More mini lathe issues

I am trying to make my first real part. A replacement pivot pin for a lock blade knife. It's a cheap knife. I could have thrown it away and bought 50
of them for the time I have spent so far, but it's a learning process. Its taught me a lot so far, and the knife was a gift from my son a couple years ago for Christmas.
Here is my problem. I Can turn down to about .250 with no problems. Since the cap on the pin is .383 that part is easy. The shaft of the pin is .204 however. Whenever I get down to about .225 - .230 the tool bit wants to climb down under the work piece. At this point several things go wrong all at once. My tool post tilts towards the work piece no matter how tightly I have adjusted the slide tension bolts (and the slide will still move) forcing me to have to adjust it again. And it usually bends the work piece. Also, sometimes I get nasty gouges and galls on the stainless steel rod I am working with. Also it chips the carbide cutter and I have to resharpen it.
Not sure what I should do. Obviously finding a way to stiffen the tool post would help, but I am not sure how to do that. The first idea I have had is to put the slide tension adjustment bolts and spacer on the back side of the slide. Then there is no mechanical room for the tool post to lift up on the front side. That in itself will require some work on the mill. It would make it more difficult to adjust tension on the slide, but I think it would need to be adjusted less often as well.
The other idea I had is to make a tool holder for a good quality flex shaft handle, and chuck it up in the tool post with a small end mill. I would have to watch the speed very carefully as in one direction I'll get a combined cutting speed of the lathe and the end mill. By cutting in two directions simultaneously I should get a very good finish, and with the cutting surface at the middle instead of the top edge of the tool should greatly reduce the tendency of the tool to try and climb under the work piece. I'm wondering if this is one of those things where a combination machine might be able to do the job faster and easier.
Or maybe I am totally missing the point.
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A manual should have come with the lathe showing the correct turning speed for the diameter you are working with. At this point you should be using the highest speed possible for your lathe. Second possibility is your tool is not exactly centered on the shaft you are turning, and finally, the tool may not be sharp enough. Any and all could contribute to what you are experiencing, and there are probably some other possibilities, but check these first.
Paul

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Not really. It showed gear change and safety stuff, but not much else.

I did not know that. I will try max speed and see what happens.
Second possibility

Well, if I look closely it actually looks like it is a tiny bit above center, but that could be an illusion. Maybe a few thousandths.

A good possibility. I suppose I could swap out to a brand new tool for last few hundredths.

Thanks Paul.
Bob
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If you do not have a bench grinder or belt sander, you ought to think hard about getting one. Grinding a HSS tool bit seems to be a problem for a lot of people. But it is really quite simple. If you already have a HSS tool bit, you can use touch it up using a bench stone or some sandpaper backed by something flat.
Why don't you post where you are located. There might be someone close who could show you a lot in not too many minutes. Or maybe you could use a digital camera or webcam to show close ups of what you are doing. Just do not post pictures in RCM.
Dan
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wrote:

Hold your 6" steel scale vertically between the tool bit and the work. Advance the cross feed until the tool bit holds the scale against the work piece. Is the scale vertical or tilted forward or back? Figure out whether the tool is center height, above or below center?
Center it!

Learn to sharpen a HHS tool and use them! Save the carbide for hard stuff and production. Self ground HSS tool bits allow you considerable more flexibility in tooling then pre-ground carbide tools.
As far as speed goes, learn to calculate cutting speeds. Make up a chart of "recommended cutting speeds" and use it until you get a feel for the material (then use it anyway :-)
Regards,
J.B.
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    Hmm ... I have never seen a modern lathe manual which has this information -- just how the controls work -- if you are lucky.
    Accessory books, like the _How to Use a Lathe_ books by South Bend and Atlas (each focused on their particular line of machines) may have general information about how to calculate the speed for a given SFM (Surface Feet per Minute), but you need another book (like _Machinery's Handbook_), or to look it up on the web to determine the proper cutting speeds for a specific combination of workpiece alloy and tool material. You get faster speeds with carbide tools than with HSS, and faster with HSS than with the old carbon steel tools. So -- you look up the SFM from the workpiece alloy and the tool material, then calculate the RPM from the starting diameter of the workpiece and the SFM which you just looked up.

    Given the maximum speed likely available in a "mini lathe", and the size of your workpiece, yes, I think that this is probably right. If you start getting chips which turn blue and you are using HSS tooling, you may be turning too fast, but I doubt that you can turn that fast with that diameter of workpiece.

