Whats the longest unsupported workpiece you've turned?

[double a-ron]

I recently switched from manual turning to cnc turning and had to pretty much through out my old ideas of extension ratios. Bored jaws, ridiculously high clamping power and and a much more rigid machine have allowed me to turn 4 x d on my TL-15. Has anyone gone higher?

[CalG]

I once turned an 18 inch long piece of 2 inch PVC pipe....


Turned it into scrap, I did! ;-)

[KIWIMIKE]

turned 1.8m between centers, print rollers on a falcon teach lathe,

[scadvice]

I recently switched from manual turning to cnc turning and had to pretty much through out my old ideas of extension ratios. Bored jaws, ridiculously high clamping power and and a much more rigid machine have allowed me to turn 4 x d on my TL-15. Has anyone gone higher?

Actually, we need more info. What problems are you having? Chatter, taper, wobbeling??

I once turned 3500 parts in aluminum (6061) that had a 20 x d on a CNC Mazak holding .0005 tol. I still have some of those parts. Hint: I used material that started out over 6 x the d, I made one pass, and cut a taper.

There are tricks you can do. Example, a friend of mine was turning the OD of a thin stainless welded tube about 1 and a 1/8 " diameter and 14 inches long he was having to hold .001 on diameter and roundness. It had a weld on the inside and not very round on that I.D. The solution was to fill the tube with a Bismuth alloy. When Bismuth is alloyed with other metals, such as Lead, Tin, and Cadmium, its expansion is modified according to the relative percentages of Bismuth and other components present. As a general rule, Bismuth alloys of approximately 50 percent Bismuth exhibit little change of volume during solidification. Alloys containing more than this tend to expand during solidification and those containing less tend to shrink during solidification. Also it melts at a very low temp somewhere around 160 to 224 deg F depending on the alloy.
So, he picked the alloy that had a .0005 expansion. A few test samples and he was good to go. No chatter and met all the tol. without a problem.
Steve

[double a-ron]

First, when I say unsupported I mean no tail stock, steady rest or follow rest. The material in question is ground O1. The problems I had on the old LeBlond were mainly chatter related. Do to worn out hard jaws, 25 year old gibs that probably need to be adjusted and the fact that the big 15" manual chuck on it can't even come close to the kind of holding power the 8" power chuck on the tl-15 I have can.

When I went to cnc it seems like ever month I push that extension ratio further without any problems, I was just wondering how far other people have gone without having any chatter issues. Also let me clarify that by turning, I mean normal turning as in the same feeds and speeds you would normally run when the work piece is either supported or not sticking out of the chuck very far. Up to this point if I have to do a long part I buy material that is way oversize and turn the part in sections. It works well but is not only expensive but also a waste of material. The other way I do it is to use the bar feeder and program a double push, but this can be touch and go as far as being accurate. I guess my main problem is I'm to afraid of ruining an insert because of chatter and have been slow to push the envelope.

One more thing, anyone with a TL use the sub spindle as a tail stock?

[scadvice]

So are you talking about the same job over and over? If so, what's your stock diameter and it's finished diameter? The diameter tolerance over the lenght? Also, what is that lenght you want to turn? Plus, what is the finish desired. A general rule, to avoid chatter, is a small nose radius and sharp edged tool, a higher feed rate to turning speed ratio, but not always.
Steve.