Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

I've been searching for a very long time but have been unable to figure out what these drill bits are called. I saw a video on youtube some years ago where a guy talked about what drillbits he was using for flat holes for magnetisation. I didn't pay it much attention back then but of course I can't find the video any more.

So anyone know what the drill bits are called that are used to make flat holes?

The closest I've been able to get would be tungsten carbide cutter bits or burrs but I can never find a set with the type I need.



The one circled could work but I can't find any sets of just this type of bit. The sizes I need are from 2mm-10mm with 1mm increases, so 2,3,4,5,6 etc.

Anyone know what this type of drill bit is called and where to get them? Without having to pay £10 per drill bit?

Reuleaux Triangle Bit, you can probably find them online or at a wood working specialty store.


Automatically Appended Next Post:
Or wait that's to drill a box shape....... I completely misunderstood flat, if you're looking for a flat bottom that's a Forstner bit.

I don't worry about making the bottom of the hole flat. I use a standard drill bit that creates a very shallow cone pit. The epoxy cement fills it.

 Bobaram wrote:
Reuleaux Triangle Bit, you can probably find them online or at a wood working specialty store.


Automatically Appended Next Post:
Or wait that's to drill a box shape....... I completely misunderstood flat, if you're looking for a flat bottom that's a Forstner bit.

But I've found no store that sells them in the sizes I need. Smallest I've been able to find was 12mm.

I'm not sure they go much smaller than that, the smallest I've seen was around 1/4-1/8" know Dremel has a bit for it but I think that's a 1/4" as well. I wish you luck!

You can get machinist bits for doing wire guage flat bottom holes (flat bottom or bottoming is the names most often used). They are expensive though, and you will need to deal with a machinist supply store as opposed to regular hardware type stores. Also, they will walk on you, so without using a mill or drill press trying to get the hole started is a PITA.

You might consider looking at brad point bits (they will have a bottom that looks a bit like an "M" or a low angle bit like a 118 degree metal bit. The pointed tip makes it much easier to start the hole without having the bit wander all over the place.

Forestner bits are another option, but finding those smaller than 1/8 inch is almost impossible.

Places to look would be supplies like McMaster-Carr, MCI, or Grizzly.

What is the benefit of a flat bottomed hole?

I got mine in a hobby drill bits set which had cutting disks, buffers, normal drills etc. Try looking for something like that.

 Flinty wrote:
What is the benefit of a flat bottomed hole?

Magnets glue in stronger is what I've been told

With a regular bit, you are left with a concave hole (rounded bottom).
Magnets used b modellers tend to be flat rounds and as a result, won't SIT flat in a round bottom hole.

A flat bottom hole will allow the magnet to sit flat.

What you are looking for is an endmill.

http://www.amazon.com/gp/product/B003CYKFCO/ref=oh_details_o03_s00_i00?ie=UTF8&psc=1

An endmill is basically a drill bit on steroids. It is generally used for cutting sideways, but can also be used for plunge cutting just like a drill bit.

Related, but if you are ever in the market for a drill press, don't get one! Get one of these instead:

http://www.amazon.com/Grizzly-X2-Mini-Milling-Machine/dp/B0000DCZ7E/ref=sr_1_2?ie=UTF8&qid=1380154809&sr=8-2&keywords=mini+mill

It serves all the purposes a drill press does, but the table on the bottom and the vertical head can be slid around with 0.001" precision using the dials. This is basically the home version of the most fundamental machinist tool out there. They are built for machining metal using end-mills, boring heads and plain old drill bits; so wood and plastic are a breeze to it. I have one of these and I use it for drilling perfect little magnet holes in minis with an endmill (among other things of course. using it for magnetization was just a happy coincidence).

Edit : changed the link to the exact endmill I use for magnets.

Cowbellicus wrote:
What you are looking for is an endmill.

http://www.amazon.com/gp/product/B003CYKFCO/ref=oh_details_o03_s00_i00?ie=UTF8&psc=1

An endmill is basically a drill bit on steroids. It is generally used for cutting sideways, but can also be used for plunge cutting just like a drill bit.

