Here is what I am trying to make:
Here is where we left off at the end of the last blog with the ball marked up to locate the 22 constellation holes (the small ones) and the 12 primary holes
Today was used to drill the constellation holes. These holes are done first as the are needed to remove waste that the curved undercutting tools can’t reach. They also provide some space for the cuttings to go as the inner balls are turned.
A few words about the importance of doing careful work while drilling these holes
The constellation holes have to be drilled with great care because if one is messed up then the project becomes a practice ball instead of the nicely finished curiosity you might have been dreaming about. The following list are the things you need to do this work properly. These observations are based on my hard earned experience.
1. A good chuck that will hold the ball tightly while being turned.
2. A Jacobs chuck to fit the tailstock of your lathe (preferably the kind you can tighten by hand).
3. Sharp drills are essential. Dull drills wander and will knock the ball off center, even with a good chuck
The drill bits
Only four drills are actually needed as follows: 9mm, 6mm, 4mm and 3mm. These drill only about 4mm each as you can see by the depth marks when lined up. Each hole is drilled until the depth mark gets to the ball surface. The 5th drill is a 9mm twist drill used to start drill the primary holes which will be reamed out to 18mm after drilling.
For the constellation holes I have used brad drills for the first 3 used on each hole starting with the largest bit. and a twist drill for the 4th and smallest bit.
I used the brad point drills because my twist drills in the correct sizes weren’t sharp enough and I wanted to get on with the work.
The brad bits work well enough as long as the brad isn’t wider or longer than the drill which follows it. Sharp twist drills are the bit of choice though because the spurs on the brad bits cut slightly deeper on the outside perimeter of the hole than in the center.
Drills lined up on their depth marks to show the length of the hole at each level above
Here the bits are line up under my lathe bed and ready to use (as mentioned above, only 4 will actually be used, the shiny ones)
drills ready for use. above
Preparing the Chuck
Sandpaper grippers have been stuck on with double sided tape to the interior of the chuck and around the inside rim of the chuck collar. I had to add an extra layer to the ones in the collar as the ball was still a little loose with only one layer (not shown).
The ball chuck ready above
It’s very important to make sure your headstock and tailstock are properly aligned to insure that all holes to be drilled will point to the center of the ball (Think radial holes)
The headstock/tailstock are properly aligned above
Proper mounting of the ball in the chuck
The ball is being mounted in the chuck. Please note that I am applying pressure on the ball with my revolving tailstock center first to center the ball and secondly to keep it in place while I tighten the chuck collar.
I am using my battery drill, but only to screw in most of the way to save time and effort. A regular screw driver is used for careful final tightening to prevent dragging the ball off-center. This is done gradually by keeping a pretty even gap between the collar and the chuck body all around as it is tightened.
Mounting the ball in the chuck above
I took the authors advice from the book, which is to begin with the largest drill bit first and working towards the smallest. This helps prevent drill wander and knocking the ball off center.
The first hole is started in the picture. It’s very important to take it slow and easy and not force the drill in to the ball too quickly. I blow out the sawdust between each drill bit. When finished you will have drilled 22 constellation holes, each with 4 drills or actually 88 holes. Establishing a good routine helps to keep the work moving at quicker pace.
Having the right attitude for this sometimes tedious work
My advice on drilling these holes is to take your time and regard each hole as a small somewhat delicate project and give yourself a pat on the back each time one is successfully completed.
Turning the rim around the constellation holes
The last part is to turn the little rim around the hole as soon as it’s finish drilled. Less is better than more might be a good thought to have while doing these rims. If your ball is still centered perfectly all will go well, otherwise you have a rim that is wider on one side than the other.
The rim part was a challenge. I use a miniature skew chisel to turn them. I can’t say that I am entirely satisfied with the result, but not to worry, I know I will get better with experience.
First hole started above
Todays grand finale
The first 5 holes completed without any major disasters, whoopee!
First five holes completed above
And finally all 22 holes completed (whew).
All 22 holes satisfactorily drilled above
My next blog in this series will cover the special tool rest I made and actually turning the 4 inner balls. I can’t guarantee that this work will go well. If successful, I will blog it. If not I will have to turn a new ball and drill those 22 holes again. I really hope that won’t happen
Thank you for reading this. It’s too wordy, but I want the readers to be aware of some of the pitfalls which can avoided with good practice. The following links cover all the blogs in the series to date.
-- Mike, an American living in Norway.