How do you avoid OOR?

[cestmoi]

This is probably an extremely elementary question. I posted a pen here last week (my 3rd attempt at pen making) for feedback and was advised that it might be a little out of round. I understand that this happens when the tailstock and/or mandrel are tightened too much. However, I don't really understand how to avoid this problem. If I don't tighten the tailstock or the screw on the mandrel enough, the wood spins on the mandrel when I use my roughing gouge. How do I tighten it "just enough" without over-tightening it? I do not have one of those chucks that allows you to turn between centers without a mandrel.

 

[Haynie]

The mandrel is a problematic piece and IMO it is the weakest link for the beginner. Some folks turn for years on a mandrel and never have an issue. Others like me struggle with OOR. IMO it is the length of the mandrel that causes the issue. I am fortunate to have a metal lathe with a 3 jawed chuck. I don't have one on my wood lather. I removed the taper and now adjust the length of the mandrel instead of using spacers. Better than that is to turn between centers with wicked sharp tools.

It could also be that your mandrel is no longer straight.

 

[Jim Burr]

You can try a Mandrel Saver from PSI or go BTC...no chuck required!

 

[cestmoi]

You can try a Mandrel Saver from PSI or go BTC...no chuck required!

Ok, Jim, total beginner here. What does BTC mean? My mandrel is adjustable, so maybe I shouldn't use any spacers and keep it as short as possible?

 

[lorbay]

You can try a Mandrel Saver from PSI or go BTC...no chuck required!

Ok, Jim, total beginner here. What does BTC mean? My mandrel is adjustable, so maybe I shouldn't use any spacers and keep it as short as possible?

Between Centres.

Lin.

 

[ed4copies]

Pens are oor (out of round) due to two most frequent causes:
1) mandrel is bent ---especially if you are using a standard, non-adjustable--about 7 to 8.5 inches long. It is easy to bend these in the middle, causing OOR at that location (usually one end of each of the two blanks)
2) Bushings are not drilled dead center. I didn't believe it either, but bushings are not drilled first, they are turned to size, then drilled. It IS possible to have them off center, resulting in OOR.

There are other causes, but I am pretty certain the above will cover over 80 % of the oval pens that come off a lathe.

 

[ed4copies]

You can try a Mandrel Saver from PSI or go BTC...no chuck required!

Ok, Jim, total beginner here. What does BTC mean? My mandrel is adjustable, so maybe I shouldn't use any spacers and keep it as short as possible?

EXACTLY correct!

 

[Displaced Canadian]

When you tighten your tailstock you should just put enough tension on it so the live center spins. You should be able to stop it with your hand.

 

[cestmoi]

When you tighten your tailstock you should just put enough tension on it so the live center spins. You should be able to stop it with your hand.

But if I do that, then my wood also stops when it comes into contact with my chisel. Hmmm. Maybe I'm expecting the beginning of the process to go too quickly, and I'm just supposed to chip away little tiny tiny bits at a time until the blank is round?

 

[Displaced Canadian]

The nut on the mandrel has to be tight. Not the live center. Unless you have a mandrel saver. The first few passes you do have to be a bit gentle until you get the corners knocked off.

 

[edstreet]

Could be what others have already stated about bent shaft, bushing at fault.

Or perhaps you are applying to much pressure while cutting, thus causing the mandrel shaft to flex, thus causing OOR. All because the chisel is to dull to start with.

FYI you can also have OOR when you turn between centers.

I am going to go with D) All the above is possible.

 

[ed4copies]

When you tighten your tailstock you should just put enough tension on it so the live center spins. You should be able to stop it with your hand.

But if I do that, then my wood also stops when it comes into contact with my chisel. Hmmm. Maybe I'm expecting the beginning of the process to go too quickly, and I'm just supposed to chip away little tiny tiny bits at a time until the blank is round?

The beginning stages of turning the blank are immaterial---you get off the stuff you don't want. Make the nut as tight as you want, it doesn't matter yet.

