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Old 01-14-2011, 10:31 AM   #1 (permalink)
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Default what size brass tube?

Does anybody know of a pen tube that the 7mm slimline pen tube would slip fit into? I've made several one-piece slims in the past, but was never really satisfied with the integrity of the nib end of the blank. I measured a 7mm tube last night, and the actual outside diameter of it was .350". So I guess I'm looking for a tube with an inside diameter of .352-.353 or so. I'd be afraid to go smaller than that, as I don't want the tubes to bind, but if I go much larger, then the parts might rattle some, not to mention that the blank material would be dangerously thin on the nib end if the tube was too large.

Thoughts?
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Last edited by dow; 01-14-2011 at 10:34 AM.
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Old 01-14-2011, 11:05 AM   #2 (permalink)
 
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Hi Dow, .350 is the biggest slim line tube I have ever seen. My slim tubes measure .268 o.d., the closest I have on hand that would be a slip fit is an 8mm pencil tube with an i.d. of .280 Hope this helps.
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Old 01-14-2011, 11:11 AM   #3 (permalink)
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Quote:
Originally Posted by CaptG View Post
Hi Dow, .350 is the biggest slim line tube I have ever seen. My slim tubes measure .268 o.d., the closest I have on hand that would be a slip fit is an 8mm pencil tube with an i.d. of .280 Hope this helps.
EGAD! I measured the wrong tube, I guess. Thanks for the correction, Cap. Now I feel like a total eejit. I know that 7mm and .284 are the same calibers in rifles. Why did I forget that when it came to brass tubes?
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Old 01-14-2011, 11:20 AM   #4 (permalink)
 
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I THINK a 7mm tube will fit inside an 8mm tube
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Old 01-14-2011, 11:30 AM   #5 (permalink)
 
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EGAD! I measured the wrong tube, I guess. Thanks for the correction, Cap. Now I feel like a total eejit. I know that 7mm and .284 are the same calibers in rifles. Why did I forget that when it came to brass tubes?[/quote]

LOL, I am sure glad I am not the only one who has those moments.
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Old 01-14-2011, 05:26 PM   #6 (permalink)
 
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Gary,

Another option if you have an archery shop nearby is to take a 7mm tube with you and see if there is an aluminium arrow shaft the right size. They come in a number of odd diameters.
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Old 01-14-2011, 06:43 PM   #7 (permalink)
 
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Quote:
Originally Posted by dow View Post
I know that 7mm and .284 are the same calibers in rifles. Why did I forget that when it came to brass tubes?
Well, measurement nomenclature is different for different applications. 7mm is actually about 0.276 inches, matching neither a 0.268" od brass tube, nor 0.284" diameter bullet.

When we refer to a "7mm tube", we really mean a tube that fits in a 7mm hole with reasonable space for glue.

Rifle caliber names (when they bear any relation to reality at all), typically refer to the diameter that the barrel is bored to before rifiling (the grooves cut into the barrel to make the bullet spin). In order to form a gas seal when fired, the bullet needs to be the diamter of the rifiling (or a couple of thousandths larger). Therefore, a 7mm bore, with grooves cut for rifiling, takes a 0.284" diameter bullet.

Welcome to the wild world of misleading measurements.

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Old 01-14-2011, 10:22 PM   #8 (permalink)
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When I first started making bullet pens I would split a piece of a 7mm tube and slide it on a tapered punch and then I would slide the 7mm not sliced in it with glue. Then sand, glue fills the slit and is a good fit.You can see the fit when milling no gap. I then bought some 8mm brass tubes and to me seems a bit slopy to much gap, not centered. So the next bullet pens that I make, I will go back to my orginial way and slice.
You did say 7mm slide into right..
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Old 01-15-2011, 09:29 PM   #9 (permalink)
 
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Quote:
Originally Posted by dow
Does anybody know of a pen tube that the 7mm slimline pen tube would slip fit into? I've made several one-piece slims in the past, but was never really satisfied with the integrity of the nib end of the blank. I measured a 7mm tube last night, and the actual outside diameter of it was .350". So I guess I'm looking for a tube with an inside diameter of .352-.353 or so. I'd be afraid to go smaller than that, as I don't want the tubes to bind, but if I go much larger, then the parts might rattle some, not to mention that the blank material would be dangerously thin on the nib end if the tube was too large.

Thoughts?
I use the replacement perfume applicator tubes, woodcraft number 149764

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