In penmaking:8mm does not necessarily equal 8mm!!

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ed4copies

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One of my pet peeves with this "industry" is the inaccuracy of describing the brass tubes by using the diameter of the HOLE you drill for that tube.


When we say we want an 8mm tube, it is NOT 8 mm!!!!! The actual outside diameter of the "standard 8mm tube" is actually 7.7mm or .302 inches.
More importantly, the inside diameter (where you are going to put the press fit parts of your pen) is .290"


HOWEVER!!!!! Some of the 8mm circuit board tubes have an inside diameter of .2865 inches.


SO, can they be made to work? Yes, with SOME MODIFICATION!! THIS IS NOT A "PLUG AND PLAY".


Personally, I would use a chain saw file and remove some brass from the inside of the circuit board. MAY have to sand some off the insert part of the couplers from the pen kit. MAY have to use adhesive to hold everything together when I was finished.


I would charge my customer accordingly!!! YOU are the PEN maker!!!
PLEASE MEASURE ALL PARTS BEFORE ATTEMPTING ASSEMBLY!!!!!


Always remember in penmaking 8mm does NOT equal 8mm. This is also true of 10.5mm, 3/8", 12.5mm, 7mm, etc!!!



I hope this will save you some grief!!!
 
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randyrls

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Ed; My own pet peeve is that the drill bit on the instructions is OFTEN not the best size (needs smaller), so I print the instructions and write down the best size drill bit for a sliding, slip fit. I have a 115 set of bits and a metric set too! AND a set of "odd-ball" bits like 13.3mm where 13mm is too small, and 13.5mm is a bit too large.

My calipers and micrometer get a workout.
 

ed4copies

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View instructions as "suggestions". The bushing layout and pen parts layout can be VERY helpful. The rest of the information is your option--change it if you think there is a better option!!


USUALLY the hole drilled for oily wood is larger than one that will work well for acrylic. MOST instructions do not mention this.
 

monophoto

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Ed's point is very good. I've found that the wall thickness of brass tubes purchased at the hardware store is quite different from the wall thickness of brass tubes supplied with pen kits. That's a big deal because the kit components are press-fit inside the tube, so if the tube dimensions are slightly different, they won't fit.

For me, the message is that if I want to have spare tubes, I need to purchase them from the same place where I buy the kits they will be used with. And I have to double check dimensions - a good reason to have good calipers on hand.
 

jttheclockman

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Now I never really ran into this problem that I know of. If we are to have to worry about the inside diameters than we all have a problem. The use of other tubing than what is designed for pen kits iis always thicker and thus makes it harder to press fit parts. Pen tubes are thin so that they have enough flex to allow the parts to stretch the tube for a snug fit. Remember these are just friction fits. I believe the use of CA glues does not allow the tube to move because that is a rigid adhesive unless you use the flex CA. That is why I believe epoxy is the better adhesive. I also believe the key is to ream the edges of tubes and also take a file and run it through the tube to just loosen up the fit. If loose always add some red loctite and you are golden. As to the point of inside measurements I have never measured those.
 

TonyL

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Thank you Ed. For me, this will take some of the pleasure out of turning. Of the close to 3k pens that I turned, this was the first time that I experienced this. I should have known when the bushings didn't fit, but I blamed it on the bushings (PSI brand). Thanks for your help.
 

ed4copies

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To add to the confusion, we recently received some "10 mm circuit board blanks" that were actually 3/8" (nominal, as is "standard") This meant the inside diameter was so small it could not be used. Fortunately the penmaker called me to TELL me this--he realized the bushings did not come close to fitting.


Stuff happens, so ALWAYS check the parts to be sure they ARE what you NEED!!!
 

jttheclockman

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I should have mentioned too, that it is a practice with me to always slide the tube over the bushings before I even glue into a blank. That will show me the right tube is being used. Now if the plating is too much on the parts that is a problem I have not run into yet for over 12 years.
 

bjbear76

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I also had this issue with the latest batch of Stratus kits. The new batch of tubes had a slighter smaller ID and I could not insert the fittings without cracking the blank. Luckily I still had a few of the older tubes that I could use.
 
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