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Over the top ball turning attachement

Dabbler

Well-Known Member
#61
You will end up with a far superior product if your stick out is minimal. If you must stick due to limitations of your lathe/ball turner, consider getting a 2" diameter stock and threading it for your balls, and your deflection will be minimal.
 

John Conroy

Well-Known Member
Premium Member
#62
As Dabbler suggested, somthing like this to mount your ball blank on adds stiffness and resist deflection while providing tool clearance between the chuck and the ball. This one has 3/8" threads on the ID and I use a short stud to mount the ball blank.


You might also consider putting a bend in your handle so your hand stays further from the chuck (toward the tailstock) when the tool is swung behind the center line of the ball. Using a center in the tailstock is not really practical if you want the balls fully finished on the tailstock facing surface. 20181111_135329.jpg 20181110_111949.jpg
 
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#63
Interesting..... Interesting...… Interesting..... Looks like tool geometry is a big part of my issues.

2inch1.JPG

I decided to try and turn a 2" ball, just to see if it could be done. Here you have a 2" long piece of 2" dia aluminum mounted on a 1/2" bolt shank. Note the nice finish across the top. I did that with the swing in the vertical running the saddle power feed. Can't get much better than that! Now, note the crappy finish on the right side of ball. Hmmmm…. what the heck is different doing that part other than not using the power feed?

2inchSwarthaA.JPG

The swath while turning the ball portion looks like this, no matter which side of the ball I worked on and the finish was crap.

2inch2.JPG

When I got close to turning the left side of the ball to the center line, I decide to advance the tool only last time to the center line and cut back from center to outside. I had for the most part been advancing outside to center.

WELLLL the tool grabbed way more of the ball than I expected and started carving a rather deep slice off the outside of the ball. I figure I had pooched it for sure. That cut kept advancing rather smoothly though producing a much much better finish. It was pretty obvious the tool was now cutting on one side of the carbide insert rather than the point.

2inchSwarthB.JPG

The swarth in this case looked like this.

So, now I need to find the right tool geometry.
 
#64
oooops…...

I was attempting to square up one end of a 1" X 4" X 7" piece like this

View attachment 3959

The end mill grabbed and stalled. The down feed on this mill is terrible.

View attachment 3961

Pulled the head over a good 4 degrees or more.

Now I have to re-tram it.

Won't attempt this sort of thing again.
About the down feed....I have virtually the same mill and have cursed the down feed also. If you ever come up with a solution I'd love to hear it. Mine has about .045" of backlash that I cannot get rid of. Great project BTW. It's on my to-do list.
 
#65
About the down feed....I have virtually the same mill and have cursed the down feed also. If you ever come up with a solution I'd love to hear it. Mine has about .045" of backlash that I cannot get rid of. Great project BTW. It's on my to-do list.
Haven't found a solution as of yet, but I'm still looking. Mine seems to build up a bunch of backlash (mm's worth) and then dumps it all at once. Very Very frustrating.
 
#66
So.... in my quest to find the proper ball turning tool (I tried every tool shape I have on hand) I have ended up turning an Acorn LOL.

ACORN.JPG

While in the process of this experimentation I upgraded to a 4-jaw chuck. Setting that puppy up was a real learning experience. Going to be while before I'm proficient with that exercise.

Today I'll be picking up a 3/8" HSS tool blank and will attempt to grind an appropriate tool profile. Any suggestions other than a "shear tool" profile?
 
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RobinHood

Active Member
Premium Member
#68
From what I can see, the basic shape should be like this:
56F4A07F-9807-47D9-B13A-AC1ED5FC0A18.jpeg
The nose radius is exaggerated in the top view. Make it razor sharp and it should cut just fine.

On second thought, the shear tool geometry I suggested earlier will probably be less effective since it only cuts on one flank by design. You may also run into clearance issues with it.
 

Bofobo

Well-Known Member
#70
I want to relay an experience about turning a ball, it was in shop and he was turning a ball with cnc, now as he began to get close to a spherical shape the tool path set at a constant depth of cut had an acorn shape that under more power ended “violently” as it tried to follow the circle pattern as it ran onto more material than it could move, in your machine (having owned one myself) the extra pressure flexes the assembly and the extra heat likely ruins the cutter, now, i suggest try making smaller cuts, each progressive tool advancement should be minute untill a near sphere is reached, and dont forget cutting oil, its messy and can smoke a bit sometimes but it makes for much better times had on the mini lathe
 
#71
From what I can see, the basic shape should be like this:
View attachment 4275
The nose radius is exaggerated in the top view. Make it razor sharp and it should cut just fine.

