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hwingo
06-16-2010, 03:38 AM
Hey guys,

I know the following question has a great many vairables but I need to seek wisdom from the experienced.

I have moved to a different location. My lathe is still on it's shipping pad. It is not level nor have I attempted to make it level. I am waiting for the concrete pad to be poured before taking it off the shipping pad and setting the lathe in its final resting place. I have turned a couple of very short pieces (~1.5" long X 1.25" dia with the lathe sitting on the shipping pad). Turning took place with the work piece sticking from the chuck's jaws by approximately 1.75". I did not use the tail-stock. I was basically doing a "tickling cut" to slightly reduce the diameter by only several thousandths.

I ended up cutting an unintentional taper. Can't remember which way the taper ran. There was about .002" difference over all length (approx distance 1.5").

Can this much taper, over such a short distance, result if the lathe is not level or is it more likely that I have somehow managed to cause the head to become misaligned during shipment?

Harold

Ian B
06-16-2010, 03:53 AM
At the risk of being hung, drawn & quartered here, I'd say that having a lathe level or not has no effect on how it cuts or whether it turns taper. Lathes are found on ships, and they seem to do fine.

What's more important is if the lathe is sitting on uneven ground, such that the bed twists (assuming the lathe has 4 feet on the ground as most do, not 3).

A bit of shimming under the feet might sort the problem out.

Ian

MuellerNick
06-16-2010, 04:17 AM
At the risk of being hung, drawn & quartered here, I'd say that having a lathe level or not has no effect on how it cuts or whether it turns taper. Lathes are found on ships, and they seem to do fine.


I won't pitch and tar you! :D
But "leveling a lathe" means something different. It means by most to get the twist out of the bed (with the help of a level).
But I doubt that any bed can have that much twist to get the numbers posted.


Nick

hwingo
06-16-2010, 04:24 AM
I won't pitch and tar you! :D
But "leveling a lathe" means something different. It means by most to get the twist out of the bed (with the help of a level).
But I doubt that any bed can have that much twist to get the numbers posted.


Nick

So are we saying that the head may be out of alignment? Keep in mind that the lathe is bolted to a wooden shipping pallet and the "legs" are not touching the ground.

Harold

MuellerNick
06-16-2010, 06:32 AM
Well, for the stickout and diameter, I don't expect that much deflection. But before paniking, I'd accept it for now, and level the lathe ASAP.

No further guessing, mix the concrete! ;)
Nick

EVguru
06-16-2010, 06:55 AM
Keep in mind that the lathe is bolted to a wooden shipping pallet.

That could well be the problem.

You haven't told us what kind of machine this it. Many of the smaller lathes, even something like a Myford can have considerable stress 'put in' to the bed if bolted down unevenly.

jimmstruk
06-16-2010, 08:06 AM
Harold, you stated you did not use the tailstock. Could your chinese chuck be not perfect? Also, after a good level and set up remember that the tail stock has a side to side adjustment too. That can remove a taper problem.sometimes. JIM

oldtiffie
06-16-2010, 09:04 AM
Harold.

"Leveling" is bit of a misnomer.

All that is theoretically required for the lathe so be as it was when it was manufactured - assuming no or minimal wear or distortion - is for the lathe bed to be "flat" and that all important parts to be co-planar.

It just so happens that if that plane in which all that stuff is horizontal it makes it easier to check, and if necessary to correct with a good level until all those points are in a horizontal plane.

If the lathe was tilted say 5 degrees and all points were co-planar, it would probably work just as well as if it were horizontal - but it would be lots harder to measure - although it can be done with a very good inclinometer.

"Starrett" 199 "master levels" - or equivalent are the usual levels of choice for this sort of work.

After the lathe (bed) is set level the alignment of the head-stock may be next and after that some test cuts. If the test cuts are not satisfactory as regards taper etc. the lathe bed may be "tweaked" by twisting it by adjusting the leveling screws that fasten the lathe to the floor/slab/bench.

It can be very frustrating and often counter-intuitive.

But that's life.

Wait until you have set the lathe level on what-ever it is mounted on - slab or bench etc. - and see if there is any real adjustment really required.

hwingo
06-16-2010, 09:26 AM
That could well be the problem.

