Drill bits for metal and using them properly

[Al Smith]

I have no idea who made those carbide bits .Titanium coated .I think they were used to drill oil holes in steel automotive engine crankshafts .Ford motor company .For me they were just free salvage .I've got larger solid carbide bits but those are in my shop .I've used those to drill the heads from 3/4" socket head grade 8 bolts from brush chippers .Once you get the tension relieved on the bolt under a situation like that you can "peck " it right out . BTW it's not a 5 minute job .
In the CNC application I think those went into a holder that acted like draw collett and those into the spindle with a locking device .When they changed the tools it was as a unit not just the bit .In my use it's just in a 14 N Jacobs chuck .In the Bridgeport mill that's held in the spindle with a threaded drawbar system .

 

[Al Smith]

Off the subject a little bit .Oak contains tannic acid which will do a number on high carbon steel bolts .As a result eventually it etches away at the socket head bolts ..You are better off on a knife change of brush chipper knives is to use new bolts .Those I think were 3/4" 16 2.5 inches long or about 2 dollars a bolt times 16 .A lot better option than spending a couple hours drilling out the bolts .The last I did I gave the guy enough bolts for two knife changes plus a can of never seeze and a couple carbide bits because that was the last I'll ever drill them out .He must have taken me seriously because he's never called me since .

 

[srcarr52]

I use a diamond laced grinding stone dresser to get a sharp corner on my wheel - yes, it can be tedious if the wheel is f-ed up.
I can get some pictures, I'll look into it.

What did I send You, HSS-Co or Solid-Carbide?
I can't recall, sorry.
I am glad You are getting some use out of whatever it is I sent You.

HSS-Co drills and some nice taps, mostly spiral flute.

 

[Wilhelm]

Turkey oak sap smells like cat pi$$, and does so for years of seasoning.
I kinda got used to it over the decades, but it is certainly an acquired smell.

 

[Wilhelm]

HSS-Co drills and some nice taps, mostly spiral flute.

Cool, thanks for the reminder!
I thought it might have been HSS-Co since You also mentioned taps.

 

[Nutball]

That is close, but You made a rookie mistake.
1) Do not grind the "cross cut" so deep that they intersect! On a 1/2" drill bit leave an about 1mm untouched center (circled in red) otherwise You risk breakage of the weakened center thus losing the bits tip.
2) Grind the "cross cut" a little further into the cutting edge so that You get a secondary cutting edge which will also be more resilient to wear (blue lines)

But You get the idea.

View attachment 359964

I had another drill bit in front of me I was trying to copy. From what I remember, it also was ground like how I did mine, but though it was an individually bought more expensive bit, it still probably wasn't the high end stuff like you are used to. I'll try those suggestions. I just thought that there shouldn't be any non cutting surface in the middle of the tip, so I intentionally intersected, but then I guess they cancel out sort of, so I might as well leave a bit of untouched center. Also, I wanted to grind all the way to the peak of that line so there would be a cutting edge and not a simulated dull edge (like filing chainsaw teeth too low to actually sharpen the top edge).

 

[r7000]

I didn't read all the posts, but when drilling "metal" you have to really the know or be sure of the metal you are drilling into. Because if what you want to drill into is a tool steel type of steel, which is as hard or harder than your drill bit, then the bit won't cut and the bit will lose. At the very least it'll cut a fraction of an inch and then be done.

So you can't just go to depot/lowes/wherever and pick up the most expensive type drill bit with the fanciest package and expect it to drill through any metal, you may have to mail order from a reputable supply place a "real" drill bit to cut through the metal you are working with. For a Stihl bar, I don't expect that to be soft easily cuttable A36 steel. The Stihl bar is also going to be hardened, to allow the chain to ride on it without wearing the bar in short order.

As for using the right bit properly... straight inline pressure, moderately appropriate pressure, do not over pressure the drill bit into the material, allow the bit to cut, don't overspeed the bit to smoke the bit, better to go too slow spinning the bit to take longer to cut through than overspeed. Use a cutting lubricant when appropriate, to keep the bit and material from overheating. The goal is to cut through, not melt through. Read up and familiar with all the different types of steel and alloys, as well as drill bit material and what drill bit material can and can't cut what.

 

[r7000]

larger diameter bits need to spin slower, relatively speaking, than the smaller bits because the outside diameter of larger bits spins faster.... mathematics... so often a larger 1/2" or 3/4" drill bit you can easily overspeed... watching it spin thinking oh i can go faster.... don't. there's probably published recommend rpm for bit sizes... generally once it seems to be cutting acceptably and generating nice shavings that's fast enough, then you use good judgement to make sure the bit and material is not overheated.

