Taper attachment turning - uneven results

I have used this lathe with the taper attachment in the past with satisfactory results. Today I decided to make a 5MT taper test piece and it was very frustrating. I can't say what is causing the problem but the piece was ending up with a wavy diameter. I think I've seen other refer to is as, "bumpy"
I used a brand new 5MT taper sleeve to indicate the taper attachment setting. It was very time consuming but I got it within less than .001" for the length of the taper sleeve. While doing this I was not getting any abnormal deflections in the DI.
When I started removing material I was getting, what seems like, a loading and unloading of some moving part. I guess it could be the cross feed or the taper attachment or a combination but I ended up walking away because I was so pissed off.
The way the telescopic attachment works, and I think most machines are similar, seems like it would easily expose backlash in the cross feed. When normally feeding the cross slide the lead screw is loading the nut and whatever slop is in the screw/nut is removed by the operator. With the taper attachment the cross slide is pushed or pulled by the bar and the "rabbit" that fits over the bar. This arrangement seems like maybe I need to make the gibs in the cross slide and the taper attachment much looser than I have them. Would loosening the gibs be a good place to start trying to solve this issue?
Another thing I am wondering is if it would make better sense to run the spindle in reverse to do the turning? This would make the tool pushing against the work force the cross slide back so it would be applying pressure against the taper attachment instead of how it operates when the spindle is in forward.
Does this make sense?
Thanks

You have to think backwards, in terms of backlash, when using a taper attachment... I try to get as far past (to the right) with the carriage, get backlash out, and then travel, before cutting zone starts. Helps get all the slack out. Also, oil all the taper attachment ways well..

Thinking further.. It could be a case of Stick/Slip.. Check to see that what needs to be tight is tight, and what needs to move, has clearance to move. Dry runs with an indicator are what I use in such cases.

I agree with Davis about starting far enough from where you will start cutting to get all of the slop out of both the TA and the cross slide before it starts cutting.
Also having the TA and cross slide dovetails clean and well oiled will help a lot.
I usually clean the entire TA and lube it before I even start to set the angle.
Another thing I find important is to set the DTI tip so that it tracks on the part at center height while using it to set the angle.
I sometimes put one indicator on the cross slide and another Long travel one on the carriage.You can get the angle off of the centerline of the TA set to the Taper Per Inch very accurately even without a gage.

A third endorsement for "engage the carriage way, way earlier than you normally would to get all the slack out."

IMO, loosening gibs on ways that still slide never solved anything, except for taking a machine apart.

If the turned taper remains "bumpy" even two or three inches after you've engaged the carriage, make sure the taper slider is actually snug on the taper bar (no slop) and that there are no chips interfering with the slider on the bar. The TA on my lathe is "enclosed" but all that means is that I can't see 90% of the chips that have gone in through the open ends.

Good suggestions all. Backlash is lack of rigidity and so you must eliminate all backlash and anything which may be loose must be secured. Your lead screw is in good shape? any chips on it? Is your taper attachment secure and lubricated? How about your compound? What about slippage of any belt driven drive? Material is chucked securely? How are you holding the material by collet, three jaw chuck or four jaw chuck? Are you running the material between centers using a dog? If you are chucking it and it is a longer part or even a shorter one have you tried using a live center for rigidity? Tool selection matters also. something which cuts with less tool pressure goes a long way.

challenger,
Try cutting from left to right instead of right to left, i.e. feed towards the tail-stock, you need the action of the taper turning to be against the cutting force.

