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clockboy

Drilling a pivot problems

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Has anyone had an issue or advise for drilling a clock pivot. I am at a loss with this now. I made a lathe flag to guide the drill exactly into the pivot (which it does) but the drill just does not cut. I have broken several drills now (0.40mm) and the drills I am using are carbide from "Eternal tools" so not cheap . I have also annealed the pivot but still no success. These failures are on a test piece and now worried I am worried that I fail on the real job. I have now ordered some 0.50mm drills so hopefully a bit more strength. Maybe I need pivot drills (spade shape) but I have only found some on ebay (USA). 

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What's a lathe flag? How fast are you turning? Did you catch the center first (usually with a handheld graver, could be with a centering drill)? Are you drilling blued steel? With oil, dry?

And lastly, but I've seen it numerous times with experienced guys, are you turning the right way?

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Yes French. A flag is a plate fitted to the rest. You drill through the plate with the drill that is going to drill into the pivot. Then you give it a counter sink so the pivot then spins centre. Then you drill the pivot from the reverse of the plate. This gives a perfectly centred hole. There are some vids on YouTube showing how they are used. The problem I have it starts the hole but only drills a shallow hole. Maybe the drill is getting dull. If you look at this vid you cans a flag being used.




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Ah ok. Speed? Blue steel or annealed (not blue drawn back, 'fresh' steel). How much pressure are you putting on the drill?

When drilling hardened steel, even if drawn back well past blue, it's good to go fairly slow. Even really slow. Like as slow as your lathe can go. The drill HAS to bite, it has to make a chip. If not, you're work hardening it. Rub some more and the carbide is dull, then more pressure, then snap. Drill a little, pull out, clean off the drill, repeat. A cutting oil is helpful but if you don't have any try any animal based oil, bacon fat is particularly good. Minus that try whatever oil you have. Make sure it's cutting, and if it stops, change (or sharpen, but that's tricky) drill.

If it's not cutting it's rubbing and if it's rubbing it's killing the edge on the drill and work hardening the part. Biggest problem I see is guys running too fast, even the kids we get in the shop with a 4 year watchmaking school diploma under their belt.

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12 minutes ago, nickelsilver said:

Ah ok. Speed? Blue steel or annealed (not blue drawn back, 'fresh' steel). How much pressure are you putting on the drill?

When drilling hardened steel, even if drawn back well past blue, it's good to go fairly slow. Even really slow. Like as slow as your lathe can go. The drill HAS to bite, it has to make a chip. If not, you're work hardening it. Rub some more and the carbide is dull, then more pressure, then snap. Drill a little, pull out, clean off the drill, repeat. A cutting oil is helpful but if you don't have any try any animal based oil, bacon fat is particularly good. Minus that try whatever oil you have. Make sure it's cutting, and if it stops, change (or sharpen, but that's tricky) drill.

If it's not cutting it's rubbing and if it's rubbing it's killing the edge on the drill and work hardening the part. Biggest problem I see is guys running too fast, even the kids we get in the shop with a 4 year watchmaking school diploma under their belt.

Thanks I think that is whats happening because it does drill for a while and then stops cutting.  I am wondering if I anneal it again but use sand to cool it as apparently a small pivot can air cool and effectively harden the metal. I have ordered some 0.50mm carbide drills for bit more strength. I am only using a tiny amount of pressure but they still snap. 

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If you're just heating past blue no need for sand, but if you're going red yes, it should cool as slowly as possible. But on an actual clock arbor you can't really do that, so keep going and get your chops. Even straight blued steel is drillable with carbide.. French clock arbors not necessarily (but gently heat past blue and yes).

The old guys would harden their drills and sometimes gravers in mercury for really hard materials or to get a graver that takes a killer edge and leaves brass polished looking. I've tried it and it really works! Not recommending it though, carbide is definitely safer. Though you shouldn't breathe the dust if you grind it.

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Thanks oldhippy I did do that. Heated to cherry red and carbide drills. I might have been drilling too fast and blunting the drill because it does drill for a while but then stops cutting. I have ordered some more drills (0.50mm) and will re-visit it again when they arrive. 

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1 hour ago, clockboy said:

Thanks oldhippy I did do that. Heated to cherry red and carbide drills. I might have been drilling too fast and blunting the drill because it does drill for a while but then stops cutting. I have ordered some more drills (0.50mm) and will re-visit it again when they arrive. 

CB...You have to also remember the old timers saying.. A walking drill will wander off..  With such hard steel a slow speed is a must, I don't envy this job, trying to drill down a  2mm is bad enough, but a 1mm. Take care mate..

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I'm no expert in this particular field, but I will offer my twopence worth.

From experience machining, drilling and cutting other small stuff, (circuit boards, models, lock pins.. those sort of things) I know this is not an easy task.

Working with small (thin) drills and very long drills can be a really touchy exercise. Drilling very hard materials is also an art in itself, so combining the two can be a real head scratcher. It has probably been at least twenty years since I last played with a lathe, but I do remember one important rule, which nickelsilver  has already stated. If in doubt, go slowly, lubricate constantly.

If you take one of the broken drills, and put it in the vice, and snap it with a pair of pliers you will see how little energy  a drill that size can take.

One other trick might be to peck at the bottom of the hole, so take a small chip, back off a fraction, take another bite, back off etc. Be careful once the drill is in to any depth, as the moment it binds up .. snap .. and the stub can be a right pig to remove without damaging the work piece, so use the minimum pressure to actually take a bite out of the metal, but do make sure you are actually removing material with each cut, not simply warming up the tools.

