8mm Pens

[rbaron]

I purchased a kit that has 8mm tubes. The directions on the paper that came with it said that I needed a 7mm mandrel. Is that correct?

It would seem to me that the 8mm tubes would need a 8mm mandrel. Do they even make a 8mm mandrel?

Thanks..... Rich

 

[TonyL]

That is true when using a mandrel instead of turning between centers. The 8mm bushings are hollowed-out so that they slide/fit onto a 7mm mandrel. Make sure that your mandrel is 7mm. Actually I thought the mandrel is .247 inches (slightly less than 7mm). See what others have to say. Sorry that I can't be more sure.

 

[Jim Burr]

As we all know from reading and studying...it's the bushings that matter. 7mm hole on a bushing that...well who cares what size the bushing is...it fits on a 7mm mandrel!!

 

[monophoto]

There typical mandrel is made from 1/4" diameter rod. There are a few suppliers that specify a different size mandrel, but the 1/4" seems to be the most common.

7mm pens are made using brass tubes that are 1/4" ID. The 7mm bushings slip over the mandrel; when you turn the blank down to the diameter of the bushing, it will provide the material thickness over the 7mm tubing intended by the pen designer. I just measured the OD of a typical 7mm bushing, and hence the OD of the finished pen, at about 8.4mm.

I've made a couple of 8mm pens that use bushings that have an 1/4" ID, and with a stepped OD - a narrow section that I measured about 7.5mm and that slips inside the 8mm tubes supplied in the kits, and stepping up to the OD specified by the pen designer.

I'm not aware of an '8mm mandrel'.

 

[rbaron]

Monophoto, Tony & Jim,

Thanks much for the help. I guess the pen is ok on the 7mm mandrel. I'll turn it tomorrow and see what (if any) problems I have and let you guy's know.

Rich