Secret to using pure carbide drill bits revealed

[MrAl]

Hello,

Recently (somewhat so anyway) i had another carbide bit break off while hand drilling something.
This time was very different however.

What usually happens is the bit fluted part breaks off right up to the shank, so there is no flute
left to grind to a new point and reuse the bit. What happened this time however was the
bit fluted part broke right in half, which left about half of the fluted part still connected to the
shank. The break was quite nasty, almost left the fluted end in a diagonal across the flute rather
than a straight across break which would allow it to be easier to sharpen. In any case i was
able to sharpen the bit again using the Dremel.
The sharpening was a bit difficult because this was a number 66 drill bit (typically used for ic pin
holes) so i ended up with one half of the flute (cross section) sharpened as a new drill bit would
be and the other half sharpened as a reverse direction drill bit would be (not correct). Even
though one half of the cross section of the flute end was sharpened the wrong way, the center
was still pretty close to actual center so the bit drills through PC board material pretty nicely.
It seems like it would be harder to break this way too, with the flute length only about a
quarter inch now when normally is is at least one half inch long and breaks easy.

I will be using it in the future quite a few times but right now dont have any holes to drill
so this shorter fluted length being stronger theory has not been tested yet.

See the idea here is if this actually does make it stronger and thus harder to break that new
bits could be cut off half way and resharpened, making a stronger bit and last longer.
Of course it is also possible to cut it off so that only 1/8 inch flute remains, as it only
has to go through 1/16 inch PC boards (or thinner).

Im pretty sure i could guess what a finite element analysis on the three bit sizes would show,
but i was hoping for comments involving actual real life trials, or even ideas.

Any ideas about this; that is, do you think it will be harder to break with only 1/4 inch fluted
section as opposed to the full 1/2 inch (or longer) normally fluted section?
Or 1/8 inch flute remaining might be better?
Of course if you have tried this in the past already please comment.

[Robert Reed]

My take for what its worth. I have found that if the drill bit does not enter exactly perpendicular the bit has a 10 fold chance of breaking. Also it should be fed with a light pressure so as not to warp the shank under load. Any angular offset at any location on the shank and it will probably break. I agree that the shorter bits will get around this problem - but, if too short then visibility becomes a problem. I use a floor mounted machine with a 5/8" chuck, so I probably need to have 1" of bit exposed so as not to obscure vision upon entry. smaller chucks and/or dremels would accept shorter bits before visibility becomes a problem. Also high quality tool steel bits are less prone to breakage tha solid carbide ones. I still break a bit now and then but not to the frequency where it becomes a nuisance.

[MrAl]

Hi Robert,


Thanks for the comments.

I might start using HSS bits again as i use them sometimes anyway, but this recent
breakage brought up the possibility of using carbide bits in a more convenient way
so i thought i would ask around to see if anybody ever did anything like this.
I like the carbide bits because they drill so fast into the board when the HSS
seems to take much longer or require more force to get them to go through.

Visibility isnt a problem for me because the shank is tapered near the start
of the flute anyway, so even with a short short flute i should be able to see
it ok.

Wow, a big drill press, you use that for tiny bits like #66 too?

[Robert Reed]

Yes it is overkill but I can manage the small bits with a prior center punch for guidance. I also use very small machinists starter bits to 'spot ' the holes occasionally. I know there are better tools out their for the job, but I guess it all comes down to what one has at hand and is familiar with. One note of interest is a commonly accepted fact that HSS will take a sharper point than carbide tips. However it won't hold that point as long as carbide will. The problem I have run into is that the term Tool Steel is used rather loosely these days. If their is any reference to Asia on the package - forget it. I am still using a complete set of Good HSS drills made by the Cleveland Twist Drill Co. which are now going on 35 yers old, and exept for regular sharpening have performed quite well. Carbide for all its attributes is still a very brittle material.
With your visibility allowing the short shank drills you are using should really alleviate breakage to a large extent though.

[CeaSaR]

Quotes:

"5/8 chuck" and "Wow, a big drill press, you use that for tiny bits like #66 too?"

Sounds like the Tim Allen guide to PCB drilling!

So far you guys have pretty much hit the general physics of the shortened "tiny" bits
in that they flex easily and need to be perpendicular for proper operation. Also, they
cannot be pushed hard at all, as a bend or warp will only hasten breakage due to the
cutting edges not meeting the material properly, requiring more force to engage, causing
even more deflection, etc. A vicious circle. The best way to ensure longevity is to:

a.) Keep the bit sharp
b.) Keep it perpendicular
c.) Do not exceed recommended pressure
d.) Keep the bit cool

I have several smaller bits (between 1/8 and 1/16) that broke along the flute. I kept these
and use them for pilot holes. These bits can withstand greater pressure do to the shortened
flex length. They are great for what I use them for.

Lots of times I will use a finish nail to for a pilot drill. The super sharp point drills into any
hardness of wood. I only broke 3 when I refastened my 100 year old yellow pine floor simply
because they overheated.