 

[Squareground3691]

HSS-Co drills and some nice taps, mostly spiral flute.

Left hand spiral , right hand cut , yup as Shaun said are better than straight flute in cutting action, and tougher alloys .

 

[Al Smith]

For a large hole you are better to "step " cut with several sizes of drill bits .Increasing size and decreasing speed of rotation .As long as it is feeding out a chip it's removing the heat with the chip .One of my large drill presses that came over on the Mayflower has feeds and speeds for bits up to 3 inch .I've got drill bits over 2" but have never used one .

 

[Wilhelm]

Left hand spiral , right hand cut , yup as Shaun said are View attachment 360085 better than straight flute in cutting action, and tougher alloys .

That one "pushes" the chips down into/through the hole being tapped.
Also, as it is that tap is not suitable for tapping blind threads/holes.

These carry the chips out to the top of the hole being tapped.


Also, the one on the left is suitable for tapping blind threads/holes.
Whereas the one on the right is excellent/suitable for tapping aluminum as it has much sharper polished cutting edges compared to the black/left tap - but it dulls much faster tapping steel and it is not suitable for processing blind holes.


I have posted pictures of the black tap in action in the chips thread.

I won't even bother with posting pictures of straight flute taps.

 

[Wilhelm]

For a large hole you are better to "step " cut with several sizes of drill bits .Increasing size and decreasing speed of rotation .As long as it is feeding out a chip it's removing the heat with the chip .One of my large drill presses that came over on the Mayflower has feeds and speeds for bits up to 3 inch .I've got drill bits over 2" but have never used one .

True!
Tiny OD drill bit needs high rpm whereas a big OD drill bit needs to turn slow.

 

[Squareground3691]

That one "pushes" the chips down into/through the hole being tapped.
Also, as it is that tap is not suitable for tapping blind threads/holes.

These carry the chips out to the top of the hole being tapped.
View attachment 367753

Also, the one on the left is suitable for tapping blind threads/holes.
Whereas the one on the right is excellent/suitable for tapping aluminum as it has much sharper polished cutting edges compared to the black/left tap - but it dulls much faster tapping steel and it is not suitable for processing blind holes.
View attachment 367754

I have posted pictures of the black tap in action in the chips thread.

I won't even bother with posting pictures of straight flute taps.

That one works well in titanium and harder stainless steels .

 

[Wilhelm]

That one works well in titanium and harder stainless steels .

In nearly 30 years of metal working I haven't had the pleasure encountering a tap of that style.
Interesting design!
The left-hand flute gives the cutting edges different angles than a right-hand flute tap has - so many things that seem negligible yet they make all the difference.

 

[Squareground3691]

In nearly 30 years of metal working I haven't had the pleasure encountering a tap of that style.
Interesting design!
The left-hand flute gives the cutting edges different angles than a right-hand flute tap has - so many things that seem negligible yet they make all the difference.

The pressure angle is reduced a lot with left hand spiral.

 

[Wilhelm]

I used a tap identical to the black one posted above to cut threads into ISO 12.9 grade bolt steel (~ SAE ASTM A574).
Out of 6-7 different taps that I have in M5x0.8 only that ONE made it through the 12.9 steel several times and survived - I almost gave up on getting those threads tapped.

 

[srcarr52]

That one "pushes" the chips down into/through the hole being tapped.
Also, as it is that tap is not suitable for tapping blind threads/holes.

These carry the chips out to the top of the hole being tapped.
View attachment 367753

Also, the one on the left is suitable for tapping blind threads/holes.
Whereas the one on the right is excellent/suitable for tapping aluminum as it has much sharper polished cutting edges compared to the black/left tap - but it dulls much faster tapping steel and it is not suitable for processing blind holes.
View attachment 367754

I have posted pictures of the black tap in action in the chips thread.

I won't even bother with posting pictures of straight flute taps.

If a straight flute tap doesn't have the angled spiral point it's a glorified thread chaser. Sure you can tap a few holes with them in a pinch but you're always tiny bit or torque away from disaster.

 

[Wilhelm]

If a straight flute tap doesn't have the angled spiral point it's a glorified thread chaser. Sure you can tap a few holes with them in a pinch but you're always tiny bit or torque away from disaster.

Ya gotta work on Yer pullout game wif thems!

 

[srcarr52]

Ya gotta work on Yer pullout game wif thems!

Seems like there is never enough lube with them either.

 

[Wilhelm]

The grind on straight flute taps is pushing the chips down.
This is why they are unsuitable for tapping blind holes and why they seem to always be short on lube.
But their design makes them the simplest and most cost saving to manufacture.