# Mandrel diameter?



## Scooley01 (Dec 9, 2010)

This may be a stupid question, so forgive me in advance.

All of the pens I've done so far have been 7mm tubes.  This is mostly on purpose, because I don't have the money for new bushings and drill bits every time I feel like making a new pen.  

When you do something like a 10mm or a 3/8" tubed pen, do you have to also purchase that diameter of mandrel?  I ask because the tubes I have now fit snugly on my mandrel, if they were any bigger they would wobble off center.


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## hasha2000 (Dec 9, 2010)

This is when bushings come into play. The middle diameter stays the same while the outer makes for the size needed for finished pen.
Gatsby bushing shown:


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## Scooley01 (Dec 9, 2010)

Do the ends of those bushings slide into the tube to make up the difference in ID there?  Or are the tubes thicker?


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## hdtran (Dec 9, 2010)

Scooley01 said:


> Do the ends of those bushings slide into the tube to make up the difference in ID there?  Or are the tubes thicker?



As shown in the photo, the tube (glued in the blank) slides onto the narrow part of the bushing, until it butts up on the shoulder of the bushing.  The large diameter of the bushing matches (theoretically, anyway) the diameter of your pen hardware.  The inside diameter of the bushing hole is just a hair bigger than the mandrel diameter (in fact, the inside diameter is the same as the inside diameter on your slimline bushings).

Some pens have different sizes for nib hardware, center on nib-side tube, center on clip-side tube, and clip hardware!


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## Robert Taylor (Dec 9, 2010)

the hole in the bushing fits the mandrel. the small diameter of the bushing fits inside your tube. the large diameter of the bushing is the same diameter as the kit parts. hope this helps.


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## Scooley01 (Dec 9, 2010)

yeah, the Designer NT from PSI is the first non-slimline I've done, and it has different bushings for each end...but because it's a 7mm tube pen, the bushings still just sit against the blank, so I wasn't clear on how the different diameters work.  Now I know!  

Thanks


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## hasha2000 (Dec 9, 2010)

bettyt44720 said:


> the hole in the bushing fits the mandrel. the small diameter of the bushing fits inside your tube. the large diameter of the bushing is the same diameter as the kit parts. hope this helps.



What they said...


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## jskeen (Dec 9, 2010)

If you want to be able to skip the whole bushing/mandrel/out of round blank issue, you could try just turning the tubed blanks between a 60 degree drive center in the headstock and a 60 degree live center in the tail.  Will fit any size tube, is much less likely to warp, flex, bend or get superglued to your blank.  You do have to be able to check the outer diameter of the blank with a pair of calipers and freehand it down to the correct size to match your kit parts, but really that's not much harder than getting it down to the same size as the bushings, and it eliminates the possibility of the bushing being poorly made/off center/out of round.  

There are a ton of posts about turning between centers or TBC here, a quick search should get more info than you want to read, but the concept is very simple.  If you are interested, feel free to ask.  

James


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