You haven't told us what kind of machine this it. Many of the smaller lathes, even something like a Myford can have considerable stress 'put in' to the bed if bolted down unevenly.


Harold, you stated you did not use the tailstock. Could your chinese chuck be not perfect? Also, after a good level and set up remember that the tail stock has a side to side adjustment too. That can remove a taper problem.sometimes. JIM

EVguru: The lathe is a PM12X36.

Jim: Naturally it's possible the chuck is off. That having been said, the chuck I am using is a 8" Bison 6-jaw chuck. The chuck is new (perhaps 8 to 10 total hours of use).

Good Morning Tiffie and others having responded. I suppose that I will be able to realize more when the lathe is properly set. I just couldn't imagine such a short piece having so much disparity that close to the chuck. If the piece were 12" inches with the end free of support then I could wrap my head around "cause & effect".

Harold

MuellerNick
06-16-2010, 10:09 AM
One needs a really bad juck to get some taper. If the jaws' gripping faces are really conical, then it's doable.


Nick

Errol
06-16-2010, 10:29 AM
hwingo, once you level it up and set the headstock your lathe will cut true.

In answer to your original question, yes, being even slightly out of level, you will cut a taper.

I too, have moved, and with building the shop and doing the million things one does when moving, I never gave the lathe much attention.

One a recent job, after having days (literally) of frustration cutting unintentional tapers, I went back and reset the headstock, taking hours of time. Everything good.

One day I checked the level at the tailstock end, and had to tweak it a bit.

Guess what! Now lathe was cutting tapers again! So I had to re-level both ends, and realign the headstock again.

Ok, now things are great, but I was one of those that for decades believed "level" was not a critical thing. Now I know that even a quarter of a turn on a leveling bolt will cause tapers.

#1 on my machine tooling "to buy" list is a decent level.

Alistair Hosie
06-16-2010, 11:05 AM
Question is the tailstock lining up with the headstock? maybe the tailstock is needing tweaking a little to centre it. Alistair

sidneyt
06-16-2010, 11:21 AM
Could your chinese chuck be not perfect? JIM

How would the chuck have anything to do with the workpiece having a taper? If it had been a Bulgarian chuck it would have made no difference.

lakeside53
06-16-2010, 11:44 AM
If the chuck is not mounted (or machined) square to the spindle, it will move the workpiece in an arc that increase with distance from the chuck, and that cuts a taper that gets smaller towards the tailstock.


One of my lathes cuts a taper that INCREASES in diameter as you proceed from the chuck - and it's not work-piece deflection... that needs to be tracked down, but can't take the lathe out of service right now..

EVguru
06-16-2010, 11:50 AM
If the chuck is not mounted (or machined) square to the spindle, it will move the workpiece in an arc that increase with distance from the chuck, and that cuts a taper that gets smaller towards the tailstock

No, it doesn't.

If the cutting tool is moved parallel to the axis of rotation then you end up with a parallel cut. The chuck being off centre or off square just means the axis of rotation wouldn't be down the centre of a round bar.

lakeside53
06-16-2010, 12:21 PM
I need to think about that..

OK.. yes... I was thinking about an incomplete cut (basically shaving off one side at the far end)... fully machined, it will be cylindrical.

gwilson
06-16-2010, 01:20 PM
Your headstock probably needs adjusting to get it parallel to the bed. This problem has nothing to do with bad chucks. Lathes on ships are made level WITH THEMSELVES so they turn true. Has nothing to do with movement of the ship. If I had to level a lathe on a ship,I'd turn the test piece before bolting it down tight. then,rather than attempting to use a level,which would be useless,I'd turn a bar between centers,and adjust the bed of the lathe until it turned a true bar. IT WOULD BE necessary to set the lathe up on shore before it ever went on the ship,and adjust everything. Then,on the ship,just bolt it down,adding shims till it again turned true.