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Here's another trick if you are using a large lathe with a small drill, or even a tiny drill in a relatively small lathe.

As the man says (at great length at the start of the video), its all about feeling when the tool is actually biting and removing material. At the scales you are working at, you can also feel when it starts to go pear shaped, and bind against the tool, and perhaps stop the disaster before it happens.
 

 

Edited by AndyHull

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Clockboy, you aren't trying to continue drilling with a broken drill in the hole are you?

One thing that's nice about making your own spade drills is they can be "waisted", or tapered back slightly. In case of breakage they are far easier to remove, in fact they usually just fall out. Robert Porter wrote a nice little pamphlet on making carbide spade drills and a simple jig with a pinvice to aid in that. You'll need a diamond lap (or two), I think Eternal has those at pretty good prices.

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An update guys re-the re-pivot. All was going well with hole gradually being formed when I slightly twisted the drill and I mean very slightly and the very tip of the drill snapped off inside the 0.50mm hole I had drilled. Despite my best efforts I could not remove it so I failed.

Luckily someone sent me a fly which was nearly the correct size and I have managed to adjust it to fit and the clock is now on test running a treat.

However as a matter of interest I received (after the failure) a pivot drill sometimes called a spade or mascot drill with a size of 0.55mm. As an experiment I used it on another test piece and it worked an absolute treat. However the issue with spade drills they do not clear the waste so you have to go slowly and because of their shape keeping a straight cut is not so easy BUT it did gave me a perfect hole with very little effort.  Next time I will use a pivot /spade drill they seem to have more strength and cut great.

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A "fly" is that like a female that fits over the shaft (now that sounds off) and has a pin on the end as that is what I was going to suggest to fix the problem.

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If you don't have any 'true' cutting oils then often readily available substitute automotive oils can be used.  Basically the hotter the metal is at the tool tip or the tougher the material, the better high extreme pressure (EP) oils will work as the EP additives only become 'active' at these high temps.  Automotive lubes that give increasing effect would by Hydraulic Oil ISO VG 15, 22 or 32 (mineral oil NOT the brake fluid type), mild EP gear oil (SAE80 or lower), high EP gear oils (SAE80 or lower). Hydraulic oils have anti-wear additives and some lubricity additives.  EP Gear oils will have varying levels of extreme pressure additives such as chlorine, phosphorous, etc, and can be quite thick so may need to be thinned with a lighter oil (hydraulic oil ISO 15 or 22 or 32 is ok).  Oils will help with lubricity and are gentler heat removers, but are not so good for chip removal.  Watermix fluids (suds) can also have high EP levels but are quite severe at cooling but can be better for chip removal, however these are specialist products and unless you can cadge some off a local machine shop then can be expensive to buy as the package size is quite large (often 25L is smallest at £3+ per L).  Your lathe must also be compatible with watermix fluids, whereas oils are invariably ok.  Also EP oils can stain active metals such as copper, brass, silver etc so bear this in mind if post machine cleaning is not possible, normally EP oils are not required on these type of materials which require oils with good lubricity or cooling.

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On 1/29/2019 at 8:39 AM, clockboy said:

I have also annealed the pivot but still no success.

It might be that you haven't annealed it.  Just heating to red doesn't anneal it, you have to cool very slowly - either as a cycle in a heat treat over or a box of ash (how I do it).   The ash is an excellent insulator, put a red hot file in the ash and it can still be warm the next morning.  If you just heat to red, a small part will immediately quench in the air around itself....granted, air is a slower quench than oil and won't get it as hard as an oil quench, but its a quench none the less.   After that, it may well be harder than the tempered piece you originally stated with.

If working with a properly annealed piece, I would not use carbide drills and would fairly strongly prefer HSS.  HSS is obviously more than hard enough to drill annealed tool steel (that's the norm) and the problem with carbide is its so brittle.   With that small a dia, it will snap with the tiniest off centre force.  Even near microscopic chips in the cutting edge spell the beginning of the end- hss won't do that.

I also agree that you should watch the speed.  While the theoretically speed might be some crazy high number, you can't possibly feed fast enough to get there because you need to make a chip not dust or rub.  Experiment a bit, but I think the problem is the part is not annealed and carbide drills can be trickier to use.

putting a bit of oil on the end of the drill can't hurt.  It reduces friction and localized heat build up

 

 

Edited by measuretwice

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Thanks the pivot was annealed and cooled in sand to aid the slow cooling required. All was going well until I twisted the drill (marginally) and the tip of the drill broke off inside the 0.50mm hole I had drilled. I found no way of removing the broken tip. Since this failure I have experimented with a pivot drill sometimes named mascot or spade drill and the results were very promising. Keeping a pivot drill straight and removing the swarf is another issue but the cut is good.

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I like the pivot drills, I've got a bunch they work well.  Still, I'd be suggestion a hss drill over the carbide...their brittleness makes them very unforgiving as you found out the hard way :)

Edited by measuretwice

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I know you have overcome this issue, however I had the same issue last week and remembered this post once I fixed it. attached are photos of how I did it, I did not have to drill the rock hard steel, just made a bush like brass fitting. I used a grinding stone to take the pinion length back a bit soldered it onto the shaft, put it in the lathe and drilled a 0.3 hole in the brass till it hit the pinnion and then locktighted the pinnion wire in. The last to photos shows it all together in the movement.

Flypin1.jpg.2dafc961ef6b091e6e57b82df23c23cc.jpgfrenchsilk5.jpg.47ef12da01745671c04399ca998ab132.jpgfrenchsilk6.jpg.ed9bdb0562c87567bcd3a09a001553be.jpg

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