Clausing 5914 chatter -- update

The latest experiment was to use a grooving tool bit that came with the lathe. The business end is 0.205" wide, tapering to a neck about 0.75"
back, so the sides of the groove being machined are not also re-machined, and minor inaccuracies of perpendicularity (of tool to work) are not important. This toolbit was ground out of a 5/8" square HSS bar.
If not in back gear, it squealed and chattered badly. With the back gear, grooving was possible, and largely without chatter or squeal.
But as the groove got deeper, and the diameter of the remaining stock because small, the toolpost tipped more and more. Cutting was intermittent, even under slow power feed. By hand, the chips were 0.203" wide and about 0.0045" thick. Eventually, the tool bit was pulled under the workpiece, and the tip of the toolbit broke off.
While all this tipping was going on, I was feeling the lathe. It turns out that it was the cross-slide (fixed angle, moves perpendicular to the bed ways) that was loose, so I have been tightening the cross-slide gibs up.
Joe Gwinn
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On Mon, 14 Apr 2008 12:11:09 -0700, Gunner Asch

Cannot do that on my lathe the chuck would fall off <G>
Richard
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That is pretty darn wide for your class of machine. (not knocking it since it is my class of machine also). I'd thin it down a bit.
Wes
http://wess.freeshell.org/clausing/Clausing.html -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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Well, it came with the lathe. Perhaps it was for the other, larger machine. But it would have worked had the toolpost et al not tilted and self-fed into the cut. And I had the same problem with a blade 0.125" wide.
It's the same as one gets when climb-milling with a mill that has too much backlash. Self-feeding causing the machine to bite off more than it can chew.
Joe Gwinn
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The gib screws on the 5914 push the gib lengthwise, versus pressing down on the gib from the side, so this won't work. I'd be afraid of pushing the gib in far enough to lock cross-slide in place. It might prove difficult to unwedge it.

As an experiment, perhaps I can clamp the cross-slide to the saddle with a C-clamp.
Joe Gwinn
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I did tighten the gib to the point of significant drag, at least at the ends of the travel. The center is a bit looser, as would be expected from the age of the machine.

It worked. A loose cross-slide gib is thus a good part of the problem. The original gib is worn, leaving a sort-of groove. I don't recall that the dovetails were that worn. Will have to look into this more deeply.
With the broad-faced grooving tool (0.205" wide), I cannot make a chip thinner than 0.005" or so, and easily get to 0.010" and have seen 0.020". It appears that the elasticity of the machine is such that when one cranks down sufficient to start cutting, once cutting commences the cutting depth immediately becomes 0.005", because the tool force is now down versus towards the spindle axis.
With the 0.125" wide cutoff T-blade, I get much the same effect, but was able to cut a steel bar off without excessive self-feeding.
Joe Gwinn
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It's my recollection is that only the gib itself had visible grooving. I can sand it flat and put some shims behind it to get the overall thickness back into range. Or get a new gib. One of the reasons I chose Clausing is that parts are available -- expensive beats unavailable.
But I don't have a shaper or anyplace to keep one. A surface grinder would also work, if I had a place for it. Actually, I think one can make a gib on a vertical mill (plus a little sanding/fitting), although it will be a multistep process involving the manufacture of multiple special jigs.
I wonder if gibs must be cast iron, or would brass suffice? I would guess that if brass were best, brass would be used, and yet cast iron is universally used.

For steel, the back gear turns out to be essential. Clamping the cross-slide did not allow me to cut a steel bar off without chatter except when using the back gear.
By contrast, cutting aluminum of similar size off did not require the back gear. The chips were still relatively thick, so we are still seeing the spring effects that prevent cutting very thin but wide chips.

I do have a thinner blade and will try it. Thinner blades ought to allow one to cut thinner chips as well, as the force will be proportional to the blade width.

To tell the truth, I've been doing it the hard way as a way to diagnose the and fix the problems with and find the limits of the machine. It has been very productive. Cutting steel off seems to be the acid test.
Joe Gwinn
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[snip]
It's $153.65. I'm still thinking. It would be a lot of work to make one, and I don't have a lot of free time. Could be worth it. And one can easily blow that much on a few items of tooling.

I will make the measurements.

Thanks, ... but steel is already plenty of Trouble.
Joe Gwinn
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My fear is that gibs from a parts machine will also be worn.

I do like the idea. I just looked -- there is plenty of meat and the drilling and tapping job would be dead easy, as the compound is rectangular, with machined surfaces all around.

I'll be doing some measuring, to see how worn the dovetails are. If they are not that worn, then I'll probably get a new gib. If they are worn, then it's the side-clamp screws. Actually, I might do both.
Joe Gwinn
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