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

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Have a BT1337g it’s been a great lathe. Recently it’s been gaining an appreciable amount of taper to an astounding .150 thouthandths when I chuck a 5” 6061 1.5” round bar and dial it in to zero concentric. To add further clarification this isn’t a tailstock issue or a bed level issue. 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. The tailstock when used is aligned perfect and I can center a perfect hole in a part however whether I use the tailstock “or not” the part tapers. Majority of the time I don’t use a tailstock it gets in the way for the little parts I make. I’ve been talking to the manufacturer and they believe it’s the lead screw nut and cross slide gibs. I tightened the gibs to the point I could barely crank by hand to attempt ruling out issues and checked the bed for wear though were talking a 1 year old lathe with a hardened bed. Using a straight edge it is straight across showing now wear. So then I thought perhaps an issue with the gap bed and though I’ve never removed it I did have a fastener come lose recently and saw the manufacturer had short screws where the threads barely caught and the casting let loose so I removed the gap bed and cleaned it all up, paint removed, grease, etc.., cleaned to near new and reassembled with longer screws and the problem still exists. The saddle/carriage feels solid and tight physically when I grasp it but it’s obviously pulling away the closer it gets to the chuck. Spindle bearings are solid and no runout the machine is overall healthy. There is approx .015 play in the lead screw with the saddle locked down. I don’t see how that is going to give me .150 taper. The taper is back to back no matter which lathe chuck I use or how I set up the machine It duplicates itself precisely every time. When I used just the cross slide to cut instead of whole carriage I still got taper but it wasn’t as much. Does this sound like I’ve just worn out the gibs and lead nuts? I’m going to have the parts shipped 2 day air in the morning and see if they help but I’m a little Leary if it is going to fix the issue. If anyone else has ever had this occur that would be great to hear your experience. I do use the cross slide and carriage a lot and the lathe is used every day for the past year since new. It gets a good 2-3 hours a day use. Hopefully I’ve covered all questions you may have. Photos of taper attached. Thanks.

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If it is not the gib on the back of the saddle, then I have to think more. Have you put a long straight bar in the 4 jaw and used a DI to zero it and then run the DI from end to end? Not spinning the shaft. What is the runout? Run it on the top and then the side where the tool would hit it.
 
What’s your intended depth of cut?
 
If you try turning something between centers you can check that the head hasn't moved out of line, a part between centers "should" turn with no taper even if your head is out of line.

only mention as you say you get the same using the compond set to zero degrees (sorry if i miss understood that)

Stu
 
I did some further testing and took the saddle down and saw the lead screw nut has the locking screws on it to remove backlash so I tightened it up and put it back together and locked my turret in place (no swing/etc), and it still tapers. I cut 4 different parts back to back all down to the exact same specs using the power feed for consistency. The 4 parts are all exactly the same identical taper. This is weird. I’m starting to conclude something happened and this lathe is junk. I did have a parr crash a few months back but I’ve used this lathe hundreds of times since. It’s the past couple weeks that it really aggressively changed where parts have become unusable. If the manufacture can’t help figure it out I’m going to ask if they will trade it in at a discount of course. Even if half it’s better to let them rebuild it and deal with it and start new. My only other thought is convert it to Cnc but I don’t really have the time and it’s nice to have a manual lathe around the shop. I do have all the components here, ballscrews and servos and a few PCs I could go ahead and do it. I feel like it’s defeating me.
 
stupoty said:
If you try turning something between centers you can check that the head hasn't moved out of line, a part between centers "should" turn with no taper even if your head is out of line.

only mention as you say you get the same using the compond set to zero degrees (sorry if i miss understood that)

Stu
Click to expand...
It tapers no matter what. If I push all my body weight into the carriage while it’s power feeding I can almost eliminate the taper. If I push on the saddle or turret it does nothing. It’s a carriage issue and the bed is straight and not worn. The next thing is probably pull the carriage maybe where it rides on the bed has worn. That’s gotta be the issue I’ve tried everything else.
 
Looking at your first two pictures where you are measuring the bar, I see a difference of 0.0145", not 0.145". Or am I reading your calipers wrong?
Agreed still a taper, but an order of magnitude less.

-frank
 
Here is a link to a YT video I made that best explains the issue.


It is a private video and requires use of the link out of respect for the manufacturer until the issue is resolved. Any issues let me know.
 
francist said:
Looking at your first two pictures where you are measuring the bar, I see a difference of 0.0145", not 0.145". Or am I reading your calipers wrong?
Agreed still a taper, but an order of magnitude less.

-frank
Click to expand...

I’m sorry you’re correct I’ve been running on a couple hours sleep. Frankly I’m a bit burnt out at the moment between work and trying to alleviate this issue. I did upload a video here that clearly shows the issue occurring. It also doesn’t help I’m a metric guy and I know everyone here is probably standard units. I would normally resort to .41mm ;-)
 
That almost looks like the head is out of line with the bed, rotated a bit clockwise looking down on it. Not sure how that could happen, if it was going to move I would expect it to go in the other direction.

You need to put a bar in the chuck and run a dial indicator down it as @pdentrem said above.
 
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