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Look at that! A new toy :) DIY pivot drill


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Well, this went wrong. The pinion was to thick and/or the hole is to big compared to the staff diameter and/or i tapped it to hard. 

Snapshot_20160821_1.PNGSnapshot_20160821_3.PNG

Not to mention that the drill was first broken in the hole and i had to turn it out first. 1 of 3 staffs repivoted succesfully until now. Need more experience or better tools  :D

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Learned much from this case however.

First, noticed that the drilling bit batch ordered last time is completely is a waste. The cochleate shape of them is deformed and not regular. 

Second, the method how i wanted to mke this was totally wrong. Now i have found the copy of a hungarian watchmaker book where the procedure is written precisely. One has to drill three time as deep as the diameter of the hole. The pinion with a small taper has to fit in the hole all the way down and has to come off. And then cut it a bit shorter, so if one put it back it will tight fit and not over-stress the hole walls. It is easier to make another pinion until it fits like above than start again from scratch. 

Now i have shaved the staff and started drilling again... with proper drills :)

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Understood about the taper, good tip. My pivot drilling jig is still in my head, but ordered loads of bits and pieces from China. Waiting for the parts to arrive, so hope I get some of the good micro drills and not a reject set! On your picture of the pivot when you say "just got right the center" - what preparation do you do to the broken pivot? Do you file it flat first or what do you do before you try to get the pilot center? I take it that you found the center on your pivot drilling machine?

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16 minutes ago, Michael said:


"what preparation do you do to the broken pivot?"

Getting the center with a pivot drill indicating that the tool is OK, leading the drill to center. This is done by the female cone which is also slef-made. Need one for all drill size. Currently i have two. 

First i file down the broken tip to get a half-cone ended staff. Like on the pictures. That end will made the staff turning centrical in the female cone. Then i use the drill with the corresponding cone which does not allow the drill to wobble and get the initial hole perfectly centered. From this point you can use smaller drills, since the small initial hole will lead the drill not the female cone. See the cross-section of this on the picture posted previously!

The book suggests to find the center previously by hand. This goes to drilling tools without drill-leading female cone. On lathes "finding the center" with hand is not easy (at least for me :) ). Picture 318 showing "Köldök" which will mislead the drill. 

pivot drilling.jpg

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The extension was falling off two times while turning the pivot. Then i filed down a bit from the end. After that it was holding well and the staff was finished succesfully. :) 

After the video the endshake was also adjusted. The pivot thickness will be fine-tuned by the owner, since that jewel is broken and need a replacement. 

Edited by szbalogh
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  • 4 months later...

Very innovative!  I have a watchmaker's lathe with a drilling tailstock, but I have it in one place and it's not easy to break down and set up wherever I need it.  Plus your work gets across many of the essentials of repivoting.  I find that to avoid breaking drills I have to be very careful to make sure the lightest touch produces sworf (curlings).  If not,  then the metal has to be annealed, drilled and re-hardened.  Thanks!

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Scbalogh,

As usual your approach to watch restoration and repair problems is innovative and brilliant. At this point the only thing holding you back is not having better equipment. You have too much talent to be held back by equipment issues.

david

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  • 1 year later...
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  • 2 months later...

I’m currently working on my own pivot drilling machine, but I’m having trouble drilling the female centers. Would you mind telling me how you did it? I ground a 3 flats in a piece of hardened silversteel, but the cutter dulls super quick (I‘m using 6mm 4140, maybe that’s too hard)

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JDG123,

Drilling into a piece of hardened anything is going to present a problem. Ending up with a precision part introduces additional machining issues.  If precision is of little or no concern just center drill a piece of unhardened drill rod and harden it.

If high precision is required a lot of additional steps will be  necessary.   Several machining techniques are required to make the ID and the OD concentric with each other. This is a problem also faced in the manufacture of collets.  

A drilled hole will not be precise nor will it be particularly round.  The way a round hole is achieved is with a single point boring cutter.  To make a high precision tool start with a piece of oversize, unhardened  drill rod. Face cut and drill the center drill with a  center drill bit.  Follow up with a normal bit the size of the pilot end of the center drill and deepen the hole to allow clearance for a small boring bar.  A small boring bar can be made by taking a small two flute endmill cutter and grinding off one of the flutes.  Bore the sides of the center drilled hole with the tiny boring tool at the same angle as the drill with very small cuts. That should give you a precise angled hole.  Turn the drill rod around and do the same thing to the other end.  Next turn the part you just made on centers down a few thousandths over the desired finished OD.  Now you will have a precision center and the OD will be concentric with the ID.  Harden the tool by heating it.  After heat treating put the part back on centers and turn (or grind) the OD to its final dimension.  Since the part will be hard this will  require an extremely hard cutting  tool like carbide, ceramic or CBN.  

These are a lot more steps than most watchmakers would want to take but the result will be an extremely precise and concentric cup center.     

Edited by david
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Riiiiiight, that’s actually a lot more steps then I’d be looking for. The thing is, the centers I’d like to have should be about 1mm in diameter, so a boaring bar probably won’t be practical for me (I‘m doing this on a modelengineers lathe). 
I can’t just use a center drill, because there would still be a flat from the chisel edge. Do you have any ideas other than my makeshift form cutter? It has a very negative rake, maybe I could make the same sharp tiped cone again and file down one half of it flat like a Seitz reamer? 

 

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My comparisons to the Seitz reamer is mostly about the shape. A cone cut in half.My smallest boring bar is a Komet with around 3 mm in diameter, with that I also won’t get a „sharp pointed“ cone. I do have a 3mm endmill I could modify, but my lathe doesn’t have a quickchange toolpost, getting that boringbar on center would be almost impossible. 

On my watchmakers lathe I could use a graver to find the center and cut a cone, the problem is, that my toolsteel gravers don’t cut the 4140 and my biggest collet is a #50 (the material has to be 6mm...)
 

 

 

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