Ray

Thanks all. I'll try the suggestions her as well as look again to make sure everything is well lubricated.
The part I am working with is held between centers and driven by a lathe dog. The headstock center is newly cut and the tailstock has a live center.
I think feeding the tool left to right is a good idea.
One thought is to make the taper attachment cut larger to smaller? Currently I am set up and turning small to big. This set up makes the taper at attachment push the cross slide away from the work and will (does?) allow any backlash in the leads crew nut to "float". In other words the lead crew and nut backlash is never taken up unless I am misunderstanding something. I know when I was checking the cross slide yesterday I could pull on it and feel the backlash. This was after moving the tool in the proper direction and after the slide was already being moved by the TA.
Thanks

There was a thread on this a few years ago that had all kinds of info too. Forrest wrote a ton on this. This first thing i thought when i read #1 is did you clean it and lube it. I would suggest take a few passes and mount a mag base on the cross slide and .0001 or .0005" indicator on the taperslide and see if you see vibration and then take a 2nd pass cutting. Be sure to screw is against the nut to eliminate the backlash. Rich

challenger said:

One thought is to make the taper attachment cut larger to smaller? Currently I am set up and turning small to big. This set up makes the taper at attachment push the cross slide away from the work and will (does?) allow any backlash in the leads crew nut to "float". In other words the lead crew and nut backlash is never taken up unless I am misunderstanding something. I know when I was checking the cross slide yesterday I could pull on it and feel the backlash. This was after moving the tool in the proper direction and after the slide was already being moved by the TA.
Thanks

Click to expand...

Your normally want to organise things so that the taper attachment is pulling the tool deeper into the work as you traverse along the bed, rather than letting it float out of the work (which you seem to have had).

I tried every which way today and got no good results. The taper attachment is creating a bind. I don't know if it is actually the taper attachment or if it is a combination of the taper attachment along with some wear in the carriage but it is causing the carriage to crab. When the taper attachment starts moving the cross slide I can watch the carriage start to crab (swivel if you will) and actually lift up a little as it rides up on the front vee way.
I took the entire carriage apart today as well as the taper attachment. I am trying to consider my options and deal with this. One thing I may try is to rework the carriage ways so the carriage bears on the outer part of the "wings" in both the front Vee way and the rear flat way. When I took the carriage off I could clearly see that these surfaces were worn so that the entire length of the ways of the carriage were bearing on the bed ways. I am probably going to look into scraping the carriage ways to restore them so the outer sections contact the ways as they did when new. I understand there is a lot to consider in doing this especially for someone with no reconditioning and/or scraping experience. I certainly can't afford another lathe at this point so I am leaning toward scraping the carriage to the bed. I know the results are not going to be ideal and that having the bed reground is the best way to go but I have to take a less expensive route to see if I can get an acceptable result. I've talked with a few people that have done this one Sheldon lathes and have had moderate to very good results so I'm likely going to dive into this and see where I get.
I'm pretty frustrated with this situation so I have to cool my head a bit before I commit to this project.
Any helpful advice, as always, is appreciated.
Thanks

If the saddle doesn't crab as you call it with-out using the taper attachment, I can't believe it does it when using it. Have you check the clearance in the taper bar and the draw bar clamp? You need to figure out how to add some pictures. I is hard to help with-out them. You said it tights on the ends. try shorter shaft. What ate you turning? The pipe again? Buy some leaded cold roll and I always had good luck turning that material.

Please, stop and think

...Before making a disaster.
The reason the taper attachment is pulling up your carriage is because they aren't anymore on the same plane: the taper attachment is seldomly used and only slightly worn. Contrarily, your ways are badly worn. Therefore, while engaged, the taper attachment tries to make the carriage moving on its original plane, therefore lifting it from the bed.
I'm sorry, but there is no shortcut. How would you scrape the carriage to match the worn, uneven bed? What kind of reference are you using? Removing even more material from underneath the carriage (increasing therefore the distance between the taper plane and the new carriage plane), how would anything improve?
Since you're a member of the SheldonLathe Yahoo group, I suggest you to search the archives: you'll find plenty of comments from John Knox dissuading average people from adapting the taper attachment of one lathe to another one, since it spells a lot very precise alignment and fitting work. Although it is never spelled clearly, the big problem is indeed having the taper attachment and the carriage traveling on the same plane. This is something somehow straight-forward with a brand new or extremely-evenly worn bed, but it's close to impossible if the wear is not completely uniform. If you want to fix something, you'd better bite the bullet and do it the proper way. Shortcuts generally lead directly to the scrapyard.

