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Driling through steel- need bit reccomendations

nevetsw18

Active Member
Greetings!

On my Onex (not RV related but figure it can help other builders in search of quality bits) project I have to drill 4 holes through a 1/2"-3/4" stack of steel plate in the wing fold mechanism. I bought a cheapish "U" size bit being that I only need it for 4 holes, hole #1 took me forever with a ton of lubricant and I'm pretty sure my neighbors at Hicks could hear my choice words from a few taxiways away.

Can anyone recommend a specific company or type of bit that could speed up my drilling? Willing to spend enough to get the job done the right way.

Thank you!

Steven
 
Building an airplane was full of learning and I love to learn. Leaning the proper way to drill was important with all the holes we need to drill while building. I think it was in the Van's building guide that I read the right way to drill.

The harder the metal the slower the bit speed and the greater the pressure.
It boils down to needing to get rid of the heat generated. You HAVE to create chips. These chips get rid of that heat. If you are not generating chips you are not pushing hard enough or your bit is too fast. At that point you have probably already burnt the bit.

It is more about technique than the bit. I was amazed when I learned this very simple but important part of the build.

Forgive me if you already knew this.
 
Get a copy of Machinery's Handbook.
http://new.industrialpress.com/machineryhandbook
Buy one from a yard sale or used from epay or amazon etc. They are the Go-to book for everything machinery, tool, etc.
I've got a 20th edition, 1976. Twist drills start on page 1655. (after reamers, which you probably want as well)
Pg1668 "Steel for Twist Drills" lists Cobalt High Speed Steel drills as capable of withstanding cutting speeds beyond the range of conventional high speed drills and have superior resistance to abrasion but are not to be compared to tungsten carbide tipped tools.
Also, learn how to sharpen drill bits.
Good luck.
 
Steven,

Attached are a couple of links to a speed and feed chart and speed and feed calculator.

Tool steels for drill bits come in a wide range of materials. Look for labels like HSS (High Speed Steel) , Cobalt, M2. Most of the Titanium nitride drills have good base steel. Avoid anything that says "Carbon Steel"

Also pilot drilling with a bit that is about the same size as the web helps on larger drills.

Hope this helps.
Alan

http://www.custompartnet.com/calculator/drilling-speed-and-feed

http://www2.mae.ufl.edu/designlab/Lab%20Assignments/EML2322L-Drilling%20and%20Milling%20Speeds%20and%20Feeds.pdf
 
You mentioned a 'U' drill size which is 0.368" diameter. This must be for a bushing as it is an unusual size for an aircraft bolt. The steel is likely 4130 which is a fairly high alloy. I highly recommend using a drill press, you don't say if you are using one. I would recommend a cobalt drill bit, and a pilot hole the same diameter as the thickness of the web on the 'U' drill. The speeds and feeds have already been covered in previous posts. Generally the harder the material the lower the speed and the higher the feed, which means lots of feed pressure on the drill press. You want to see the drill actually making chips. You probably don't need lubricant but if you want to use it consult Machinery's Handbook under cutting fluids.
 
You mentioned a 'U' drill size which is 0.368" diameter. This must be for a bushing as it is an unusual size for an aircraft bolt. The steel is likely 4130 which is a fairly high alloy. I highly recommend using a drill press, you don't say if you are using one. I would recommend a cobalt drill bit, and a pilot hole the same diameter as the thickness of the web on the 'U' drill. The speeds and feeds have already been covered in previous posts. Generally the harder the material the lower the speed and the higher the feed, which means lots of feed pressure on the drill press. You want to see the drill actually making chips. You probably don't need lubricant but if you want to use it consult Machinery's Handbook under cutting fluids.

I drilled 4130 with 118 deg and/or 135 deg HSS (high speed steel) bits throughout my build. Yes, slow speed, yes high force, and YES lubricant. Without debating which lube, I use a synthetic auto engine oil. Nothing special, really. It cools/lubes the high pressure friction in the chip making process. If it smokes, stop and let it all cool a little, or flood with more oil. If you are making curly swarf, then your speed/force is just about right. Just chips, likely too fast.

Edit: Oh - I dont use hardware store bits - I get them from machine tool supply - MSC, Travers, Penn Tool, Pan American (cobalt)
 
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A while back I had occasion to drill about 100 1/4" dia. holes in 304 stainless steel bars. I asked a machinist friend and he pointed me to Guhring Series 659 TiN Coated Cobalt, heavy duty, stub length, 130? point, web thinned bits. I bought a couple ($25 each!) from MSC direct. Those things were awesome! It appears that Guehring doesn't offer a Series 659 bit in "U" size, but this one might be just as good (and a lot cheaper). I also bought some soluble oil and a mister on Amazon and used those to cool the bit.
 
A 3/8" diameter drill bit is too large in diameter to drill without first drilling a smaller pilot hole! 4130 actually drills quite easily. Match the "dead center" width to a slightly larger diameter drill bit, (#30 drill would be appropriate to a 3/8 diameter drill), use cutting oil, moderate pressure, fairly high RPM (2,000 to 3,500), and pull drill bit out of hole fairly often (peck drilling) to allow chips to escape from around flutes. You be amazed how easily the 3/8 will then go through the steel (like butter.)
 
Wow- the braintrust is amazing

Thank you gentlemen for the helpful reading material and bit recommendations!

I should have provided more detail, the Onex has folding wings and this particular drilling is through the spar for the long pin that secures the wing in place. It's drilled and then reamed to final size.
 
"It's drilled and then reamed to final size."

A reamer will follow the drilled hole, not make it's own perfectly aligned and precisely placed hole. If the drilled hole is a mess the reamed hole will be a good looking mess :)
 
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