Pens not turning round
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mrcook4570
Member
Any one or combination of the following
*Not using 60 degree center
*Too much pressure from tailstock
*too much pressure from knurled nut
*bent madrel
*headstock/tailstock out of alignment
*dull tools
*morse taper not clean
Try to relieve some of the stress on the mandrel. Frequently rotate blank 60 to 90 degrees without rotating the bushings while finish turning/sanding.
*Not using 60 degree center
*Too much pressure from tailstock
*too much pressure from knurled nut
*bent madrel
*headstock/tailstock out of alignment
*dull tools
*morse taper not clean
Try to relieve some of the stress on the mandrel. Frequently rotate blank 60 to 90 degrees without rotating the bushings while finish turning/sanding.
While all of these things about the mandrel can be at fault, we always ignore the most common cause for "out of round" - we are sanding it into the wood. This can happen on a perfect mandrel.
A piece of wood that is spinning in the lathe can pass through 4 changes in grain orientation (flat/vertical/flat/vertical) with every revolution of the lathe. Since the wood is sanded away more easilly in the flat grain than in the vertical grain, we will sand it into an oval shape. This is compounded in softer wood because of the tear-out in the softer flat grain and our need to use a coarse sandpaper..
The solution is a better finish off the turning tool so there is less sanding and starting with a finer grit. Then always sand with the grain with the lathe off, and concentrate on the vertical grain sides of the pen barrel.
A piece of wood that is spinning in the lathe can pass through 4 changes in grain orientation (flat/vertical/flat/vertical) with every revolution of the lathe. Since the wood is sanded away more easilly in the flat grain than in the vertical grain, we will sand it into an oval shape. This is compounded in softer wood because of the tear-out in the softer flat grain and our need to use a coarse sandpaper..
The solution is a better finish off the turning tool so there is less sanding and starting with a finer grit. Then always sand with the grain with the lathe off, and concentrate on the vertical grain sides of the pen barrel.
Kaspar
Member
Also, variegated density in the same piece of wood can cause this.
To ensure perfect roundness (As perfect as possible anyway) I will usually release the knurl and rotate the piece(s) a quarter turn on the mandrel periodically. It provides a great way to check for eccentricity, too. If you are perfectly round there will be no "ka-chunking" on the tool as the reoriented piece turns.
Theoretically it would be possible to turn something almost round even with a slightly bent mandrel, by averaging out the eccentricity in the manner I've described. Better though, to figure out why it's screwing up. [
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To ensure perfect roundness (As perfect as possible anyway) I will usually release the knurl and rotate the piece(s) a quarter turn on the mandrel periodically. It provides a great way to check for eccentricity, too. If you are perfectly round there will be no "ka-chunking" on the tool as the reoriented piece turns.
Theoretically it would be possible to turn something almost round even with a slightly bent mandrel, by averaging out the eccentricity in the manner I've described. Better though, to figure out why it's screwing up. [
]
alamocdc
Member
Originally posted by Kaspar
<br />Also, variegated density in the same piece of wood can cause this.
To ensure perfect roundness (As perfect as possible anyway) I will usually release the knurl and rotate the piece(s) a quarter turn on the mandrel periodically. It provides a great way to check for eccentricity, too. If you are perfectly round there will be no "ka-chunking" on the tool as the reoriented piece turns.
Theoretically it would be possible to turn something almost round even with a slightly bent mandrel, by averaging out the eccentricity in the manner I've described. Better though, to figure out why it's screwing up. [
Yep! I've had this problem w/Wenge.[xx(]
Dario
Member
You got lots of good tip but I'll add this too.
Make sure you mill the ends of the tubed blanks properly before turning.
Make sure your bushings, spacers and knob is clean and there is no "gunk" or CA buildup especially on the sides.
Engage your tailstock BEFORE tightening the mandrel knob.
Make sure you mill the ends of the tubed blanks properly before turning.
Make sure your bushings, spacers and knob is clean and there is no "gunk" or CA buildup especially on the sides.
Engage your tailstock BEFORE tightening the mandrel knob.
I agree whole heartedly with everything that has been already posted.
I especially experience this with my glue ups because I purposely change the grain orientation to give a different appearnce using the same wood.
Another thing that may be the culprit is sloppy milling where you score the tube if you use a drill press with the pen mill.Depending on the kit/bushings you use the fir in the tube may not be as precise as it should be.
Another factor in the milling of the blanks is that sometimes the tube gets peened over at the edges and it is not always concertic.
When in doubt go to Russes site and check out the lathe tune up section, it may be that your head and tail stock are off center.
I rqan into this as a constant problem when the bearing on my JET mini were on the way out(nothing lasts forever)
The last and most important factor may be that:
Shirt happens!
I especially experience this with my glue ups because I purposely change the grain orientation to give a different appearnce using the same wood.
Another thing that may be the culprit is sloppy milling where you score the tube if you use a drill press with the pen mill.Depending on the kit/bushings you use the fir in the tube may not be as precise as it should be.
