PM 1440 - First Failure

Well, I just had my first failure with my PM 1440. The cam-lock on the tailstock broke. This lathe has been just so amazing compared to my other
Chinese lathes that I got my feelings hurt. LOL.
It wasn't a particulary hard fix. I had to pull and split the tailstock to remove the shaft, cam, and pull block. I found the cam was held to the shaft with a spring pin (or roll pin if you prefer). It had broken. I know why it had broken. Spring pins are strong, but not as strong as you might think. When ever I do some heavier drilling (like clear a hole with a 1" drill bit) I tend to bump the handle firmly with my hand. That cumulative force surely is what caused the pin to break.
The other issues is the pin is in my opinion a little short for the job. I think its a standard length pin though as I had several the same length in a box of assorted spring pins I bought a while back for emergencies. I think as a result the shorter than full depth engagement in the cam allows it to flex more when I bump the handle. Since I had a pin and I was in the middle of a project I put it back together and dialed the tailstock back in. I may find it hard to break the habit of bumping the handle so eventually I am sure it will fail again. When it does I would like to be ready with a better solution. My first thought was to use a solid stainless dowel cut to length. Throw some Loctite on it and call it a day. Drilling and reaming for a nice light interferrence fit might be tedious, but its within my capability. Just a few tenths so it stays in place, but can be driven out easily enough. If the fit is to both parts, the cam and the shaft, there shouldn't be any slop to allow the pin to cause wear. Are there any issues with that? The other thought I had was to make a new cam that has to be pressed onto the shaft eliminating another other possible play/wear issue. A one piece shaft and cam is not a practical solution. I'd have to drill out the side of the tail stock and the insert a bushing to support the shaft. Not impossible, but a lot of unnecessary work and seriously overkill. On the other hand it would probably outlast me. LOL.
This brings us to failure number two. After I put it back together I threw a piece of stock in the chuck and turned a point to align the tailstock to. Then I threw a dead center in the tail stock and started lining up the points. When I got out my loupe I found the center was blunt. Looked like maybe it was dropped. I couldn't see it with just my glasses on, but it was clear to see with the loupe. Thinking maybe I dropped it and didn't remember I got one out of the tool cart that had never been used before. It was also blunt. It was a nice tiny dome, but it was blunt. Orders of magnitude bigger than the tip on my turned point. Atleast it seemed uniform so I dialed it in as best I could. I realize even with hardened and ground steel handling is coming to take off needle tips from an object that heavy, so maybe that's the norm. I don't know. Both centers came with the lathe so perhaps they are just lower grade Chinese parts. Do all dead centers have a domed tip when looked at under a glass?
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Ever hear of "Machinist's Elbow", caused by forgetting to remove the center?
Since you may want to machine to finer precision than you can see, the better way to center the tailstock is with a chucked indicator riding on the conical surface. A quick check is to grab a milling edge finder in both the spindle and tailstock chucks. --jsw
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I figured I'd use an indicator to dial it in closer when I need it. Not sure I agree about the edge finder. I am sure my tail stock drill chuck isn't "that" good, and I tend to leave the three jaw on the head stock for speed. I keep trying to convince myself I can learn to be as fast as the guys showing off on YouTube with their 4 jaw, but I don't think I have another two ot three decades to master that skill. LOL.
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A trick for that is to zero the indicator dial with the crossfeed on a low jaw, rotate halfway to the high jaw, then adjust out half the reading. Two revolutions get me within a few thousandths, then I position the indicator for equal + and - deflections around a major division. --jsw
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On Monday, November 28, 2016 at 12:34:15 PM UTC-5, Bob La Londe wrote:

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I don't know whether this is common knowledge or not, but an old machinist showed me how to get the alignment pretty damned close without a loupe. You bring the two points together, and capture a piece of flat stock between t hem - he used his 60 degree center gauge. Any misalignment becomes immediat ely obvious by the tilt of the metal.
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On Monday, November 28, 2016 at 12:34:15 PM UTC-5, Bob La Londe wrote:

* I don't know whether this is common knowledge or not, but an old machinist * showed me how to get the alignment pretty damned close without a loupe. * You bring the two points together, and capture a piece of flat stock between * them - he used his 60 degree center gauge. Any misalignment becomes * immediately obvious by the tilt of the metal.
That makes perfect sense. I use a metal scale all the time to set the height of tool holders. Don't know why I didn't think of doing that between centers. Nice.
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"Bob La Londe" wrote in message

