Yes quiet expensive, but durable, to not say indestructible in modeling use; the milling cutter have more than 30 years of heavy use and they work better than any Dremel new one or similar modeler offering.

I don't really want carbide bits.  They are sharp and can last, but they are extremely brittle - they will not tolerate any bending, you must use a good drill press with little runout (wobble) and clamp the item.

A #70 bit is quite large by microbit standards at .028" so it should be fairly robust.  I use a powered screwdriver with a micro chuck attachment to drill holes.  Not sure of the RPM of the tool bit it will drill through brass quite well!  Light steady pressure and let the bit do the job.  The last set of bits I purchased were labeled for "welding tip cleaning". Twelve bits starting at #76 through #55 I think.  Sharp and rugged.

I tried the inexpensive high speed steel bits in a drill press, #70 bit at 1750 rpm drilling through a cast brass headlight to run wires.  It simply annoys the brass and does not produce chips.

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I should probably mention that DBCity has micro brill bits down to #79 and in metric down to .05mm (.0020").  Smaller can be had but ya have to call them.  And pay thru the nosehttps://drillcity.stores.yahoo.net/newmidrbi.html

"I can not find my machinist guide at the moment, but as I remember for small bits 1750 rpm is much higher than recommended for these materials"

Dovetail grooves are used to hold the O-ring in place during installation or maintenance. This groove design is relatively uncommon as it is expensive to machine and should not be used unless absolutely required. The dovetail groove construction is only recommended for O-rings with bigger cross sections, .139 inch (3,53 mm) and bigger.

Also, I have bought drill bits used for drilling PCB circuit boards and in CNC machines. They have a larger shank than a standard drill (helps reduce breakage) they are usually 0.3mm to 1.2mm (that's about a #81 bit to #56)

Small drills can be spun much faster than 1750 rpm, their small diameter means they need very high rpms to get their surface speed up. I'll check my micro drill press tomorrow and see if I can tell what it's rpm range  is....DaveB

I get good tools from http://www.ottofrei.com - they specialize in jewelery making stuff. Prices are mostly reasonable, and I have found that most of the "unreasonable" ones are due to the products being significantly different than average (jeweler's saws being most obvious example). There are certainly other places, but they seem to have everything in stock all the time. Notably cheaper than MicroMark, for example, when they carry the same thing. Or sometimes at similar prices but better quality tools.

My bits (buy in Europe) comes from a professionnal jewelery hardware store, tap comes from a professionnal watchmaking hardware store, and all my little milling cutter from the dentistry hardware.

Although I use several suppliers, because they represent several good manufacturers like W. L. Fuller, I usually buy standard drill bits from McMaster-Carr. They stock bits specifically designed for softer materials like aluminum, brass and bronze.

The bits are first rate even the smallest one cut like a new; course they break like the other if you work not properly with them, the same with the taps.

I do the same with brushes, and all the hardware necessary for modeling use;it comes from the professionnal hardware, I never have regret to make the investment

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I can not find my machinist guide at the moment, but as I remember for small bits 1750 rpm is much higher than recommended for these materials even when using 118°, "slow-spiral" bits. At the moment I do not have any #70 bits, but I have no problem drilling brass castings with standard 118°, #60 carbide or "slow-spiral" bits when running in the 400 to 900 rpm range. Slow going but very precise.

Got the first highly recommended by Jack Burgess in his video.  The second was when searching for really small dies.  Both are US companies if that makes any difference.https://drillcity.stores.yahoo.net/https://minitaps.com/drill-bits-wire-metric/

The products I have received from Widget Supply  https://widgetsupply.com/  have been good quality.  I have not purchased bits from them but they list High Speed Steel HSS bits in the small sizes.  They also have lots of other tools and materials of use to modelers at reasonable prices.