old machinist trick I use when I need to drill a big hole in some thin sheet metal. just fold the cloth a few times and power on at low speed.. it works everytime..
JRD77VET he tricked you the second sample had more metal to hang on to the first one got crushed after the metal was removed the second one the metal near the hole didn't get crushed because of the extra length and the angle bit the proper way is to pinch it between two plates so the edges don't distort
I'd say your proper way is good, but any way the job gets done RIGHT is the proper way. The fabric trick is good, and a little less hassle than two plates sandwiching the work piece.
I've used fabric with drilling, fabric would still not work on any sample that was drilled the same as the first. Both samples were different, thus clamping forces were different. Fabric, in no way could fix the hole as newton laws wouldn't have changed on the forces acting on the metal, as the drill went through
I learned that as a tool and die apprentice from a old guy it works and why it works a drill has two flutes so it jumps around because no support in other directions the cloth helps with the stability till it gets to full dia thats why it works so well
I have used the procedure of clamping the thin piece between two slightly thicker pieces when drilling. It can be almost anything even wood to sandwich the thin piece to obtain a round hole. I believe the cloth prevents the cutting edges from catching and becoming a center then releasing in a random order creating the odd-shaped hole. Not catching would be the condition when the thin piece is sandwiched with a thicker material. This is an interesting fix to a problem.
The cloth takes up the space in the relief angle. You could also do a custom grind with a very shallow relief angle. But clamping it between other plates works aswell, it is just not that easy sometimes..
Rasmus, just so that we are on the same page, the (relief angle) is the clearance ground into the end of the bit's flutes. If you regrind the (rake) instead of the relief to near 0 degrees the excessive biting into flexible working stock will be reduced. This is why most lathe and mill tooling has very shallow to no rake.
+Maddin1313 If I got my shirt caught in a mill I don't think I'd be remarking on the hole so much as frantically reaching for the emergency stop and screaming for help. Had a jacket get caught in the lead screw of my lathe once, not while I was wearing it thankfully (set it on the bench when I took it off, pull cord got caught). First instinct was to try to pull it out, but there's no way any human could have done that. You wouldn't believe how tight my heavy winter coat got wound around that screw. Pulled tight enough to rip the fabric to bits. If I'd been wearing it, I'd be a dead man.
+Output Coupler But since it probley is wired like (most) shops...there is NO emergency stop switch..and no, on off switch...you have to unplug the cord...
I worked a machinist for years, and I honestly had never seen that technique. we typically put a piece of scrap wood under the hole when drilling thin metal which also prevented it from catching the bit and spinning. This was an interesting new trick
I enjoyed watching this video. It brought back a lot of memories of my toolroom days. I was a tool and die maker for a lot of years and learned this, and other, tricks from the 'old boys' when I was an apprentice. They are lessons that you have learned that you never forget and sometimes will use later in life when working in the shed. I still have my old wooden toolbox, over 50 years old now, and it is still full of the tools I used. Thanks for posting.
hey, I learned this tip from American Machinist Magazine in 1966 and it still works. This method works better than just drilling with out some cloth, paper almost any material that is dense and will fill the flutes. Using cloth , with a pilot hole will result in a accurate size hole with minimum bur, try it!
Brilliant! I've felt this effect many times when using my hand crank drill, but never came up with a solution for it. Now that I've seen it, it seems obvious. The cloth packs into the flutes and keeps the bit functioning as a round cylinder rather than only having two points of contact at the cutting edges.
Fasten hating. I swear that the humble drill press or pillar drill as we call them in Britain, is the most dangerous machine in the shop. It lulls you into a false sense of security and then all hell breaks loose as huge, invisible, stringy chips come gushing out and try to flay you alive! (Comment may be deemed to use unnecessary exaggeration for dramatic effect in some States.)
Pretty cool that someone with useful knowledge is willing to share,We always used flat bottom drills, especially on real thin stuff. Tool&Die traded is dying , not lack of work but from lack of workers. In the right place it's a 65k to 130k A year job once you top out.
As an apprentice in the fifties I was taught to do this to produce a clean round hole and stop chatter and it worked, the reason drills make an odd shape hole is because the back off from the cutting edge is greater than two degrees per side also if the angles are offset and different.The guy that said "He threw the rag in there to trick people who can't understand simple things, is the simple one, I certainly would not have had him working for me in my factory, little knowledge like that is dangerous.
