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center drills vs spotting drills

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  • oldtiffie
    replied
    Pecking order

    After Dave went to the trouble of looking, I thought I'd better get off my freckle and look a bit further.

    I wanted some proof or verification that the extended ("floating") and "self-centreing" of a drill in a chuck in a tail-stock method worked on small holes - as I said in one of my earlier posts in this thread.

    Further, it works just holding the drill in a pin vise/chuck in your hand and "peck-drilling" as well. The higher the speed and using preferable carbide drills is much better than slower speeds.

    I first saw and used this in the Instrument Shop and Tool Room - over 50 years ago. I have had occasion to use it since.

    It is all counter-intuitive and it looks as if it won't or can't work - but it sure can and does.

    Very sharp drill are essential as the drill has to cut and not push its way through.

    http://www.youtube.com/watch?v=bh4L65V1SqQ

    http://www.youtube.com/watch?v=vg5MiJqJ1po

    And a spade or centreing bit - similar to what I posted a pic of earlier:
    http://www.youtube.com/watch?v=2vdEHGngCZY

    Pin chuck (there are several types):
    http://www.alimed.com/alimed/product...,20436,455.htm

    http://www.google.com.au/search?hl=e...m&oq=pin+chuck

    http://www.justtools.com.au/category462_1.htm

    http://www.google.com.au/search?hl=e...0&oq=pin+chuck

    Leave a comment:


  • oldtiffie
    replied
    Thanks

    Originally Posted by oldtiffie
    There was an excellent video (U-tube) posted here not all that long ago about a bloke who was using a lathe at a pretty good speed to drill very small holes in a brass jet for an IC engine of some sort or another.
    Originally posted by koda2
    OldTiffie,
    I believe this is the URL you are looking for:

    http://www.youtube.com/watch?v=q6-4oyIoku4

    However, on my computer it is now a dead link
    Dave A.
    Thanks for the try Dave - appreciated.

    No result here either.

    Leave a comment:


  • Scishopguy
    replied
    Technology marches on

    When I started out in T and D, DRO's and CNC machines were not available. Everything was layout lines taken from part models, sent down from the "big three" in Detroit, and transferred to slabs of tool steel. Trace and profile of male and female halves of dies was done on Hydrotels that were older than I was. The boss would calculate the proper diameter of tracer finger and cutter to use to get the correct clearance for metal thickness to be used in the die. Center punch marks made in the layout department were pretty close to dead on (by those days standards) and we had to pick them up by wiggler, center drill, or tiny drill bit. Of course, when you are drilling a series of 3" spring pockets into a dieset, on a Fosdick 4' sensative radial drill, a couple thou either way is lost in the noise level.

    We produced some amazing tooling and I will never forget the cars that we made tooling for. The headlight bezel for the 73 Camaro was particularly interesting because the design required a sheet of .032" aluminum to be drawn about 6" deep in one hit. Reality sank in and we ended up having to draw it in 3 seperate operations to keep it from splitting out. Each draw left a shock line and that is why the inside of that bezel had a flat black coating from the factory, to hide the shock lines. OOPS...Engineering change!!!

    Sorry, didn't intend to ramble and hog the thread.

    Leave a comment:


  • loose nut
    replied
    Originally posted by Carld
    From my experiences locating from a center punch mark is marginal at best. The issue of getting the center punch mark in the exact place is a hit and miss affair.

    I use three ways depending on the needed accuracy of the location. For within 1/32" accurate I use a center punch and a wiggler. For within a 1/64" I use cross hairs marked on the work and a wiggler. For within +/-.001" I use home on the corner of the work and the DRO on my mill.
    What Carl said!!!

    Boilermakers use center punches, machinists use DRO's. I do both so I use both but at the appropriate time.

    One reason a center punch will break is that just because it hasn't broke yet doesn't mean it isn't dull. A dull bit will break just when it is the worst time. When ever I get a new center drill out I dunk one end into the layout fliud to mark it as unused and then I only use the other end until I feel it is dull. After that I grind the dull tip off so I don't confuse it with the other end.

    If you want a spotting drill but can't find them (they are not the most commonly found bit ) then take a broken center drill and regrind it to the right angles, a make-do spotting drill.

    Leave a comment:


  • EVguru
    replied
    How many people are actually running a centre drill at the recommended speed for the pilot diameter?

    Leave a comment:


  • madokie
    replied
    center drill???

    for center drills to work really well,not only does the drill tip need to be sharp, and accuratly ground but the angle part of center drill needs to be sharp and free from nicks and dings also. to get precise center hole in home shop, its best to use steady rest, and finish center hole by cutting, with HSS in coumpound toolholder.and also make sure pilot hole is deep enough so live center doesnt bottom out in pilot hole ,and create wobble.i have never bought center punch, i always use broken taps,reground by hand, good hard steel, free too.

    Leave a comment:


  • J Tiers
    replied
    Originally posted by Scishopguy

    Another issue that comes up a lot is picking up a center punch mark accurately. One of the old diemakers told me, after the boss had left, that I would have better results if I used a really small drill and just touch the dimple left by the punch. You can see which way it deflects and correct with the BP table until it lines up. Then you step up by drill size and the hole comes out on the money.
    That's exactly what I do...... Didn't know it was a "recognized" method... it works very well, but obviously depends on the accuracy of the layout.

