Carriage play at back of ways ??...

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56type

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Was looking to eliminate unwanted taper in the lathe (Atlas 10100 Mk.2) when cutting a work piece and while checking for the source ran across some play/slop at the rear of the carriage. I mounted a DI to the bench and found the carriage would lift 0.003 when I lifted up on it at the back of the carriage. Doesn't seem to have any vertical movement at the front of the carriage. Gibs are tight with no front-to-back movement when pushing/pulling on carriage.

Is this a normal/expected amount of movement ?? Just to be clear the direction of the movement I'm referring to is in the Z axis, not front = headstock end of carriage & back = tailstock end of carriage. The movement happens when the carriage is lifted vertically up from the top of the ways.
 
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questions...
what diameter material are you turning
what material are you turning
are you between centers or without support
is your tooling on center

normally the carriage is being pushed away from the work, not really lifting unless you are way over center on tool height.
or unless you are parting, then lift can be significant

you may do well to check the plate that bolts to the back side of the carriage, add shims or otherwise reduce the clearance, if the wear is uniform- otherwise you'll need to live with some slop
 
I think it is the nature of the beast; the back of the carriage is quite light, and the front is much heavier, and is cantilevered over the front of the bed, tending to lift the back of the carriage, this is why it is a good thing, especially for smaller lathes, to have a taper attachment to add weight to hold the back end down, if one does not have a taper attachment, a weight could be added to the back end to achieve the same result. I do not think that rear gib adjustment would do much good, as bed wear usually makes tight adjustment impossible, resulting in snug fir towards the tailstock and loose fit nearer the headstock.
 
Ulma Doctor said:
questions...
what diameter material are you turning
what material are you turning
are you between centers or without support
is your tooling on center

normally the carriage is being pushed away from the work, not really lifting unless you are way over center on tool height.
or unless you are parting, then lift can be significant

you may do well to check the plate that bolts to the back side of the carriage, add shims or otherwise reduce the clearance, if the wear is uniform- otherwise you'll need to live with some slop
Click to expand...

I've moved the lathe to a new home on a tool cabinet I recently bought and after thinking I had it leveled, I was turning a 3" dia. steel workpiece with 3.380 stick out, the center of the workpiece was bored out far too much to use a center (making a jackshaft to mount 3rd pulley to a delta dp-220 drill press to reduce it's speed). While turning the part I was getting a 0.003 taper over the 3.380 of material that was being cut, with the end farthest from the headstock (unsupported) coming in at 0.003 larger than at the chuck end. I was taking 0.005 cuts with the small carbide insert cutting tool. I then finished the part and removed it. Found a 5.750 length of steel round stock that's 1" in diameter that I'm going to make into a test bar. I set the DI in the middle of the length sticking out from the chuck (5" total stickout) dialed in the piece n the 4-jaw and made the a first cut of 0.005 1" back from the end of the work to start the "barbell" shape of the test bar with a collar for measuring at each end. After taking the first cut I stopped the lathe & measured the same 0.003 taper in the first cut, again with the larger end at the tailstock end of the work (0.990 at chuck end & 0.993 at tailstock end unsupported) the collars remain uncut at 1" dia . I've since re-leveled the lathe adding a 0.005 shim at the headstock rear foot & a 0.019 shim to the tailstock end front foot.

In leveling the lathe for a second time, I noticed I was able lift the carriage 0.003 at the rear which happened to correspond to the amount of unwanted taper being turned (??). I haven't made a second cut yet to determine whether the shimming had the desired effect of eliminating the taper. I wanted to rule out the play in the carriage as a possible cause otherwise I could keep adding more shims without correcting the root problem...My line of thinking was that the unsupported end of the work could be trying to climb the cutting tool while at the same time causing the carriage to deflect enough induce the taper. It would seem though that with the forces the work would be applying to the cutter in a downward direction that the carriage would be forced down against the bed ways rather that lifted away them (??)...Thought I'd check with those more experienced than myself before ruling it out as a cause of the unwanted taper. Thanks, I appreciate all the help getting the lathe dialed in/aligned to make it run true.
 
You are not going to be able to align the bed on a flimsy rolling cabinet with only a piece of plywood on top, the bed is stronger than what you have attached it to. The forces acting on the cut are not all downwards, but also towards the front of the machine, which could lift the back of the carriage. I do not see how a cut that is constant throughout the length of the cut could create a taper situation. Do an experiment and add weight to the back of the carriage to hold it down, perhaps 10 - 20 lbs weight and see if it makes a difference.
 
I would be checking RO at spindle and chuck and on different diameters, how true the ways are first.
If you lock the carriage, set the compound to .2 degrees and make your cut using the compound what variance are you getting?
 
I have the same lathe and I suspect the solution is a bigger machine if accuracy cutting steel is required.

john
 
56type said:
Was looking to eliminate unwanted taper in the lathe (Atlas 10100 Mk.2) when cutting a work piece and while checking for the source ran across some play/slop at the rear of the carriage. I mounted a DI to the bench and found the carriage would lift 0.003 when I lifted up on it at the back of the carriage. Doesn't seem to have any vertical movement at the front of the carriage. Gibs are tight with no front-to-back movement when pushing/pulling on carriage.

Is this a normal/expected amount of movement ?? Just to be clear the direction of the movement I'm referring to is in the Z axis, not front = headstock end of carriage & back = tailstock end of carriage. The movement happens when the carriage is lifted vertically up from the top of the ways.
Click to expand...
The Z axis is from the TS to the HS on a lathe. I think you mean in the Y axis direction if that was possible or straight up? Do you have an anti-lift device (gib) on either or both ways on the bottom of the carriage? They will run under the bed ways. If so adjust the movement out.
 
Before attempting to do anything about the 0.003" that you can lift the rear of the carriage, you need to pull the tailstock off of the bed or maybe part way off, crank the carriage to the right end of the bed and measure the lift. There should be a shim pack between the M6-55 Carriage Bearing plate and the carriage. You can reduce the lift by removing shims. However, you should not remove more shim than the lift with the carriage at the right end of the bed or you will find that you cannot crank the carriage all of the way to the right end of the bed. However, I doubt that carriage lift is your problem.

More than likely, either the bed isn't level or the spindle is not parallel to the bed, You might try mounting a piece of steel solid round in your chuck, loosening the headstock clamps, and pushing to the rear on the dnd of the bar while re-tightening the clamp bolts. Or you might try Rolli's Dad's method of aligning the bed.
 
Also, they make what is called a bull-nose or pipe center that you could try.
 
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