Concentricity issues, help?

[cool44]

I have made 3 successful kitless fountain pens so far. The first successful one was slightly off concentric. It was passable as it is fairly hard to tell. The next two appear to be getting worse because it is very obvious something is off. Where it is most noticeable is once the pen is capped you can see/ feel that it isn't even all the way around at the joint.

For the pen body, I start off by turning a tenon and then putting the die to it for m12x.8x3 threads when it's in a 4-jaw chuck. Next I drill the blank and tap the inside for m10x1.25 (still in 4-jaw chuck).

I then take the blank out of the 4-jaw and move to a jig I have in a collet chuck that is threaded for m10x1.25. I screw the blank onto it with a threaded piece to support the outside threads. I move the 60 degree live center up to it for support and turn it size. Once shaped I'll part a little off the end and finish. I do the same for the cap without the tenon.

I have checked for alignment of the headstock and tailstock. With a magnifying glass it is really close to perfectly aligned with both the live center retracted in the tail and fully extended.

I am looking for suggestions as to what can cause my pens to get worse. Any help will be greatly appreciated.

dave

 

[duncsuss]

Are you sure the problem is the concentricity of the (barrel body) to (barrel threads)?

Could it be the concentricity of the (cap body) to (cap threads)?

Test by holding the body horizontal at eye level. Screw the cap on and off, looking to see if the mass of the cap rises and falls with respect to the top edge of the barrel.

Then hold the cap and turn the barrel in and out, to see if the barrel rises and falls with respect to the top edge of the cap.

 

[cool44]

I am not sure which it is. I guess it could be either or both. All I know is that when you screw the cap onto the body it is very obvious the two don't line up right. My best guess is that it's a little of both and the issue is accentuated when the two go together. Any suggestions?

dave

 

[SteveG]

Try taking wall thickness measurements around the problem areas on both M and F threads. This will help pinpoint where and what is off center, and will allow going to the next step (whatever it is) to resolve the issue. It could be only one is off, which will narrow the search for causes.
Steve

 

[duncsuss]

My first thought is to check that the jig you're holding in the collet chuck is absolutely square and on-axis. If you've made a dimple in the middle of the sticky-out end, use a center in the tailstock to ensure it's aligned before clamping down the collet.

FWIW, I have similar problems sometimes -- drilling from opposite ends of (e.g.) the section, the holes aren't always aligned perfectly in the middle.

 

[cool44]

Okay I may have figured it out. I originally said the headstock and tail stock lined up pretty well. I noticed the other day that when I went to drill out a body that the drill bit was not going to go into the cap perfectly on center.

I guess that the error in the alignment was not noticeable until the tail stock was further away from the headstock. I got it lined up and then the pen I was making cracked and I had to go out of town the next morning. I will post an update when I get home and make a pen over the weekend.

Thanks for your help.

dave

 

[cool44]

Okay so I proved that it was the misalignment of the headstock and tailstock. When the tailstock is far enough away to use a drill bit it can be off +/- 0.050" from side to side and +/- 0.010" up and down. What I have to do to combat this is to put the tailstock in approximately the position it will be to perform whatever operation I am wanting to do. Then I put my live center into the headstock and a brad point drill bit into the tailstock. I line the two up (using shims in some cases) and voila! my concentricity issues are a thing of the past. I then put the work piece in and all is well in my world.

Now this does take extra time and is kind of a pain in the butt but I'm generally not in that big of a hurry. When it does become an issue I'll have to spring for a better woodworking lathe or a decent metalworking one.

Now that I can make a pen that is concentric I will post a chronicle of my kitless pen making adventures.

dave