The 'X' axis crank/leadscrew on one of our 'M' head Bridgeports is sick. I need to get an idea of how much down time to schedule for repairs (and how many $$$).
Symptom: When moving the 'X' axis at approximately the 1/4 and 3/4 areas of the full travel, the shaft goes into some sort of oscillation mode and vibrates terribly. Feels like it is wobbling from side to side or hanging up and releasing. Does it worse with the power feed but still does it with hand cranking. I'm suspecting either a really dirty half nut assembly or a completely trashed lead screw.
Anyone had the problem? How to pull the table? Can I get parts?
This unit is pretty tired but the capital budget got eaten up by a new Haas TM-1 that no one is trained on. If it was my decision alone I'd have spent the 2 hours pulling it apart in early January, had a month to deal with it, but alas, it's still sick. Politics rears it's ugly head again.
No, not really. First, get it to this position, and hold both X and Y handles at the same time. Bump the X handle. If you feel movement in the Y handle, the "yoke" that holds both nuts has gotten loose - not too unusual, especially on an M head, presumably round-ram machine from pre 1958.
Get a table to support the machine's table. You can use the knee to match the heights. Place the table to the right of the machine. Oh, if you have a power feed, then maybe a cargo strap and a hoist or engine crane would be better. Remove the nut and handle on the left side, then remove 4 SHCS that hold the handle bearing bracket on left and just pull it off. The left bracket is the one with the constraining bearings, so the leadscrew can slip out of the right bracket if you take the right handle off. (I think this is how this works.) You should be able to just push the table right. Be careful, it is actually possible to just launch the table right off the machine onto the floor. You can push the table to the right enough the work on the yoke without fully removing the table.
Yes, but not knowing what is needed, it is hard to say. Not much of the table/knee innards on the Bridgeport has changed much since 1938, when my machine was built. (They did make the knee longer for mory Y travel.)
Anyway, you may have worn the threads right off the X nut. It is a bronze piece that is held in a keyed hole in the yoke by a big-headed screw that is then locked in place by a smaller screw. When the nut wears, it can be slit and then the big head screw pushes the halves together to reduce backlash. You may have junk in the threads, misalignment of the yoke, or wearout of the nut/leadscrew set.
There is an oil hole in the center of the table, in the bottom of the middle T slot. You have to line up the X table position with a mark on the front of the table so the hole lines up with the nut. If you haven't oiled this in, say, the last 20 years, that is likely the problem. You can also oil the X screw from underneath the machine, but you can't get to the Y screw easily.
No, it happens most of the time, happens the worst when just backing the table out of the way for a tool change.
Power feed on the right so that would have to come off also? Can I take the whole screw out without touching anything else? I'd expect it to be pretty awful, worn in the center, that would tell a lot.
I've been looking at the manuals Iggy posted, it shows the back lash takeup adjustment.
Time's the problem. I can get a grad student working and done with a simple Bridgeport level part in less time than I can trust him/her to not bury the spindle into the vice on the TM-1. These are folks on a timeline that does not include becoming a CNC affectionado. About 1 in
10 will spend the time to overcome the TM-1 and TL-1 learning curves.
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