Wobble question

[Hippie3180]

Whether it's wrong or right, I often turn my fountain pen cap most of the way, then turn my body and look at fitment before I finish my cap and then body. I understand that's it's most likely proper to use calipers to measure, but I tend to create my shape by eyeballing and checking for flow and fit. This means I take me cap and body off of the mandrels, sometimes this results in a wobble. What's causing this? The result of this wobble is a cap that then is out of round. I've always turned this way and I don't always get the wobble upon placing my cap/body back on the mandrel.

Of course a cap that is out of round is not a good result in relation to the body. I've seen other turners with this issue as well. What is happening, can I overcome/fix this?

I probably should have put this within a kitless context, I am talking about kitless pen making here.

 

[d_bondi]

Hi Michelle.

I assume that you are using a triple start tap and die, is that right? It is possible that if you aren't getting the cap threaded back on the same start, that this could be your issue. Try marking the mandrel and blank so that you can get it back on the same start every time. It could also be that your cap isn't faced perfectly perpendicular to the centerline of the threads. This alone or combined with not starting on the same thread each time could mean that it isn't sitting exactly perpendicular with the centerline of the threads and could create a wobble.

I too turn the cap first, but try to get it done and sanded to 800 dry before taking it off the mandrel. Then I turn the body to match the cap. Removing the body from the mandrel and putting it back on the mandrel multiple times has not created problems for me. I, at least in part, chalk that up to the fact that the internal threads on the body are single start. You get it threaded on the mandrel exactly the same every time.

I hope this all makes some sense.

 

[Hippie3180]

Hi Michelle.

I assume that you are using a triple start tap and die, is that right? It is possible that if you aren't getting the cap threaded back on the same start, that this could be your issue. Try marking the mandrel and blank so that you can get it back on the same start every time. It could also be that your cap isn't faced perfectly perpendicular to the centerline of the threads. This alone or combined with not starting on the same thread each time could mean that it isn't sitting exactly perpendicular with the centerline of the threads and could create a wobble.

I too turn the cap first, but try to get it done and sanded to 800 dry before taking it off the mandrel. Then I turn the body to match the cap. Removing the body from the mandrel and putting it back on the mandrel multiple times has not created problems for me. I, at least in part, chalk that up to the fact that the internal threads on the body are single start. You get it threaded on the mandrel exactly the same every time.

I hope this all makes some sense.

Yes, that does make sense. I was thinking it might have something to do with the triple start threads. This little wobble causes my cap to be out of round slightly to the body…if that makes sense.

I'm very visual and just need to see everything together as I work.

 

[Hippie3180]

Also, thank you, I will be sure to try the marking to see if that helps.

 

[d_bondi]

Also, thank you, I will be sure to try the marking to see if that helps.

You bet. It could be many different things, that is just what comes to mind first. I hope it works for you.

 

[rixstix]

How is the mandrel held? 3 jaw chuck, collet or other? Are the mandrels going back to the same position in the chuck?

 

[egnald]

Rick, rixstix, could also be on to something as implied by his question. Even a slight wobble in your mandrel would be amplified by the time it gets out to the end of the cap. Rick Herrell posted a video last year on what he does to insure alignment of pin chucks and mandrels whenever he uses them. The link is here.

Dave

 

[Hippie3180]

How is the mandrel held? 3 jaw chuck, collet or other? Are the mandrels going back to the same position in the chuck?

I'm using a collet, with custom made mandrel.

 

[d_bondi]

Rick and Dave bring up good points as well. I also use a collet chuck and mandrels by Rick Herrell. When I first got the mandrels, I put them in the collet chuck to check the whole assembly for runout and did note some differences depending on rotation of the mandrel in the collet/collet chuck. My collet chuck is within 0.001" on the inside rim and I have no doubt that Rick Herrell's mandrels are true, so it must be my collets. I have a reasonable set, but not a real high end machinist quality set, but did notice that by loosening the chuck and turning the mandrel in the collet, it might get better or worse. Also check the inside of the collet and chuck for debris, etc.

I hope you are able to work it out soon. And please let us all know what you think it was.

 

[NJturner]

I have been a long time woodturner with a lot of that time dedicated to pen turning and I cringe every time I have to remove my stock from the lathe - whether its removing the mandrel, taking something out of a collet, or removing it from my 4 jaw chuck. It's not that I am positive things are not as true as they can be, but a wood lathe is not exactly the picture of precision like a metal lathe or commercial milling machine. Even the headstock bearings have enough runout in them to possibly be the issue, and as previously stated, so could the slight difference of one thread start versus another - and that's not a big amount of change we are talking about, but still can be noticed!

I always mark my stock, headstock thread, and my collet or chuck before removing anything with a matching index line, allowing me to get everything back to the same spot, jaw, or whatever, but more times than not, I get something occurring that causes a slight eccentricity. Pens are most susceptible to the slightest misalignment because of the size and most of us build our pens to be very visually exciting - meaning we give them a very close look, showing up the most minor of flaws. Short of moving to a quality metal lathe, or not ever taking your project out of its snug home in the collet or mandrel, sometimes stuff happens.....lol. I'd look at your workflow and see if there is a way to make a minor change to minimize collet, mandrel, or chuck changes and see if you can narrow down the issue to where its not a nuisance.

 

[Hippie3180]

Thank you all so much. I do clean debris out of my headstock often as that can definitely be a problem that I am aware of. Hmm, I didn't really realize the collet itself could be off.

I will start marking all the things to see if that helps as well as look at a system for not removing pen parts until finished (although I am no optimistic about that.) I guess this is why so many convert over to metal lathes.