Adjustment Needed?

[mecompco]

Did my first turning of steel today on the 12x36. My project was to turn round stock to a diameter--should be pretty simple. Used the 4 jaw chuck and live center. Everything seems to work OK, but I noticed that the closer to the chuck the I got, the smaller the diameter got. Over 5 thousandths over 5 inches.

Why would this happen, and what can I do about it? Thanks!

Regards,
Michael

 

[Franko]

The problem is with your tailstock alignment.
This is from the PM 1127 manual.


If the stock is thinner at the chuck end, the tailstock needs to be adjusted toward you the amount of taper.



If the stock is thinner at the tailstock end, the tailstock needs to be adjusted away from you to the amount of taper.

 

[mecompco]

The problem is with your tailstock alignment.
This is from the PM 1127 manual.


If the stock is thinner at the chuck end, the tailstock needs to be adjusted toward you the amount of taper.

View attachment 105695

If the stock is thinner at the tailstock end, the tailstock needs to be adjusted away from you to the amount of taper.

View attachment 105696

Hmmm--I think I've got my tail stock alignment pretty g00d (at least as good as I can get it by eye-balling the two centers. I didn't mention it in the original post, but I also tried it again w/o the center. It is half-inch stock, so I didn't think there'd be much flex trying it that way. Got the same results. Perhaps more experimentation is in order.

I never noticed this turning wood as I've been doing, but then I don't suppose a few thousandths makes much difference when turning wood.

Thanks for the suggestion.

Regards,
Michael

 

[RJSakowski]

Tool pressure causes the part to flex. More flexing as you go out so the diameter grows. This is common and more pronounced on smaller diameters. There is much written about this problem

 

[mikey]

How long a piece are you turning? Did you turn it supported by the tailstock? How far is it sticking out? Are you using HSS or carbide? How is your lathe mounted and how is it leveled - shims or leveling bolts?

My first impression is that your lathe is out of level and is cutting a taper but we cannot tell unless we know what your setup was. I would suggest chucking a piece of 1" or better round stock (mild stuff - mild steel, aluminum, brass) in the chuck with a stickout of at least 6-8". Use a sharp cutter and take a light roughing cuts of about 0.010" from the unsupported tail end of the piece and cut close to the chuck. Use power feed if you have it and continue these cuts until you can cut all the way from end to end. Then take a very light finishing cut, maybe 0.001-0.002" depth of cut. If you get a taper with this then your lathe is out of level.

If the piece is larger at the tailstock end then the front mounting at the tailstock or the rear mounting of the headstock should be higher. If the piece is smaller at the tailstock end then the rear of the tailstock or the front of the headstock needs to be raised.

 

[mecompco]

Mikey, this was .5" stock, about 5" long (~1" in the chuck). I tried it first using the tailstock, then again unsupported. The lathe is on a rolling cart--I have no idea how level it is (I got it set up this way). Up until this point, I've only used it for wood an it's been fine.

I do have power-feed, and was using it. Not sure how to adjust the height of the tailstock--there does not seem to be any adjustment that I can see.

Thank you for your advice--I will try it on some larger stock and see what the results are.

Regards,
Michael

 

[T Bredehoft]

The illustrations are looking DOWN on the lathe, there is no vertical adjustment needed or possible.

 

[mikey]

Mike, having your lathe on a rolling cart means it is very likely out of level and you cannot expect the lathe to turn accurately that way. Sorry but some things are just that way. Actually, turning a small taper like you have is good for the setup you're using.

If you want the lathe to turn accurately you must mount it on a solid bench or cabinet. You must then have some way to adjust the ends of the lathe to bring the ends of the lathe into alignment. I'm sure you've heard of leveling a lathe; this is what they're talking about. If the bed of the lathe is twisted then it will turn a taper, as you now know well. Typically, a lathe is leveled at four points, although three points is ideal. There are usually two height adjustment bolts at the headstock end and two at the tailstock end. These bolts are then adjusted to bring the two ends of the lathe into alignment so they are in the same relative plane. Some lathes don't have adjustment bolts so shims must be used but the end result is the same; both ends must be aligned so all taper-producing twist is removed.

My comments above were referencing these height adjustment bolts and given your cart set up, they are totally not applicable. Sorry about that. I knew a guy who owned a Craftsman 12 X 36 and he did some amazing work with that lathe. He has passed now but he showed me that the lathe is capable of fine work if you set it up to do so.

My best advice is to build a cabinet. You can ask for advice on this forum and get all the help you need to design it and even make it mobile if that is a priority. If you build it, provide some means to accurately level the lathe and your taper adventures will go away.

 

[mecompco]

Mikey, thanks for the detailed reply! Below is a pic of my setup. Yes, I've read about lathe leveling, but that's about it--for what I've been doing, it hasn't been a problem (wood turning). The cart is pretty stable--1.5" ply for a top with lag bolts down through the 2x6s into the cart. I do see the three bolts that secure the lathe to the top--I assume these would be used for leveling?

Do the floor/cart/lathe all have to be level, or just the lathe? Any quick suggestions on an easy fix (I will read up more on how to level). I'd really like to keep the setup as it is, if possible. Thanks again.

Regards,
Michael

 

[John Hasler]

Mikey, this was .5" stock, about 5" long (~1" in the chuck). I tried it first using the tailstock, then again unsupported. The lathe is on a rolling cart--I have no idea how level it is (I got it set up this way). Up until this point, I've only used it for wood an it's been fine.

I do have power-feed, and was using it. Not sure how to adjust the height of the tailstock--there does not seem to be any adjustment that I can see.

Thank you for your advice--I will try it on some large

Mikey, thanks for the detailed reply! Below is a pic of my setup. Yes, I've read about lathe leveling, but that's about it--for what I've been doing, it hasn't been a problem (wood turning). The cart is pretty stable--1.5" ply for a top with lag bolts down through the 2x6s into the cart. I do see the three bolts that secure the lathe to the top--I assume these would be used for leveling?

Do the floor/cart/lathe all have to be level, or just the lathe? Any quick suggestions on an easy fix (I will read up more on how to level). I'd really like to keep the setup as it is, if possible. Thanks again.

Regards,
Michael

None of it needs to be level. The lathe bed needs to be flat. Leveling is a means to that end.