Now back to your practical problem: it is well possible that, if you move a few more inches away from the headstock, the wear on the bed is more uniform. Therefore, you could start your work with a considerably-longer piece and try cutting your taper closer to the tailstock.

Just to give you an example, last summer as a demo during the July show, I was cutting MT3 blanks on our 16x8 gearhead Hendey at Tuckahoe and I had your very same problem (with the saddle near the headstock while using the taper attachment, I could insert a .018" feeler gauge between the saddle and the inverted-V; with the taper attachment disengaged, I could insert at most a .003" feeler gauge). Useless to say that the finish was horrendous, I had plenty of chatter and, by reversing the direction of the carriage, the tool would rock back and forth at least .010" (and there was no backlash involved, since it has a non-telescoping TA). Moving the production half foot toward the tailstock solved almost everything.
With the taper attachment disengaged, that lathe cuts fairly straight and it is still possible to take .1" cuts (on the radius, not the diameter) without any problem.

Paolo

I spoke with John Knox about this issue I'm having and I've read as many posts as I could on the group site. I'm not familiar with the archives?
John is an excellent guy and he explained the scraping process to a degree. He also cautioned me about scraping the carriage. He did however mention he has had success with other people in guiding them through the process of scraping a 001-003" from the center section of the front and rear way areas. He offered to help me as well if I decide to do any scraping. I thought more about the lathe last PM and I decided to put it back together and reevaluate the problem. Seeing the replies this am makes me think it is the best thing to do as well.
The taper attachment came with my lathe BTW. It was part of the machine when it was originally sold. I'm pretty familiar with the difficult, and often impractical, process of trying to adapt a ta from one machine to another. I've stumbled across and read many posts about this.
I think one of the problems with the telescoping TA is that they are always attached to the lathe. Therefore the sliding parts of the TA are being moved any time the apron is moved. I realize that it is so to zero and that it isn't moving the cross slide but the ways and gibs of the TA are bound to get wear and the wear is going to be in a localized part of the TA just like it generally is on most lathes. This could be avoided if the operator moved the TA a little as part of a PM process but I'd bet money this didn't happen. Another thing I dislike about the TA is that it adds a lot of weight to the carriage saddle and the weight is not supported by the clamp/rod because the rod is not tight in the clamp bracket. It floats inside the hole in the clamp bracket. I've read this little bit of slop was engineered into the design to help prevent binding???
Richard- am not familiar with leaded cold rolled material but I'll be looking into it and getting some. Actually the lathe, prior to this ta episode, was turning more accurate than ever. I had just finished doing the two collar alignment and then the tailstock alignment using the method you recommended. The stub turned to the of the tailstock quill is the only way to align the tailstock IMO. Your recommendation was very helpful. To answer the question of what I'm turning, I am trying to make a spindle sleeve. It is a "short" mt5 taper. The pipe I turned was for the two collar test and it served it's purpose and is now retired.

I greatly appreciate these replies and advice. I don't know how to pinpoint the source, and possible fix, to this taper turning problem but I'll do more reading and see if I can find ways to isolate possible culprits.
Thanks

challenger said:

I
Richard- am not familiar with leaded cold rolled material but I'll be looking into it and getting some. Actually the lathe, prior to this ta episode, was turning more accurate than ever. I had just finished doing the two collar alignment and then the tailstock alignment using the method you recommended. The stub turned to the of the tailstock quill is the only way to align the tailstock IMO. Your recommendation was very helpful. To answer the question of what I'm turning, I am trying to make a spindle sleeve. It is a "short" mt5 taper. The pipe I turned was for the two collar test and it served it's purpose and is now retired.

Click to expand...

Thank you I have been teaching that tailstock alignment method my whole career as my Dad showed me how simple that is compared to buying an expensive test bar or test bar set. The 2 collar method is also the easiest for an lathe owner unless your building a new one. Many here use the 2 collar method between centers. The spud method is how many of us pro's do it.
I'm not sure who John Knox is, never heard of him as a matter of fact? I also would teach you...doing anything in May? lol...