CeaSaR

[MrAl]

Hi again,


Robert:
I guess i sounded a little surprised because i would have thought that a bit
drill press like that would be made for bits 1/16 inch and up, and would have
a little too much play to be used with bits as small as #66.
I do like the HSS types, but the last one i got at the hardware store dulled
down so fast it wasnt funny. I am in the process of getting more though,
different make, to try.
I like carbide because they seem to drill through so fast and with little
pressure, especially the #75 size.

Ceasar:
I've used a pin to drill dip package pin holes before, but it causes what
i call the "Ant hill effect", which causes a pile up of material (copper)
around the hole, which i dont like. It does work though, and i even tried
one with the point sharpened like that of a regular drill bit, and it
worked a little better. I still like the carbides best though, except for
their tendency to break when the wind blows

I've also tried nails in the past for drills, and the hardened ones (like
for concrete) work really nice when they are sharpened to a point, and
even make nice small center punches too. Sharpened to a chisel point and
they make nice little chisels for removing odd bits of copper from the
top of circuit boards after etching when some small parts get left on the
board. Takes it right off.

I use those stainless steel screws now for flooring, especially outdoor
deck flooring, because they dont rust. They also have a well formed
square inlay head that accepts a square shank driver bit...much better
than phillips head or slot head screws. Holes the deck flooring down
even in winter when the water freezes into ice and expands and pulls
regular nails right out of the floor joists below...which would need
pounding again come spring. The stainless are more expensive but they
probably last forever. Three inch size never come out

[Lenp]

In a previous thread I mentioned that I used the carbide bits with very little breakage in old bench drill press with a 1/2" chuck. A good drill chuck and low shaft runout is the real key to success. Many drill presses on the market today have cheap chucks so consider an upgrade. Years ago I tweaked my press's Morse taper spindle/chuck fitup for minimum runout by cleaning and polishing the parts and after finding the optimal chuck position, using Locktite to keep it there.

Any side loading and the bit's history. Hand holding, with a Dremel or otherwise, is nearly always an excellent broken bit generator. I do break some bits though, by moving the board before the bit's cleared or the little pesky critters will fall on the floor, which they nearly never survive.

Hint:
All is not lost though. The broken bit shanks can be repointed and used as a stylus for a vibrating engraver, or in a pin vise as a scriber.

Len

[Dean Huster]

I don't break carbide bits unless they're getting dull (whereupon they start to pile up the debris a la the "anthill effect" as previously mentioned. I don't use them in any drill press designed for massive bits. I certainly don't try to use a Dremel by hand. My Dremel mounts in the drill press stand made for it. I use a collet, not a 3-jaw chuck in the Dremel. I make sure that the board is as close to the end of the bit as possible so that the "head" doesn't have to be extended any more than necessary which would create unnecessary play in the "quill".

Dean

[MrAl]

Hi again,


Len:
Yes i dont know how you get by with such a large drill press. I guess it is very
precision compared to the one made by Dremel for its Dremel tool. That one is
quite nasty really, and when it is tightened up then it's hard to feel how much
pressure you are putting on the bit itself. I suspect a bit of forward wobble
too which means after the bit punches through the other side it will try to pull
the bit backwards toward the rise post, which will surely break it.

Yes, all is not lost, but now i have plenty of styluses for engraving, or scribes
for scribing One thing for sure, i wont run out of styluses he he.


Dean:
The drill bit starting out close to the board sounds like an interesting idea.
I might have to try that with the more recent stand made for the Dremel.
I know they discontinued one of their older type drill presses.
What kind of drill press are you using, and do they still make that one?

[Dean Huster]

Mine was actually the Craftsman version of both the "Dremel" tool and the drill press stand. Both are made for Sears by Dremel and all Dremel accessories fit fine. They were bought around 1997. The tool is shot right now because the brass thingie at the end of the armature that inserts into the plastic coupler (a high-failure part) is broken. I need a new armature. I don't think it's worth replacing, although I haven't checked prices yet.

The "perfect" drill press would be a 1/8 hp, 3250 rpm motor with a shaft that's big enough that it can be turned, center bored out and threaded to accept standard Dremel tool collets mounted in a homemade double-tube slide with rack-and-pinion drive.

Dean

[MrAl]

Hi again,


Sounds like i would be better off constructing something to do this with rather than buying
something already made.

I had also considered the simplest of all possible construction: a hinged arm with Dremel
attached to the end. When the arm is 'folded' down, the bit makes contact with the
work which lays flat on the bench. The movement only has to travel 1/4 inch so the
run out due to the curvature of the motion of the end of the arm would be almost
negligible. Might work for thin boards like PC boards.

The key design points would be a very wide hinge with very little play in the axis,
and as long an arm as possible with no tendency to bend or warp in any way.
This could be done so that the drill bit movement is guided with relatively high precision.
Would be interesting to try.

