I have often wondered why the brass tube sizings are as they are in the case of some ballpoint pen kits.
Let's compare a couple of ballpoint kits, a Slimline (which uses a 7mm tube) and a Bolt Action (using a 3/8" tube).
The 7mm tube has an inside diameter of 0.246" and a Schmidt (or Parker ?) ballpoint refill has a diameter of 0.230"
So, the Bolt Action would still accept its usual ballpoint refill if that kit were designed with a 7mm tube.
Now, the 3/8" tube has an actual O.D. of 0.364" and the 7mm tube has an actual O.D. of 0.266", the difference in diameters being 0.098".
That means that if the Bolt Action were designed to use a 7mm tube then the wall thickness of the blank would be 0.049" greater, after drilling for the tube, gluing the tube in, and turning the blank down to the usual bushing size .
And the thicker wall would mean less blank transparency, and hence less need to paint the brass tube and/or the inside of the blank,
thus saving the pen maker both time and money .
Any good reason why kits could not be designed and made with the smaller brass tube in such a case ?
Other kit pen examples could enjoy an even a larger increase in the blank/barrel wall thickness.
Any comments ?
I should add that the 7mm tube size would not be suitable for downsizing ballpoint kit brass tubes in all cases.
My main thrust is to downsize to a suitable size in order to increase the blank wall thickness.
Some ballpoint pen kits utilize a twist mechanism which would require a tube of larger size than 7mm.
Thanks to Drewby108 (whose reply is immediately below) for raising the size requirement of kits that use twist mechanisms.
My questioning the tube sizes of some kits does not apply to fountain pen kits which have to accommodate ink cartridges
but rollerball kits could have their brass tubes reduced just like ballpoints.
Also, obviously, for kits with caps, the sizing considerations for the cap tube depends on what the cap has to fit over.
Let's compare a couple of ballpoint kits, a Slimline (which uses a 7mm tube) and a Bolt Action (using a 3/8" tube).
The 7mm tube has an inside diameter of 0.246" and a Schmidt (or Parker ?) ballpoint refill has a diameter of 0.230"
So, the Bolt Action would still accept its usual ballpoint refill if that kit were designed with a 7mm tube.
Now, the 3/8" tube has an actual O.D. of 0.364" and the 7mm tube has an actual O.D. of 0.266", the difference in diameters being 0.098".
That means that if the Bolt Action were designed to use a 7mm tube then the wall thickness of the blank would be 0.049" greater, after drilling for the tube, gluing the tube in, and turning the blank down to the usual bushing size .
And the thicker wall would mean less blank transparency, and hence less need to paint the brass tube and/or the inside of the blank,
thus saving the pen maker both time and money .
Any good reason why kits could not be designed and made with the smaller brass tube in such a case ?
Other kit pen examples could enjoy an even a larger increase in the blank/barrel wall thickness.
Any comments ?
I should add that the 7mm tube size would not be suitable for downsizing ballpoint kit brass tubes in all cases.
My main thrust is to downsize to a suitable size in order to increase the blank wall thickness.
Some ballpoint pen kits utilize a twist mechanism which would require a tube of larger size than 7mm.
Thanks to Drewby108 (whose reply is immediately below) for raising the size requirement of kits that use twist mechanisms.
My questioning the tube sizes of some kits does not apply to fountain pen kits which have to accommodate ink cartridges
but rollerball kits could have their brass tubes reduced just like ballpoints.
Also, obviously, for kits with caps, the sizing considerations for the cap tube depends on what the cap has to fit over.
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