Drilling a hole in steel

[Delgetti]

Hello, I bought a hammer cam jumper for a Buren 12 as a spare part. Unfortunatly it seems there are two versions of it out there and on the part I got the hole in the middle is missing. I have a drilling machine but never worked on watch parts with it so far. So two questions:

For a hole of 0.5 or 0.8 which rpm shall it be? I found tables speaking of 15000 to 20000?

Should I use any cooling fluid? Which one and how?

Any help and further comments highly appreciated.

 

[jdm]

No fluid is needed. Small bits need high speed to give the bit the most momentum and prevent it from catching and breaking, just use what you have even if it breaks there will be no problem removing it. 

[Nucejoe]

Is there a male locating pin to enter the hole you will drill ?     Challenging to located the hole without proper tooling. 

 

[nickelsilver]

For small hole drilling you'll see massive rpm recommendations, this for the theoretical sfm or surface feet per minute. The upside is the tool manufacturers who researched this are right. The downside is to get the cut you want in~0.4mm of material at say 10krpm you have to feed at 50mm per minute, or 0.8mm per second to get that, which is undoable without a cnc machine. You have to get through your piece in 0.5 seconds, otherwise the drill will be rubbing rather than cutting which will dull it and work harden the steel part and you press harder and something breaks.

 

The up-upside is, if your drill is capable of cutting the metal, you can hold the drill in a pinvice and do it at 5rpm and get your hole (Scottish members hold your tongue). Levin wrote a terrific pamphlet on small hole drilling, where they destruct the recommended sfm and focus more on the feed per minute, and of course they had a drilling attachment for their lathe that allowed a very fine feed.

 

I'm pretty sure a normal HSS drill will cut your part, and a drill in a pinvice carefully used will get through 

Edited January 31, 2021 by nickelsilver

[RichParker]

Don't try and go through in one go, peck at it, take your time....those tiny carbide drill sets are pretty good for it

Edited January 31, 2021 by RichParker

[AlexanderToerzs]

Nickelsilver is absolutely right. Try not concentrate on the revs per minute but on the feeding. This sounds a bit on the esoteric side but when feeding the drill try to "feel" it cutting away the metal. A "beautiful" curly chip is always the sign of successful drilling. Think of the old masters. They made perfect holes in the 19th century and had bow and handwheels only to drive their drills. Do you have a scrap watch drawer? You could take a similar piece and practice. An old setting lever spring for example.

Cheers Alex

[JohnR725]

On 1/30/2021 at 6:11 AM, Delgetti said:

For a hole of 0.5 or 0.8 which rpm shall it be? I found tables speaking of 15000 to 20000

I think you'll find that you really don't have to worry about the drilling speed. Because your drilling set up doesn't go this fast.

What becomes interesting with the speed of carbide tools is they usually specify a really fast speeds especially if there cutting or milling at fast speeds. So they will work fine if the speeds all slow down. Then with carbide it's really important that everything be nice and solid.

[rodabod]

I’m sure a pin vice would be fine. For hardened steel, I try to use HSS-Co or as good a drill bit as I can find. 

[Delgetti]

Gentlemen, thanks for all the comments. I have to admit I didn‘t make it so far, ruined 8 drill bits with pin vice and machine with no effect to the steel (that jumper seems to be damned hard). Or maybe the quality of the drills was too poor. I will buy new ones with better quality and try again.

[jdm]

is tne post for the hole machined with the plate? Maybe it can be easily removed to check how it goes with screws only.

[Nucejoe]

Isn't this a spring?        No wonder why you are going to break 8 more drill bits.

 

 

[nickelsilver]

Whether you are using HSS or carbide a light touch is good. I wouldn't have been surprised that this part wasn't heat treated as it was made from a stamping and the work hardening would honestly be enough for it. Sounds like it was also heat treated. It could be only carbide will bite into it; lots of carbide drills available for little money. They are wicked hard and the same brittle.  Go slowly, let it bite, continue slowly. Once the carbide chips the tool geometry goes to hell, and while it will often still bite into the material you end up 0.10mm from where you started.

[JohnR725]

4 hours ago, Delgetti said:

Or maybe the quality of the drills was too poor.

As others have stated it's a spring it's supposed to be hard..

The easiest way to do this would be with something you don't have which would be an EDM machine. Strangely enough there are hobbyists out there that have these because going to commercial shop would be very expensive they don't like one-off jobs.

If you Google drilling hardened steel you'll find links like the one below. The indication is your carbide should be able to drill the hole but? I don't know if the shape on the end is writes because that's probably a circuit board drill designed for drilling copper circuit boards. But no matter what it should build a drill your spring but you have to go very very slowly or you'll break the drill.

You can also look up drilling holes in glass. This can be done with diamond grinding compound's it tends to be really slow though.

https://www.practicalmachinist.com/vb/general/drilling-hardened-steel-189678/