drill bits

[deereman64]

Looking for advice. I'm trying to use my old mowing blades and this means drilling some holes in them. I have a drill press and I bought a titanium drill bit from Lowes. The drill was blunt almost immediately I bought the most expensive bit but do I need a professional to drill for me?

 

[Scooby074]

You should be able to drill it.

Keep your speed on the slowest speed. Lots of drilling lube like RapidTap or equivalent.

Also, the bits at most of the box stores are crap. Avoid the Chicom stuff. Get yourself a good set of Trimuph or Clevelands. If your only going to drill a couple holes, go to a industrial supply house and get the size you need. If the blades are real hard, you might have to get a Colbalt or Carbide bit, but id try a good quality HSS bit first.

Also, dont underestimate the benefit of drilling a pilot hole first. This can go a long way to being successful and keeping your drill sharp longer.

 

[JoelD]

Obviously first responder to your post knows his stuff.

I concur with all he said.

Pilot hole particularly good point, makes a huge difference.

I own a drill doctor and would've spent 10X's the cost on drill bits without it.

I've had good luck with craftsman HSS bits.

Joel

 

[deereman64]

thanks for the advice

whats a drill doctor?

 

[Scooby074]

A Drill DR is a electric bit sharpener. I have one. I highly recommend it especially if you invest in quality bits. Some others arent crazy about it, but it does a pretty good job and is relatively idiot proof. Unless you were taught how to sharpen bits by hand and do it frequently, the Drill Dr will likely do a better, more consistent job.

Theres a fair number of posts on the Drill DR here on TBN. They usually end up like the Deere vs Kubota threads with people on one side or the other

 

[JRP]

Here is another thought:

Take a good file and see if the file will cut the steel, or just skids. It the steel is hardened the file wonk cut nad you must anneal the steel.

If it cuts, use the above advice. The drill speed should be not more than 400 divided by the diameter, and slower for hard material.

To anneal the part, heat where you want to drill with a torch until it is approaching red, then let it cool slowly. This will remove heat treatment and soften the metal.

 

[JRP]

I forgot to add:

If the tip of your drill bit has changed color, like it got dark then it was annealed by the heat and has softened. Throw the drill bit away.

 

[rcrcomputing]

Great thread!

So, why do some of you like HS bits rather than titanium or cobalt?

And by pilot, do you mean for a 1/2 hole, drill a 1/8" hole first?

And.... Just to make sure I've got it... If I use a 1/2" bit, go max 200 rpm?

 

[Scooby074]

Great thread!

So, why do some of you like HS bits rather than titanium or cobalt?

And by pilot, do you mean for a 1/2 hole, drill a 1/8" hole first?

And.... Just to make sure I've got it... If I use a 1/2" bit, go max 200 rpm?

Most of the Ti or Cobalt bits commonly available are just thin coatings. IMHO they dont add any life to the bit after the first sharpening by the user. After the coating is gone, you essentially have a regular HSS bit, thats only as good as the steel that made it. so your further ahead by buying a quality bit made from quality steel, rather than paying for a miracle coating.

A solid cobalt or alloy and carbide bits are a different story. With them you have the benefits of a stronger material for the life of the bit, but at the cost of increased brittleness and much higher price. I 'd only use these in a situation where they were required (ie: hardened steel)

Drill speed can be a pretty complicated calculation that can depend on several factors. Yes 200RPM for 1/2" would be ok, but to get the more precise speed for a specific steel you can look here : Machine Shop 1 Drilling Machines

For pilot hole size and steps theres a formula somewheres that slips my mind now. I usually start with 1/8. Starting small helps in getting an accurate hole position. then 1/4. then 1/2. Those would probably be the largest steps you should do (maybe even too large <50% would be more ideal). You can be as granular on the steps as you want. All you lose is time. The idea is to not overload the bit by taking small increments. Taking small steps also can result in more accurate and "rounder" holes.

Another consideration is feed speed. A general rule of thumb is "High speed / Low feed" and "Low speed / High feed". in other words, small drills = high speed = low feed rate

 

[oldhippy]

Drill bits on tool steel (which is what have your) blades are will work harden if you stop as you drill. When you start to drill keep a steady speed and don't stop until you drill all the way through. If you are going to drill in the same holes that the drills burnt up in then they will be hard. If you have to drill in the same holes you may need to apply more pressure when you start. I will kind of bounce a drill bit in a hole when it is work hardened to get it to break through the hardened surface and get to the softer surface underneath. Hope this adds to the good comments made by fellow tbhers in this post. Lots of luck big dan