To me, if the taper attachment is attached to the back of the saddle and the shoe had clearance when it was new, and as the cross-slide wears down that error would fall down the taper bar. The Doctor may be right, but to me it doesn't make sense. But I am not to old to learn something. It is interesting seeing you learning and sharing your lathe adventures.... Rich

PS: I spoke to Challanger on the phone and he is a pretty sharp guy and not some kid. I think many have assumed he was a kid and have talked down to him....

are you sure the carriage gib screw has no slop in the gib?

How about a bent lead screw lifting the carriage as it revolves?

The carriage gib had play in it up until about 3 months ago. The Sheldon design for this, and a couple of other gibs, is poor IMO. I understand they made changes but in my lathe the gib has a slot in it and it is adjusted by a flat head screw that fits, when new, snuggly in this slot. The screw head is machined to be thick and holds the gib from moving in/out. The problem is that people adjust the gibs and the slot made for the flat blade screw driver gets deformed. Now the screw driver slot starts eating away at the slot in the gib and it goes down hill. When I got my lathe there was a piece of shim stock between the screw head and the gib. To add to the problem the holes for these screws isn't deep enough and the threading is poor or at least in my machine they were. I made another screw for this gib and the compound gib. The screws I made from some long Allen head set screws. I added a collar that is the thickness of the original screw head and used locktite to locate it about 1/2" down the screw head. The screw is longer than the original and I chased the threads which had muck and crap in them big time. On the cross feed I also put a thread insert in the hole because the threads had gotten messed up at the start and starting the screw was real sloppy. I guess I got lucky that the insert lined up with the threads that were deeper in the casting. To hold the gib I put a jam nut on the end. Now the Allen head is turned to adjust the gib snug via the added collar and the jam nut holds the gib in place. Basic stuff. Just like most adjusting screws that hold gibs in dove tails with side pressure but this is pressure applied to the end of the tapered gib.

There are no bends in any of the lead screws BTW.
I did more looking on the Web and it seems like there is a common theme with people like me posting about their machine problems. Many, including myself, think worst case scenario when their lathe acts up. I was looking at photos of some lathes that people had no real complaints about. These were seasoned machinists as best as I could tell and they posted photos of vee and flat ways that were much more worn then mine and they get fine results from them. This, along with the cautionary comments here made me pause, remove my head from my ass, just temporarily of course, and try to examine what has recently changed that made this lathe start behaving MUCH worse than it ever had. I've always been able to use the whole machine just fine and with little or no complaints from the lathe. Then it hit me. I'm not ready to say this is the cause of the problem but I have a feeling it may be a big part of it. I really hate to admit this because it is so embarrassing but I think the problem may be due to using the wrong oil on the ways and other sliding parts. I had an oil can that I put pneumatic oil in and I put it on the shelf by my lathe. When I decided to try and turn this taper I cleaned the TA and wiped down all the ways etc and applied this oil instead of regular way oil. I didn't even notice that I was using the wrong oil until I came out today to look at things with my head outside of my ass. Again, I'm not saying this will fix things but the pneumatic oil is not very slick compared to any oil and it is almost tacky compared to way oil.

I'm going to start putting it back together soon. I cleaned everything yesterday so I'll reassemble and apply proper oil and see what happens.

Thanks Richard, I wish I were a kid! Well maybe not the way things are these days. What is going on in may? I take it you have a class scheduled yes? Your assistance has been invaluable here. I think your experience and systematic approach to machine issues is hard to argue against although I see that some do take exception to some of the ways you do things. There are more than a few ways to do any things but I've been finding your methods and techniques to be easy to understand and efficient. Hey, if I can understand something it is flat out easy to understand.
Thanks, hopefully I'll get back with some good, albeit embarrassing news.

