Help with pivoting going wrong!

[pkamargo]

Hello!

I was happily ending to drill an arbor for pivoting it, just reached the desired depht when the drill broke and a piece got stuck inside the hole.
I was using a 0.35mm carbide drill.
Now, anyone does know any good trick to remove the broken drill from there???? PLEASE!!!!

[Bob Tascione]

Hi Pkamargo,
I've had luck doing a few different things. The fact that carbide is so brittle may be a benefit here. I don't know if your broken drill is a spade drill or twist drill. If it's a spade drill you can sometimes break it into pieces by inserting a piece of steel with a wedge shape filed at the end between what's left of the drill and the arbor wall and then leverage against it. It's important not to hit the drill from that backside as this can drive it deeper into arbor. It's also important not to use a hardened piece of steel as this can also break off causing even more problems. Another thing that has worked for me is to heat the arbor tip up and try wiggling and picking the drill out. Putting some oil in the hole will sometimes help. I've had good success with this technique. Another thing that has worked for me is to get the arbor end cherry hot (only the END should be tempered..it's important to fasten some type of heat sink to the arbor to stop heat from reaching the pinion) so the heat is transferred to the carbide drill and then plunge immediately into cold water. This will often shatter the piece of carbide. It will also harden the arbor end if it's made of high carbon steel so you will need to temper it afterwards before driving a new pivot into the hole. If you do shatter the broken piece you can then remove the pieces by pressing and pulling a piece of rodico into and out of the hole.
I think you have a good chance of getting the drill out but...if not then there is another simple fix we can discuss.
Please let us know if any of these suggestions work for you pkamargo,
Good luck,
Bob

[pkamargo]

Thank you for the suggestions, Bob!
It is a twisted drill. I'll try some of these things and I hope any will allow me to take that drill out. Soon will let you know the result.

[pkamargo]

No way, it is still there. I tryed everything except the first tip that applies for spade drill.
I don't know if heating and throwing in cold water shattered it - I repeated the process 3 times... I don't have the rodico so I tryed to get it out poking and wiggling with a thin wire and then holding the arbor with a plier and hitting the plier (not the arbor) on a steel block so the inertia would make it come out. No success.

Next suggestion...?

(If nothing works I will try to place the pivot in the remaining not so deep hole and hope it will stay there.)

[Bob Tascione]

plug.jpg (29.31 KiB) Viewed 6974 times

Sounds like you gave it your best pkamargo.
Short of finding someone with an EDM machine to burn it out I can't think of any other way to remove it.
If the hole you drilled isn't deep enough then the other fix I mentioned in my previous post is a very easy option for you considering your excellent lathe skills.
You would need to cut the end of the arbor off just beyond the depth of the carbide drill. You could then make a more or less double ended pivot (see pic). That is one end would be the pivot, then a body would be the same diameter as the arbor and it's length would equal the length of arbor material you removed (shoulder to shoulder). You would need to drill the hole depth to equal about 3 times the diameter of the PLUG end. File a small flat on the plug to allow the air to escape when you press it into the arbor. If you would rather not press it into the arbor you can always make it a snug slip fit and solder it into the arbor. If you're not comfortable drilling into the arbor again then you can reverse the process by drilling the hole into the shoulder of the extension pivot (rather than having a plug) and turn back a shoulder on the arbor for the part to fit over. If you make the body of the part the same diameter as the arbor and the shoulders perfectly square and polish everything together the repair shouldn't be noticeable. It will also be strong as the plug length AND the shoulders will support it.
That's a quick fix but you may be able to come up with something better.
Good luck pkamargo and please let us know how things turn out.
Bob

[pkamargo]

Hi Bob,

Since an EDM machine is not avaiable and I don't have a diamond drill of this size too, I guess that the broken carbide drill will stay there forever....

The construction you suggested is a nice solution and would be the only choice if the broken drill was occupying all the hole.
However before going to this I will first try to use the reduced depht hole to install the pivot. Hope I can fit it tight enough.

Thank you for all the suggestions.

[david pierce]

Pkamargo,
There are two types of E.D.M. machines. One is called a wire feed E.D.M. and is generally used to manufacture stamping dies. The other type is called a carbon E.D.M. and is used in the manufacture of forming dies and molds. If you can contact a shop that makes plastic injection molds they will probably have a carbon E.D.M. machine which is the machine required to burn out unwanted hard material broken off in holes. You might also try a small diamond burr powered by a flex shaft. A company called Harbor Freight sells these items and can be accessed from the internet.
Since you need to save the pinion gear on the other end, you might also consider cutting the damaged part of the pinion shaft off past the damaged portion and turning a shoulder on that end. Then make a new pinion end with a hole in the other end to accept the turned shoulder. The new part will then need to be hardened and tempered to the correct hardness and then pressed over the turned shoulder with a staking set. A small amount of Loctite will prevent the joint from comming loose but if you should ever have to seperate the joint for a future repair, just apply heat to the area and the Loctite will come loose. The final turning and polishing can be done after the unit is assembled and the Loctite has cured (@24 hours).
David Pierce

[OldTimers]

David,
Does Harbor Freight carry diamond burrs that small now (.35mm or .014)?
I finally purchased them from a dental supply (Bobs recommendation) a couple of months ago. The ones at Harbor are cheaper plated burrs. I purchased sintered burrs which are expensive but last much longer. I don't remember the name of the supplier but might have a receipt in my paper mess. Found them on google. Made in China and are excellent.
John

[pkamargo]

Hello all,

Just want to let you know that I succesfully installed the pivot and concluded the service. The clock is now happily running at his owner's home.

----
David -
You wrote "Since you need to save the pinion gear on the other end (...)" - but sorry, I never mentioned any pinion gear...