    Indeed so.
    Good Luck,         DoN.
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When I took a night school machinging course years ago, the instructor said that you should be getting chips that come off shiny but turn light blue as they cool. He also said that HSS tools should last about an hour before you need to resharpen them. He was talking about using bigger machines and optimizing the time machining versus the time sharpening tools. I usually do not try to remove metal that fast, but I am not trying to make a living doing machining.
Dan
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On Mon, 4 Jan 2010 05:16:51 -0800 (PST), " snipped-for-privacy@krl.org"

One of the jobs I had as an apprentice boy was making planer heads from old line shafting that was removed from a large woolen mill. these were 8 inch shafts and we were machining them into a two inch shaft about 4 feet long incorporating an approximately 3 foot long cutting head.
At the time I was working approximately 3-1/4 hours a day in the shop and going to school the rest of the day.
We were (as best I remember it) taking approximately a 3/8th deep cut and the chips were coming off hot - brown and blue. No one ever started and finished a cut during his approximately 3 hour shift. We sharpened the bit once a day.
I can't say that this was the best speed and feed but it certainly typified the usual shop practice before carbide became commonly used.
Regards,
J.B.
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On Jan 5, 12:51am, snipped-for-privacy@gmail.com wrote:

When you say sharpening once a day, is that once per 3 hour shift?
Dan
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On Mon, 4 Jan 2010 18:17:19 -0800 (PST), " snipped-for-privacy@krl.org"

Perhaps I should have said "approximately once a day" as I know the bit must have got sharpened but I don't remember ever doing it. It seemed to me that I either took over just before or just after a new cut was started. One day I got to start a new cut; the next day I sat there and watched the chips fall in the pan.
Regards,
J.B.
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Bob La Londe wrote:

You prolly have forgotten more about this than I will never know so please pardon the question.
Is your tool bit set a tad low in the tool post? As on page 21: http://www.littlemachineshop.com/Info/MiniLatheUsersGuide.pdf
--Winston
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LOL. I know next to nothing about running a metal lathe so I don't think so.

I do not think so. Not sure how to measure it, but if anything when I bring the free center upto the tool the tool looks like it might be a couple thousandths above center.

I will read.
Bob
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A common trick is to pinch a 6" scale vertically between the tip of the tool bit and the workpiece. If the top of the scale leans away from you, then you're tip is above the workpiece centerline. If the top of the scale is leaning towards you, then your tool bit is below the centerline. Basically you're using the scale to indicate the tangent of the circle (if viewed from the end).
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That is a good trick. I will remember that one.
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Bob La Londe wrote:

Another way to check is to run your bit across in a facing cut. If the tool is low, you will leave a nub. If on center, the nub will disappear when you reach the center. If the bit is high, there will be some tool distress when you get to center, so start low, which is what sounds like is happening.
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    Looking at this part again -- I have to ask -- how far is the workpiece sticking out of the lathe chuck? Generally, for something held only in the chuck, the maximum extension should be about four times the diameter -- and as you turn the diameter down, you have to shorten the workpiece a bit. The workpiece tends to flex upward, and climb over the tool bit.
    Now -- do you have a live center for the lathe's tailstock? If so, can you center drill the end of the workpiece and support it with the live center? You may have to leave a piece of larger diameter near the live center, and cut it off when you are done. Oh yes -- also beware of parting off while the workpiece is supported with a live center. It will jam interestingly as you get to the final cutoff point.
    Good Luck,         DoN.
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HSS, honed sharp after grinding, at center height, removing ~0.005 per pass. Support the work with the tailstock. I've made stainless #0-80 screws 1.25" long that way.
jsw
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wrote:

Wow, that's pretty aggressive. I have been only removing .002 .003 per pass. I will try a much faster turn rate as one poster suggested.

I need to get some center drills I guess.
I've made stainless #0-80

With my beginning level of skill that task looks all but impossible. I am impressed.
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Bob La Londe wrote:

Follow rest to prevent the part from climbing up over the tool bit?
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When I got my mini lathe, one of the many issues I found was that the slide could rock slightly even with the gib plates tight. I took off the slide, put sharpie marker on the ways, and set it back down and slid it back and forth. The areas where the marker rubbed off showed where it was making contact. As expected there were high spots in the middle of both the flat and V-shaped ways on the slide. After adjusting this with some careful manual filing and grinding, the slide was much more stable.
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