Best way to drill Clock Dial hole

[Cuckoojohnboy]

Hi - I have a clock in for repair that I purchased a new replacement movement for the worn out one. It has been talked about before here on the forum because the winding holes are different than the original movement- Hermle 1161-850. The face dial looks to be baked on enamel. What is the best way to drill a new hole for the new winding arbor? Anyone have experience doing this before? I'm a bit concerned it might flake the edges of the hole.

Thanks!

John

Incidentally I have already purchased a plate to cover the hole from a local trophy shop.

 

[shutterbug]

Dangerous, that! You'll need a diamond drill to get through the fragile part of the dial. Start small and use lots of coolant. Don't rush it.

 

[Willie X]

First, it would be unusual for a clock that has a Hermle movement to have a vitrified enamel dial.

To test, look closely at the old holes. If the surface at the edges are very smooth, as if they were melted together, it might be real enamel.

Try touching the inside edge of the old center hole (the one that will be plugged) with the ole Dremel running at high speed with a small abrasive burr. If it just grinds away normally you have baked enamel paint. If the burr chatters and throws out little shattered pieces, as if you are grinding glass, that's real enamel.

Either way, you will have to be very careful making the new hole. I would probably use the Dremel all the way. Diamond bur for the vitrified enamel, regular abrasive burr for the painted (baked) enamel. Go slow, don't want to build up much heat in the process.

Good luck, Willie X

 

[eskmill]

Cukoojihnboy stated: "baked on enamel." Is this a coating similar to that used on wood, sheet metal and the like that would have been brushed or applied and then left to cure? (cure meaning harden, dry either by exposure to the atmosphere with or without additional heat)

Or is this coating similar to dining table wear such as dishes and plates made of clay but with a glass hard glaze?

Unfortunately the English language has several meanings for "enamel." Enamel may be a paint, varnish, lacquer or a glossy over-coating on porcelain.

Drilling holes in thin steel, aluminum, zinc, brass or other metals has to be performed with care to avoid tearing the thin edges. On these thin metals, a punch and die usually results in a clean hole without burrs or tears.

Drilling through a porcelain coated or glazed clock face requires grinding away the glass-hard coating and the metal substrate beneath as has been suggested by both Shutterbug and WillieX

 

[Scottie-TX]

Assuming of course it's not porcelain, I've had good success with the multi-bit - a stepped drill. As you go from step to step, check center often. If it begins to drift you can always pull it back with a file or dreml. Tape over the target will help prevent chipping and drill from face side.

 

[Jim W]

I haven't tried the stepped drill approach (I don't have one) but I have successfully made a new hole in a painted metal dial by first drilling a hole about 50 mils smaller than the required diameter then enlarging it using a repairman's taper reamer (see Merritt's catalog). This way the center doesn't shift. I taped over the target painted side first, as Scottie advised, before reaming..

Jim W

 

[Jerry Kieffer]

Hi - I have a clock in for repair that I purchased a new replacement movement for the worn out one. It has been talked about before here on the forum because the winding holes are different than the original movement- Hermle 1161-850. The face dial looks to be baked on enamel. What is the best way to drill a new hole for the new winding arbor? Anyone have experience doing this before? I'm a bit concerned it might flake the edges of the hole.

Thanks!

John

Incidentally I have already purchased a plate to cover the hole from a local trophy shop.

John
Assuming you are dealing with enamel, porcelain, or similar product, drilling, grinding and reaming has ended up looking like a birds nest by my hand.

Personally, the most successful method to date has been as follows.

(1) I first mount the dial to a milling machine bed with a piece of flat plastic under the area of the new hole. The Mill allows proper/accurate positioning of the hole and assures it will be located as predetermined.

(2) I next machine the hole OD on a piece of mild steel and bore a ID to a thin wall as seen in the attached photo sample

(3) Next, the steel stock is mounted in the mill spindle and operated at about 200-300 RPM

(4) I then coat the new hole area with automotive valve grinding compound and engage the hollow steel stock with light pressure for about 3-5 seconds.
This is repeated until the hole is cored out. Fresh compound is added about every third or fourth engagement.

This produces a very clean chip free hole with a very high stress free success rate.
One caution. It will not work well with a drill press because of spindle/chuck runout that will cause chipping.

For painted surfaces, I use the same Milling machine setup for the same reasons, except I first machine a half size hole with a center cutting Endmill. I then machine the full size hole with again a Endmill. In effect, endmills perform a cutting/boring operation that produces a very clean and round hole.

Jerry Kieffer