it moves slow and at it's own pace, usually a plus for us! I believe if it started out flat & true you can bring it back, except for wear or extenuating circumstances, it'll just take time.
Movement is always measurable, just not always the direction we want! And everything moves!
I don't know about ringing it back, anything is possible though. In the case of Camel-back straight edges I guess I always thought those things were about one step short of granite when it came to stability.
And sometimes dark is the stuff dreams are made of. Coal, Iron, Smoke & Fire!!
Click to expand...

You'd be amazed at what gravity will do with just a little bit of help.
 
You must log in or register to reply here.
Back
Top