[Robert Reed]

Hi Lenp
As To:
"In a previous thread I mentioned that I used the carbide bits with very little breakage in old bench drill press with a 1/2" chuck. A good drill chuck and low shaft runout is the real key to success. Many drill presses on the market today have cheap chucks so consider an upgrade. Years ago I tweaked my press's Morse taper spindle/chuck fitup for minimum runout by cleaning and polishing the parts and after finding the optimal chuck position, using Locktite to keep it there."
Could you expand a little on this item. I am interested in attempting the same thing.

MrAl
Yes , a ridgid hinge will be mandatory. I have found that the "piano" type hinge is quite wobble free. Sounds like a neat idea. Be sure to let us know how it works out.
Oh and one more thing in regards to my large drill press is that I never drill smaller holes than #58 or pitches smaller tha 0.1". Hope I didn't mislead you on that reply.

[MrAl]

Hi Robert,

Oh i see...the #58 bits are about 50 percent thicker than #66 and 100 percent thicker than #75.
I think they hold up better because of that so maybe they wont break as much.
The #66 break pretty easy and the #75 break when the wind blows

[Lenp]

Robert,
The first thing to do is to determine if there is wear or slop in the quill bearings. Insert a length of clean round ground steel shaft stock 6" or so into the chuck. Set up a dial indicator to measure the distant end of the shaft while you apply lateral pressure to the chuck, not the rod. The amount of deflection will indicate the wear or movement in the bearings. The side movement on mine was just a few thousands. The only cure for this, if it is excessive, may be to replace the quill bearings. One option may be to index and then rotate the spindle bearings in theor assembly to average or cancel the runout.

Many commercial presses use a Morse tapered chuck mount. If yours uses a threaded chuck there may still be some hope, so follow on. Use the same set up as above but now turn the chuck by hand to measure and note the largest run out. Remove the chuck, using a wedge or what ever means your machine recommends and measure the quill run out. It will probably be way less because of the chuck or the measuring position on the quill, but, it gives an idea of the quill’s health.

Clean the inside and bore of the chuck with solvent to remove any debris and lubricate the chuck jaw mechanism. Be sure the jaw faces are clean. Use light oil inside the chuck but don't oil the bore. Oil in the bore might not allow the tight fitting tapers to seat properly. Polish the bore and drill quill with crocus cloth and wipe clean. Wipe a very light skim of oil on the quill, not the bore and reinstall the chuck, without setting the taper tight.

Reinsert the shaft stock with reasonable tightness and measure the run out again. By rotating the chuck on the quill, you may be able to locate a 'sweet spot' where the chuck and quill errors cancel, and run out becomes less. Make a witness mark on the chuck and quill to show their positions. Remove the chuck, clean the bore and quill and reinstall at your witness marks. I used a skim coat of Locktite on the quill but that is optional. It holds the chuck for nearly forever, but, makes it a bear to remove it if ever necessary.

Now, if yours is a threaded chuck the run out may be worse than any tapered chuck and there may be little that can be done. I feel that threaded chucks belong on hand drills not drill presses, but that's only an opinion. Measure the quill run out, and play as above, but insert a thin shim between the dial indicator and the threaded quill so the indicator point doesn't bump on the threads. Since there is considerable play in the threads of these chucks, the most probable cause for a bad fit and run out, aside from a bad quill or bearings, is the flat mating areas on the quill and chuck that contact when the chuck is tightened, Clean and polish these but be careful not to change any angles by excessive effort. Since the chuck cannot be rotated for adjustment I would suggest trying hard fiber shim washers between the chuck and quill. It may improve the run out since, in effect, you are increasing that space and rotating the shaft-chuck thread engagement position. Being somewhat soft, the fiber washers may average any high spots and improve it. Maybe soft metal, like a copper automotive oil pan drain plug seal, or, dare I say it, lead, would work! The down side is that if you use the press for drilling big holes in railroad tracks it will probably destroy the shim washers in a short time!

The last thing to check is to be sure that the press table, which can be rotated on some presses, is 90 degrees to the chuck. A square and the shaft stock can be used to check and adjust this it if necessary.

Not all presses are equal and it may not be possible to improve the accuracy so maybe a replacement chuck might be in order. In any case, runout less then about .006" is generally hard to acheive with a jaw type chuck. For greater precision, a colet chuck is required, but may not be available or adaptable to a common drill press.


I find that a high drilling speed fro these carbide bits is best since it reduces the tendency to increase feed pressure. A little slacker than normal belt also helps to minimize any motor vibration transmitted to the quill.


Good luck, I hope this helps.

Len

[Robert Reed]

Lenp
Thanks for that execellent and thorough information. Mine does use a Morse taper and the table is adjustable and periodically tested for square by using the bent wire "coat hangar" method. I have checked runout occasionally, but never under load. Your reply has given me a good insight on methods to check and hopefully cure any problems. First chance I get, I will put them to work.