Eric, your absolutely correct in what you say, that is a trick if you like to say that, in cutting a piece on cloth and folding it a few it three times and placing it under the drill before drilling, I even used folded emery cloth, does the same job to stop distortion and chatter.
Well, I suppose a drill with two cutting edges is very difficult to ensure that both cutting edges dig equally or in at the same time on the circumference of the first hole and so what happens in a sequential manner is as follows. One cutting edge digs in before the other or unequal in nature and so the drill is not faced with only rotational forces but with a side force which will cause the uncircular effect which may proceed in a thin workpiece and in any way the hole will be larger than the drill. Since the drill is working in an additional cantilever action and the bite varies then the drill will also vibrate in a lateral direction which becomes a very complex vibration along the circumference of the hole. All this is very complex indeed. I presume that the cloth under the drill will enter the primary hole and also cause heavy friction and so the drill cutting unequally on the two edges will find some sideways , lateral restriction and so the cantilever action is eliminated as the drill is supported at its cutting point and not as before only on the chuck side. Hence the drill is guided in by the cloth effect. My brother who worked in the RAF was always told to throw away all the blunt drills which they used to rivet the aluminium sheet covering on planes, on the assumption that any hand ground drills will be off centre and the hole will thus be greater than the rivet which was unsafe in a pressurised plane. One day they run out of drills and the store keeper said that the work had to stop till his new order came in. My brother who was a skilled toolmaker before the joined the RAF knew how to grind drills and he arranged for a jig to do it though he always found that manual hand grinding a drill is fairly easy if one is experienced enough. Precision drilling is not as easy as one thinks, and the effect of the cloth to support the "free" end seems to be a good idea. There is a lot of interesting mathematics that one can associate with such a " simple mechanical situation!" So many "beautiful" artistic effects exist in the workshop and I would go as far as saying that in this case the vibrations and other circumferential vibrations may be looked upon as Music and not just a noise as many people associate with a workshop.
I totally agree with this description of what happens. When you don't have a hold down vise, the drill punches through in one spot, and the material flies upward and starts spinning. It's always tilted though. When in the vise, the material bends and the hole skews. That's why he said that the drilling works correctly at first. I think the cloth tries to spill through any gash on the relief angle side, and slows down the tearing, allowing the edge on the other side of the drill enough time to begin cutting, and thus a balancing force to keep the cut straight.
I've been a metal worker, machinist and precision sheet metal, for the last 42 years. I have not ever seen this, but am willing to try it out. One just never knows, but up to this point, I have used a step drill to make large-ish holes in thin metal.
Instead of using a cloth I use a piece of the cloth backed sanding rolls we have in the shop or at home. I'm a retired machinist, to do this right I use my custom ground drill bits, they work like sheet metal bits with a pilot in the middle and the flutes are undercut to the edge when the edge point is what controls the "round" of the hole. This is a great example of how to do this with what you have available.
Learnt that from my father (aircraft sheetmetal guy) 60 years ago. Enough paper or rag and the speed can be increased much faster than shown. Been using it regularly ever since. Works with folded cardboard or a stack of folded newspaper too. It is all about a temporary bearing to keep the drill from wobbling. 1" drill on a piece of 20 gauge works fine. A pilot hole 20% bigger than the flat tip of the big drill is best. Works fine with hand held tools too, especially our modern variable speed hand tools.
Stopping @2:00 to talk trash like I know it. That standard drill bit is not round but is designed to cut a round hole in thicker material. A stepped bit with one cutting flute will do a much better job on the thin stuff.
Archangel, thank yo so MUCH! Do you mean those brass colored sorta conical bits that have abut 5-6 steps? I have 'em, but never used them. Are they a BIG missing spot in my tool box? PLEASE REPLY OK?
I also used the stepped bit for cutting a hole in a plastic tank to mount an outlet. It worked really well and left a nice clean hole. Not like a hole cutter which leave a rough cut edge.
A sheet metal bit. The bit has a center point and the cutting edge is present only on the circumference. It cuts like a compass by scoring the outside of the hole being cut in the sheet, like a small hole saw. A standard bit moves the piece about, wobbles, as it cuts from the center toward the outside. Creating the odd shape hole in the sheet. The problem is each hole size needs a corresponding bit size. More tools.