Once the blank is round and about a half inch diameter, your cuts need to be right. So, if necessary, reposition your thumb nut once the blank is round.

 

[mywoodshopca]

I find if I turn the barrel on the bushings at least once I loose almost all the OOR. (IE: Stop the lathe, loosen the tailstock, turn the barrel 1/2 way around and retighten, this would allow the "oor" side to be rounded down as well)

I have been trying to do all TBC when available.

 

[ed4copies]

Please don't take this as "preachy", but if you know you have a problem that is making your pens out of round, any "compensation" will not make them right, just better, but still not round.

Diagnose and repair----there are not a lot of variables.

FWIW,
Ed

 

[plantman]

I have always dissagreed with "the nut is to tight' and you are bending the mandrel thread. You would realy have to crank on that nut, and something would have to be sloppy or out of round to begin with to apply any lateral pressure on the mandrel. I will use a pliers to tighten the brass nut if I am turning a very hard wood and it keeps slipping. I can't say I have never had a out of round piece, but I don't think it was from a to tight mandrel nut. If your ends of your blanks are round, and the centers are out of round, your mandrel is either bent, or you are apply to much pressure with tools that are not sharp enough as ED said. Here is a quick check you can do on your mandrel. Ingauge the tailstock. Need not be super tight. Move up your tool rest until it touches the mandrel. slowly turn your mandrel by hand. see if there are any gaps betreen the tool rest and the mandrel. If there is, that is the point where it is out of round. You can tap on this point with a brass hammer until it runs smooth. Another test you can do is run your tailstock up to, but not touching your mandrel. Turn the mandrel slowely by hand and see if the point stays lined up with the hole in the end of the mandrel. If not gently bend the mandrel until it lines up to the tailstock point as you turn it. After this adjustment go back and repeat the first test. You could also use a dial indecator to true your mandrel. I always keep spare mandrels handy if I don't want to spend the time truing the one I am using at the moment. I usualy turn both blanks at the same time, and need the full length of my mandrel on my mini lathe. I have an adjustable mandrel that I can turn shorter objects on if needed. One other test you can do is move your tailstock up to your headstock and lock it down. They should meet up center to center. Slowley turn your headstock by hand. If it wobbles out of center, you may have a bad bearing. Want to check your mandrel for straightness? Roll it on a flat surface. Jim S

 

[robutacion]

Yes, mandrels can be mongrels, they bend so easily and you have to check their straightness all the time, this is the only way to continue using a mandrel and get good results HOWEVER, if the mandrel is straight and everything else is OK but you are putting too much pressure with you gouge, is only one thing that I can say, try the " Flap Disc System"...!:wink::biggrin:

Good luck,

Cheers
George

 

[Paul in OKC]

Well, I usually try to stay out of these topics, but here goes. Out of round is really not the correct term. What you have is a concentricty issue. The inside and outside of the pen are not rotating on the same plane, or axis. Out of round can happen, but usually when sanding due to soft/hard wood due to grain alignment, mostly when sanding. I do not subscribe to the too tight nut theory, or the too tight tail stock. Just don't think you could tighten it that much. One thing I did not see above is the trueness of the ends. If they are not square, it can cause a slight 'cocking' of the blank allowing what little play there is in the bushing to the mandrel all go to one side. Also don't think you can push hard enough while cutting to cause this. Any flex in the mandrel would be relieved when lighter cuts are taken. Just my thoughts.

 

[sbell111]

I'm definitely not buying the theory that pushing too hard with the chisel can cause OOR. Sharpening your tools to avoid having to use excess force is a good idea because failing to do so will cause your blank to blow up, of course. However, pushing hard is not going to make one side of the blank bigger or smaller than the other as you push the same amount on all sides.

I put much greater stock in the theory that the end of the blank wasn't milled perfectly squareor that there was some foriegn material in the tube that you forced the bushings over or even that the mandrel was overtightened.

