Enlarging a drilled hole, best procedure?

Not reading any replies, take it to a machine shop. Seriously find one that does odds and ends jobs not production runs, they are pretty reasonable. I got some bolts machined for the lower a-arms on my 57 ford, cut to size, bored and tapped, for less than what the only guy to sell new ones would've charged for them. $25 to do the 2 bolts.

 

-One quick note: "Cobalt" does not make a drill bit harder. Cobalt simply makes a cutting tool resist wear a little better at elevated temperatures.

It's useful in an industrial setting, but to the average shop guy like most of us here, at best it helps the drill simply stand up to a bit more abuse, a bit longer.

But it is not "harder", the cobalt does nothing to help the actual cutting action.

Unless it's solid cobalt, of course. But really, you'd be lucky to even get the 3% to 8% cobalt a drill needs to actually be stronger, in a box-store bubble-pack. Cobalt is extremely expensive, and if adding, say, .01% instead of 3% still legally allows them to put the word "Cobalt" in 72-point type on the package, but still mark it up by 50%, hey, why not?

Doc.

 

In my experience, every HAMB'er has buddies with the "tools". Hook up with your machinist buddies and borrow a "Die Drill" bit. The best bit for reaming or core drilling. These things love the RPM's. I have used them to scary RPM's where they have been lit up cherry red and they cut like butter. Hell, if you were near by I'd lend you mine. Regards, Rhys.

 

When I need to drill a hardened material or even when trying to drill out something hard I buy a cement drill or masonary bit. I usually touch up the end on my grinder to make it better but you dont have to. A a masonary bit will drill thruogh almost anything and it realiivety cheap. (less than $10.) Home Depot is where I bought the last one.
It is an inexpensive practical solution to this problem.
Don

 

Pishta, die grinders are only about $10 at Horrible Freight
and you said you have a carbide burr.

 

Best for application IMO is low SFM with one of these:
(bottom of page)

http://www.sowatool.com/catalogue/pdfs/DrillsReamers/p155.pdf

 

Yeah, cheap, but no air compressor. I got a Makita at work that goes down much lower than my "hobby press" And I can put some weight on it for future big hole jobs. I got them both drilled late last night. Drill, sharpen, temper, repeat. Thanks for all the constructive help guys. "Get a better hobby.." thats pretty funny..Yo JC, Maybe HO scale model trains? See you at the next convention.

 

The formula for machine tool speed is RPM = CS x 4/D. Which is cutting speed (100 for mild steel) x 4 all divided by tool diameter. Which puts you around 700 RPM, this is too fast for something hand-held and not locked down.

If you have a drill press, line up the hole with the spindle, clamp the part down to the table. Chamfer the hole with a countersink to the size you want to drill or a bit bigger is fine.

I'd go with something slower like 400-500 RPM, use some cutting oil and you should be able to drill the hole to 9/16 in one shot. Reamers are only meant to remove 1/64" of material maximum.

Best of luck, hope this helps, always good to make friends with people that work in or own machine shops!

Bob

 

Just a thought for the future: never modify the part that would be changed during maintenance. In other words, it truly would have been better to modify the arm, rather than the ball joint, since the ball joint will need replacement, and do you really want to do this every time you replace ball joints?? Even if it's only one more time??

Cosmo

 

Remember....speed burns...feed breaks. At the correct feed/speed, a decent drill (bit as some say) will do hundreds of holes like this. Like someone said earlier, adjust the feed/speed until you get a nice curly chip. If the press is too fast, you are wasting your time. All you will do is rub the edge off the drill as soon as it starts cutting. BTW...you can't ream that much.

 

Take your time and give a rat tail file a try.

 

I was thinking the same thing. Have your considered using a helicoil or thread bushing to bring the threaded hole down to 1/2"? Maybe even just drill it out and use a bushing to size the hole and a bolt and nut like the drum set up used.

 

The general rule for reaming/enlarging a hole is half the speed and twice the feed of standard drilling applications. The old guy in a previous post knew to grind his drill to closely resemble the cutting edge on a reamer as shown here to get it to work:

http://www.bssa.org.uk/cms/Image/Speeds%20and%20feeds%20for%20drilling%20and%20reaming%20stainless%20steels_3.jpg

 

bobss396 has the right formula to get started. In a situation such as your in, I would use a cutting speed 65-75 max because of the drill bits.

Most people don't realize that you can't run high speed steel too slow, but you can feed it too hard, that increases your chip load. By running it slower will be less likely to have it work harden or knock the cutting edges off your drill.

Setup is everything, rigidity, rigidity, rigidity.... As everyone has eluded to, hold it down tight, go with a low RPM, and don't feed it too hard. If it is work hardened, you will get really small fine chips, nothing curly will come out of the hole. (I said I was going to write tech on this, this is something I really need do.)

Dashman's Hot Rod & Speed Parts www.dashman.net

 

http://www.icctool.com/webdoc22.htm
Wow, only 77 bucks for the size he needs... Not sure I'd loan out a $77 solid cobalt bit. Sorry...

Pishta,
Find some way to drill at a lower speed, and flattening out the flute angle is a good idea for small steps up in large holes.

 

i can see its been said..but i'll say it again..slow it down, yer going waaaay to fast

 

Opening existing holes in steel, go slow and peck away at the hole, don't try to do it in one shot.

Bob

 

Get a reamer and stop f..... a round

 

Reamers aren't designed to take as big of a bite as going from 1/2" to 9/16". 1/64" max, certainly not 1/16"

 

What he said which is why I suggested a core drill. Here's some reaming guidelines to back that up:


http://www.cjtkoolcarb.com/catalog/Technical/reamertechnicalguide.htm

 

Here's another vote for taking it to a machine shop. They'll likely charge you less than what a proper bit will cost.

 

Even my wife sends people down to have me do minor machine shop work for them. If you were local, I'd say, come on down! Just about any small shop would do it for next to nothing or nothing.

Bob

 

Just buy the right fuckin ball joint and be done with it!

 

Uncalled for