My dad taught me this when I was 15 or so. But we used paper shop rags. Readily available in pretty much every shop. Works well when stepping up any drill bit
I was shown this method about 20 years ago and it never worked for me but I didn't fold the cloth a few times. Looks like that is the trick. Good to see it in person thanks to RU-vid and your time to make the video. I like the slab mill at the end. It looks like a nice but expensive tool. Keep up the good work.
This is a great method, and I have always found it particularly useful to prevent countersinking tools chattering in challenging cases, eg using a hand drill with a big or unsuitable countersinking cutter in a tricky material like high nickel, tough and/or work hardening alloys.
Wow! I never knew that and I've been machining since the early 70's! I usually drill sheet metal a little undersize and then ream it but I'll try that trick the next time I drill thin metal. -'lil stan
That is a neat trick and I can come up with no reason why that would work. When my co-worker told me that my sheet metal hole will not be round, I thought he was crazy. To prove him wrong, I drilled a 1/4" hole in some sheet metal. It was way out of round, with 3 noticeable sides. He told me to use the stepped unibit....works well. Never too old to learn.
cnc and machinist..... perfect example of an oxymoron. load program. push start. not machining. machining is when you know the cut is going good because you can feel it in your feet. machining is grinding wierd tools for just one job. machining is doing stuff like in this vid because the machine you are using was built before you were, but its the only job around, maybe if you owned the shop ..... what you do is the result of what I did. what I did was built you a machine that a monkey could operate. I did that using shit machines you sneer at because thats what the suits asked for. now you sit in front of what I built. pushing a button like a monkey, I pity you. a bird that has never flow.
Luke Warmwater there are far too many machinists like you around.. Thanks for making every shift seem so long and home seem like it’s so far away.. I hope you understand that it also takes skill to program and set up cnc machines. It’s not all just as easy as loading in a program and hitting cycle start. And regardless you shouldn’t have such a chip on your shoulder about being a machinist. It’s a very ordinary/generic career. Sure you can do very complex things, but you can still be an idiot too. It’s amazing how in less than a decade of wearing multiple hats in machine shops how many balloon heads I’ve come across just like you.
Actually you should never wear gloves while using drills, mills and lathes. Glove get caught and rip your arm off or worse. I wear gloves for welding and that's it.
This trick is not easily understood although I've used it for 60 years. It works on thick parts as well as thin sheet metal. Example; 5/8 mild steel with 1/2 pilot hole to be enlarged to 3/4 with two flute drill. Vise is not clamped down. Drill will dance around and chatter dangerously and refuse to cut a round hole, but throw a folded rag over the hole and you get a smooth, round, chatter free hole. Explanation; the compressible rag cushions the cut by filling in the clearance behind the two cutting edges. This is not voodo and really has to be experienced but it does work.
A much safer and consistent way of cutting regular holes in thin sheet metal is to use a different shaped bit. The tapered shaped bit you used digs in at the ends and pulls the sheet upwards. If you use bits that are brad point, primarily designed for cutting dowel holes in wood the cutting points are at the centre of the bit and at the periphery. This results in a nice circular hole, no violent movements of the sheet and no cloth fiddling about. The brad maintains position in the centre and the cutting tips cuts down a small "wheel" to punch out the hole.
It's good to see this sort of knowledge passed on. I learned this in my first year as an electronic engineering apprentice, for drilling neat holes for mounting potentiometers etc. It helps to ensure that the chip comes out of the rag and up the flutes, to avoid scratching the face of the work.
I noticed that too. Some people will clamp the vice down so tight that as such a big drill is taking out so much material and leaving the sides with very little support, the vice pressure will then try to collapse the hole some, and so when the drill's flute comes around, the material will try to migrate into it just enough to make the cutting edge of the drill start to cut outside of what's supposed to be the hole's finished diameter
It was in the sixties that an old timer Tool and Die showed me that, and over the years while being a member of many yahoo groups I have mentioned that little bit of info that you don't get from the machinist bible, I have used it many times and it works every time, a chunk of Plasticine is also a good thing to have in your toolbox as well
+William Ward - Plasticine™is a brand name for a kind of modelling clay. The clay (fine particles) is bound together with oil rather than water so it won't dry out and get hard. It's that heavy dark green (traditionally; available in a variety of colors these days) modelling clay you probably used as a child. It's not a ceramic, and cannot be kiln fired. In the shop, it's great for making dams to keep liquid confined on a flat surface, and for damping vibration, among other things. Toy stores and artist supply shops are a good source. Sculpey™ is an oven-bake clay. Not anything like Plasticine.
