Making a Cutting Edge

Today I "learned" alot! haha. I had big plans of ordering some annular cutters and broaches and all sorts of stuff. Then all of a sudden its project time. So I have a set of dewalt cobalt bits up to 1/2" and a chinese set up to 1". There sure is something to be said about quality products.
My question is, what is the recomended drill bit step size? We were doing 9/16 to 1/2 to 13/16 to 1" The 1" bit was completly shot and we only managed to get one complete hole drilled all day! We got everything pre-drilled to 1/2 and 13/16" but by the end of the day the bits were ground to nubs. Which brings me to the second thing I learned about, Drillbit sharpening. There is alot that goes into that, have alot to learn there. Sometimes I could get a really good on and it would eat it up like butter, but could rarely duplicate it. Lots to learn! I'm planning on going to town next week to get some proper bits

i usually only make the pilot hole the same diameter as the flat across the point of the drill bit otherwise you can burn off the outside edges of the bit in short order. ie- approx. a 3/16 pilot hole for a 1" bit. the small pilot hole allows for a slower, more controlled cut with the large bit and i use lots of ' RELTON RAPID TAP' or similar

56wrench said:

i usually only make the pilot hole the same diameter as the flat across the point of the drill bit otherwise you can burn off the outside edges of the bit in short order. ie- approx. a 3/16 pilot hole for a 1" bit. the small pilot hole allows for a slower, more controlled cut with the large bit and i use lots of ' RELTON RAPID TAP' or similar

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Excellent, good info, that was the main problem was the outer edges kept chipping off. Ill look into that oil, I was just using generic 10w30 oil to keep the bit cool. Does the type of oil make a difference?

That Rapid Tap stuff is for real. I use it for drilling and tapping all the time. It makes it so the cutting edge of the bit or tap bites and also keeps in cool so it doesn't burn the cutting edge up.

I used to hang out with an old machinist, now deceased, he would say the reason drill bits and cutters are sharp till the center. He always used a small pilot hole also. When sharpening drill bits get a really fine stone on a small bench grinder works the best. And keep it cool.

alaskaforby4 said:

Excellent, good info, that was the main problem was the outer edges kept chipping off. Ill look into that oil, I was just using generic 10w30 oil to keep the bit cool. Does the type of oil make a difference?

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tap magic is another good brand

ok, good to know, I’ll pick some of that stuff up. My friend brought a Evolution mag drill over with a annular bit. unfortunately, he didn’t have the correct size. But it was an impressive tool. I plan on going into town next week and ill pick up a 1” drill bit and hopefully a 1” annular cutter bit with a normal drill shank, if theres such a thing. And some quality cutting oil.

alaskaforby4 said:

ok, good to know, I’ll pick some of that stuff up. My friend brought a Evolution mag drill over with a annular bit. unfortunately, he didn’t have the correct size. But it was an impressive tool. I plan on going into town next week and ill pick up a 1” drill bit and hopefully a 1” annular cutter bit with a normal drill shank, if theres such a thing. And some quality cutting oil.

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look at the spiral reamer line. they work much better than a drill bit but don`t forget the cutting oil. I think these are called carr. reamers

There are lubricants and there are coolants. Oil is a good lubricant but a poor coolant. Water is an excellent coolant and a lousy lubricant. Drilling really wants coolant with a touch of lubricant. Tapping wants lubricant with a touch of coolant. Real life is a compromise. Water with a dose of washing soda makes a good coolant. The washing soda retards rusting.

As for pilot holes, I agree with those who say the pilot diameter should be about the width of the chisel point of the next drill. Slightly smaller is better than slightly larger. If you are burning the outside corners of your drill bit, you are turning it to fast. 1" bit on a cutting edge I would start 150 to 200 rpm.

Annular cutters are good, but how are you going to resharpen them? They allow you to put oversize holes in with undersize equipment, but are somewhat fragile.

As for sharpening drills, a good sharpening guide is indispensable. It helps you insure both flutes are the same angle and same length. So you say "I sharpen them all by eye". Thats like saying I will level this 1 acre building pad by eye, don't need a story pole. An expert may be able to come close, but a beginner will turn out a hopeless CF.

If you weld 2 standard nuts together side by side , flat to flat you get 120 degree angle between them . Correct angle used to be 118 from what I was taught . Close enough.

Each side on a regular drill bit is supposed to be 59.5 degrees.

I put 20 3/4” holes in a bunch of 1” steel plates last week with an annular cutter ( drill press adapter used). I was done in a couple of hours. Spent more time moving pieces and chamfering the holes than the actual drilling. Had the press set to 280 rpm. Annular cutters are the way to go and I will purchase more sizes as I need them. Cam

Good quality large bits are expensive so i try to use them carefully and resharpen regularly to avoid unnecessary burning

well after a 4hr drive, i returned without a cutting edge as the steel suppliers plasma cutter broke down. disappointing to say the least. But! i did get a cutter for 68$ and a 1” bit for 109$ as well as a small burring tool. I burred out the holes that were 15/16 and then reamed them. lots of metal splinters with that little devil. I tried the drill bit and chipped the edge while coming through the bottom. very disappointed with that! I then went to the cutter, and that is one fine piece of machinery. I got some cutting and tap oil, it seems very sticky, I was amazed at how much it helped. I drilled 8 holes, no problem. Very happy with round 1. not sure what hardness of steel it is, but will surely help with experience for cutting the 450. thanks for the help and advice. Will hopefully pick up edge after the holidays

the only potential problem i see is that it may be hard to keep the bolts tight because the bottom of the surface is worn and may not allow the new edge to seat flatly. if its a problem you could add a few weld beads toward the front of the mounting surface which would help to support the new edge

Or weld on o strip of flat to fill the gap between the two edges

56wrench said:

the only potential problem i see is that it may be hard to keep the bolts tight because the bottom of the surface is worn and may not allow the new edge to seat flatly. if its a problem you could add a few weld beads toward the front of the mounting surface which would help to support the new edge

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Volvomad said:

Or weld on o strip of flat to fill the gap between the two edges

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I was thinking that I'll cut the buckets edge, back and inch or so, to get out of the inverted taper. Then come back in and cut the buckets leading edge at a 45* or so and the correct taper. Like you say, Adding a few beads between the two would be helpful so I wouldn't have to cut so much back. Once I get it squared away I plan on applying hard facing to the leading bucket edge

..well, I got the edge! That AR450 is no joke. It laughed at the annular cutter, rubbed its little edges to nubs. I ended up using it as a marking tool and blowing a hole through with plasma. I then tried to round out the holes a little better with cutter...that didnt work. I got the holes through, just need to spend some time with the burring tool to get them precise. I kept thinking about what Nige said.. “is it practical though?” haha, I am still enjoying this, but I believe I may buy my next one!

At least you had fun and you do nice work. Was you cutter carbide or HSS even the carbide ones dont hold out long on ar450 I wouldnt be surprised to see it broke in half along that row of heat affected zone

I’ve had similar results trying to drill a base edge to accept a bolt on. All it did was wreck the bits.
Torch works okay and you need to cut the countersunk portion for the bolt head anyway.