flat bottom countersunk holes?

[jebster]

i have a bumper that i want to sink some cap head screws in to get them flush. you can see the bumpers in my build thread (http://www.rccrawler.com/forum/1-9-s...sters-6x6.html). any suggestions on what type of bit i could use? basically i want to drill a cylinder out. i tested a typical bit on a piece of scrap aluminum and it did make the hole ok but the angled bottom isn't working for me. input welcome.

[Mr.Joshua]

Very cool build!
Try a forstner bit...it probably won't work on too many holes or on wood again but i bet it'll work for you. Pre-drill with a small bit to line up the starter point in the bit.

[sumquak]

try double drilling with a flat bottom drill. grind the point off a drill and some angled relief in the middle so it only uses the outer 1/3 of the flutes. sorry i don't have a pic but done this hundreds of times when an endmill wasn't an option.

[jebster]

thanks for the input. i think those are just what i'm looking for. i see a few places that carry them. most look like 1/4" is the smallest size. that might be about right.

Originally Posted by Mr.Joshua

Very cool build!
Try a forstner bit...it probably won't work on too many holes or on wood again but i bet it'll work for you. Pre-drill with a small bit to line up the starter point in the bit.

[jebster]

Originally Posted by sumquak

try double drilling with a flat bottom drill. grind the point off a drill and some angled relief in the middle so it only uses the outer 1/3 of the flutes. sorry i don't have a pic but done this hundreds of times when an endmill wasn't an option.

have you done this on drillbit in the 1/4" or below size? seems like it would be tough to get the relief in the middle on a small bit.

this does make me regret throwing out my broken bits!

[PhilB.]

What you should use is a counter bore tool. With a pilot on the tool, you could use a handdrill but a drillpress would give you depth control. Try
McMaster-Carr

Phil

[sumquak]

Originally Posted by jebster

have you done this on drillbit in the 1/4" or below size? seems like it would be tough to get the relief in the middle on a small bit.

this does make me regret throwing out my broken bits!

anything smaller than an 1/8 i use a microscope too see it. there isn't a whole lot of material left in holes that small, so you can get away with a less perfect tool.

i've ground drills into boring bars and groove tools for special situations and always have a few junk ones laying around for this reason, so i don't throw all of them out

[SMR 510RR]

Counterbore is the way to go...With the pilot lining it up is foolproof and they come in sizes specifically for cap head screws.

[WHITE-TRASH]

Pilot point drill bits as a follow up to a standard bits pilot hole will do the trick.

[jebster]

thanks for all the advice. one of the reasons i support this site!

i was about to put in an order to mcmaster anyway so i think i'll throw one of these bits in the shopping cart.

[rlockwood]

Originally Posted by SMR 510RR

Counterbore is the way to go...With the pilot lining it up is foolproof and they come in sizes specifically for cap head screws.

This is the most correct answer. Piloted counterbores are designed for this. Other stuff might work, but a piloted counterbore is very proven

[rangercat23]

Originally Posted by SMR 510RR

Counterbore is the way to go...With the pilot lining it up is foolproof and they come in sizes specifically for cap head screws.

Originally Posted by rlockwood

This is the most correct answer. Piloted counterbores are designed for this. Other stuff might work, but a piloted counterbore is very proven

X2
I use these at work a lot, right tool for the right job.