Turning slim/trim lines center band problems

[keithbyrd]

I am probably missing something very insignificant - if so please tell me so I can be embarrassed and move on!
I turned 5 pens of the slim and trim styles. I checked the center bushing to ensure they made the center trim abnd- holding them next to each other - perfect match. I turn the pen get the balnk to perfect match with the center band, finish the pen with CA 6 coats thin and 4-8 medium depending on grain anf filling and when I assemble the blank is about 1/32 proud!
I just thought - is it the thickness of the finish? If not - what causes it and how do I fix?
If it is the finish why doesn't it effect the nib and cap?

Your help is appreciated!

 

[darrin1200]

Hi Keith

You would be amazed at how much CA will build up as a finish. Some people (including me) actually turn the pen a hair undersize, then build back up with CA.

 

[Jim Burr]

Hi Keith

You would be amazed at how much CA will build up as a finish. Some people (including me) actually turn the pen a hair undersize, then build back up with CA.

Especially on slims!!! There is not a lot of room to mess around with these. I'm just finishing up some PFS pens and they are all slims. The wood ones go just a hair under the bushings. 5 coats of CA bring it up to the bushings. A way around this is to make your own centerband an then you can make a fatter pen without the "girdle" look:wink:

 

[azamiryou]

... 6 coats thin and 4-8 medium...

That could certainly be it... medium builds pretty fast.

If it is the finish why doesn't it effect the nib and cap?

I've found that CA doesn't build evenly for me. It looks smooth, but when I check with the calipers, one end is building faster. Varying the way I apply it helps - left-to-right for one coat, right-to-left for the next, occasionally drop it in the center and push it out towards the ends...

While the CA is liquid, it will tend to migrate to the thickest part of the spinning barrel, so this could be a factor for you as well, especially for the trimline where the center band is a little thicker. This effect is reduced if you slow down the lathe. Of course, faster-drying CA (thin) will have less time to migrate, and you can try to compensate by wiping away from the high points while applying.

 

[leehljp]

Calipers! Leave the bushing "measurements" behind and go with Calipers. When you do this, you will notice the differences in sizes before the pen is complete. Consistency will become the norm.

 

[keithbyrd]

... 6 coats thin and 4-8 medium...

That could certainly be it... medium builds pretty fast.

If it is the finish why doesn't it effect the nib and cap?

I've found that CA doesn't build evenly for me. It looks smooth, but when I check with the calipers, one end is building faster. Varying the way I apply it helps - left-to-right for one coat, right-to-left for the next, occasionally drop it in the center and push it out towards the ends...

While the CA is liquid, it will tend to migrate to the thickest part of the spinning barrel, so this could be a factor for you as well, especially for the trimline where the center band is a little thicker. This effect is reduced if you slow down the lathe. Of course, faster-drying CA (thin) will have less time to migrate, and you can try to compensate by wiping away from the high points while applying.

My guess is that you hit my problem square on the head! thanks!

 

[keithbyrd]

Hi Keith

You would be amazed at how much CA will build up as a finish. Some people (including me) actually turn the pen a hair undersize, then build back up with CA.

Especially on slims!!! There is not a lot of room to mess around with these. I'm just finishing up some PFS pens and they are all slims. The wood ones go just a hair under the bushings. 5 coats of CA bring it up to the bushings. A way around this is to make your own centerband an then you can make a fatter pen without the "girdle" look:wink:

I was thinking about doing that and then got in a hurry! I think I will go ahead and do that for these - Thanks Jim!

 

[keithbyrd]

Calipers! Leave the bushing "measurements" behind and go with Calipers. When you do this, you will notice the differences in sizes before the pen is complete. Consistency will become the norm.

What type of calipers do you use? Are there some that are easier/beter to use than others?
Thanks for the advise!

 

[Carl Fisher]

Any set of dial calipers will do if you are just transferring measurements from kit parts to your blank. I prefer a style that lets you lock the caliper to a setting to you don't accidentally change it as you move from the part to the lathe.

I'm also partial to a good old analog dial, but many will use a digital that is good to a 5-digit display 00.000 so you can read down to .001 precision

 

[kovalcik]

What type of calipers do you use?

This is a good Harbor Freight item. They have several styles that are very affordable.

 

[leehljp]

These are the ones that I have:
Digital Calipers - Save on these 6 Inch Digital Calipers

HF often has them on sale or offer a coupon in the back of Popular Science/Pop Mechanics/ Woodworking magazines, car magazines. Each ad is different but some of them have a coupon for $9.95.

I have seen the same basic model from other companies also. I personally don't trust all plastic models as I have had a couple warp on me over time, but that is me.

 

[Dave Turner]

+1 on digital calipers. I also use the Harbor Freight digital ones. Make sure you get the metal one that measures in 1/1000 inch increments. The less expensive "composite" one only measure to 1/100 inch (I have both). I'm amazed how much I depend on my calipers. I turn down to just proud of the bushings (if I use bushings at all - I always turn between centers). Then I'll slowly creep up to the desired diameter without bushings using frequent lathe stops to measure. I can usually get to within a few thousandth's of an inch of my target. I typically aim for either the exact component diameter or a few thousandth's inch less depending on the wood I'm turning and how much sanding I think will be needed. A CA finish will add anywhere from 5 to 10 thousandth's depending on number of coats (I typically use 12) and the amount of sanding/micromeshing that gets done to the CA. I like the final finished diameter to be a few thousandth's proud of the component. When micromeshing, I also round over the edges starting with the tan grit (just enough to feel, not really to see unless with magnification). For this to work well, you must sand the ends flat after the CA is applied but before the micromeshing. This gives a seamless feel to the finished pen.

 

[keithbyrd]

Thank you all - I appreciate the advice and tips! Sounds like the calipers will be right next to my woodchuck pen pro!

 

[cwolfs69]

calipers are the only way to go. i have 2-3 sets around the shop all the time.
i also turn my wood undersize, build oversize with CA, and sand/polush back to finish size. i rough sand, remove from lathe and finish mill, sand, whichever to length, then back to polish to size. it is amazing how much more accurately and true you can finish with something hard like CA instead of the wood.
just my $0.02 worth.

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