One theory that hasnt been added to this thread is the case where the blank hasn't been milled quite down to the tube. This will require you to crank down the mandrel nut a bit extra to keep the blank from spinning. It will then likely tighten onevenly, forcing the blank to be ever so slightly cocked on the mandrel.

 

[kovalcik]

The tightnes of the mandrel nut is not a factor. That can be cranked as tight as you want. It is the tail stock pressure on the end of the mandrel that will cause bowing of the mandrel. A mandrel saver is a good idea as it replaces the nut and removes the pressure at the end of the mandrel.

Do not discount the bushings as part of the problem, especially is some pen styles turn okay and others are OOR. You can buy better bushings from a couple sources for the most popular styles.

 

[kovalcik]

I'm definitely not buying the theory that pushing too hard with the chisel can cause OOR. Sharpening your tools to avoid having to use excess force is a good idea because failing to do so will cause your blank to blow up, of course. However, pushing hard is not going to make one side of the blank bigger or smaller than the other as you push the same amount on all sides.

While your theory makes sense, I was teaching a new turner with a "heavy handed" approach, and when he was done, my mandrel had a noticeable bow, so it is somehow possible to bend a mandrel with too much tool pressure.

 

[Tiger]

I find if I turn the barrel on the bushings at least once I loose almost all the OOR. (IE: Stop the lathe, loosen the tailstock, turn the barrel 1/2 way around and retighten, this would allow the "oor" side to be rounded down as well)

I have been trying to do all TBC when available.

I find this very "hit or miss". I've tried different variations where you stop and turn a quarter revolution as well as 1/2 way round, still get OOR most of the time, sometimes I get lucky and it's concentric.

 

[TonyL]

I have corrected two OOR pens (1 of mine, and one of my friends), by re-turning them between centers. I use my mandrel for MM-ing double barrel pens. I may just be one of those hard mandrel pushers. Turned over 25 between centers (no mandrel) and all concentric. I just ain't cut out for a mandrel (and I do have a mandrel saver and quite a collection of mandrels LOL). TBC took the frustration out of turning for me. However, I know there are many that have the skills, experience, touch etc to use a mandrel probably 2 feet long if they had to.

 

[Paul in OKC]

One other thought in this. If you are using the stock live center that came with the wood lathe, most of those centers are more 'pointed' for penetrating wood. If that is the case, the tip of the center is hitting in the bottom of the recess in the end of the mandrel, and not seating properly in the 'chamfer'. You can just file the tip off a bit until the center sets in at least on the angle. That was my first and only issue with mandrel turning. Once I figured that one out, no problem.

 

[jcm71]

What has not been addressed yet in this thread is lathe alignment. All OOR problems boil down to a misaligned lathe (including lathe hardware). Is the mandrel bent? That's causes a misalignment. Is there foreign matter in either of the MT2 housings? That causes misalignment. Have a bad bearing? Alignment issue. Tightening down too much? Alignment.

For all practical purposes we live in a 3 dimensional world with three axises; X, Y, and Z. Your lathe has to be aligned in all three axises, otherwise you will have OOR turnings.

For discussions sake:
The X axis runs horizontally from left to right as you are looking at it.
The Y axis runs vertically and perpendicular to the X axis from top to bottom.
The Z axis runs horizontally from front to back perpendicular to the other two.

Everyone knows your DC and LC points should line up exactly when you advance your tailstock to the headstock. That does not guarantee an aligned lathe. The rotational (X) axis of your dead center (mandrel) should coincide with the rotational (X) axis of your live center. If those two axises do not make a straight line, no matter how far apart they are, you will have OOR turnings. The further apart they are, the larger your OOR problem will be. As brought out earlier, the shorter the distance the better. It is easier to bend a full length pencil than one only 3 inches long.

 

[jcm71]

Disregard this post. Not my previous. I was going to challenge a statement of a previous poster, but on reflection saw that he was right.