Making a pinhole body cap

[TWX]

0.25mm is very small, you'll need a very light touch not to snap it just with the pressure and have almost no feedback. You'll also need to be careful you don't load it and jam the flutes with swarf, multiple small touches would be the way to go.

So this is basically what I have in-mind. Image not to scale.

Based on your comment, I think I'm better off drilling the countersink first, so that the pinhole requires removing as little material as possible.

 

[480sparky]

The pinhole I purchased uses two materials. A thin small disc with the actual pinhole in it, mounted to a larger disc that gives it rigidity. That is what I mounted to my body cap.

 

[Soocom1]

I STILL need to either find or rebuild my zoom pinhole.

With the mirrorless it might turn out to be quite the chore!

 

[weepete]

Based on your comment, I think I'm better off drilling the countersink first, so that the pinhole requires removing as little material as possible.

That's the way I'd go. Might have to grind a new angle on your countersink bit to make it a bit shallower too, should be easy enough to calculate with a little bit of trig, that way you shouldn't accidentally break through and you'll get the taper you want. Should be easy enough to centre if you have a 3 paw chuck too to get it started.

 

[Derrel]

$9.50... my gawd... think of how far that much money would go at Kentucky Fried Chicken.

 

[480sparky]

$9.50... my gawd... think of how far that much money would go at Kentucky Fried Chicken.

$5 Fill ups - KFC.com

 

[TWX]

Based on your comment, I think I'm better off drilling the countersink first, so that the pinhole requires removing as little material as possible.

That's the way I'd go. Might have to grind a new angle on your countersink bit to make it a bit shallower too, should be easy enough to calculate with a little bit of trig, that way you shouldn't accidentally break through and you'll get the taper you want. Should be easy enough to centre if you have a 3 paw chuck too to get it started.

Since I'll be using a drill press with table-mounted vise I'll just set the drill press extent to not let met drill all of the way through. I'm half-tempted to take an old drill bit or length of rod, chuck it into the drill press, and use a file to file it to a needle-point for making the actual hole, bottoming on the table of the press.

 

[Derrel]

How about using an actual needle and using a drill press to poke it through a Small section of an aluminum drink can?

 

[TWX]

How about heating an actual needle with a torch and then using a drill press to poke it through? I think the idea of using a drinks can makes some sense

I may try that. I don't currently have a pin-vise though, and I'd need one in order chuck something quite that small. Most of the sub-mm drill bits I've found for sale have 3mm shanks, that should work in the chuck on my drill press, as would a nail with the head cut off or some other length of steel.

Come to think of it, a nail might be my best bet for the final hole since nails are already tapered most of the way so very little material to remove, different hardnesses are available, and there are even nails that have flat edges instead of being only based on round wire, so there are some options. One of the flat-sided nails might actually work best since the corners might make for good cutting edges that could be filed to a single point.

 

[weepete]

Since I'll be using a drill press with table-mounted vise I'll just set the drill press extent to not let met drill all of the way through. I'm half-tempted to take an old drill bit or length of rod, chuck it into the drill press, and use a file to file it to a needle-point for making the actual hole, bottoming on the table of the press.

Drill bits are normally hardened high speed steel, too hard for a file, you really need to grind them to reshape. Wood bits already have a profile with a point, though getting an accurately sized hole will be challenging. A brad or auger point drill bit may be an option. Carpet tacks are sharp and have very fine points. Also if you want to keep the accuracy of the hole size you could centre drill it, poke a carpet tack just through then use a 0.25mm drill bit as a reamer and very gently hand ream it out. The biggest thing will be marking it up to get the centre, if you are just doing it with a centre square I'd mark it on the outside so the square is flat on the job, should be easily able to get it within 0.5mm then.

 

[TWX]

Well, my 10-pack of 0.25mm drill bits arrived. Everything I've read suggests using these by-hand will just break them, and my drill press' runout is to high. A buddy has a dremel drill press, sometime this weekend I'll take 'em over. I might pre-counter-sink a divot nearly all of the way through first using an end-mill though, to leave less than one mm of thickness to the body cap, give the dremel the best chances of not breaking the bit.

 

[Soocom1]

OK.
Couple of points to consider from someone who was been there done than aspect.

When drilling into plastic, the material (typc. a pvc type or variant) will not drill nicely unless you back both sides with tape. This is because the drill isn't actually "drilling" the plastic but more like tearing it. just tearing in it a round fashion.
The hole itself unless its specifically cut in a very specific manner will do two things.
1:
The plastic can heat up and start galling. If it does that, the hole will be many times larger. So heat is an issue here.
2:
The plastic of the cap will deflect under pressure. So an under basement behind the cap is highly advisable to prevent the deflection, and a small piece of wood clamped down on the top is advisable as well. It requires a bit higher level set up but will yield a better overall result.
If your friend has a cross slide vice, use it! You can pre-set the drill hole and make a first class professional hole over something else.

The under and over layering of the support material will also act as a heat sink of sorts with just enough ability to prevent heavy gailing.

 

[TWX]

Thanks, I'll keep that in mind. If I can drill down with a larger bit until I'm less than a millimeter from breaking through, I figure that should make the job of the final bit a lot easier. I don't know if I'll be able to put tape or anything else on the pre-drilled side, but I will do so on the undrilled face for sure. I'll also put some kind of stabilizing thing behind, I've done that to avoid tearout on other projects. Don't know if he has a cross slide vise or not.

I have five body caps with which to test, all blank third-party without any writing on the front, so that should help a little when it comes to having something smooth on which to work as opposed to having lettering to contend with.

I wonder if blowing compressed air down along the drill bit would be enough to help with heat/galling. The bit is so small that I'd figure any airflow might provide enough heat dissipation.

 

[Soocom1]

Thanks, I'll keep that in mind. If I can drill down with a larger bit until I'm less than a millimeter from breaking through, I figure that should make the job of the final bit a lot easier. I don't know if I'll be able to put tape or anything else on the pre-drilled side, but I will do so on the undrilled face for sure. I'll also put some kind of stabilizing thing behind, I've done that to avoid tearout on other projects. Don't know if he has a cross slide vise or not.

I have five body caps with which to test, all blank third-party without any writing on the front, so that should help a little when it comes to having something smooth on which to work as opposed to having lettering to contend with.

I wonder if blowing compressed air down along the drill bit would be enough to help with heat/galling. The bit is so small that I'd figure any airflow might provide enough heat dissipation.

The air isn't a bad idea, but it involves the friction coefficient so for a highly precise level I truly wouldn't have the best answer there.

I can tell you that doing round work on the lathe has yielded mixed results. The real kicker here IMO would be to predrill a smaller hole in the top wood brace first so that the final hole drilled is still covered by the wood to prevent the tearout.
But use a fresh bit to do the work. I learned the hard way that a tiny drill bit and lots of friction heat makes the bit a dull boy.

Plus the extra pressure to cut through can likely break the bit with the friction. I have witnessed a 1/8 bit snap in multiple pieces when the plastic had enough friction to actually stop the motor.

 

[TWX]

Yeah, drilling a hole smaller than 0.25mm is not in the cards for the wood backing. We'll see how it goes. I have ten of these bits and they were not expensive, so even a little bit of failure isn't all that big of a deal.