out of round

[ahoiberg]

the last few pens i've done have come out out of round on the nib end... checked the bushing, checked my mandrel, can't seem to find what the problem is... i use a collet chuck also which i thought was supposed to give you nice, round turns... could i be putting too much pressure on the nut of the mandrel?

any ideas?

thanks.

 

[Milpaul]

make sure your sizing bushing is all the way on the rod part of the mandrel and not on any of the threads. Even if it is slightly on the threads this will allow some play. Also be sure to sand lengthwise also, this will help.

 

[Randy_]

Do you use a 60° live center?

 

[Rifleman1776]

Shorten your mandrel and do only one half of the pen at a time. That will eliminate 99.999% of the flexing. Make sure your tools are sharp, sharp, sharp to prevent you having to push and force cuts. Or try the no mandrel method of turning.

 

[ahoiberg]

thanks for the replies. randy, i just use the live center that came with my jet 1014. i assume you'd recommend me investing in a 60deg live? if so, any suggestions on where/who to get one from? milpaul, you might be on to something there... i'll have to check and make sure i'm on the rod all the way. and frank, i may try the one half at a time method... thanks again.

 

[Monty]

Also, hate to point out the obvious, but are you sure you don't have "B" kit and bushings on an "A" mandrel?

 

[leehljp]

If the blanks have been end milled even a tad off of square, the bushing can be forced up tight to the off-square end and that will produce the out of round. Learned that the from experience.

 

[ahoiberg]

hank, interesting... i might have to sharpen the old barrel trimmer to see if that's the culprit. mannie, never hurts to cover all the bases, but i'm sure they're all 'A' parts.

 

[Randy_]

Originally posted by ahoiberg
<br />.....i assume you'd recommend me investing in a 60deg live? if so, any suggestions on where/who to get one from.....

Yes. The common recommendation is for the #1189 from http://www.littlemachineshop.com/products/product_search.php?critFast=1189 . That is what I have and it has worked OK for me; but recently there have been some postings by people who had trouble with them so I'm not sure I feel comfortable making an unqualified recommendation.

A few people have ordered from Grizzly and I don't recall anyone having problems with their live centers. http://www.grizzly.com/products/H3408

If you want to go more upscale, you can pay near $100 for LCs from Oneway, Nova and Sorby. Some of these live centers should not be run at more than 2500 RPMs so you don't want to be running your JET at its top speed or you could have a problem.

 

[BigguyZ]

This is the Grizzley LC I bought. I haven't tried a ton of them, but this one works smoothly.

http://www.grizzly.com/products/g5686

 

[ahoiberg]

this may sound like an elementary question, but what advantage does a 60 deg live give you over the stock one i got with my jet? and is this other live only good for small turnings such as pens or will it also give me an advantage with bowls and such?

 

[Paul in OKC]

Originally posted by ahoiberg
<br />this may sound like an elementary question, but what advantage does a 60 deg live give you over the stock one i got with my jet? and is this other live only good for small turnings such as pens or will it also give me an advantage with bowls and such?

The main thing is that the stock center doesn't have a 60 degree taper on the end, while your mandrel has a 60 degree 'socket'. The stock center point bottoms out before the taper seats in the mandrel. I have always used the stock center (6-7 years now at least) and what I do is to knock the point off the factory tip a bit. Lets the center seat into the mandrel.

 

[Randy_]

Originally posted by BigguyZ
<br />This is the Grizzley LC I bought. I haven't tried a ton of them, but this one works smoothly.

http://www.grizzly.com/products/g5686

The LC pictured is a "heavy duty" center in the terminology of some. There have been a couple of posts by folks who bought something similar and had a problem. The pen mandrel did not have enough surface area contact/friction to drive/spin the live center. May have been a freak situation; but pens and the other small projects we do on our JET mini and similar lathes really shouldn't need the bigger live center. The single bearing, $12 one seems to be more than adequate.

 

[Randy_]

Originally posted by Paul in OKC
<br />The main thing is that the stock center doesn't have a 60 degree taper on the end, while your mandrel has a 60 degree 'socket'. The stock center point bottoms out before the taper seats in the mandrel. I have always used the stock center (6-7 years now at least) and what I do is to knock the point off the factory tip a bit. Lets the center seat into the mandrel.

What happens in many cases is the tip of the live center gets buggered up sooner or later and won't seat in the mandrel "socket" exactly centered and will cause an "out-of-round" turning....or at least that is the theory.

Actually it is a little more complicated than Paul suggests and I prefer to use the 60° live center; but if his system has worked for 7 years, I can't really argue with success. This is a little difficult to describe and requires your visualizing some solid geometry. Hope I can do this without confusing you. It is assumed that the centering hole in the end of the mandrel has a standard 60° taper, although I have never seen that assumption actually verified. If you stick a 60° cone(the live center) into a 60° hole(the end of the mandrel), the contact surface is a "flat," truncated cone-shaped surface whereas if you use the original LC tip(which is around 30°) the contact area is just the very tip of the LC point.....a much smaller contact surface. Now, if you grind off the tip like Paul suggests,(assuming you don't mess up and grind off too much) the contact area is no longer a point; but is now a circle. Better than a point but not nearly as good as the truncated cone. No matter how much of the tip you grind off, you will never get a proper fit of the live center and the mandrel if the taper angles are not the same. It would be sort of like trying to use a #1 Morse taper tool in your #2 Morse taper JET spindle.