On second thought, the shear tool geometry I suggested earlier will probably be less effective since it only cuts on one flank by design. You may also run into clearance issues with it.
This makes more sense to me. I ground a sheer tool and that was a big fail. Will save it for future experimentation.

Will grind the other end per your image and give that a try. I think the rounder the nose radius the better actually.

Bofobo: I have been making many many light cuts.. adnosium. A better finish occurs when a more substantial cut is achieved.

2inchSwarthaA.JPG

The Acorn shape is due to me reworking one side over and over again.
 
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#72
So, I ground this tool from scratch. Was the first time I have attempted such a thing. Took a few hours or more to achieve a shape that I thought might work. Lots of breaks to allow both the tool and grinder to cool down.

TOOL.JPG

End result turned out pretty good for a novice IMHO.

EGG.JPG

Finish on my aluminum ball is much much better now, however I appear to have turned a bit of an egg LOL.
My 2" ball has been reduced to approx. 1.8" after all of my experimentation.

The tool proved sharp enough as it sliced off the ridge on the acorn in a single pass no problem. Needs to have the sides relieved more as it didn't appear to cut all that well as the tool approached the horizontal on the ball stem. The other thing I noticed is the aluminum appears to gall(?) and stick to cutting edge. Would cutting fluid alleviate that?
 
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PeterT

Ultra Member
Premium Member
#73
Hard to say, but on regular aluminum like 6061 the smear finish is usually indicative of things like rubbing (not quite right tip geometry, not close enough to center, insufficient rake angle...). Or an extended contact edge. Cutting fluid will help but its not a cure all for finish. It helps with aluminum sticking to tool tip which in that mode can degrade finish. A shot of WD40 will tell you that right away. I would have expected the better finish to be on the largest diameter of the ball where the speed is highest. You can actually get nice finishes with even a smallish (1/32" rad nose) tools in aluminum. especially in your application where you might be passing over the same shape without increasing feed like finishing pass. Its getting there. Tool geometry is an art in itself. But you have to have rigidity in the system. If the mandrel is bendy or the ball turner has excess slop in the hinge action, or the swing action is not aligned....it will show up in the work,
 

Bofobo

Well-Known Member
#74
I would think aluminum cutting fluid better than wd-40, in the shop we used silver diamond shaped inserts for aluminum that always left a beautiful finish. Had some time back there just yesterday CDB42734-2AEC-4F7D-A255-A99C3D19E1F9.jpeg fixing up a dual fork seal, by removing a shoulder....
Use some emery cloth to finish the surface and hit the buffing wheel
 
#75
Not one to give up readily I decided to try turning another 2" aluminum ball.

This time I turned a mandrel hoping to get around the excessive hang out dilemma.

MADRIL1.JPG

The threaded stub is 3/8-16 NC.

MANDRIL2.JPG

This arrangement gave me no end of grief. So I went back to using a 3/8" bolt and the steady rest.

STEADY.JPG

This worked better. The 3/8" bolt stub proved not to be a good choice. 1/2" was better.

HALFDONE.JPG

I got this far. Now all that I had to do was setup such that the ball was as close to the chuck as possible and finish the right side. That didn't happen. When I positioned the ball close to the chuck the run out made it impossible to turn. Truing the bolt shaft in the chuck caused the ball to wobble badly. Truing the ball caused the bolt shaft to be excessively eccentric. I gave up at this point.

Ends up.....

PROBLEM.JPG

The root problem was that the threaded hole in the 2" X 2" round stock had been drilled on center but at an angle off axis. Either drilled badly or the tap did something unexpected. I kind of knew this from the get go but thought the flaw could be turned out of the equation. NOT.

In any event the stepped mandrel didn't work out very well. It wouldn't allow the swing to come down low enough and the chuck jaws didn't appear to have enough holding power for the amount of stick out.

Live and Lean.

Back to the drawing board.
 
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