Drilling A Hole With A Flat Bottom?

[Soeren]

Hi,

Anybody ever tried to drill a fairly shallow flat/square-bottomed hole (like 5..10mm in diameter)?

I have to embed some cylindrical magnets in 10mm thick aluminum and so far, my best idea is to start with a regular drill bit and then squaring the bottom with another bit that I grind flat-ended for the purpose. Another thought is to use a tungsten tipped router bit, but they're hard to grind to a completely different angle and may be too much bother for the few holes I have to make

Anyone tried something similar and if so - how did it go down?

Any alternative suggestions?


To do it on a large industrial mill would be the right way and very easy, but would also involve a bit of travel presently, so I'm trying to skip that

[Keithh28]

Have you tried a spade bit?  I know they're designed for wood, but if you're willing to burn a few up, I think that would be the easiest. Spade bits have a pilot point that might end up going all the way thru your sheet, depending on thickness, is that permissible for your application?  Other than the small pilot hole, the bottom should be nice and flat. If that won't work, your router is the best bet. Is it a plunge router, or do you have a router table for it?

Another option would be to cut all the way through with a hole saw, use a band saw to cut the plug to the desired depth, then weld or epoxy the plug back into place.

Other than that, the usual...use lots of oil, flush/blow out the shavings often. Good luck!

Keith

[newInRobotics]

Can You use counterbore bits?

[Keithh28]

That's a great idea, probably less chatter than you'd get with spade bits.

Keith

[Soeren]

Hi,

Have you tried a spade bit?  I know they're designed for wood, but if you're willing to burn a few up, I think that would be the easiest. Spade bits have a pilot point that might end up going all the way thru your sheet, depending on thickness, is that permissible for your application?  Other than the small pilot hole, the bottom should be nice and flat.

I try to avoid using spade bits, so I have plenty to snuff, but spade bits are very hard to control (because theyre flat raher than cylindrical). That's why they use the pilot spike and for wood it sorta work, but a pilot is a no-no here anyway. Besides, they don't make a flat, but rather a very flat cone unfortunately, Just like the cylindrical router bits (not sure what their name is).

If that won't work, your router is the best bet. Is it a plunge router, or do you have a router table for it?

I wouldn't dare using a plunge router for this - around 20k RPM could make a mess of it in a blink. I'm imagining a solid drill stand and going very slow with plenty of white spirit to lubricate.

Another option would be to cut all the way through with a hole saw, use a band saw to cut the plug to the desired depth, then weld or epoxy the plug back into place.

Easy now my tiniest hole saw is about 10 times the hole I need.
I'm not too keen on having a plug that may work loose at a critical time, but I did think about using two plates, one the height of the magnets and the other to get the total to the 10mm I need. Then weld the pieces together, but that's just a lot of extra work

Thanks for the suggestions though

[Th232]

Why not just use a centre-cutting endmill?

Easy enough to just chuck one up in a drill press, a hand drill would also be possible if you're careful enough.

[Soeren]

Hi,

Can You use counterbore bits?

Not for this project I'm afraid. I need the holes to be like:  |__| so I can bond the magnets with cyanoacrylate (super glue) and be certain that they are flush with no kinks.

For now, I think I'll stick to using two drill bits, one of them ground flat, I'm just not sure how hard the core is. Cheap drill bits are probably the best, as I believe the better ones are made "softer" at the core. Perhaps a "Dremel" is needed for the center, where no rotating bit can cut - I better practise on some MDF

Thanks

[Soeren]

Hi,

Why not just use a centre-cutting endmill?

Easy enough to just chuck one up in a drill press, a hand drill would also be possible if you're careful enough.

Yes, but unfortunately they are all at the same place as the mill (who said "get off your lazy butt" )

It takes a certain amount of courage to attempt that with a handheld drill I guess, but thanks for the suggestion

[jkerns]

A brad point drill with give you a decent hole with a little dimple in the middle.  http://www.wlfuller.com/html/brad_point_drills.html  You should still be able to glue OK even with the little dimple (I would think)

[wheagy]

Would it work to drill a hole with a standard bit and then inject a small amount of epoxy or other non shrinking glue/resin in the bottom of the hole and let it dry?  With the right kind of glue, it should find it's own level and dry relatively flat. 

Win

[Soeren]

Hi,

A brad point drill with give you a decent hole with a little dimple in the middle.  http://www.wlfuller.com/html/brad_point_drills.html  You should still be able to glue OK even with the little dimple (I would think)

I'm not sure if the ones I have are all that flat, but I could test it on a scrap of MDF. Whether they're good for alu is quite another thing tough, as I usually use HSS drills even for for hard wood, to ge the most precise holes - but defiitely worth a try (I have a set that has seen zero work that I can test to destruction).

Thanks

[Soeren]

Hi,

Would it work to drill a hole with a standard bit and then inject a small amount of epoxy or other non shrinking glue/resin in the bottom of the hole and let it dry?  With the right kind of glue, it should find it's own level and dry relatively flat. 

Might be worth trying as well.

Thanks


I'll post an update when the deed is done, on what worked and what didn't, but the actual drilling is scheduled for around Tuesday (at a friends home) as he has got a fairly heavy and precise drill press.

[waltr]

I think your first idea may be the easiest to do with the equipment available. Aluminum is pretty easy to cut. Just ensure enough back clearance on the flattened cutting edge and grind in the drill's web to have the flat cutting edge go all the way to the center (like an 2-fluke end mill).

Hint: practice of a piece of scrape.

[Gertlex]

Yes, but unfortunately they are all at the same place as the mill (who said "get off your lazy butt" )

That's the origin of so many regrettable decisions in robot building

[Soeren]

Hi,

Just ensure enough back clearance on the flattened cutting edge and grind in the drill's web to have the flat cutting edge go all the way to the center (like an 2-fluke end mill).

Yes, my original thought was more or less to just cut the drill perpendicular, like slicing a bread, but it needs the relief to cut properly of course - Thanks for reminding me

Trying to brush up on my drill vocab and knowledge I found this PDF which may be helpful to others.

This started out as a slightly annoing problem, but it's growing into a worthy challenge in its own right.

Thanks

[Soeren]

Hi,

Yes, but unfortunately they are all at the same place as the mill (who said "get off your lazy butt" )

That's the origin of so many regrettable decisions in robot building

And of some clever inventions as well (here's hoping for the latter)