Thread: Out of round pen barrels

There are numerous reasons for out of round, another one is your tailstock not lining up with your headstock. This is one of the most common causes in my experience.

To see whether that is your problem, put a dead centre in your headstock, your ive centre in your tail stock and see how they line up.

Another test is to put your mandrel in the athe without any blanks on it and put a dial indicator on it to see how concentric it runs, you may be surprised at how much difference there will be between the readings at the headstock and at the tailstock.

A lot of people on IAP are using the between centres bushes made by JohnnyCNC and are reporting good results.

The collet style mandrels allow you to adjust the length of mandrel to suit. right down to one blank length, thus eliminating the need for heaps of spacers If the bushes are not a neat fit in your tubes then the tube can push to one side of them ,only takes a few thousandths of an inch to give you runout or non concentricity so you take down to the bushes neat all round ,but when removed for assembly you find its slightly offset from inner tube to outer diameter , there are enough variables in all these things to make it very hard to pinpoint.kits can vary slightly in tolerances and so can bushes ,the only certain way to get concentric is between centres ,most times the kits and bushes are good enough ,but odd ones will show problems , cheers ~ John

Hey Tiger,

When I use a mandrel, I use a Collett type and have it as short as possible, Single tube pens I turn with a Dead Centre in the Headstock and a Live in the Tailstock, no problems since,

The biggest hassle was getting the Tubes square to start with. That was my Problem at the start.

Good Luck

HazzaB

Hello,
I have been having the same problem, so I asked a local woodcraft employee. He told me that my tail stock may be the problem. I am using my stock tailstock, and he said it is basically too pointy and a 60deg cone tailstock might fix the problem. This may also be a solution. #2MT Pen Mandrel Saver at Penn State Industries you should watch the video it looks really cool.
I hope this helps

Thanks guys for your input. Tried a couple more pens this afternoon.

I tested the headstock tailstock alignment, the tailstock was no more than 1/2 mm below. The mandrel did show some runout without any blanks attached, more than I had expected. The interesting thing is that the barrel nearest to the headstock on the edge closest to the headstock also came out of round. I would have thought that runout would have been worse along the mandrel so that out of roundness would be greater at the tailstock end, with me it seems to occur more often along the middle of the mandrel. It's possible that the ends aren't square but I use a disc sander set-up to square the ends of the barrels and didn't think there was an issue there. I'll investigate a better squaring system later but I did find out that slackening off the tailstock and making light finishing cuts did reduce out of roundness.

Tiger, "no more than 0.5mm" is 20thou, that is a lot of run out at the tailstock!

What about side to side movement of the tailstock as you slide it along the bed?

You can test your mandrel with a pencil. Start up the lathe with the mandrel in it. Support a pencil with the tool rest and bring it gently to the middle of the mandrel. Stop the lathe and look at the mandrel. If the pencil mark goes all the way around then the mandrel is perfectly centred. If not then flex it away from the centre of the pencil line (highest point). Test it again, and you should find the pencil line going further around the mandrel. Keep going until the pencil line goes as close to all the way around as you want it to. Most mandrels I have used needed some adjustment.

Peter

This problem is so common that 800 ideas have been floated to "correct" it. New methods that cost extra $$$$..I have been doing this so long I have grown roots in front of my lathe. If I were you, BEFORE, I spent anymore $$$: If you wish to keep your mandrel: Turn your barrel to near completion. Look at the ends. Loosen the nut if it is out of round. Turn barrel 1/4 turn..turn a little bit. Stop, turn barrel 1/4 again, etc. You will have a round barrel..Keep an eye while sanding. I have done this for years and I am a production turner. I can't afford all the gizmos that come done the pike, when a simple way will suffice. I read on another forum that the bearings in the new mandrel saver are crap & PSI says they will improve as one uses. How one improves square-ish bearings is a mystery! Good luck

Turning Between Centers iliminates all the issues with turning out of round barrels.

Les