Bob, I don't know how much trouble you want to go to on this job, but you might consider reaming for a taper pin.
Tom
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That's probably the best idea yet for the next time it fails. A tapered solid pin will be stronger, and it has the advantage of being able to be tapped out. As opposed to a solid dowel Loctited in place that would also require heat to knock out. It was already all back together with another under engineered spring pin when I posted, but as I said before I expect it to fail again.
Thank you.
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wrote:

If you are worried that the tail stock center doesn't come to a sharp point just grind it.
Back in the days of turning between centers it was a common job for apprentices. Make sure that both the headstock and center were clean and had no burrs, install the tail stock center in the head stock and re-grind it with the tool post grinder. Usually both centers were ground at the same time.
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I might do that, but I think I'll indicate it in next time I need real precision. I do have a cheap crap coaxial indicator and a couple decent Last Word indicators that haven't been dropped yet. I'm sure I can make one of the work ok.
I don't have a tool post grinder. I am working on a tool post cross drill though.
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On 11/28/2016 12:34 PM, Bob La Londe wrote:

Why would one want it to be sharp? Other than for aligning the tail stock?
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Um... ok. LOL. Thanks Bob.
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    [ ... ]

    Well ... there are hardened centers, designed to go in the tailstock, and mild centers, designed to go in the headstock and be trued up before use. The hardened centers are more likely to have good sharp tips.
    But remember -- the center drills are designed to drill a small hole followed by a 60 degree countersink so the point normally floats in air -- or in whatever lubricant you may have put in the center hole. :-)
    As an alternative way to center the tailstock -- do you have a Blake Coax or one of the import clones thereof? If so, put the shank of the coax in a collet or in the chuck (collet is better, if you have them), and set the finger to either trace the ID of the Morse taper socket in the tailstock ram -- or put the center in and trace on the OD of it. Set the spindle to a slow speed (back gear) and adjust the tailstock to minimize the wiggle of the needle. Note that some lathes when new come with the tailstock just a little above center, so as the tailstock wears, it first gets closer to center before it starts getting worse, so you proably won't be able to find a truly wiggle free position.
    Good Luck,         DoN.
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    [ ... ]

    BTW -- at one time, a "live center" was simply the rotating center in the headstock spindle, and the dead was one in the tailstock. They were otherwise identical -- if the same Morse taper. Once we started getting centers mounted in bearings so they could rotate in the tailstock, the name drifted.
    And the "live" one in the spindle was typically soft so it could be trued *just* before mounting the workpiece. The "dead" one in the tailstock was more likely to be hardened.
    And have you ever seen a "half center"? A hardened center for the tailstock with almost half of the diameter ground off so a facing tool could get to the center hole to finish the end of a shaft. I've got one of those -- but too small for my main lathe. Nice for doing things that the ball bearing center won't allow.

    In which case, let it remind you. :-)
    Old lathes tended to have a cavity in the casting near the front where the ram comes out, and a plug/dipper in there. It used to be filled with white lead to use as a high-pressure lubricant for the dead center -- before the world got scared to death of lead and mercury. :-)

    O.K. So you have those as an option.

    I didn't mention the pinched plate because of the questionable state of your centers. I first learned about that in the manual for a Unimat SL-1000 (where the headstock rotated instead of the tailstock offset for turning long tapers). And they showed a double-edge razor blade as the pinched plate. I often use a 6" scale for quick-and-dirty center checking.
    Enjoy,         DoN.
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On Tuesday, November 29, 2016 at 8:32:01 PM UTC-5, DoN. Nichols wrote:

It's good you brought that up. A lot of more recent home machinists may not realize this. A live center is one driven under power. A tailstock center with ball bearings is...a ball-bearing dead center. d8-)
For precise work, you mount the live center and turn a new point on it with the lathe compound. Then punch a witness mark on it, and a matching one on the center collet, so you can line them up again later for less-precise work.

Mine is still filled with white lead (1945 South Bend 10L). My tin of it is almost empty, though.
--
Ed Huntress


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On Tuesday, November 29, 2016 at 10:12:54 PM UTC-5, snipped-for-privacy@gmail.com wrot e:
<snip>
BTW, traditionally, dead centers are hardened only for the last 1/4 inch or so. All of mine are, and they're 60 years old or more. The hardening leave s a distinctively different color to the steel -- the result is a cone 1/4" long on the very end -- so it's easy to tell when one is a hardened center or not.
--
Ed Huntress


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    O.K. But does it also match the tailstock? I can't see using a half-center in the headstock. :-)
    Enjoy,         DoN.
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