I'm planning to make custom mandrels for kitless pen turning ... BUT ... if they can be bought I'd prefer to buy.
So, here's my plan ... for what I think is a fairly common scenario, namely, a cap to body thread of 13mm x 0.8 triple start.
The cap internal thread would require drilling the cap with a drill bit of diameter 12.2 mm.
The internal diameter of the hole could be 12.2 mm for the full depth of the hole.
The hole would have one blind end, open at the other.
At the open end, internal threads (made with a tap) would occupy the first 7 mm, or so.
The depth of the hole (open end to blind end) would be, let's say, 60 mm as a possible example.
Let's say this mandrel is used for turning and shaping a piece of Alumilite, prepared to fit the mandrel thus:
The Alumilite could have a length of about 65 mm, and, if it's cylindrical, an O.D. of 15.5 mm or so.
The Alumilite would need to be drilled to a depth of 60 mm with a hole diameter of 12.2 mm.
At the open end of the hole, the hole would be tapped with a 13mm x 0.8 tap to a depth of 7 mm.
So the mandrel could be made having the following features:
1) a flat end, which butts up against the blind end internally
2) a uniform cylinder of diameter 12.2 mm for a length of 53 mm
3) a threaded portion of length 7 mm with 13mm x 0.8 threads having an outer diam. of 13 mm
4) a cylindrical stub of suitable diameter and length for gripping by the headstock chuck jaws ( or collet )
Does this all sound like a reasonable way to make a mandrel to support and hold the Alumilite for shaping ?
I should add that the mandrel shape that I am envisaging would be quite similar to that shown by @jalbert recently in this thread:
My example above produces a uniformly cylindrical mandrel, basically. . But the shape could be altered to suit a blank intended to have a slightly more "interesting" profile. . The mandrel design shown by @jalbert might be in the latter category, as it has a stepped cylindrical shape, possibly intended to allow the external surface of the material to have a taper, narrower at the closed end.
So, here's my plan ... for what I think is a fairly common scenario, namely, a cap to body thread of 13mm x 0.8 triple start.
The cap internal thread would require drilling the cap with a drill bit of diameter 12.2 mm.
The internal diameter of the hole could be 12.2 mm for the full depth of the hole.
The hole would have one blind end, open at the other.
At the open end, internal threads (made with a tap) would occupy the first 7 mm, or so.
The depth of the hole (open end to blind end) would be, let's say, 60 mm as a possible example.
Let's say this mandrel is used for turning and shaping a piece of Alumilite, prepared to fit the mandrel thus:
The Alumilite could have a length of about 65 mm, and, if it's cylindrical, an O.D. of 15.5 mm or so.
The Alumilite would need to be drilled to a depth of 60 mm with a hole diameter of 12.2 mm.
At the open end of the hole, the hole would be tapped with a 13mm x 0.8 tap to a depth of 7 mm.
So the mandrel could be made having the following features:
1) a flat end, which butts up against the blind end internally
2) a uniform cylinder of diameter 12.2 mm for a length of 53 mm
3) a threaded portion of length 7 mm with 13mm x 0.8 threads having an outer diam. of 13 mm
4) a cylindrical stub of suitable diameter and length for gripping by the headstock chuck jaws ( or collet )
Does this all sound like a reasonable way to make a mandrel to support and hold the Alumilite for shaping ?
I should add that the mandrel shape that I am envisaging would be quite similar to that shown by @jalbert recently in this thread:
Mandrel making
After suffering through using aluminum mandrels for years, I am undertaking what will be a horrifically unpleasant task: Retooling all my mandrels in steel. I grabbed some free-machining steel off eBay for the project (12L14) as I’ve made tool holders from it before and it machined quite well. I...
www.penturners.org
My example above produces a uniformly cylindrical mandrel, basically. . But the shape could be altered to suit a blank intended to have a slightly more "interesting" profile. . The mandrel design shown by @jalbert might be in the latter category, as it has a stepped cylindrical shape, possibly intended to allow the external surface of the material to have a taper, narrower at the closed end.
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