    Leave a comment:


  • Guest's Avatar
    Guest replied
    Originally posted by oldtiffie
    There was an excellent video (U-tube) posted here not all that long ago about a bloke who was using a lathe at a pretty good speed to drill very small holes in a brass jet for an IC engine of some sort or another.
    OldTiffie,
    I believe this is the URL you are looking for:

    http://www.youtube.com/watch?v=q6-4oyIoku4

    However, on my computer it is now a dead link
    Dave A.

    Leave a comment:


  • Carld
    replied
    If it is in a drill press or mill I have very little problem removing the broken drill you describe without flipping the work over. I use a carbide drill of my own making.

    Leave a comment:


  • Black_Moons
    replied
    I broke a 1/8" bit I often use to pilot holes (its only got like 3/4" of flutes so its rather rigid) off inside some mild steel when it was only like 3/16" deep, really looked like a pain to remove from that side. thankfuly I could drill through the backside but I agree, removing a small drill from a hole is a big pain.

    Leave a comment:


  • Carld
    replied
    From my experiences locating from a center punch mark is marginal at best. The issue of getting the center punch mark in the exact place is a hit and miss affair.


    I use three ways depending on the needed accuracy of the location. For within 1/32" accurate I use a center punch and a wiggler. For within a 1/64" I use cross hairs marked on the work and a wiggler. For within +/-.001" I use home on the corner of the work and the DRO on my mill.

    Using a center drill, spotting drill or stub drill will only give results equal to the tolerance of the chuck and spindle bearings no matter how well you locate it on the work.

    There are reasonable expectations and unreasonable expectations when marking or laying out work. Many machinists have higher expectations than the machine is capable of.

    For instance, you can expect better tolerance on a mill than a lathe as far as using the tailstock is concerned. The tailstock has more slop than a worn out mill will have so be careful of your expectations.
    Last edited by Carld; 12-31-2009, 03:28 PM.

    Leave a comment:


  • Scishopguy
    replied
    Re: Center Drills

    There has always been several schools of thought on precisely starting a hole. Some preferred center drills, some like spotting drills, and each has some merit that the other does not. I have found that "installing" a center drill in a chuck takes a little care. First, the drill chuck must be in reasonable condition and free of chips and grit. When you start the spindle you need to look at the body of the center drill and see if there is runout. If so, clean and try again. Same holds true for spotting drills. Second, as GhopShop said, you need to peck drill or at least be gentle or the point will likely wander. When I was first starting out I would occasionally break the point off a #1 or #0 center drill. It mostly happened when I was in a hurry or got heavy handed with the downfeed. I have had pretty good luck with breakage, having a couple #00 center drills I have used for the last 5 years. Another thing that helped was getting the ability to resharpen the points on old, well used center drills. The Drill Doctor does a really nice job of this. I also split the points, which makes them less likely to want to wander. You can resharpen about 2 to 3 times before the tip is gone. I have had great success with rehabing used tooling this way.

    Another issue that comes up a lot is picking up a center punch mark accurately. There were two way explained to me years ago. The lead man in the assembly department at the Tand D plant I worked said to use a center drill and carefully line up the punch mark. One of the old diemakers told me, after the boss had left, that I would have better results if I used a really small drill and just touch the dimple left by the punch. You can see which way it deflects and correct with the BP table until it lines up. Then you step up by drill size and the hole comes out on the money. A lot of the layout punch marks were in big die sets and were for spring pockets so it was not such a big issue but that lesson has been handy when working on "touchier" layout jobs such as face pannels for electronic devices.

    Just my $0.02

    Leave a comment:


  • Boucher
    replied
    Sharp Carbide is best.

    There was a package of small carbide center drills in some stuff that I bought in an auction. They turned out to be very sharp and worked great. There were some carbide spotting drills also guess I need to try them. Sharp carbide continues to amaze me. I also got a bunch of reground milling cutters in both carbide and HSS. This place went out of business. Sure wish I knew who their grind shop was.

    Leave a comment:


  • mmambro
    replied
    "The use of either the tip or both parts of the center drill makes the following drill start on an 'edge"... the first contact is somewhere up on the cone of the following drill tip."

    Sorry, I should have mentioned that I use(d) the tip of the center drill only for the smallest sized drills (so that a cone is provided for the drill tip).

    Re the Dankroy center punch: The beautiful sliding fit of the perspex lens in the punch body is one of the things that really distinguishes the Dankroy from the others; it fits as well as the punch does. I was shocked to discover that the lens from optical punches made by other manufacturers are a loose to sloppy fit!

    It sounds like I paid more for my Dankroy than my brain wanted to remember ;-)

    Mike

    Leave a comment:


  • DR
    replied
    Not sure if this has been mentioned.......spotting drill points also break fairly often. The extra thin web makes them weak at the tip.

    The difference is, a broken center drill tip is difficult to remove ( books with hints on machining all have a trick or two to remove a broken center drill tip).

    A broken spotting drill tip usually can be removed easily by hand.

    Leave a comment:

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