+Peter W. Meek Peter, you are right on, I used it all the time in the toolroom, we made our own punches it those days, as small as .032 dia and rectangular, turned in the lathe, heat treated , then ground on a centre grinder, but the tips and heads had to be surface ground to length, that's where the Plasticine came in, try to grind say 3/8 off the tip .032 dia, impossible as soon as the wheel touched, no more punch, stick a blob of Plasticine and cover the punch down around the holder (V block) feed gently into the side of the wheel it takes 3/8 off in one pass, punch is ready for install, we also used it to make a dam for coolant when drilling 62 Rockwell die sets with Stelite drills, Plasticine dampens vibration,
Drills are for making holes. Reamers are for making round holes of the proper size and shape from drilled holes. Double margin step drills are a half-way measure for quick more or less round and properly sized holes. This is a neat trick for improving one-up drilled holes in thin metals, but in thicker metals the bottom half of a drilled hole will be a lot rounder and more properly sized than the top half. Nothing wrong with what was done on the vid, but I encourage people who want to know more about machining to study and experiment and learn all they can about the right way to do things. Pretty sure that men and women who know things about machining from the ground up may be in demand before long. Bless those who are hungry for knowledge. As always, you are the hope for the future....Joe.
WHO Uses automatic feed on a drill press?? Another old machinist trick is to drill it in stages; never go from a small hole to a big hole in 1 step, & never use the finish size bit either. Make it so your finish size bit only takes off 0.20 to 0.30"
paul rogers sure sounds like wasting a lot of time to me. The actual rule on pilot drilling is that your pilot drill should be, at minimum, the same diameter as the web of your next size drill.
After running a Carlton drill press for over three years, (it seemed a lot longer than that, it really did....) I found a way to step drill that always works. If you are drilling a hard metal, (like steel) your pilot drill needs to be about 75% (or more) of your finish drill. For any soft metals, (like brass, or aluminum) the pilot drill should be about 25% or less than the finish drill size. For drilling thin metal parts, (like sheet metal, or shims) put a scrap piece of metal (made of the same sort of material) down over the part, and then drill through both of them. Or use a drill guide. But I love this method, using the piece of colth! I've not seen it before, and I would love to give it a try, Thanks!
I was shown this idea by a Old English machinist at ALCOA in 1985 .A cut off old leather glove finger tip works perfect.It is used to slow down drilling in brass & Aluminium also.
I get the hack and it’s great. Turn up your RPM a bit and use the handle not the feed. That material Cut and looked like stainless. So just keep it cool with oil or water bottle with coolant. The drill will get dull because of the material. Probably sure you already knew that. Loved how the aluminum was cut with the fly cutter. Love it when things get machined that easy.
Tip: Don't go from a small hole directly to the big, final diameter hole. Predrill the hole via intermediate steps and use the cloth technique for the last step. This way you will get a cleaner drill hole, less heat and no potential discolouring of the material, And you don't bend the thin sheetmetal when drilling.
For anyone that is open to trying this method, when there is a hole already in brass or bronze and you are going to enlarge the hole with a larger drill, it seems to grab and pull itself thru the material. Fold up a little cloth and place it before 2nd drill and it will go nice and smooth thru the pilot hole.
Nationalism is just as bad as racism. Don't say, "American is the best." Say, "America is a great country." The difference is that in the first, I'm comparing my country to all other countries, and declaring all other countries inferior. In the second, "I'm declaring my country great without putting other countries down. How would you feel if someone declared you inferior to them? This is how you make people in other countries feel when you say, "America is the best."
A criminal or a megalomaniac in my opinion. I agree with you. I'm an American and I cannot accept that those two are the cream of the crop of 300 million people.
I'm continually amazed at number of people who troll youtube with apparently no other goal than to bash the US. This is the perfect example, a 4 minute video about how to drill a circular hole and Ras turns it political. I'm not even sure the metal-smith is from the US.
Thank you for this! I'm a younger machine repairman and this is definitely something I know I'll use. Just another thing for my bag of knowledge/tricks
+Kip Saechin does anyone know what vise is that? It's not the standard Kurt vise i know Does it have a angled face to the movable jaw???? , what is that black piece on the left side?????