Unfortunately, this business of using a 60° live center is not something that is intuitively obvious to most turners and it doesn't get mentioned in most books or pen turning instructional tapes and DVDs. Changing to a 60° live center may solve your problem or it may not. There are probably a dozen or more common problems that can cause "out-of-round turning and more and a few uncommon ones. Sooner or later you will certainly figure it out; but the process can be frustrating until it is resolved.

I wish you luck!!

 

[Paul in OKC]

Good description there, Randy. I agree that my way does not give the 'full' seat, but I also do not turn the volumes of pens some of y'all do so the wear and tear on mine is not as great. I have meant to get a 60 degree center, just not on the high priority list. I have only replaced the tip on my factory center once. As for assuming the center in the end of the mandrel is 60 degrees, it is assumed so because they use a center drill to put it in and most (all should be) have a 60 degree set on them.

 

[Mudder]

Randy,

In theory you have a good point but you fail to take in to account manufacturing tolerances. Is the cone exactly 60 degrees 0 minutes and 0 seconds? probably not. Is the 60 degree center hole exactly 60 degrees 0 minutes and 0 seconds? Probably not. So what you have is an area of contact that is most likely a circle where the two imperfect 60 degree angles intersect. Take into account that there is some sort of runout and radial play on the bearing and Paul's methods do not seem all that bad.

Food for thought.

 

[DCBluesman]

I turned at least 200 pens with my original 30-degree live center. I had to learn to work a little harder by rotating blanks on the bushings and by using a little hand sanding, but it worked just fine. I'm glad to have changed, but it's a long way from being an impossible dream.

 

[leehljp]

Originally posted by ahoiberg
<br />this may sound like an elementary question, but what advantage does a 60 deg live give you over the stock one i got with my jet? and is this other live only good for small turnings such as pens or will it also give me an advantage with bowls and such?

Answering this question from a different perspective: The 60° center is used with a mandrel, i.e. metal to metal. Your stock LC came intended for turning wood. You "are" turning wood, but only on a metal rod. This is the reason that most WW lathes come with a 30° center.

30° (?) LC center = direct wood contact
60° LC center = metal to metal contact

 

[Randy_]

Originally posted by Mudder<br />Randy, In theory you have a good point <b>but you fail to take in to account manufacturing tolerances.</b> Is the cone exactly 60 degrees 0 minutes and 0 seconds? probably not. Is the 60 degree center hole exactly 60 degrees 0 minutes and 0 seconds.....

Not at all, Scott. That was exactly what I was pointing to when I made the comment about the socket angle being unverified.

It is assumed that the centering hole in the end of the mandrel has a standard 60° taper, although I have never seen that assumption actually verified.

I just skipped over the details assuming it would be obvious to most; but your comment certainly emphasizes the point.

Originally posted by Mudder<br /><b>.....and Paul's methods do not seem all that bad......</b>

I never suggested that Paul's method was bad. In fact, what I said was to the effect that you can't argue with success.

.....but if his system has worked for 7 years, I can't really argue with success.....

Bottom line, though, is that quite a few people have posted about buying 60° live centers and having their out-of-round problems disappear so changing live centers does work!! Even Paul acknowledged that he planned to buy one when he found a few minutes.

 

[Randy_]

Originally posted by leehljp
<br />30° (?) LC center = direct wood contact
60° LC center = metal to metal contact

That is generally true; but lots of successfully people use the 60° live center for for direct contact with wood as well or when using one of the no-mandrel techniques.

 

[ahoiberg]

thanks for everyone's replies! it should straighten things out for me. the odd part about all this is that i've turned a number of pens over the last year without any out of round problems, or a negligible out of roundness. so, i'll try some of the ideas and if all else fails, i may have to get me a 60 deg LC. thanks again all.

 

[Monty]

Another thing to check is the diameter of the rod as compared to the ID of the bushings. I have 2 "A" rods from different companies and the diameter is different by a few thousands. This could throw everything off if there is a slight wobble because the bushings do not fit snug.

 

[leehljp]

Originally posted by Randy_
<br />

Originally posted by leehljp
<br />30° (?) LC center = direct wood contact
60° LC center = metal to metal contact

That is generally true; but lots of successfully people use the 60° live center for for direct contact with wood as well or when using one of the no-mandrel techniques.

Yes, of course. That is correct. I should have clarified that my comments were directed at the way that most LCs come on the lathe as standard, and give a concise reason/purpose. I have used the 60° on wood also.

I need to be more precise in my words but a Japanese mindset often directs me to assume way too much on the part of the hearer. Boy, do I need to clear this stuff out of my mind! [] [] 4 years to retirement and then back to good old Southern speak and red neck thinkin'!

 

[Grizzlyss]

I replaced my standard LC for a 60 degree HD live center and it made a big difference. But there is the odd time, I still get one out of round, hopefully the new Jet Slow Speed Wet Sharpener will fix some of that, but I also have to look into the bushings being off, and the threaded part of the mandrel rod out of the way. I thin the threads could be causing a lot of the problem now that I think about it. Sure am glad that we have this open forum for the exchange of ideas and experiences, they sure help out a lot.

Sheldon

 

[Randy_]

Originally posted by Grizzlyss
<br />.....But there is the odd time, I still get one out of round, .....

That may have nothing to do with your equipment. Russ F. posted a very interesting comment recently about wooden blanks that get out-of-round during the sanding process because the grain of the wood causes the wood to be more resistant to removal in certain directions and less resistant to removal in others.