Non-round pen fix.

[pinscar]

Non-round pen fix.

Here is the first of two real basic questions in two separate threads so others with the same question but unwilling to admit they need help. When I turn my pens, they come out "oblong" i.e. not perfectly round; it is very obvious when I role it across a very flat surface.

I am working with a very hard material with inconsistent density or hardness if you will. I try not to use lots of pressure when I turn and keep my tools as sharp as I can. I use the highest speed when turning. When I get within @1mm of the final diameter, I use CA glue to fill the voids and to "even out" the density or hardness. I am switching to carbide cutters which should hold the sharp edge longer and decrease the temptation to apply more pressure on the blank. I am making a homemade "steady" and I sometimes only turn on the mortise half of the mandrel. I have even sanded when the blank is not turning to even things out.

Any thoughts or ideas?

P.S. I've found a source for new carbide cutters that is very cost effective, however, the cutters are sold in packs of 10. I would like to have 3-4 different sizes and shapes: round, square, triangular, trapezoid, etc., but would rather not spend $200.00 and end up with a lifetime supply of 50 carbide cutters. I would be better off to pay $10.00 to $15.00 each and only get 5. Anyone out there want to split the purchases? Call it $4.00 each plus shipping. Email me at capantler@bellsouth.net.

 

[Skye]

1. Just how hard a material are you turning?

2. Buy new bushings. That or turn with slimline bushings and then measure your way to final dimensions that way you're not bouncing off out-of-round the bushings. This is my #1 suggestion.

3. If you tighten up on the tailstock too much, it'll bend your mandrel. Just tighten it enough to secure it.

4. Use a 60 degree live center in the tailstock so it mates with the indentation in the end of the mandrel better. It'll help keep the mandel centered.

5. With relatively sharp tools, wood that's anything short of stone, regular turning tools should be fine. I think you're putting too much stock into high end cutting tools, when it's not your problem in the first place.

 

[leehljp]

There are several issues that can cause OOR.
1. Mandrels that are OOR
2. NOT using a 60° live center. Most wood lathes do not come with 60° live centers. The 30° centers do not fit properly in the 60° cup of a mandrel. The result is that after a while the 30° point will bend a tad and the mandrel will develop a slight wobble.
3. Too tight tail stock on the mandrel.
4. Unsquared blank ends and then tightening the nut can push the blank into an OOR situation.
5. Bushings OOR.

1, 2, 3 can be eliminated by using a dead center on the head stock and using the "no mandrel / mandrel-less method.

 

[ed4copies]

One possibility:

The hole in your bushings is off center.

I never believed this was possible, until I turned "mandrel-less". There is NOTHING ELSE there, except the bushings, yet things were not "spinning true".

Now, I realize I have to test the bushings - I throw out the "bad" ones, my pens are now GREATLY improved.

FWIW

 

[steve_mcloon]

I would add 2 more possibilities to Hank Lee's list:

6. Lathe head stock and tail stock not alligned.

7. Too much sanding (Wood is never equal density throughout, so softer areas abrade faster than harder areas when sanding. It shows up most often in cross-grain pens where long-grain and end-grain abrade at very different rates.)

 

[marcruby]

I'll throw this in -

If it's a hard materiel, are you pressing hard when you are turning it? This can force a mandrel off center. (yet another reason for mandrel-less bushngs)

 

[fernhills]

One good possible fix. When you mount your blank on you tend to make it tight so it won`t skip on you, but when you get near final dia. you can loosen it all up and move it around on mandrel and then just snug it up again and continue to turn to final dia. That helps me. Carl

 

[itsme_timd]

Just my 2-cents here as I had the same problem... others have said the same.

- Don't overtighten the mandrel thumb screw or the tailstock.
- Make sure to just tap the tailstock lightly into the mandrel and lock it down, then crank it in to a snug but not oversnug hold

When I disciplined myself not to do these 2 things it solved my out of round problem. I have a friend that turns with me from time-to-time and he cannot stop the overtightening. He gets frustrated because when it gets to the finishing stage he gets inconsistent finish on his pens, usually acrylics where it's veru noticeable.

HTH!

Tim

 

[redfishsc]

One possibility:

The hole in your bushings is off center.

I never believed this was possible, until I turned "mandrel-less". There is NOTHING ELSE there, except the bushings, yet things were not "spinning true".

Now, I realize I have to test the bushings - I throw out the "bad" ones, my pens are now GREATLY improved.

FWIW

Out-of-round holes in the bushing are a possibility (had not thought of that though, but some calipers should quickly diagnose that issue).

However, you mention that there is nothing else there---- don't forget that if you don't clean out your MT hole before inserting the dead center in the headstock, you might get some runout.

That obviously isn't what was happening with you since swapping bushings solved your problem.

 

[whteglve]

My vote is the bushings. I had bushings that the hole in the center bushing was off center. I went back to Klingspor to swap it out for a good one and ALL of their cigar bushings were off center like that. I guess they can win a lot of medals in the olympics but can't drill a darn hole on center.

 

[Jarheaded]

I'm not sure if this will help, but try a bigger hammer.

 

[ed4copies]

Out-of-round holes in the bushing are a possibility (had not thought of that though, but some calipers should quickly diagnose that issue).

However, you mention that there is nothing else there---- don't forget that if you don't clean out your MT hole before inserting the dead center in the headstock, you might get some runout.

That obviously isn't what was happening with you since swapping bushings solved your problem.

Also, if the morse taper is the problem, putting a dead center in the taper would result in the "dead center" being "off center" when it turns. Should be easy to identify.

 

[Daniel]

I'm with Johnnie, and if it breaks it needed replacing anyway. I've never seen the off center bushing comment before. The issue of out of round pens is one that has been hunted down for nearly everyone, it is obviously a complicated problem when after all this time new reasons for it are still being found.

 

[leehljp]

I'm with Johnnie, and if it breaks it needed replacing anyway. I've never seen the off center bushing comment before. The issue of out of round pens is one that has been hunted down for nearly everyone, it is obviously a complicated problem when after all this time new reasons for it are still being found.

Daniel,

I posted a pict with VISIBLE off center hole about two years ago. I can't find the post now and I am sure the link is broken. When the Sierra's first came out there were several comments about the early bushings being OOR or Off center.

I have a couple of other bushings that when I miked them, I found that the they were drilled Off Center. I usually reply that bushings are OOR but technically I should be saying OC. OC bushings result in OOR pens and explaining the correct technical differences to the masses, uninitiated and newbies seems to go over their heads - until they get deep into the problem. . . so I just keep it simple and use OOR for OC.

I don't think "new reasons" are being found either, but some of the explanations are clarified for the non-technical minded. You may have just missed these explanations: Too much pressure from a dull chisel, too tight of a tail stock, 30° LC in a 60° mandrel, B mandrels better than A, misaligned TS, soft, hard grain sanding differences, tightening the mandrel too tight against unsquare blanks - I read all of these within the first 6 months of joining in early 2005.