Determining if the Headstock and LiveCenter are off?

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TurningIdeas

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Hey everyone, I'm a newb pen-turner. Got a mini-lathe from Penn State Industries, and I bent my mandrel shaft on some of my first pens. So I bought a mandrel saver, and a new mandrel shaft. After turning a pen last night, it started rattling. I tried tightening the mandrel with wrenches that came with the mandrel and shaft, but that didn't help either. Is it possible to mess up the Mandrel itself? Did I buy a mandrel shaft that was busted from the beginning?

Any help on troubleshooting a rattling lathe would be helpful. Here is the mandrel I'm using. Just ordered a replacement from Amazon: https://www.amazon.com/dp/B073FB35LQ?psc=1&ref=ppx_yo2ov_dt_b_product_details


I ran 3 more pens in the last 24 hours, and it seems to be making a difference, but I'm still getting a little shake at the end of the mandrel shaft. I'm trying to determine if my lathe is just not machined correctly, but there is definitely a difference in contact towards the tail stock vs the headstock. Any ideas on troubleshooting?

Thanks.
 
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pssherman

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Are you using the knurled nut that came with the mandrel? The mandrel saver is supposed to make direct contact with the bushings/spacers and should not be using the knurled nut. It is meant to place compression on the blank without compressing the mandrel.
 

TurningIdeas

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Are you using the knurled nut that came with the mandrel? The mandrel saver is supposed to make direct contact with the bushings/spacers and should not be using the knurled nut. It is meant to place compression on the blank without compressing the mandrel.
I'm not using the knurled nut. I put a lot of pressure on the mandrel saver to the bushings, the mandrel shaft was rattling in the mandrel saver when I did this. Even with a brand new mandrel saver. I made sure to not apply too much pressure with the mandrel saver and the new mandrel because I was worried I would bend it still. Working with 7mm slimline kits that came with the PSI mini lathe.
 

TurningIdeas

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Are the threads well inside the the mandrel saver? The threads have a smaller diameter than the smooth shaft and could be a source of rattle.
Yeah, the threads of the mandrel shaft are in the mandrel saver. Should I just go further up the mandrel so the threads are further in the mandrel saver?
 

rherrell

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Even if a dead center in the tailstock and headstock line up your headstock/ tailstock can still be off.
Put the tips of your index fingers together, now, with the tips still touching move one finger a little to the side, that's an example of how your headstock can be off even if the centers touch.
 

monophoto

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Back to basics -

1. Check that your headstock and tailstock are aligned. There is no way to adjust the tailstock, but you can align the headstock. Put the spur-type drive center in the headstock, and the cone live center in the tail stock. Extend the tailstock quill as far as it will go, and then back off by turning the handle one turn. Slide the tailstock up to the headstock, and closely inspect how the two points align. Note that alignment involves two dimensions. Fixing a misalignment in the vertical plane is difficult (theoretically , shims could be inserted under the headstock if the headstock is low, but if the theadstock is hign, there probably is no simple fix that I would want to attempt). So I would consider vertical misalignment to be a manufacturing defect and contact PSI Customer Service about a warranty replacement. However, that's a rare situation fairly unlikely. A more probable situation is that they won't align in the horizontal plane. That's very easily fixable - there are four socket-head screws attaching the headstock to the bed ways, and the lathe was supplied with a hex wrench that matches those screws. Loosen the screws, and twist the headstock until the headstock and tailstock drive points are aligned in the horizontal plane, and then tighten the screws. To be cautions, check the alignment again - and again.

2. The other possible problem is that there is too much backlash in the tailstock. Loosen the tailstock clamp, and then grab the tailstock and wiggle it to see if it can rotate about an imaginary vertical axis. The tailstock is aligned to the bedways by means of a machined rectangular protrusion on the bottom that fits between the bedways. Many lathe owners have observed that the protrusion is very slightly too narrow, and as a result, the tailstock can rotate just a bit. On my 12" Turncrafter, I get about 0.6 degrees of rotation - yeah, that's pretty small, but its enough to cause the horizontal plane alignment to shift a millimeter or so on the horizontal plane. There is no simple fix for this problem - you simply have to be aware of it and account for it in using your lathe. There are two times when this can be a problem:

When drilling: on the lathe - the fix for this problem is really simple. Mount the blank in a scroll chuck in the headstock, spin the lathe, and use a skew to cut a small dimple exactly on the center of rotation where you intend to drill. Then, with the drill bit in a jacobs chuck mounted in the tailstock, slide the tailstock up to just before the bit touches the blank, and wiggle it until the bit is centered on that dimple - THEN lock down the tailstock and drill the hole.

When turning pens using a pen mandrel - the fix here is very similar to the drilling situation, except that you should align the tip of the cone center to the end of the mandrel. The problem, however, is that if the mandrel is bent, the rotational axis of the tailstock won't be aligned with the rotational axis of the headstock, and that causes the rattling you have experienced. You can minimize the problem by turning one blank at a time even though the mandrel is long enough to turn two blanks simultaneously - making the mandrel shorter reduces the alignment error. Also, in my experience, if you have aligned the headstock and tailstock as described above, and if then observe how that alignment can shift as a result of tailstock wiggle, you can pretty much eyeball where the tailstock needs to be within that 'wiggle range' so that the tailstock axis is aligned with the headstock axis. It won't be perfect, but it will be close enough, and will compensate to some degree for a slight bend in the mandrel shaft. Obviously, replacing the mandrel shaft is will fix the problem - temporarily, until it becomes bent again. I'm sure that someone will point out that a better solution is to throw away the mandrel and turn pen blanks between centers, but I'll let them speak for themselves.
 
