Need Help from the machinists in the crowd...

Robert Hankins

Robert Hankins

Joined
May 19, 2003
Messages
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How other than using a step drill can I get a flat bottomed hole?

Don't have much experience with machinist lingo or tools
Is there a bit that does that? End mill?
Need about a 7/16th or 1/2 " hole with a flat bottom.
Need to drill in to G10 as well as annealed blade steel.
 
Hopefully Dan Gray will see your thread. I believe he was a tool and die maker. I use a step drill for the Loveless bolts I am now just getting into using. If I did not have that I might use a center cutting end mill. It will give a square shoulder but I would sink it slowly and periodically raise it out of the hole to cool.

RL
 
Some guys are using center cutting end mills, and some are using chucking reamers, which sometimes require slightly modding of the reamer.
Some will also say that neither should be done on a drill press. However, it has been done for years I'm sure. Just don't use your press as a mill repeatedly.
The best option, IMO, would be one of the more expensive "spot facing" counterbores that MSC (or Enco, etc) sells. They are pricey at that large size, but they also have interchangeable pilot hole sizes, and come carbide tipped too.
Counterbores are made for flat bottomed holes. You just don't see the large sizes often, unless in MSC's Big Blue Book, (or similar).
Some guys even use 140 degree drill bits, which produce a hole that is CLOSER to flat, than other bits. If you need a true flat bottom hole, the 140 degree bit is no good..
 
rlinger has it right

The tool you are looking for it is a center cutting end mill. These usually have two flutes, but you can get some 4 flute center cutters too. You will want to use a coolant as you are cutting, don't rush, and make sure you back the mill out regularly to clear the shavings and let the tool cool off some. Also make sure the work is clamped very firmly and the mill is very straight in your drill chuck. A mill is much more apt to wander starting a hole than a drill bit, and if you are just a little off it can be a real PITA sometimes.

Good Luck
Ben
 
The correct way to do it would be to drill a pilot hole, then use a counter bore. It's exactly what they are designed for. A step srill is a somewhat less expensive version of a counter bore that will mostly serve the same purpose, but with some limitations. Any old end mill will work fine if you use the following procedure:

Clamp the workpiece and drill a pilot hole just large enough for your rivet/screw to pass through, then without moving your workpiece, unchuck your drill bit and chuck the endmill in and do your counter bore. By following this procedure, you should maintain good concentricity of the two holes. If you have to raise or lower your table during this procedure, all bets are off as to concentricity.

Funny this should come up today as just last night I passed on a box of counter bores that I could have had for nearly nothing because they were too large for any work I can see myslef doing. Maybe next time I visit that old tool and die maker I'll bring them home anyway.

John
 
Good God John,
I'm in desperate need of ANY size counterbore. I'll take any you can get! Hehe.
Seriuosly though. You shoot me some counterbores, I'll find something in the shop to hook you up with!
 
The cheap way to go would be to maybe file down the tip of a carbide drill bit. Drill the hole with a regular (unaltered) carbide bit, then clean out the bottom of the hole with the filed down bit.

The other answer is ...do the holes really need to be that flat? Unless you're really working with close tolerances, the hole from a regular drill bit is flat enough at the bottom to serve as a countersink, IMHO.
 
Razorhunter, I'll email the guy and see what he wants for the counter bores and let you know.

jiminy, I want to watch the filing of the carbide drill bit. I might even pay a little to watch. In my experience you're more likely to drill a hole in the file than file a carbide drill bit.

I didn't realize were talking about 7/16 - 1/2 hole. A counter bore certainly would be the right tool for that job. In G10, carbide would be preferred, but HSS should work if you're only going to do it occasionally.

John
 
yes the end mill, two flute if you don't have a hole first, or a four flute
will be smoother (with a hole.)

if you have a hole and want to line the counter hole up to it
place a drill (twist) bit in your chuck the same size as the hole you have,, use it as an
alignment pin (or a pin of the same size) then clamp the piece down
then use your end mill.
there are countless ways. :)
 
How close to 1/2 inch do you need? I know that most counterbores for 1/4" socket head cap screws measure around 0.410. I don't remember 5/16 off hand.

A center cutting end mill would work the best. Use coolant if your using a high speed steel cutter, if using carbide, no coolant, only air blast. Carbide works a little better with a little heat. The best way to add coolant if using carbide is to flood it.

All 2 flute end mills are center cutting, 3, 4, 6, etc... flute endmills may or may not be. Drilling a center hole first to relieve the pressure of the center cutting will help out a lot. A 2 flute will leave a better finish in a hole than a 4 flute. There isn't much room for chips, and the 4 flute will eat the chips more than the 2.

As was said, there are many ways. You can flat bottom a drill bit, ugly hole, not round. You could doctor a reamer, but why remove the cutting edge?