+Dan Wolf its just the vise we use at work. Im from Denmark and kurt is not the prefered make.. The black thing is a hold down block, just a block with a 14mm t-bolt through and a little "hook" that grabs a slot along the side of the vise.
It must be magic I cant get my head round the fact that the soft cloth can in some way counteracts the forces of the hard steel drill and work piece, amazing, thanks for posting
I had my own ways of solving this when I worked in a machine shop.But I can see this being a handy trick for a backyard/garage guy with limited tools and rescources.
So how have you done it? I'm thinking that he just jumped up too big of a drill size, if you gradually increase, the final pass through is more likely to be round??
georgio jansen Wouldn't the neanderthal look nice wearing a pretty silk robe? Not very warm and protective either. But it would have been good for trade. lol
Duck him and burn him!! Burn him I tell thee, for he is possessed of The Devil Himself! I bet he weighs more than a duck too. (A duck too is like a cockatoo btw, only bigger). That reminds me; A hungry duck went into a pub' one day and asked the barman if he had any bread. The barman said, "Sorry, I haven't got any bread. Would you like a beer instead?" The duck just stared at him and asked again if he had any bread. Somewhat rattled, the barman said, "I just told you, I haven't got any bread!" The duck insisted, "Have you got any bread?" The busy barman shouted at the duck, "Look, there are other people waiting to be served. If you ask me one more time if I've got any bread, I'll nail your bill to the bar!" The duck then asked, "Have you got any nails?" Furious, the barman admitted, "No, I haven't got any nails!" The duck said, "Have you got any bread?"
This is an awesome tip! Dial-chasers are a special breed that are slowly dying-off. This kind of knowledge and skill will be sorely missed in the near future. Duck walked into a bar . "Gimme a beer Barkeep!". Bartender: "Sorry, can't serve you. Your pants are down."
+DomManInT1 My guess is it grabs the chip, and stops it pulling away at the thin side walls and buckling it, but there is no way to know for sure from the youtube vid
+Rob F My bet is that it does several functions. One being that it reduces the relief angle of the cutting tool so that the cutting tool can't take a big of a bite into the material. It also probably increases the cutting pressure needed to advance to tool making it more stable in the center of the hole.
+DomManInT1 My guess is that the cloth burnishes the edge of the hole behind the cutter, reducing micro cracking, and allowing the material at the thin edge to maintain higher strength. But that's just a guess.
+DomManInT1 I think that's broadly correct. I've used this method for years; I initially discovered it for countersinking holes in stainless, which (for those who have not tried it) is very prone to facetting. It seems to me that the wad of cloth provides damping, partly for sideways excursions (particularly in the case of a drill, which lacks sideways stiffness) but in the case of a countersink, mainly endwise: it stops it grabbing and self-feeding, because the cloth is using up all the limited available volume between the flutes, and would have to compress further if the cutter 'jumped' downwards. It sets up a 'resonance' effect, and the cure for resonance (given that infinite stiffness is unachievable in practice) is damping. The grabbing and self-feeding is mainly a result of the "top rake" effect (with reference to a lathe tool), but I think you're also right: the cloth acts as a (soft) barrier to the front clearance which also helps prevent digging-in. And in the case of a drill, presumably the same effect occurs around the lands, once it is cutting at full diameter, which (in this clip, at least) is when the fun really starts. When I do this for stainless I use heavy denim, and soak it in high-sulphur (dark brown) cutting fluid - it works a treat, and also makes for much longer resharpening intervals.
Most of the time larger drills are sharpened slightly off center to allow for clearance. This results in the miss shaped hole in thin material. The drill body is not there to contain the wobble. However this is the first time I ever saw this fix. I would just sharpen the drill to a more precise center. I did it that way for 50+ years. I guess you learn something new every day. Thanks
Cardboard layers or multiple layers of paper works too. As long as it works as a bearing. Even works great using hand tools, not just a drill press. My father was a/c mechanic. He showed me that when I was 9, 58 years ago.
Indeed a valid technique. In the commercial environment, we just throw a rag at the bit... it seems to engage & work just like this. Weird, never figured out why, it just does.
Rasmus Laursen, this is a great trick, thank you for taking the time to share it. I always wonder why there are viewers who feel the need to comment about a better way of doing something in comparison to what was shown. Of course there are other and very possibly better ways to perform just about any task at hand, if you have the tooling to do so. However, the poster is not stating that this is the best way, just simple showing a trick that works in case you have the need to use it for whatever reason. Let's take it for how it is meant. I for one, appreciate learning these tricks.
