Machining question…

[tmac1956]

All:

I have a simple question. I think I know the answer but I only have one chance to get this ricght, so I sure would appreciate your input before I screw this up.

I have a round brass ball about 15mm in diameter that has a through hole of about 7mm in diameter. What I need to do is to drill another through hole 90 deg. to the existing hole. I plan on using my mill drill and clamp the thing is a vise using a small V block to help hold it in place. Do to its tiny size, finding the center of the new hole that is 90 deg. to the existing might be tricky.

Any thoughts?

Thanks!
Tom

[willofiam]

Hey Tom, what about putting a snug fitting rod thru the hole you already have and let the rod extend out enough to use as a “platform” to set on top of the vise or whatever and clamp, find center or apex from there and it should be 90 degrees from the other hole, hope that makes sense, I can see how it would work but may not be explaining it right. William

[tmac1956]

William…

That sounds like a plan.

Thanks!
Tom

[Bob Tascione]

Hi Tom and William,
In many cases this will work well William
If this is a ball then locating this way would work great but how will you clamp it?
I may be missing something though.

The back jaw of your vise will see the perimeter of the 7mm hole as a flat surface which can be used for locating against the stationary vise jaw. If you set this break out point against the back jaw and then close the other vise jaw up against the other side the hole should be pretty well perpendicular to your spindle as long as your quill is set at a right angle to the table. You should then be able to mill a small flat across the top of the ball to center drill, making it large enough to give you a good center but smaller than the 7mm.
I wrote this rather quickly so let me know if it doesn’t make sense or if I need to clarify anything.

Good luck,
Bob

[willofiam]

That makes perfect sense Bob, thats why your the best ever would it be possible to use v blocks and setting the rod into them and clamping it in there? I have not purchased any yet so I am not sure, I do like what your saying though, probably easier to find center and less farting around. William

[Bob Tascione]

Yes you can use V-Blocks but again clamping of the ball becomes an issue. Also unless the pin or rod is sacrificial it will need to be removed. Not that using a sacrificial rod is a bad idea. This sometimes helps deter drill deflection. There are many other ways to do the job. What needs to be avoided is normal clamping in the vise which will provide only one point clamping on each side of a ball. Not at all secure. Could rig a few things up to make a better clamping arrangement as well as a simple permanent fixture for doing production runs but that turns into a bit of a process.
Enjoy,
Bob

[tmac1956]

Bob.

The piece has a perpendicular slot to the hole so I was thinking that I might be able to mount it thusly. However, the idea of machining a flat before drilling makes perfect sense, as long as I dial in the center in X and Y before I center drill.

I have attached a picture… The hold down screw is in the perpendicular slot.

This would be held in my mill vice,

Thanks!
Tom

[Bob Tascione]

Hi Tom,
The flat probably isn’t necessary when machining a sphere. Although it does help prevent center drill deflection if it’s a little off center. I do this out of habit as it’s very useful for drilling a length round stock to prevent the oblong center hole that occurs when drilling into the curved surface of a cylinder.
Looking at your pic. I’m not sure what you will be drilling. Is the end with the brass rod running through it the ball you will drill?
Bob

[tmac1956]

Bob.

Yes – I will drilling through the ball hanging over the end of the V block with the rod going through it.

Thanks!
Tom

[Bob Tascione]

Thanks Tom,
Then I would think you will need more support underneath the part as well as on the sides if you wish to machine it this way.

Bob

[tmac1956]

Bob.

I have some small key stock bars. Would that work? What would you use?

Thanks!
Tom

[Bob Tascione]

I use adjustable parallels but that may or may not be an option for you. Yes any type of shim stock would help. The problem is that the drill will hit whatever is under the part when it breaks through. Another option might be to clamp the part the way I mentioned above with the other end extending out of the vise along the X Axis. You could then level the part out by running your indicator along a straight section. I would suggest indicating along the top both ball pieces but I don’t know if they are the same diameter? In any case you just need to get everything level and you should be good to go.
That looks like it may be stainless or possibly chrome plated?

Bob

[Bob Tascione]

Hey Tom,
Maybe you could rig up some type of tube as a support. This might give you support in Y and Z axis as well as leave clearance for the drill to break through.

Bob

[david pierce]

Tom,
The most accurate way to find the center of a round piece is to sweep it in with a dial indicator. The ball in the picture has some interupted areas however, you can still sweep in the quadrants. The clamping setup in the picture looks like it will not be stable enough to remain in one spot during the machining process. The V Block clamp is set back and the leverage will multiply the force against the clamp. Use the step blocks in your clamping set along with shim stock (cut up beer cans, aluminum foil, etc.) to hold the part from underneath. Add additional clamping as necessary to hold the ball in place during the drilling. If the brass rod through the hole is a tight fit you can sweep the top of the rod ends to make sure the rod is parallel with the mill bed. Another idea, if the rod is tight, would be to secure the rod in the hole with Loctite and clamp down on the rod to machine it. Once the hole is drilled the Loctite can be loosened with a torch and the rod removed.
david

[tmac1956]

David:

I wound up cutting a piece of key stock and then shiming it up with some pieces of steel bands that I saved from the mill/drill packing. I knew that stuff would come in handy one day.

Thanks,
Tom

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