Dealing with Out-of-Round?

[ehickey]

UPDATE - Dealing with Out-of-Round?

I am still somewhat new (about a year) to penturning, but I am having some problems with out-of-round turnings. I have a pretty decent Delta Midi lathe, and I have eliminated everything in between but a dead center and a live center. Just the blank in the middle. Maybe I'm not being consistent with placing my calipers in the same place everytime. Here's my process:
* Place the blank between centers
* Measure and zero my calipers to one piece of hardware where one edge of wood will meet it
* Turn down and measure every once in a while
* When I get close to zero, I will stop the lathe, measure, rotate the blank 1 quarter turn, and remeasure. At this point the two measurements will be different by about 5 thou (give or take)

I used to use a mandrel, but stopped thinking it was the problem. I was still using bushings though. Now I've stopped using bushings thinking they were the problem. Now I just don't know. Inconsistency in caliper placement doesn't account for everything, because when the pen is assembled, there are places where it is not flush and places where it is.

I've considered that maybe my tools aren't sharpened enough or correctly, which might cause me to use too much force. I do feel I push pretty hard sometimes and my skew will often "chatter" at me. Does this sound like it could be the problem?

I measured my lathe's spindel bore as best I could and it looks like it deviates by 2.5 - 3 thou. But even still, while it is on the lathe, the blank should still be round, right? Now maybe it is not concentric to the tube, but it should be round.

My final question is, am I being too particular? Is this something everyone deals with and just accepts? I look at the pictures that are posted on this site and it seems to me that the fit is typically nuts on.

Thanks in advance for your help



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UPDATED CONTENT
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I think that I have a resolution to my issue, thanks to everyone's help.
I believe that my problem has a couple of causes.
1) My drill press sucks...the spindle moves forward and backward a noticeable amount when it is lowered. I haven't found a solution to this yet, but it is causing a larger, and oval, hole than the one that is required. This is causing a loose fit for the tube
2) I use thick CA glue for my tubes and I don't get full coverage after the tube is inserted. This causes a void that provides no support for the wood as it gets thin.
3) My tools were super dull. I admit it...I am lazy. If my bench grinder is not out and set up, I will not use it. I work in a two car garage, and I have to stow tools as I am not using them. The dull tools were causing me to push harder than necessary, which was then allowing the unsupported wood to flex and cause out-of-round.

I think that all of these issues were resulting in out-of-round. Now, I'm sure that sharp tools will also cause a *little bit* of out-of-round, but I think that dull tools were exacerbating the problem.

I tested this with a sharp skew and a blank that was accurately drilled. I took light cuts and was able to measure that it was round with my micrometer. Whether it was off-center or not is another story

After that, I started by trying to lightly clean up an amboyna burl blank that I had been working on when all this started. My skew caught at a place where there was a void between the tube and the wood, split out, and the tiny chunk hit me square on the nose. Please don't ask why I wasn't wearing my face shield (as I rarely don't).

 

[marcruby]

Have you checked out the tailstock center? Does it line up with the headstock center. Make sure there isn't any play or looseness in the tailstock. Pushing too hard could be part of the problem in that it will exacerbate and slight out-of-roundness.

Marc

 

[ehickey]

I have checked the tailstock center, but only by eye. It is off by just a hair. If there is any play in the live center, it is too small for my hand and eye to see it. Maybe I should check the tailstock quill to see if it has some play. The tailstock itself seems pretty secure.

 

[jskeen]

You have pretty much duplicated my results and steps up to this point. I assume you have also probably tried banging your head against a wall and throwing thing around your shop, as these two steps seem very closely related. I have actually begun to wonder if the problem could be at least partially in the parts from the kits. If anybody out there has a pin micrometer and would be interested in measuring the standard deviation of a few kit parts and reporting it, I'm sure it would be interesting reading.

 

[Rifleman1776]

My first thought was to recommend going the 'no mandrel' method. But you have done that. You also have eliminated most variables. Good job trying to solve a problem. Hard to give advice on this without being there.
My next concern would be alignment. Bring tailstock with a live center up to headstock with a pointed spur in spindle and make sure they are dead-on with each other. Then, by hand rotate the spindle and observe if it goes off center.
Good luck.

 

[ehickey]

I'm pretty good about not throwing things as I have two small children. Once I start throwing things, they will too.

I have been extraordinarily close to punching a few holes in my walls though...

I think you might be on to something with kits, as I have wondered that too. But I think my problem is showing up before the kits even get involved, unless it is a problem with the tube being out-of-round.

 

[ehickey]

My first thought was to recommend going the 'no mandrel' method. But you have done that. You also have eliminated most variables. Good job trying to solve a problem. Hard to give advice on this without being there.
My next concern would be alignment. Bring tailstock with a live center up to headstock with a pointed spur in spindle and make sure they are dead-on with each other. Then, by hand rotate the spindle and observe if it goes off center.
Good luck.

Yes, I have brought the tailstock and headstock centers together, and there is a very, very small difference (I haven't measured it exactly yet). When rotated, there is some change, but it is definitely not in the 5 thou range, probably more like .5 - 1.5 range.

