Kitless mandrels?

[mChavez]

Hi Folks,

I am slowly butchering acrylic blanks and getting ready to turn my first kitless pen.
I've designed a pen around the SKM88 clicker mech and the parker insert, and I'd appreciate some advice about making the section.
I'm going to use M9x0.75 for the section-barrel joint.

My plan is as follows:
1) Drill a 2.5mm pilot hole in the section blank;
2) Turn the blank between centers to ensure that sides are parallel to the pilot;
3) Install the blank in a collet chuck, turn the tenon for M9x0.75; tap male;
4) Step-drill the bore for parker insert+spring. Makes sense to do it after tapping the male with maximum wall thickness;
5) Mount the blank on a female M9x0.75 mandrel/socket to shape the section & turn the tip.

This bit is where I'm a bit unsure how to best approach it.
I can make my own female mandrel from kirinite, or buy an aluminium rod and try making a mandrel out of it on my woodworking lathe. Any reasons not to use kirinite here?
I see that Beaufort have brass male mandrels, but I don't think they have a female bit on the other end?

I can simply mount the section between centers, but I'm looking at ~1mm wall thickness for the threaded section tenon, and not much thicker for the section tip - what are the chances of the whole thing snapping under the tailstock pressure?
If I mount the section blank on a home-made mandrel, should I still lightly support the tip with a live centre in the tailstock?
What are the chances of stripping M9x0.75 threads on the section while turning it to shape? I will be using carbide.

Any issues that might arise from this approach?

Thank you.

 

[ValleyBoy]

Step 1 - I wouldn’t dissuade you from doing this but it’s probably overkill (unless the 2.5mm hole is part of the finished piece of course). I would just turn the blank round to a diameter your collet can take, and go from there. It doesn’t need to be perfect at this stage.

Once you have it in the collet turn the tenon/drill the holes, and then they will be concentric with each other (even if the outside isn’t completely parallel). Then flip it onto your mandrel and do the rest of the drilling/boring etc.

You can bring the tailstock up and square/shape the sides at this point too. This is a pretty common way of doing things and you’ll be fine. I would always use the tailstock where possible (apart from when you’re parting off of course).

Also I always encourage people to make their mandrels from acrylic to start with (kirinite is my favourite). Reason is you’ll almost certainly want to change it, probably a few times, as you develop your pen design.

Once you’ve got it nailed down then I’d suggest making one from brass (my preference) or aluminium.
Cheers
Ash

 

[mChavez]

Thank you very much. Yes, 2.5 is part of the design, so it's a good starting point.

 

[mChavez]

Well, I've made a test section without ruining any plastic blanks and it even screws into the 9x0.75 barrel mandrel. No issues with using plastic mandrels, just as Ash suggested.
The 2.5 pilot hole ended up about 0.5mm off-centre. Quite a bit of room for improvement here.

Here's a question: what diameter drill do you folks use for section tips for parker inserts? I have two Parker inserts that are 2.48 and 2.54, a Beaufort at 2.52 and a noname one at 2.7.

 

[mChavez]

Here's an idea.
Poor boy's floating chuck

£1 for a 3d-printer axle power transfer gizmo (the silver coil thing). It has a bit of flex in it, so even if the tailstock is not perfectly aligned to the headstock, the die is presented perfectly square to the tenon.

Furthermore, it has some scope for compressing and extending, so I did not have to ride the tailstock backlash as accurately as I have to if I'm mounting the die directly in the chuck.

 

[mChavez]

Is everyone keeping their parker ballpoint tip drill size a secret then?

 

[flexi]

Ehhh, i drill bullet tips for slimline refills and always check with a vernier gauge, I would probably do the same on parkers, just not done any

 

[mChavez]

What tolerances do you allow for the hole vs the tip? If it's made too tight, the new owner of the pen might be unable to fit a different brand refill into it, but if it's too loose, the tip will wobble in the pen as you write with it.