Pen mandrels and bushes

[andyl]

Ok first post as a newbie so hope I don't go over old ground.

If pen mandrels have an O/D to suit a standard 7mm tube, why are the bushes I've been purchasing (cigar / elite etc) have a much larger bore size?
This only leads to the bushes running a mile off to the mandrel.

 

[Walter]

The bore size of bushes should (apart from minor differences in tolerance between manufacturers) all be the same.

Most are not manufactured to precision engineering standards and there can be some problems of fit if you use mandrels and bushes from different manufacturers.

I would not expect these to be anywhere near 1760 yards out of alignment though. :wink:

 

[Penpal]

In an ideal world this would not happen but in ours it happens all the time.

Peter.

 

[loftyhermes]

I remember there used to be two different sizes of mandrel, labled A and B, B being the larger diameter. I have a set of B bushes hiding somewhere.

 

[21William]

Simple answer is there is no set standard for pen mandrels. Manufacturers can and do make them in whatever size they like!
There was a list published on this or perhaps another forum listing all the different sizes by manufacturer but the A size are all "just a tad smaller than 1/4".
One of the biggest jokes played on pen makers is that mandrel sizes are normally quoted as fractions of an inch but designed to fit a 7mm tube!

Folks on here have found several solutions, in no particular order:
Don't use a mandrel - turn between centres.
Don't use bushes - measure with callipers instead.
Use conical bushes - can work if they fit the mandrel ok.
Use mandrels and bushes etc all from the same manufacturer. And if they don't fit make sure to complain!
My solution - make your own mandrel. I used 7mm silver steel rod and drill out the bushes to suit. Perfect fit every time.

 

[fortress]

Hello, and welcome to the house of fun Andrew. I turn between centres on everything but Slimlines. :wink:

 

[wm460]

Andy, I believe Berea is the only manufacturer that uses the B mandrel.
A cut an paste from there website.

PRODUCT DETAILS
A mandrel is a round steel rod that you slide the wood blank with the brass tube inserted onto. Unlike most other companies who offer only one size mandrel we sell two sizes. The A mandrel (sometimes called a "7mm" mandrel) which is 0.247 +0 -0.002 inches in diameter and and other mandrel which has a larger diameter, the B mandrel. This is 0.291 +0 -0.002 inches in diameter. We use the B mandrel on some kits because the thicker diameter helps prevent whip while turning and allows for a much better result.

 

[andyl]

Many thanks to all who replied.
As a metal turner of many years my initial though was to turn the blanks between centers.
So would I be correct in saying that for those that turn between centers, you take a manufactures bushes and simply cone the ends with a center drill?

 

[Walter]

Many thanks to all who replied.
As a metal turner of many years my initial though was to turn the blanks between centers.
So would I be correct in saying that for those that turn between centers, you take a manufactures bushes and simply cone the ends with a center drill?

Most people buy ready made TBC bushes already machined to fit a 60 degree centre, but as a metal turner machining your own would make sense.

You could even consider making your own bushes to better tolerances than the originals.

 

[silver]

This is my experience..

Majority of the "normal" what is called the A mandrell is 6.18 +|-.02mm tolerance.

To fit the standard of 7mm tubes, which are actually 6.75 mm +|-.05 tolerance.

There was and still is some of the Axminster pen mandrells around that were measured at 6.1mm dia, all of their bushes (6.15mm for clearance) only fit their mandrills. Having not used one of the new mandrills I am not sure if the new ones are the same or not.

The B mandrel is the old original mandrills from the early pen turning days and suited the 8mm kits, 7.3mm +|- 0.2mm tolerance. They came about because bushes had not been made or thought of.

As for me I use both methods, between centres for all including slimline. And also mandrills.

As for the slimline I have two turned fittings that go in to the tubes that are turned to size and have 60 deg taper on the ends.

I prefer to use the B mandrel on the bigger pens and often either drill out or make new bushes to suit the pens I am turning. The reason is in my view you can turn both sections at the same time of larger fountain pens minimising the risk of wobble and out of centre issues. You can also get the shape right of both cap and body to look asymmetrically pleasing..

Pic below of the end turned fitting for slimline. This x2

 

[bigbob]

Like everyone else turn slimlines on a record mandrel have not measured it but anything that requires one blank of wood or acrylic gets turned between centres I do drill my bushings for this with a centre drill.