Did noone get that? At 1:24 you see a perfectly round hole without using the cloth until it gets buggered up at 1:26 using the table feed. (nice cam move thou) The cloth does absolutely nothing, it is a fake...
Thanks for putt'n that in a vid. It's been pretty much a verbal hand-me-down pre interwebs. Other mat'ls can also work by the same priciple depending on .... ....
+Rasmus Laursen it takes up the slop area when your drilling. you also can use this trick when the drill is chattering in a center drill. it just dampens the wobble and takes up the room. also i noticed your pilot hole might be a bit big. the hole you first drill should only be as big as the web of the bigger drill. (the tip of the drill where there are no flutes and nowhere for the chips to go.) if you drill the hole that size or a little bit smaller you will decrees chatter and tool walk. sorry if i didn't explain myself good enough but i hope i helped.
+the hollow box I would guess that is the exact reason. sometimes I wrap parts or long tools with rubber bands or even rubber drawer liners to stop chatter.
I have been doing this for sixty years on thin and thick steel but most times when you have got the full diameter of a properly ground twist drill I have always obtained a round hole
In fifty years of chip walking, I have never seen the cloth hole method. With a properly sharpened sheet metal point on a drill, really thin stock can be drilled cleanly and safely. If you do not have many holes or many drills, this looks like something to try. Thank you.
Never got shown this trick and I had some really good guys training me as an apprentice. But we used to grind the drill to a different shape leaving a point in the centre and using a reverse angle so the outer of the flute cut just after the point touches but before the inner of the cutting edge touches. You end up with a round hole and something that looks like a rough washer at the end of drilling.
Full Definition of vice 1 a : moral depravity or corruption : wickedness b : a moral fault or failing c : a habitual and usually trivial defect or shortcoming : foible 2 : blemish, defect 3 : a physical imperfection, deformity, or taint 4 a often capitalized : a character representing one of the vices in an English morality play b : buffoon, jester 5 : an abnormal behavior pattern in a domestic animal detrimental to its health or usefulness 6 : sexual immorality; especially : prostitution
Don't use power feed and peck drill by hand, Simple. A machinist would know this. no need for cloth unless your that lazy and you need power feed for sheet metal..
I dont think that in this case your method would work.. But you are welcome to make a video of you doing it, looking forward to see what you have to show. Peck by hand.... Omg
when drilling thin material, the drillbit intend to pull down when almost through! powerfeed avoid this, and made the passing much better. The clothes trick are very old, but work very well. it also remove the chatter that the drill can produce when start the cut. best rgds. machinist with 34.000hrs experience
I've been using this great trick so long I can't remember who showed it to me! I use it on bits up to 50mm, which are the biggest I've got, it works a treat every time! Thanks for sharing a really worthwhile trick. Regards Matthew
Well it has been a loong time since machined something...I used the wooden block under the piece, and was told to always do that. One of the profs at school had his drill bits with a small radius between the drill OD and the web of the drill. It cut nicely through sheet metal and with minimal burr.
Drill through the thin sheet into wood. Another way is to put the sheet between two pieces of wood and drill through. Use the shortest drill bit helps as well, because the drill is bending as it breaks through the bottom of the sheet. Drilling through the sheet into something else keeps the drill supported. If you are in production, a drill jig with a drill guide (which is hardened steel) works perfect.
It also works well when drilling large diameter holes (ie 60+mm) in thicker plate, it stops the drill chatter and bounce you tend to get before it gets to full cut.
My guess is that it is preventing the drill from actually cutting when it first begins to engage, allowing the true point of the drill to slightly indent - or in this case, shape the pilot hole of - the material, making a perfectly centered spot. Drills usually walk because the cutting edges are grabbing when the drilling begins, thus causing a rhythm that can't be recovered from. This cloth is preventing the drill from actually cutting until the pressure becomes enough to erode the cloth. By the time that happens, it would have made a perfectly centered indention or a perfectly shaped pilot hole. Just a guess.
It seems to work very well, thanks to the step bits i dont have to much trouble with thin materials, but this will be useful when the step bit does not fit in the setup, thanks for sharing.
Another cool trick is turning small diameters using a brigeport. mount your part in the spindle using spring collets and holding a turning tool in a vise. If you have a DRO all the better, dont forget, the diameter will change X2 to the actual table movement.
