Drilling a nice 1/2" hole (Stepping Bits Question)

I am not a machinist. I need to drill a nice (ROUND) 1/2" hole in 3/16" and 1/8" metal. I need to use a hand drill per the application (already assembled). What advice would you have about starting with smaller bits and working up to 1/2" to achieve a nice hole? I think if I just start with the 1/2" bit I am going to get more of an oval.

Also, if I am going to use a 1/2" THREADED fastener, do I just drill a standard 1/2" for a good fit, or should I be slightly smaller and need to turn the bolt to seat it? I will use a nut on the other side

Thanks
John

 

Use a good quality Step-Drill such as this one from Irwin. Begin by a pilot hole large enough to start the Step Drill and continue slowly up to the size. You can use a Sharpie marker or masking tape to mark off the step ABOVE the one you would like to stop at. If the metal you are drilling is very thin, use a backing such as hard wood.

If you are using a 1/2" bolt, the 1/2" hole should provide clearance enough for the bolt to pass through, TR

 

When you are finished with the top side and would like a nice chamfer, turn the metal over and lightly touch down with the Step drill for a few light revolutions and the next cutter up should give you a nice clean chamfer.

Practice on a scrap piece before doing your finish pieces and you will become familiar with the tool and how to properly use it. TR

Invest a few dollars in a small bottle of cutting oil and the drill will last for ever, and I highly recommend that for the 3/16" work, TR

 

^^^Absolutely.^^^

Remember to slow the speed of the drill motor down a little for each successive step. Also, make sure the cutting surface of the bit is thicker than the material you are drilling. THey make those bits with fewer steps and taller cutting surfaces for thicker material. 1/8" should be fine, on 3/16 I would definitely check the step height on the bit. If it won't quite go all the way through, you can finish it with the back cut/chamfer.

 

^^^^ yes this is what exwestracer is referring to, see the tool second from left. This will cut through a much thicker piece of metal than some of the others with many smaller steps. Like stated just flip over if the tooling you have won't cut through in one pass, TR

 

If you want a nice ROUND hole with a hand drill, the step drill is the only way to go. What has been said above is all good advice!

 

Good advice guys. Ive found step drills do make a much more round hole than a standard drill bit. Atleast for me. As far as the Threaded fastener fitting the hole, usually the stated size of the bolt or fastener is about as small as you can go on hole size. It will be fairly tight. If you want it really,really tight you could drill the hole one size small then open it up with a file or carbide cutter for an exact fit.

 

the gut who invented them should be nominated for sainthood

 

I invented them 36 forget the sainthood, send cash

 

I agree, a step bit is the way to get the job done. As mentioned above, make sure to have a good quality pilot bit that will get you started before using the step bit.

 

Keep the bit lubed too.

 

Try Blair roto broach cutters they make a nice clean hole.
http://blairequipment.com/

 

I use my Uni-bit a lot!! It'll eat right through 1/8 and 3/16 material!! And if you go just a little more after you get the desired hole size, the next size will kind of chamfer the edges and slick them up!!

 

Bolts have rounded fillets under the head, so the hole needs a chamfer larger than the bolt fillet to prevent knicking the bolt. Especially with a close fitting hole.
A well made flat washer has a chamfer to prevent damaging the bolt.
Nowadays some industries consider washers a waste of time and money.
Around WW2 and thereafter flat washers were "required." I still think they are.
http://theimmaculateconsumption.files.wordpress.com/2010/01/not_without_a_washer.jpg

To ensure the bolt fitting thru and ease assembly of components a "clearance" hole is usually required.
http://www.engineershandbook.com/Tables/taphole.htm
Official clearance hole sizes require drills in 1/64 increments

But when I'm drilling holes and the other component has a clearance hole I use a nominal sized drill and chamfer both sides. If the bolt is too snug (rare, and usually due to the 2 or 3 lobe oval effect ) I use a hand reamer to touch it up.

 

All great points thus far,

Uni bits are expensive though. One thing I like about them is they rarely get "hung up or snagged" on the steel and they can't "suck" in at the last second like a larger bit sometimes will.

 

i just found some stepless bits from harbor freight they drill a super round hole also but you have to be right on top of watching the size(check as you go )these have worked real good for me in real thin metal and plastic not the best idea for your situation but wanted to put it out there

 

The three pack of step bits from Harbor freight is dirt cheap and I can't kill them.
There's one at Homedept in the electrical dept that goes up to 1-3/8" .

 

If you are looking for a round hole yes this is a great tool. But if you are trying to get a straight hole that is another issue .Most if not all of these bits have a slight tapper to them so as you step up in material thickness a straight through hole will not be possible . Those with reamers would suggest to get to a finished size you would do your last step with a reamer on the thicker sheets .On the thinner metal I always use the step drills . I posted some time ago about sharpening a UNIBIT and didnt get a response from anyone that has succesfully done this .I would love it if someone has real knowledge (not speculation) of this process .

 

That 3 pack of unibits from HF is one of the best things they sell there. We buy them every time they go on sale, something like $ 7.99 for 3 of them, and you will pay more than that for one at most places. The bigger sizes get expensive at places like Lowes, around $ 25 each, if I recall.

Overall, the drill bits in general at HF are not bad at all. The gold HS ones they sell in the tin boxes last really a long time and resharpen well too.

Don

 

Sharpening them - if its just in need of a touch up a chainsaw file does a great job.
If its really whipped out of shape , I haven't been able to get it back, but I've only seen them get that bad when stainless and stupidity were combined while using a step drill.

 

Explain the procedure if you would as it really helps the unknowing how to aproach this .

 

We usually end up with one of the steps in a step drill that goes dull on us. The rest are fine until you get to that one step. It would be nice to know how to resharpen those.

Don

 

Maybe i'm missing something here but i just pilot drill and use 1/2" twist drill, never had an oval hole ever unless you have to much drill speed.

 

I'm not disagreeing with the majority of posters on step drills,
but I also wholeheartedly agree with DirtyJoe........The Blair
Roto Broach's have really served me well for producing 'clean'
round holes and are great for cutting spot welds loose too.

I think they both have a place in a well equipped tool box.

Ray

 

The unibit will get a small burr that rolls over on the cutting edge.
The small chainsaw sharpening file will take that burr off exposing the edge again.
Pretty easy to see how it works if you have both in your hands.

Couple quick passes keeps it nice just like , like the barber strops his straight razor or the butcher sharpens his knife. Let it go too long and the filing takes more work than its worth to just buy a new one but you can get it back if its not too bad.

 

Thank you to all. I am going to try and find the bits at HF.

John

 

HF step bits suck! Get them from Home Depot or lowes. You want the ones that say uni-bit. I think they're made by Irwin.


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Uni-bits are MAGIC! Once you use one you'll never live without one.

 

A nice thing is the taper transition from one size to the next; as long as you keep the thing perpendicular to the surface they do an excellent job of keeping you on center. Sometimes you need more than one of the typical three piece set to avoid skipping a size that can mess up your centering.

 

If I need a real nice edge, I usually drill a bit under size then finish to final size with a high speed burr on a die grinder,