I'd go with an endmill.

Jamie
 
Ive used both a modified reamer which work's great for both wood and metal as well as a wood cutting spade bit . i just re gring them to flat cutting it takes about 5 min each .you can also re grind a drill bit to do the same thing but it will want to grab more than say the reamer .if you use the drill bit use something over it as a stop , a piece of brass tube work's well . if you go the end mill route pre drill the hole fisrt to prevent it walking around the hole you want . Good luck to ya !
 
Dan Gray said:
yes the end mill, two flute if you don't have a hole first, or a four flute
will be smoother (with a hole.)

if you have a hole and want to line the counter hole up to it
place a drill (twist) bit in your chuck the same size as the hole you have,, use it as an
alignment pin (or a pin of the same size) then clamp the piece down
then use your end mill.
there are countless ways. :)
Click to expand...
to add to this..
more..


it won't walk it will brake first if walking happens with an end mill the part is moving..
if you're not sure use the two flute end mill.

I still think the four flute will make a cleaner (round) hole due to less chatter , blow the chips out..
but you'll need the center hole drilled to use it.
but in most anything other than steel I'd point you to the two fluted end mill to be safe.. also using a mill you can cut holes on a finished handle
unlike modified drill bits and the like , and remember stops on the drill bits will mare your surface..you can use size blocks to jack up you parts for the deeps you need, just set up the spindle so it bottoms out at contact with the end mill
then place the size block under the part hence the depth you'll get or get a V mill :D
 
Dan Gray said:
I still think the four flute will make a cleaner (round) hole due to less chatter , blow the chips out..
but you'll need the center hole drilled to use it.
Click to expand...

Unless you have a center cutting 4 flute. Not very hard to find. I'd still drill a center relief hole though.

I mainly use 2 flute for pocket work to get a better finish. I'll go with 4 flute for about everything else, higher feed rates with the same chip load than a 2 flute.

Of course it also depends on the accuracy. The intended use wasn't mentioned, so finish may not be an issue. When I'm making dies, I don't worry about finish on counterbores for springs, but I will for other parts. (Of course for those I usually either edm them or jig grind them.)

Jamie
 
Blinker I did assume that you were making knives only and would be mill/drilling wood or the like
and using a drill press.. I use an older Vertical nee mill with DRO myself but I try to make my suggestions here as simple as I can for all who see this here..
but you know what happens to someone that assumes.. :footinmou :)

I hope this helped Blinker as well as all the rest that had input.and if you are in the area, if you'll like lessons in machine tool/ing also, let me know
I'd be glad to help.. you're welcome to my machine shop for some tips anytime.. :) as well as anyone else here.
 
Keep in mind, folks, that the ends of off the shelf end mills are ground at a 3 degree convex. In other words, the ends slope in towards the middle 3 degrees. These will not leave a flat bottom.

In the shop I work in, we use end mills for counterbores. I grind them to 1/2 degree, and they leave almost a flat bottom. The 1/2 degree is so there isn't too much engagement, and the chip can clear the end better.

To answer a question I'm sure will arise, I am a journeyman tool and cutter grinder in a large machine shop. My avatar is me at my grinder O.D.'ing some end mills.

If I can help, let me know via email.
 
Dan Gray said:
Blinker I did assume that you were making knives only and would be mill/drilling wood or the like
and using a drill press.. I use an older Vertical nee mill with DRO myself but I try to make my suggestions here as simple as I can for all who see this here..
but you know what happens to someone that assumes.. :footinmou :)

I hope this helped Blinker as well as all the rest that had input.and if you are in the area, if you'll like lessons in machine tool/ing also, let me know
I'd be glad to help.. you're welcome to my machine shop for some tips anytime.. :) as well as anyone else here.
Click to expand...



Dang Dan,
I wish so much that you were closer. I would come hang out with ya in a heartbeat. I've been dying to find someone who has tools that I don't have, and knows how to use them, to come hang out with, in my area.
Why do all the sweet opportunities arise so far way?.... Oh well...
 
razorhunter said:
Dang Dan,
I wish so much that you were closer. I would come hang out with ya in a heartbeat. I've been dying to find someone who has tools that I don't have, and knows how to use them, to come hang out with, in my area.
Why do all the sweet opportunities arise so far way?.... Oh well...
Click to expand...

someone to play knives with adds a lot of motivation too.. :D

Code 3 good point I didn't think about.. that's what this is about.. :)
 
Great stuff guys Really apreciate the help.
Wondered why I wasn't getting any Emails on this thread it sure helps to remember to turn on the "Notification" when posting :rolleyes:
Holes will go into steel as well as G10. Makes sense to drill it first and clean it out with a mill.

Yes I will use a drill press untill fundage permits a Mill (LOL)
Once again this great bunch comes to my rescue!
THANKS
 
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