Saddle causing .150 taper 3” off chuck no tailstock need help.

Any progress here?

Not sure if this is helpful at all, but my machine sits on crappy basement concrete, and it moves all the time, according to the weather and precipitation. Could that be a contributing factor in your case?

I don't know much, but this shifted head stock thing seems like the most remote of possibilities in my uneducated and inexperienced mind. But something is definitely very solidly misplaced...otherwise where would the repeatability come from? Imagine a chip embedded in the rear way. As the saddle moved across it, if the chip stayed put, the saddle would cant less and less as more of the saddle had moved past it. Or imagine the path of a flat plate with one dowel underneath it. The leading edge would climb for a certain distance, and then fall for a certain distance. Each time you rolled the plate, it would travel along the same line...Like a teeter totter with a moving hinge point. Anyways, I obviously don't know the answer, but maybe this little imagination exercise would be useful. HA!
 
jwmay said:
Any progress here?

Not sure if this is helpful at all, but my machine sits on crappy basement concrete, and it moves all the time, according to the weather and precipitation. Could that be a contributing factor in your case?

I don't know much, but this shifted head stock thing seems like the most remote of possibilities in my uneducated and inexperienced mind. But something is definitely very solidly misplaced...otherwise where would the repeatability come from? Imagine a chip embedded in the rear way. As the saddle moved across it, if the chip stayed put, the saddle would cant less and less as more of the saddle had moved past it. Or imagine the path of a flat plate with one dowel underneath it. The leading edge would climb for a certain distance, and then fall for a certain distance. Each time you rolled the plate, it would travel along the same line...Like a teeter totter with a moving hinge point. Anyways, I obviously don't know the answer, but maybe this little imagination exercise would be useful. HA!
Click to expand...

Is your lathe sitting on leveling feet , free standing or bolted down?

If its bolted down this could cause a twist in the bed which may be causing the taper, if it is free standing it may have twisted a little to allow all feet to make contact with floor. If leveling feet then check level with a reasonably acurate level.

Stu
 
jwmay said:
Any progress here?
Click to expand...

I was on my phone when I replyed , sorry I thought you were the OP. my bad :rolleyes:



Uguessedit said:
Bed is perfectly level front to back and lathe is fastened to the floor. Yes I reverified leveleling and it hasn’t changed in 6 months.
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I just re read the thread to see if I missed something, you say the lath is bolted down to the floor and level, you could try loosening the hold down bolts and giving it a try.

Also perhaps the pre load on the spindle bearings has changed due to wear etc. this might be making the whole spindle cock a bit when you start cutting, although it does look rock solid on your video from what I see.

I did the angle math and I came up with about 2 degree taper. Thats quite a lot.


Stu
 
Follow up: Well I’m still contending with the issue. The manufacturer has been very slow to return calls and today I finally was able to put a parts request in although I have to wait to get a quote back in a few days it’s a painstakingly sloooowww process. In the interim I removed the compound slide and installed a machined piece of 4140 that has removed .22mm or .0085 so it has lessened the taper by 50%. Rather than two sheets of paper thick of taper it’s now one. It’s still too much for some parts I need to make that slide together. The next thing to do is to replace the y axis lead screw and nut. If that doesn’t fix it then a new carriage top. If that doesn’t work then I will call a local repair shop to come out and see what they can do. I suppose the lead nut could be moving that much under load it’s really hard to tell I cannot get anything to indicate that tells me I’m having an issue. I did cut a piece of tool steel and a piece of 6061 and both tapered identically so that was a good sign I suppose that it’s not affected by material and it’s a mechanical issue. After all this I think it’s time to upgrade to a 16” lathe if after a year of use we are wearing these parts out this fast. I would hope to get 3-5 years before replacing mechanical components.
 

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Reading through all this the one thing I haven’t heard mentioned is the saddle adjustment on the flat way of the bed. What could be happening is the saddle is lifting at the start of the cut and settling in getting closer to the chuck. One test you can do is put a mag base on the ways or casting and have it read the saddle then the topslide. Pushing down and pulling to see and verify if any play from saddle to ways. You can do the same with the compound. Have you checked for play in the spindle bearings? Pry bar, blocks of wood and a gauge try moving chuck up/down and side play.
I wouldn’t think your leadscrew have anything to do with it unless it’s slipping in the nut which you would see the handle moving. Finding the slop with a gauge will lead you in the direction.
 
The obvious likely problem is that the head is not aligned with the bed. I did not see in the posts above any reference to testing properly for spindle not in line with bed. Start there. It is even possible that the bolts that hold the head stock to the bed were never finish tightened after alignment at the factory, or perhaps that alignment was never done.
 
This is out of your owner's manual. Check B below. Sounds like the issue to me.

===================================================================
10.5 Making small taper when external turning
A) It is not on the same line between the spindle center and tailstock center. Please adjust
the tailstock according to operation manual instructions.
B) The moving line of carriage does not parallel to the spindle center. Please loosen the
lock screw of headstock and adjust the spindle center to required position and lock.
======================================================================

Good luck,
Ted
 
I’d make sure the lathe is dead level so your not compounding the error. Step 1 is level bed then you can check spindle alignment.
 
Uguessedit said:
if after a year of use we are wearing these parts out this fast. I would hope to get 3-5 years before replacing mechanical components.
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Has the lathe had very hevy use ? As cadillac pointed out vertical movement can also cause a taper to occur, this might be caused by ware on the ways, but from the amount of taper you are describing the ware would need to me massive.


Uguessedit said:
The next thing to do is to replace the y axis lead screw and nut.
Click to expand...
This is so unlikely to be the reason you are having taper issues as is any backlash. You already said it happens when using the compound slide set at 0 degrees.

You could turn the part using manual feed on the hand wheel and see if the same thing happens if you wish to prove it to yourself.

The one thing we do know is that your taper seems to be repeatable. A lose/wobbly item is unlikely to give such repeatable errors.

You have vertical element to your ways on the back side of the lath, you could put a dial indicator on the saddle and run up and down the back side of the ways to see if the caridge is moving relative to it.
 
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