+1 The tool you are looking for is an end mill.
I have them in 1/8" sizes but have been looking for 3mm versions to fit 3mm magnets and found them here:
http://www.ebay.com/itm/10-NEW-3-MM-SHANK-CARBIDE-ENDMILLS-4-FLUTE-DOUBLE-END-USA-MADE-C120-/331031817193

Try your local ebay.

 Flinty wrote:
What is the benefit of a flat bottomed hole?

Easier to get the magnets to sit flat when gluing them in.

T

 MadCowCrazy wrote:

 Flinty wrote:
What is the benefit of a flat bottomed hole?

Magnets glue in stronger is what I've been told

Ive never had a magnet break the superglue bond between itself and the hole so far.
Can't see the actual benefit of doing this? Sure its techically able to make a better bond to the more flush surface, but if you actually drill the right sized hole, you dont even need glue! the tightness of the hole is enough to keep the magnets from ever coming out of the hole again. The magnet cant do anything else other than sit flush in the hole because it doesnt actually fit into the hole in any other orientation.

My advice is to just get the correct diameter regular drill bit, and do the hole right. The problem will dissapear I promise.

edit; I can do this without using a pinvice.. just turning the bit between my fingers.. so tbh.. no excuses


start by drilling a pilot hole with a really small bit.. maybe a 1mm, they do a nice clean hole without distorting the part easily enough, make that hole the depth you need (which is the thickness of the magnet PLUS the depth of the coned drill bit tip (the depth of the bottom of the hole that you are trying to get flat)
Then get a slightly larger bit, 2mm? and bore the hole slightly larger; this will be really easy down to the depth you drilled with the last bit.
And then do the 3mm bit (for a 3mm magnet this is)

stepping up the bits like this stops you from warping the hole. Also go slow, no need for nay power tools tbh, they only risk overdoing it, slipping sideways or tearing the piece with too much torque.

to get the magnet to sit flush in the hole; get the hole drilled, (drilled right ; that is perpendicular to the mating surface, without wobbling the bit and messing up the hole while you drill it)
And stick the magnet to the side of your hobby knife, pop a little spot of glue in the hole, or on the magnet. then press the magnet into the hole with the knife; this makes it so you cant push it in too deep, and it will be sat as flush as the knife is to the surface... so pretty much perfect right? .. now wait a moment to let the glue set a bit, and SLIDE (not pull) the knife away, quickly. The magent will not have moved.
Using the knife like this can help get the polarisation right too if you stick 2 magnets to it the same orientation, one either side of the knife. they will attract together the way you need once the knife is gone (maybe stick 2 together, and slide the knife between em)

 chromedog wrote:
With a regular bit, you are left with a concave hole (rounded bottom).
Magnets used b modellers tend to be flat rounds and as a result, won't SIT flat in a round bottom hole.

A flat bottom hole will allow the magnet to sit flat.

But only if you can get the hole precisely straight. Is it really worth the effort? Are you. Not better off with a small bit of filler and a slightly deeper hole?

 MadCowCrazy wrote:

 Flinty wrote:
What is the benefit of a flat bottomed hole?

Magnets glue in stronger is what I've been told

Never had a problem that magnets did not hold ... better take a superior super-glue then?
/Edit: I forgot to mention: For myself I usually drill a hole exactly the size the magnet is ... it's a bit tricky to get it in sometimes if your glue is too fast ... but the magnet will never come out again, trust me ... which can be pain in the arse if you put it the wrong way in


Also, if the hole is completely flat and exactly the size of the magnet ... every excess of the glue will come outside which you have to clean then ...

I'm also under the impression that normal drills work better.

EXCEPT of course where someone doesn't have the depth available for the tip of the drill!

I use a 1/8" drill bit, which I can turn by hand that fits the magnets (D201 from K&J) very snugly ... almost don't need glue at all.

I use a burr like the second from the right in your photo. That's about 3mm in diameter. In the UK Hobbycraft and Boyes and other places sell them but not the likes of GW.