I have just broken 3 pcb (dremel) drill bits trying to drill a 0.35mm hole in a brass bolt.
Is there a trick to doing this successfully?
What should be the length of the hole to avoid breaking the drill bit?

I haven't tried making a nozzle for this project yet, but I have drilled tiny holes in both aluminum and brass in the past, up to ~4mm of depth.

Brass is very "chewy", so careful and steady and slow is the way.

1) slow drill rotational speed
2) cooling fluid (keep it wetted with machining fluid or at least oil)
3) very slow penetration speed. up then down, up then down, etc. blowing off material each time it comes back up (and if necessary, manual removal of material from the drill bit fluting).

If by hand, you'd better be incredibly steady. Once that bit penetrates into the material, a slight shake can be enough to sheer it. I'd recommend using a dremel drill press if possible.

Edited 1 time(s). Last edit at 08/13/2012 09:42PM by xiando.

Thanks xiando, I am planning to invest in a dremel drill press before I break any more drill bits.

If you get the press working well you could possibly recover costs of the drill press by selling additional nozzles on eBay. Best of luck.

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Charles S.
Software Engineer
Prusa Mendel I2, RAMPS 1.4, Marlin 1.0 R2, Pronterface, Slic3r

By the way, what kind of dremel chuck can take such little drill bits ? I have the bits, I have a dremel but I have no idea how to use them together

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

It isn't particularly hard to drill nozzle holes by hand using a pin-vice - cheaper than a drill press too. Takes 10 - 15 mins to go through 2mm of brass, so no good if you want to mass produce - but fine for the odd one or two.

I've seen the actual [url=http:// [url]http://www.dremel.com/en-us/tools/pages/tooldetail.aspx?pid=4486[/url]]dremel chuck[/url] work for very small bits. Might be worth looking into

Dremels come with a variety of chucks. (I have four different ones with mine) The smallest is suitable for 8-15 mil bits.

So, I bought 50 drill bits on ebay for about $18? US. Mine are .4mm, but should the same for other diameters.
They have a 1/8" shank, making it easy to chuck up in dremel or a lathe.

I have had great success in brass and copper. Not any success in steel or SS.

I have succeeded both by spinning the bit or spinning the work.

Head and tailstock center alignment on the lathe (Taig micro) is essential if you plan on spinning the work.
Any offset and the bit will find the work center and bend/break.
Spinning the bit is easier, because it will just drill a hole and not seek a natural center alignment.
RPM seemed best at dremel speeds (20k+?), but I did go much less when the bit was in the lathe collet..

I drill in 2 diameters as a first plunge, then 1 diameter in and all the way out to clear chips.
Patience is key, as every time I plunged carelessly, I break a bit in the hole, usually scrapping the piece and the time already invested in previous setups and shaping operations. arg.

I have done it several ways including a kludged c-clamped dremel axis for precise plunge control.

I like spinning the bit and plunging the work. Have gone full bit depth using this method, about 5mm+ depth.

I've broken a few bits, but at $.30 each who would mind.

Dave

I'll just copy/paste a post from my g+ projects page from the other day. I'm drilling aluminum with 0.5mm bits so it's not exactly what you're talking about, but maybe you'll find the video interesting.

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[www.youtube.com]

Here's my current process for making the nozzle tip and drilling the nozzle hole. I'm still a beginner at using a lathe so any tips are certainly welcome.

These are the 0.5mm bits I used. They work pretty well considering the price and I like the little tube they come in.
[www.ebay.com]

This is the mini chuck.
[www.amazon.com]

I have had best results with good drill bits from harvey tool. Search on there website and you can get very small drill bits.
I have used a milling machine and lathe and the drill bits make the biggest difference, i was using cheeper drill bits and had marginal sucess.

very high speed on the bit. Smaller the bit, higher the speed needed.

And if you can't hold everything *ULTRA STEADY and TRUE*, go with high speed steel. Solid carbide doesn't flex at all and will snap. HSS will give/flex a bit.

Actually you might want to consider cold rolling the nozzle. What you do is start with a bigger hole, then squeeze the metal around a thin wire that is the diameter needed. This instructable outlines how to do it:
[www.instructables.com]

I've gone thru a bunch if hss bits on lathe. my last custom nozzle was done with a 1/64inch bit, then compressed in a vise, then reshaped. it was copper. copper actually hardens when it is bent, so it worked out ok. it ended up being .3mm to .4mm oval shape, but since the hole was already there it was easy to shape with a ~.35mm bit, then a~ .4mm bit. don't just go by rating size, also measure with micrometer to ensure proper diameter.

also harbor freight has several cheap hss bits available. the issues with the smaller bits is they are not completely centric which means they are useless unless a hole is already set.


another option is to start a hole with 1/64 or 1/32 bit and let it guide the smaller bit, then sand the outside flat to remove the larger guide hole.


your time will likely be better spent just purchasing a nozzle from a reputable supplier. i would say 20-25 bucks is reasonable considering the tools and skills required.

HSS drill bits is a great idea, and so is the dremel chuck.
If the nozzle hole ideas work, I can probably sell a few $35 hot ends as end product on ebay to make up for the cost of the tools.

Make yourself a bow, with a loop around the pin vice,
and a palm piece for light pressure..

Dremel drill press and chuck with HSS drill bits worked like magic.
I used coconut oil for coolant.
I did not have much luck with the bow string idea as I did not get a good grip with the tiny #80 HSS drill bit.
Wobble was also a problem I faced with that size drill bit.

Using Free Machining Brass is considerable easier than pure brass when it comes to drilling or milling. All plumbing fixtures in the US is made of free machining brass because of this. Also, any coolant (or oil) beats no coolant when using micro sized drill bits. Soft alloys like brass and aluminum load up the flutes micro mills and drills extrememly fast. Once loaded up, they snap especially if it is carbide.

Also, drill as much of your nozzle out with a larger drill (mine is 1/8" = 3.125mm diameter) and only use the nozzle hole drill for ~1mm of the left over stock. Anytime you are 2 x the diameter, you need to step drill to clear the flutes (especially when you are drilling deep). Step drilling is completely removing the drill bit from the hole you are drilling in order to get rid of the hole's material.

See this, looks easy but I bet it isn't.
youtube