 

[DCBluesman]

Your description "there are places where it is not flush and places where it is" sounds more like a concentricity issue rather than being out of round. There are a number of reported cases where the hole in the bushing is not concentric with the outer diameter. You might want to check this next. You can overcome a bushing concentricity issue by turning your own or by purchasing some of the mandrel-less sets of bushings from johnnycnc or others.

 

[leehljp]

To clarify something that Lou brought up - OOR or "out of round" is used often as a generic term (and I am guilty of that) and it is misleading some of the time. Sometimes "OOR" is used when the real problem is OC - Off Center.

OOR produces oval shaped, caused by one of several problems
OC produces "round" but not centered - concentric; usually caused by bushings being drill off center.

When Sierra's came out, there were several batches of bushings that were round on the outside but the hole was drilled off center. I usually buy two sets of bushings (at least) for each pen type that I make. And I check to see which of the set are centered and which are not. About 1 bushing in 6 to 8 I throw away because the hole is drilled too much OC. If it is OC by more than .003, I don't use it.

I have not had any problems with Johnnycnc. His have been dead on!

 

[ehickey]

I have considered that my bushings might be part of the problem, but I have stopped using them as well. Now I am just turning with the blank between the live and dead center. Nothing else.

As far as terminology, I'm not sure what the problem is, so I'm not sure what to call it. Tonight I will try to look at one of my problem blanks and determine if it is OOR or OC.

If the problem were OC, then when I measure on the lathe, shouldn't I get a consistent reading? I assume that OC is, for the most part, like the technique of turning a taper by offsetting the tailstock (i.e. off center). Eventually, I will have removed enough material to produce something that is round. Now, it may not be concentric with the tube, but it should be round.

Thanks to everyone for the replies and help

 

[toolcrazy]

Have you tried cleaning both the MS tapers? They do collect crap in them and need to be cleaned.

 

[marcruby]

Your description "there are places where it is not flush and places where it is" sounds more like a concentricity issue rather than being out of round.

I'm assuming the Eric's description of what he has done is accurate -- that he has come down to placing the tube directly between the centers. I've had the opportunity to try that a few times late due to a bad bushing set, and, as long as the headstock and tailstock are lined up, it removes any out of round or lack of concentricity problems.

The next candidate to rule out is the question of alignment. Most people don't realize that any alignment error is doubled in turning. So what looks like a slight problem can easily become noticable to feel if not to sight. So that's the next thing to rule out. The first thing to do is clean out the MT taper joints. It takes only a bit of goop or a bit of a nick to throw the seating off.

Interestingly, overaggressive sanding can cause out of roundness - wood isn't equally hard everywhere.

Marc

 

[ehickey]

Marc is correct, I have removed everything but the blank from between the centers.

I will have to check the tapers to see if they are clean. I also plan on sharpening my tools; I have been slacking on that front.

Thanks to everyone for your help, it has given me quite a bit to think about.

 

[OKLAHOMAN]

Ok one more thought, as both Hank and Lou stated the problem is OC (off center) not OOR(out of round). Look at the hole that was drilled and the tube installs into that hole, if you have to much space around the tube it will be glued in OC causing flex in the blank as you turn and that will give you an OC finished blank, I found this especially true with acrylics. Check your drill bits!

 

[ehickey]

Ok one more thought, as both Hank and Lou stated the problem is OC (off center) not OOR(out of round). Look at the hole that was drilled and the tube installs into that hole, if you have to much space around the tube it will be glued in OC causing flex in the blank as you turn and that will give you an OC finished blank, I found this especially true with acrylics. Check your drill bits!

Hmmm...I might have to look into that one. I know that I drill a slightly oversized hole on the particular pen that I was working with last night.

Thanks for the tip.

 

[keithkarl2007]

if the brass tube isn't milled 90 degrees to the blank, it will throw the balnk off

 

[JeffinWIS]

Eric, if your headstock or tailstock center have runout, the blank should still measure round, but the outside of the blank would be off center from the tube, which would cause it to not match up with the hardware.

If you actually measure the blank as out-of-round, there is another problem.

Putting the tube directly on the centers, remember there is minimal contact area between them to actually drive the blank and securely hold it in position. To prevent distorting the tube, very little pressure can be used on the tailstock to hold the blank securely in position...with scary sharp tools and light cuts, you may be able to turn a round blank. The blank could be moving around on the centers, especially with somewhat dull tools.

To possibly narrow the problem to the tailstock end, try turning the headstock end and measuring it. Using a freshly sharpened tool, light cuts, turning a straight diameter, and no sanding...it that diameter round? Someone mentioned different densities in wood...good point...I too believe that much sanding can make a blank out of round because of it.

Headstock/tailstock being slightly out of alignment, in itself, will not make a blank out-of-round.

 

[ehickey]

Headstock/tailstock being slightly out of alignment, in itself, will not make a blank out-of-round.

That's pretty much the way that I've been thinking of it. I definitely need to sharpen my tools, and make sure that I'm getting clean, accurate holes and using enough glue (had some problems with that, too).

These are great ideas, thanks for sharing.
Eric

 

[ehickey]

Updated original post with most likely resolution in case others have similar problems.