To be having this much taper over 1 1/2",unless your lathe is twisted like a corkscrew,it has to be a mis aligned headstock. There are 4 bolts that you can loosen to swing the headstock into alignment. the headstock on modern Asian lathes sits on a flat surface. The Vee ways do not run under the headstock. I have had to adjust several Asian lathes. It is a bit of tinkering,but chuck a piece of metal in the chuck. It should be,say,1 1/2" dia. X 10" long. True it up with a few cuts,then,take a VERY LIGHT cut so as to not deflect the metal. Make sure your bit is sharp. If the outermost end of the metal comes out larger than close to the chuck,the headstock needs to be tapped a bit to swing it towards the operator. You must loosen the 4 bolts to do this,but could leave one bolt a bit snug to act as a fulcrum.

After getting the headstock aligned so it cuts a straight bar of metal, use the tailstock on a more slender bar,say 1" X 12". If it comes out tapered,adjust the tailstock sideways carefully,until the bar cuts parallel.

Lastly,I take a light cut across the faceplate,and I mean LIGHT. If your lathe will turn a true bar,and face the faceplate a few thousanths HOLLOW,it is within spec. I like my present lathe as it faces dead flat and turns dead true,which is rare.

The lathe facing hollow is because they will produce flanges that don't rock.

Black_Moons
06-16-2010, 02:25 PM
A: Chuck can not cause taper assuming you machine the whole surface of the workpeice, even a 3 jaw with 1/2" runout won't cause a taper.

B: Twists in the bed definately CAN cause a 1:1000 taper (1mil in 1"), easily.

Remember fokes! Everything steel, is actualy made of rubber! Gooie flexable wet noodle strength rubber. Just put your TDI somewhere on the lathe thats important and lean on the lathe, you'll probley cause a deflection right there.

C: Don't touch the headstock, unless you like trying to line up 300lb chunks of steel to within a micron. Straighten the lathe bed as best you can, and if theres still a problem then you can come back and *consider* adjusting the headstock, but id still highly suspect something else was wrong first.

Level the lathe, level it again after a few days of 'resting', And then realise whatever error is left, is 95% most likey operator error, like work/tool springing.

bob_s
06-16-2010, 03:37 PM
Hwingo:
Did you make the cut using the compound?
Did you check to see that the compound was set up parallel to the spindle?

oldbikerdude37
06-16-2010, 03:51 PM
C: Don't touch the headstock, unless you like trying to line up 300lb chunks of steel to within a micron. Straighten the lathe bed as best you can, and if theres still a problem then you can come back and *consider* adjusting the headstock, but id still highly suspect something else was wrong first.

Level the lathe, level it again after a few days of 'resting', And then realise whatever error is left, is 95% most likey operator error, like work/tool springing.

Thats real good advice , he needs to get it set up in its place before tweaking it and chaising his tail.
The olny time iv had to square a headstock is after a rookie crashed the lathe real hard.

gwilson
06-16-2010, 09:47 PM
There are usually jack screws on the backside of the headstock to adjust it. As I said,I've set the headstock on several Asian lathes. It just requires common sense and careful adjustments. You aren't literally lifting 300#.

hwingo
06-17-2010, 05:37 AM
Hi Guys,

I've had to pull 24 hours of "on-call" and I have not been able to respond. As always, I appreciate the various replies all of which have provided "food for thought". As things progress, I will provide an update and assuredly more questions will follow.

Thanks to all.

Harold

JoeLee
06-17-2010, 08:33 AM
The bedways could be worn slightly as you get closesr to the chuck which would cause the carriage to start to ride down from center thus cutting a larger dia. as you get closer to the chuck.
I've noticed this as being common on older machines, since that is the area that the most use.

JL...............

oldtiffie
06-17-2010, 09:20 PM
If I recall correctly, the OP - "Hwingo" - Harlold's lathe is very good and is less than two years or so old - same as the rest of a lot of his stuff - an he looks after it like a baby - as he should.

I'd be very surprised if wear was a problem.

I guess it is possible that the lathe was bumped during packing, transit or unpacking and knocked the head a bit out of line - but that's easily found and if it is the case, is easily re-aligned - but its all guess-work to date.

I'd suggest that we wait and see what Harold's advice is after he gets his lathe onto a good floor and set up and a few test cuts taken.