Another factor in the milling of the blanks is that sometimes the tube gets peened over at the edges and it is not always concertic.
When in doubt go to Russes site and check out the lathe tune up section, it may be that your head and tail stock are off center.
I rqan into this as a constant problem when the bearing on my JET mini were on the way out(nothing lasts forever)
The last and most important factor may be that:
Shirt happens!
Kaspar
Member
One other thing you might consider doing is to round off the point of the live center in the tail stock just a tiny bit. If it's too pointy you'll be, in essence, trying to see how many angles you can balance on the head of a pin, and that while applying lateral pressure to the spinning mandrel. By rounding it just a tiny bit you can have a secure fit of the live center, as this crude and overexaggerated illustration will show.
Also, watch for overtightening of the live center. Once you have the side of that cone snugly interlocked with the side of the recess in the mandrel you are as tight as you need to be.
Also, after a year of using universal mandrels, I have given them up in favor of an arbor and mandrels cut to various lengths. I always turn with the piece as close to head stock as possible. You give up two inches of distance from the source of rotation when using the universal mandrel.
And whenever possible, I use the 8mm arbor and mandrel. Much stronger, more stable turning platform. On the bigger pen kits, I now turn my own bushings to fit the 8mm mandrel.
Also, watch for overtightening of the live center. Once you have the side of that cone snugly interlocked with the side of the recess in the mandrel you are as tight as you need to be.
Also, after a year of using universal mandrels, I have given them up in favor of an arbor and mandrels cut to various lengths. I always turn with the piece as close to head stock as possible. You give up two inches of distance from the source of rotation when using the universal mandrel.
And whenever possible, I use the 8mm arbor and mandrel. Much stronger, more stable turning platform. On the bigger pen kits, I now turn my own bushings to fit the 8mm mandrel.
Rifleman1776
Member
Stan's #5 strong possibility.
What kit are you turning? Do you maybe have an 8mm bushing on a 7mm mandrel?
What kit are you turning? Do you maybe have an 8mm bushing on a 7mm mandrel?
loglugger
Member
I bring the tailstock just about up to the mandrel, turn the lath by hand to make sure the mandrel runs true. Then tighten the mandrel knob or nut tight, then turn the lath by hand and it still should run true, if it doesn’t then there is usually glue or something that is making it go astray. My thoughts are that if you tighten the knob or nut after you bring the tailstock up tight then it might bow the middle out just a little. I have a better fit on the center bands when done this way. Everyone has there own way of doing things this is just the way that I use.
Bob
Bob
Sorry about the empty post--I got distracted. Thanks to all for your responses. I will certainly check out all your suggestions.
I have noticed the epliptical turning most recently when turning a Gentleman's Pen with the Stars and Stripes Kit from Kallenshaan. The offset is not visable but you can tell that it is not even when you run your fingers over the edge. Bushings were brand new and the mandrel is adjustable so I can shorten it to only the length needed. I turned both pieces at the same time--or--I should say is sanded the barrels only--the barrels in the kit come pre-turned--you only need to add the stars and stripes and sand to dimension.
I have noticed the epliptical turning most recently when turning a Gentleman's Pen with the Stars and Stripes Kit from Kallenshaan. The offset is not visable but you can tell that it is not even when you run your fingers over the edge. Bushings were brand new and the mandrel is adjustable so I can shorten it to only the length needed. I turned both pieces at the same time--or--I should say is sanded the barrels only--the barrels in the kit come pre-turned--you only need to add the stars and stripes and sand to dimension.
mrcook4570
Member
Out of round is much more noticeable on larger diameter pens.
wdcav1952
Activities Manager Emeritus
Jim,
It could be that the sanding is the problem. Using sandpaper for shaping can lead to eliptical results and noted above. It is nerve-wracking, but a sharp skew to start the shaping process on Ken's kits should help.
FWIW,
It could be that the sanding is the problem. Using sandpaper for shaping can lead to eliptical results and noted above. It is nerve-wracking, but a sharp skew to start the shaping process on Ken's kits should help.
FWIW,
You may have identified the problem.
Russ stated in a recent thread the kerfs on some adjustable mandrels look as if they are cut with a hacksaw.
Have you taken your apart lately to see if the mating surfaces are clean? no burrs?
I have an adjustable mandrel I mistakenly purchased when I first started turing pens over two years ago because some bonehead at Woodcraft reccomended it.
It is mainly unused and I only pick it up if all the other mandrels are being used.
Another clue!
I have not turned this kit but have seen the finished product.
The body of the blank is long grain with the inlays glued in with yellow glue( thinned down).
Yellow glue is extremely hard when cured.This can have an effect on sanding.I would imagine the inlayed pieces may sand differently than the body of the blank.
I experience this all the time with my glue ups because I use a lot of different grain orientations.
Try using a piece of sandpaper on a <b>flat</b> piece of scrap wood for the final sanding.This will help take out the "bumps".
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