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

[david]

Carbide gravers are available.  Sometimes carbide is needed to cut steel that is hard. It might be something you would consider getting for general watch part turning anyway.

[Jdg123]

Right,I actually ordered some 2 and 3mm square carbide to make gravers yesterday.

I just watches a video by Stefan Gotteswinter on YouTube, and he machined a center in titanium with a Carbide D-Bit just like I imagined the Seitz reamer style cutter. I have some 6mm silversteel/drill rod on the way to me and I’ll try cutting the center while it’s soft and harden afterwards. Hopefully they won’t warp to much... if they do I’ll just get some 7mm hardenable steel and do it the way you said (cut centers harden and ground to final dimensions between centers. 

[david]

JDG123,

Keep the forum posted on your results.   That is how we all learn.

[Jdg123]

I did some more digging and found a thread on a German machinists forum about micro countersinks. They recommended using some 3mm carbide drillshafts ground into a pyramid shape (like I tried to do with the drill-rod before. I already had a piece of 3mm carbide cut of, so I decided to give it a try. The setup is very ghetto, but I got the bit shaped just how I wanted to (freestyled the angle, it’s probably more around 90 degrees, but that shouldn’t be to critical for the purpose). I was scared that the drill wouldn’t catch the center if I mess up the angles, but it seems to work fine, the tailstock of my model engineers lathe ist very stiff so it can pull itself in. I already tried it in some aluminum and the .3mm drill didn’t wobble at all anymore. The cutting edges are quite raged of the diamond wheel, but as soon as my diamondpaste arrives in the mail I’ll hone them on an old CD and Test it in drillrod.

[nickelsilver]

3 face cutters work great for this kind of work. I have a grinding machine for carbide that idexes and can be set to any angle, but you can very much just eyeball it as you've done- where it would get tricky is if the 3 faced cutter was turning in a spindle, eccentricity of the point would be a real issue then.

 

You want the start angle from the cutter to be equal to or slightly greater than the drill angle, so the center of the drill starts, not the lips. For a 3 face cutter with 120 degree cut angle (most common drill angle [or 118]), you want to set your tool to grind at 40.9 degrees to the face of the cutting wheel; if you set it at 30 degrees which seems logical the actual cutting faces will be more like 100 degrees rather than 120. With a pin vice like yours with a 6 sided head it's easy to index 3 times, and you could just lay a protractor on the vice to eyeball the angle.

[Jdg123]

These D-Bit grinders (or Stichelschleifmaschine in German) are very cool, but equally expensive...  I’d love to have a nice machine shop, with all the machines one could think of, but as a student that’s still no more than a dream... 

you’re right. The angle probably isn’t ideal for getting a drill started, but they might be okay for the purpose of a female center (maybe even a bit to shallow?)

I believe regular drills usually have 118 degrees, but does that transfer over to micro drill bits? 

 

[nickelsilver]

The ones I use 99.9% of the time, Yamamoto, are 118, those are HSS, for carbide I use Dixi Polytool and theirs are 120. For the commonly found "circuit board" drills I don't know but I imagine the are the same.

32 minutes ago, Jdg123 said:

I believe regular drills usually have 118 degrees, but does that transfer over to micro drill bits? 

 

 

[Jdg123]

20 minutes ago, nickelsilver said:

The ones I use 99.9% of the time, Yamamoto, are 118, those are HSS, for carbide I use Dixi Polytool and theirs are 120. For the commonly found "circuit board" drills I don't know but I imagine the are the same.

 

 
I bought a pack of the circuit board drills to test the setup I planed, but eventually I will make drill guides for good quality 3mm shaft full carbide drills I can buy at a reputable machinesupply store. They run about 25-30€ but as far as I’ve heard the Chinese stuff is a lot like gambling, some work, some break instantly.

[nickelsilver]

16 minutes ago, Jdg123 said:

 
I bought a pack of the circuit board drills to test the setup I planed, but eventually I will make drill guides for good quality 3mm shaft full carbide drills I can buy at a reputable machinesupply store. They run about 25-30€ but as far as I’ve heard the Chinese stuff is a lot like gambling, some work, some break instantly.

Having a choice of drill guides is a great idea. A lot of the inexpensive drills have a body diameter of 1/8" or 3.175mm, so that would be good, then 1mm and 1.5mm would cover a lot of the better makes in the sizes for watch work. Might as well make 2, 2.5, and 3mm while you're at it though!

[Jdg123]

What makes would you recommend? 
maybe they are available in my area as well.

 

[nickelsilver]

Well, the ones above, Yamamoto for HSS and Dixi for carbide but I mostly us the HSS- I make a lot of parts and they are very long lasting and forgiving in brass, german silver, and steel; Titex is excellent too but for more than 15 years I only bought the Yamamoto and Dixi. Dixi does makes spiral single lip carbide drills that are the bomb for really round accurate holes.

 

For repivotiong I usually grind them up freehand from carbide rod, spade style, reducing in diameter from the tip slightly (necked or "waisted"). Being hand ground they tend to drill slightly oversize, and that and the waist make it very easy to remove in the event of breakage. Have to have a very fine diamond wheel or lap at this size, a D7 wheel is good and 3 micron diamond on a bronze lap gets an excellent finish. With a coarser finish the edge breaks down very fast, and at 0.1mm there's not much "edge".

Edited May 18, 2021 by nickelsilver

[Jdg123]

that’s interesting! I was thinking of making my own drills for repivoting, but I didn’t want to have to anneal the pinions. I didn’t think making them from carbide would be an option. 
What diameter carbide rod do you start from? 
The smallest I can find here would be 2mm. You probably use the indexable grinder for this tough? 

[nickelsilver]

I just use the shanks of old drills, so mostly 1mm in my case, sometimes 2mm, rarely 3mm. If I'm making a larger size, like over 0.5mm, I might use the machine, but for little ones I hold the bar in a pinvice with a 4 sided head, which acts as an index in my hands, grind essentially to a screwdriver blade shape but a bit more taper, grind the lips, then grind the sides to make the diameter. It's easier than it seems, but like anything takes some practice. The drill will never be perfectly centered when ground "by eye" like this, so I hold it in a pinvice when drilling, just freehand, in the lathe.

[Jdg123]

Thanks for the info!

Edited May 19, 2021 by Jdg123

[praezis]

2 hours ago, nickelsilver said:

The drill will never be perfectly centered when ground "by eye" like this, so I hold it in a pinvice when drilling, just freehand, in the lathe.

Hi, I always found this simple setup works surprisingly well.
Do you guide the rear with the headstock?

However isn't there danger to brake tiny (<0.2mm) drills by the mere weight of the pinvice?

Frank

[nickelsilver]

7 minutes ago, praezis said:

Hi, I always found this simple setup works surprisingly well.
Do you guide the rear with the headstock?

However isn't there danger to brake tiny (<0.2mm) drills by the mere weight of the pinvice?

Frank

It depends how my mojo feels that day. Sometimes I do put a bar in the tailstock that's a loose fit in the back of the pinvise just to keep things relatively horizontal, as I do this work under the microscope it's not hard to get disoriented.

 

Anytime the drill is in the hole I'm guiding the pinvice- even with the back supported I wouldn't let it hang.