Wall thickness ????

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shawndakin

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Joined
Oct 16, 2010
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32
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Gas City, IN 46933
I am a relatively new pen turner and i have a dilema. After i have finished turning the blanks to prooper diameter, when i fit the pieces together the tip if the pen protrudes higher on one side of the pen blank. I thought if you turned it on the lathe that all the way around that section should be the same thickness. What am i doing wrong?
 
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Welcome to IAP!

This is a common problem for beginners (and veterans). You pen is being turned out of round.

If you are using a mandrel, make sure the nut is not too tight and the tail stock is not too tight as well.

To eliminate (at a somewhat large $50 - $75 range) you can get into "turning between centers". Just do a search here.

Patrick
 
Sounds like you are turning what is known as out of round.

Many reasons for this - search the forums for out of round posts and see if any of the symptoms fit. Check the library as well.

Common problems include pressing to hard on the material and bent mandrels.
 
There are a number of things to look at when this problem is noticed. First check to see that both the drive centre and live centre align perfectly. If these are true, they are perfect for turning directly between centre's as there will be very little run-out. If however the ends of your pen blanks aren't milled square to the tube, this will also cause the blank to be thrown out of round.
Applying too much pressure on your mandrel will cause the mandrel to bow out slightly. Also during the turning stage take light cuts as applying too much pressure on your gouge or tool of choice will force the mandrel away from you. If you haven't got your blanks milled properly, when they are placed on the mandrel and its tightened, it will bow it slightly. You won't see this until the pen is assembled.
 
Out of round is common as has been reported. Some causes could be (1) brass nut too tight against the bushings, (2) live center adjusted too tight against the mandrel, (3) not using a 60 degree live center, (4) bent mandrel, (5) dirty morse taper in head stock or on the mandrel's morse taper arbor, (6) out of alignment head and tail stock, (7) dull tools, (8) any combination of 1 - 7.

Once I started using a collet chuck to hold mandrels all of my (presumed) bent mandrels suddenly and magically became straightened. Using a shortened mandrel and turning one barrel at a time is a possible quick and inexpensive fix. And, no, turning one barrel at a time does not take more time.

Do a good turn daily!
Don

shawndakin said:
I am a relatively new pen turner and i have a dilema. After i have finished turning the blanks to prooper diameter, when i fit the pieces together the tip if the pen protrudes higher on one side of the pen blank. I thought if you turned it on the lathe that all the way around that section should be the same thickness. What am i doing wrong?
Click to expand...
 
I don't want to hi-jack the thread, but on my own lathe as you look in from the front they align perfectly on top but the live centre appears to be below the dead centre. Would this cause any problems?
 
Now that you have seen the many causes---all correct, you can solve your immediate problem by turning the pen with the point at the headstock. The lathe will be MOST accurate here and the nib will fit right.

You will probably MOVE your problem to the centerband location, so use pen kits with "slop" at the center band, ie, "comfort" version of slimline.

When I started, MY problems were dull tools and too much pressure directly into the mandrel, which bent mandrels regularly.

Welcome to IAP, and believe me, you are in good company---lots of folks have had "out of round" pens.
 
Here's how my lathe appears.
 

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keithkarl2007 said:
I don't want to hi-jack the thread, but on my own lathe as you look in from the front they align perfectly on top but the live centre appears to be below the dead centre. Would this cause any problems?
Click to expand...

On a wood lathe using handheld tools, you won't notice it. If you're turning cylinders on a metalworking lathe, you *will* notice the taper.

Eventually. <G>
 
ed4copies said:
keithkarl2007 said:
Here's how my lathe appears.
Click to expand...

If you are using a standard mandrel, those two points are about 8" (20cm) apart. It will make no measurable difference---IMO---Several machinists here would be better authorities on this question, however.
Click to expand...

Would it would be ok for turning between centres? I have the live and dead centres for tbc and a mandrel also.
 
keithkarl2007 said:
ed4copies said:
Would it would be ok for turning between centres? I have the live and dead centres for tbc and a mandrel also.
Click to expand...

Yes, it will be fine. On a wood lathe *you* control the cutter with your hands, and turn either to the bushings or measured diameter with calipers. Unless that offset is huge, in which case you'll be wearing the center indents on the mandrel or the centers' points faster than normal, it should cause you no problems.
Click to expand...
 
I know I speak heresy here, but I have turned between centers and I don't like it.

So, I would not be a good resource for you.

I use the "professional mandrel" (adjustable length) and turn one barrel at a time, with bushings. Have not had an "out of round" and have not cracked a blank on the lathe in months.
 
I've found one thing that's quick and easy for out of round... Sometimes when turning a blank that starts out square, the vibration (or heavy handedness) of the initial making round will do weird things. After knocking off the corners I loosen everything and reset it.

If I forget I usually end up having to toss it and start over.
 
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