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jrista

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Are you using the knurled nut that came with the mandrel? The mandrel saver is supposed to make direct contact with the bushings/spacers and should not be using the knurled nut. It is meant to place compression on the blank without compressing the mandrel.
Ironically, this can lead to problems if the shaft is not perfectly strait itself. Most of the mandrels I've purchased, even when brand new, have a curve to the shaft. It can be enough that it shifts the bushings a bit, so that with a mandrel saver, while it will directly contact the bushings, there is enough tolerance in the hole in the mandrel saver itself that the shaft can move.

If you don't have a perfectly strait shaft, then using the knurled nut with a 60 degree point can in fact improve things, as the nut, when tightened, "pulls" the shaft strait.
 

TurningIdeas

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Awesome advice everyone. Going to try and get a acrylic started tonight. Right now it seems like it's working pretty well. Seems like it's getting there.
 

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AllanS

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Not directly related to alignment of the head and tailstocks, but @rherrell sells a dial indicator post that can be used (with a dial indicator) to test how much wobble is in your mandrel.
https://www.amazon.com/dp/B016R3GLB0?psc=1&ref=ppx_yo2ov_dt_b_product_details

I'd have to imagine that if your head and tailstocks are wonky, this setup will catch that as well.

edit : video link of this in action -
 
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Wooden Dreams

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Aug 24, 2019
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Rapid City,SD
Hey everyone, I'm a newb pen-turner. Got a mini-lathe from Penn State Industries, and I bent my mandrel shaft on some of my first pens. So I bought a mandrel saver, and a new mandrel shaft. After turning a pen last night, it started rattling. I tried tightening the mandrel with wrenches that came with the mandrel and shaft, but that didn't help either. Is it possible to mess up the Mandrel itself? Did I buy a mandrel shaft that was busted from the beginning?

Any help on troubleshooting a rattling lathe would be helpful. Here is the mandrel I'm using. Just ordered a replacement from Amazon: https://www.amazon.com/dp/B073FB35LQ?psc=1&ref=ppx_yo2ov_dt_b_product_details


I ran 3 more pens in the last 24 hours, and it seems to be making a difference, but I'm still getting a little shake at the end of the mandrel shaft. I'm trying to determine if my lathe is just not machined correctly, but there is definitely a difference in contact towards the tail stock vs the headstock. Any ideas on troubleshooting?

Thanks.
I don't turn many pens or pencils. I purchased my lathe to primarily turn Segmented Urns for Funeral Homes. I don't turn many pens or mechanical pencils. The system I use, is a mandrel with direct1x8tpi https://www.pennstateind.com/store/PKM-BL.html and a mandrel saver https://www.pennstateind.com/store/PKMSTS2.html. I have had no issues with the mandrel bending, wobbling or rattling. I'm a newbie to turning (only had my lathe for over two tears). Plus, this seemed the most trouble free in the use of a pen mandrel. Seems to me, that once you bend the mandrel, the mandrel probably needs replacing. Even the direct 1x8tpi mandrel I have, has replacement mandrels, that can be screwed back in.
 
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jrista

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I don't turn many pens or pencils. I purchased my lathe to primarily turn Segmented Urns for Funeral Homes. I don't turn many pens or mechanical pencils. The system I use, is a mandrel with direct1x8tpi https://www.pennstateind.com/store/PKM-BL.html and a mandrel saver https://www.pennstateind.com/store/PKMSTS2.html. I have had no issues with the mandrel bending, wobbling or rattling. I'm a newbie to turning (only had my lathe for over two tears). Plus, this seemed the most trouble free in the use of a pen mandrel. Seems to me, that once you bend the mandrel, the mandrel probably needs replacing. Even the direct 1x8tpi mandrel I have, has replacement mandrels, that can be screwed back in.

I would offer that Urns, being so much larger than pens, wouldn't experience the kinds of issues pen turners experience with non-concentricity and out-of-round issues that can arise with even the smallest imperfections in the tools (i.e. mandrels) we use. We are usually turning down to thousandths of an inch tolerance to perfectly match the pen kit hardware.

With a Urn, even if you had some non-concentricity issues at a bushing, the scale of an urn is huge compared to a pen, and I don't think it would matter...

It doesn't take much of a curvature to the mandrel for it to introduce problems when turning a pen. All of mine appear "generally" strait, but they all have a slight curvature, and it does matter when making pens. I now turn between centers (TBC) only, with special TBC bushings, and that has largely eliminated the problems I used to have with mandrels.
 

TurningIdeas

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I was out of town for a bit. Had to call the PSI guys. Got on a call with the machinist. Turns out my belt was loose and the tail stock was off center. So got that all set up, and everything is working much better now.
 
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