My lathe is the poster child for lightweight and well worn. The ridge on the ways is well over 1/16" tall up near the chuck. But I have had little trouble using the taper attachment to get pretty decent results on tapers up to MT5.

Reading Challenger's problems and some of the advice above, it makes me wonder why I have not had problems. I understand cutting in the direction that pulls the cutter into the work, so everything is actually positively guided by the taper attachment ways (as opposed to a direction which pushes the tool away, allowing the cross slide to somewhat "float". But I have not always observed that rule and still things have (so far! ) come out ok.

I had never thought about the lathe ways wearing such that they are no longer coplanar with the taper attachment. But then again, I thought that was the reason most taper attachments slide along with the carriage, to keep them essentially in the same plane.

So Challenger's post has caused me to thing a bit about this issure, and maybe the reason my little SB gets away with it is that the taper guideway, and the follower, are not dovetailed. The follower is more or less free to rise and fall on the guideway. I always thought the square sided way was just a cost saving measure at the factory. But maybe it is also a superior design.

Thinking about Challenger's problem, maybe 1.) the alignment of the taper attachment ways is skewed, for some unknown reason. Probably the first item to inspect and address if necessary. and 2.) perhaps the connection to the taper attachment can have a vertical floating element (snug but free floating bushing) introduced at the pivot pin connection as a temporary solution, or even a "better" design element? If the direction of cut pulled the cutter into the work, and the bushing had nil slop, all the error would be taken out in the same direction.





smt

Challenger,
I don't know what lathe you are using so this may not apply in your case. I have a model 100 MK 3 Clausing on which the longitude feed gives a finish just like you describe. But not when using the half nuts. Upon investigation I found the feed gear shaft has worn out the apron hole or hopefully the bushing,(if it has one) and the gear is jumpy on the feed rack. If I live long enough I intend to fix that issue. You might look to see if a similar problem is with your machine.
Just a thought.

The bracket of any taper attachment should be clamped to the lathe bed only when the taper attachment is in use. Therefore, a properly-cared-for taper attachment should be worn out only if that particular lathe has been used a lot for cutting tapers. In normal lathe operations, the whole taper attachment moves as one piece with the carriage. Moreover, were you to keep it engaged, you'd limit the travel of your carriage to the length of your taper attachment.
I could be wrong, but I don't think that the coupling between the taper attachment bracket and the rod is supposed to be a sliding fit while the taper attachment is being used. On my my 10" Sheldon is kept constantly tight.
Maybe the wrong oil is contributing to feel more drag, but I don't think it is minimally responsible for lifting the carriage off the bed.

Relieving the middle portions of the saddle slides is something that doesn't harm. But I'd strongly recommend practicing some scraping somewhere else first. Moreover, since you recently reported success in quality and precision of turning with your lathe with the taper attachment disengaged, I don't think that the carriage rocking is the cause of this problem.

As I said before, I've experienced very similar issues using the taper attachment on an old Hendey lathe. The ways of that lathe are considerably worn and the troubles happened when the front wings of the saddle climb from a more or less uniformly-worn area of the bed to a less worn area, since taper attachment and saddle are now on two intersecting planes. You can try loosening the bolts on the taper attachment rod. But, if the rod bottoms in the groove or hole (mine has a through hole, not a groove) of the bracket, it wouldn't help you much.
Once you reassemble everything, try cutting a taper far away from the headstock and see if you find the very same problems.
I'd also suggest you to survey the wear of your ways. If the side and bottom of the way portion of the bed is not too badly damaged and doesn't show excessive wear, although it isn't the most precise method in absolute terms, I find the following setup quite handy.



The bottom of the height gauge rests against the side of the bed, while the two pins are in contact with the bottom of the way.

Marking the bed a fix intervals and using a voice recorder to record the readings will help speeding up the whole process.

To give you an idea, here are the results of surveying the bed of Tuckahoe's gearhead 16x8 Hendey (as I've mentioned earlier, without using the taper attachment, that lathe does a decent job and is still quite accurate):



Paolo