Ending threads cleanly

[soligen]

On my first kitless pens i posted a week or so ago, it took me several attempts to make a good nib coupler (I used aluminum)

I finally worked it out and got a good fitting, true coupler. However this is a small fit & finish issue I would like opinions on.

I stopped the threads just a tad (myabe 1/32) short of the barren so that I had a square shounder on the coupler for pressing in. However, I can see marks in the last thread where I stopped the die. It just looks like little divots in each place where the die stopped citting.

Other than this, the threads were very smooth, and all i did was buff them and got a good shine.

So the question. I'm new to cutting threads. Can anyone share a technique to avoid the little divots, or is this an unavoidable aspect of using a die?

Thanks

 

[Acornelius]

Did you use any type of cutting fluid? Alcohol works really well on aluminum. Not sure what the divots are, but the first few threads on the die are not full depth threads. They will probably be a little shallower the threads that follow.

 

[soligen]

I used oil

 

[BRobbins629]

Sometimes it depends on the type of die you use. The most common dies have a taper to help start the threads. Same with taps. There are finishing taps and dies which you can use to follow the starter ones and you will get cleaner ends. Other choice is to try and clean them up manually. I often take a parting tool and cut off the last few threads to make it look cleaner.

Else get a metal lathe and cut the threads on that. Usually cleaner.

 

[ctubbs]

I have tried many different cutting fluids on Aluminum and the best I have found is water, just water with a drop or 2 of dish soap. Cheap and clean. It does not evaporate like alcohol will and carries away the heat very well while lubing the threads. The very best thing for threading any metal is a metal lathe and much practice.
Charles

 

[workinforwood]

The main problem is cutting into a shoulder. I don't think any tool can make it clean completelt to the shoulder. This is why I do as Bruce said and part off the partial threads next to the shoulder. Another option would be what I think skippy does often and that is to have your outer threads screw into the pen body where they would be also glued so it can't be unscrewed. Then if you want a metal trim ring, you make one and tap it so its like a threaded washer and a few drops o glue on the last couple threads you screw it on and it is permanent and the thread run to the trim ring is perfect

 

[soligen]

Great suggestions. THANKS!!

 

[chugbug]

Thought I'd add my two cents, as I didn't see these mention here.

For cutting fluid, I use PAM (cooking oil) liberally. Even for drilling holes. For nice sharp shoulder threads and a tight fit, I do two things on the back end of the tenon:

1) make the tenon at the shoulder slightly smaller (so you'd have a very slightly back-tapered tenon;

2) undercut the back end of the tenon at the shoulder.

Making the tenon slightly smaller (in diameter) helps the tap to finish cutting the threads up against the shoulder so they are nice and crisp. Undercutting allows for the nib holder to screw tight without leaving a gap.

See attached. Hope this helps...John

 

[Texatdurango]

Thought I'd add my two cents, as I didn't see these mention here.

For cutting fluid, I use PAM (cooking oil) liberally. Even for drilling holes. For nice sharp shoulder threads and a tight fit, I do two things on the back end of the tenon:

1) make the tenon at the shoulder slightly smaller (so you'd have a very slightly back-tapered tenon;

2) undercut the back end of the tenon at the shoulder.

Making the tenon slightly smaller (in diameter) helps the tap to finish cutting the threads up against the shoulder so they are nice and crisp. Undercutting allows for the nib holder to screw tight without leaving a gap.

See attached. Hope this helps...John

John, I'm not knocking your idea, just sharing my thoughts on the idea since I used to do this myself.

Given the fact that we are taking a tube, drilling and tapping the inside to accept a front section AND threading the outside to accept a cap, we are faced with a very thin wall situation at best. Tapering the wall diameter towards the back, even slightly, just removes that much more valuable wall thickness AND strength.

I have since used the parting tool as mentioned above. Just something to consider.

 

[chugbug]

George, understand your concern as I've struggled with those issue.

First, I don't use "tubes". 2nd. When I said make the rear "slightly smaller", I meant slight "tapered". Yea, still "smaller", but the taper is stronger than actually cutting a smaller diameter at the back. And I mean VERY slightly tapered. It doesn't take much to help. No issues with wall thickness as long as you don't take too much and are leaving enough wall thickness.

Very fine line to walk. Like you say, with what we are working with, there isn't much there to work with, but you need to find a happy medium to solve your issues. Do what works for you.

John

 

[Paul in OKC]

The thinnest part of the thread is the minor diameter (bottom of the thread) and the ID pf the body. Thinning the od a tad wouldn't weaken it enough to be an issue, I wouldn't think.

 

[DrBills]

I have been online since 1981, when all there was was compuserve and local BBSes, and I rarely see a thread end cleanly.

Bill

 

[Curly]

Once the die has reached the shoulder and been removed it can be turned around and run back on until it has reached the shoulder again. You should have a full depth thread to the shoulder.

Pete