Need advice on locating holes and features on work, using the VN12.
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    Default Need advice on locating holes and features on work, using the VN12.

    These are basic mill questions perhaps best addressed in the general forum, but as a lot of smart manual machinists are here, and I am using a VN12, here is where I will post it.
    I am not a machinist, just an old woodbutcher learning new tricks.
    In woodworking, one of the basic steps to ensure repeatable accuracy is the use of mechanical stops to butt the part to. I am needing an education on accurate setup and locating features that need to be machined.

    Imagine a rectangular block 1" thick, 2" wide, and 4" long. It has a through hole 1/2" in from the end, and 1/2" in from the side. For the sake of the discussion, assume we cannot bore through, but have to turn the part over to locate the drill hole on the other side. The vise will provide a reference (stop) in one axis when the part is flipped, but the other axis will need to be relocated, ie, any stop set up to drill a hole 1/2" from an end will now need to be set up to drill a hole 3 1/2" from the end.
    So the hole center will need to be located again,on the flipped side of the part, at least in one axis.
    When using a manual mill with no dro, is layout fluid and a sharp scribe and punch the best way to do this, followed by a center finder of some sort?
    It seems like errors could add up doing this, especially when drilling from opposite sides and needing axial alignment.



    Next topic- OK, that hole got drilled OK- now we need another one, 1.28" away on the z and .325" on the y. Is it best to simply zero out the mill dials and then dial in the movement necessary on the z and y ? or would it be best to lay it out with a scribe and punch it, then center the bit over the mark?

    I realize every setup is different and this is where a lot of experience is gained- are there any particular tricks you use, especially pertaining to the Van Norman?

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    Is it best to simply zero out the mill dials and then dial in the movement necessary
    In general, that's all we had if we were not blessed with a jig boring machine with "end measures"

    DROs are a RECENT invention to us old coots

    Helps to have a plain jane edge finder. I like the one that is .200" on the small end and .500" at the large end that I have had for fifty years

    A marvelous book from 1912 is Accurate Tool Work. Its probably a scan somewhere on the net

    The thumbnail show a few holes all located by dials and counting turns

    ON EDIT - add necessary preliminaries to such activities.
    Attached Thumbnails Attached Thumbnails dcp_1401.jpg   shop-print-b.jpg   shop-print-.jpg  
    Last edited by johnoder; 11-27-2017 at 09:55 AM.

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    Quote Originally Posted by johnoder View Post
    A marvelous book from 1912 is Accurate Tool Work. Its probably a scan somewhere on the net
    Not a title I was familiar with... Published multiple times by McGraw-Hill it was coauthored by Clarence Goodrich of Pratt & Whitney and Frank Stanley of American Machinist.

    Accurate tool work (198 edition) | Open Library

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    often a fixture plate is used with a dowel pin sticking up for part with hole to go on and help with location

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    In general if you have a straight square edge you will locate all features off that edge. This holds true whether you are scribing, punching, and drilling on a drill press or using a mill or jig borer.

    In the case of the mill if your lead screw is not badly worn you can feed from the other direction after re-locating the (same) edge on the flipped part and use the handwheel markings. I'm not familiar with the VN and whether it has a second handwheel on the X axis but if it doesn't you'll have to count backwards. As a visual check against errors I would scribe, but not punch the hole locations when using a mill.

    When I lay out parts, including the drawing, I always select a corner as the "0,0" datum and all x-y coordinates are referenced to that corner. It's a good idea to mark that corner on the part (on both sides if you will flip) with a "0" to prevent accidentally indicating off the wrong edges (yup, did that once as a kid) with a sharpie or layout fluid.

    Don't use cumulative measurement because errors will add.

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    quite common for fixture to use 2 pins sticking up that locate part in fixture
    .
    often one pin is bull nose and other is diamond pin.

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    3 + 2 + 1
    .
    many parts sit on 3 points or locators. you use another 2 locators to control rotation around Z axis often picking up straight edge. then 1 locator used at 90 degree to 2 locators as it can slide along the 2 locators
    .
    hard to describe. part can sit on 3 spots and 2 pins can also be used as 3 locators too

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    OK- Thank you all- the light is slowly coming on...

    Years of using equipment (woodworking) with limited or no positional accuracy made me worry about trusting the dials on the mill. Stupid, I know- that's what they are there for, yes? I will put a indicator on the mill to reassure myself on the travel accuracy , and use a edge finder to get a reference corner and dial it in.

    On using the dials-

    On long movements, are there tricks you use to keep count of complete revolutions? Use a layout on the part to show any gross errors?
    I guess one thing might be to make the old worn dial markings stand out with a careful cleaning and re-ink the lines. Maybe I could get them dull chromed and blacken the lines- they are close together , 200 thou per rev., so a little hard to see.

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    Quote Originally Posted by stoneaxe View Post
    OK- Thank you all- the light is slowly coming on...

    Years of using equipment (woodworking) with limited or no positional accuracy made me worry about trusting the dials on the mill. Stupid, I know- that's what they are there for, yes? I will put a indicator on the mill to reassure myself on the travel accuracy , and use a edge finder to get a reference corner and dial it in.

    On using the dials-

    On long movements, are there tricks you use to keep count of complete revolutions? Use a layout on the part to show any gross errors?
    I guess one thing might be to make the old worn dial markings stand out with a careful cleaning and re-ink the lines. Maybe I could get them dull chromed and blacken the lines- they are close together , 200 thou per rev., so a little hard to see.
    .
    calipers are cheap and so are rubber bands. some use pin in spindle to push a clamped on caliper and read what it says
    .
    some use a magnetic base and test indicator zeroed at spindle and at gage block against a stop. remove gage block and move to stop til indicator reads zero again. the gage block you removed is distance traveled
    .
    dont assume a 12" ruler or scale is 12.0000. usually Starrett within .002 per foot but other brands can be off much much more
    Attached Thumbnails Attached Thumbnails carriagedro_b.jpg   millcalibration_.jpg   tailstock_dro_steelcaliper_kanttwistclamps.jpg  

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    stoneax,

    If you're not familiar with an edge finder, that's what you need (unless you're doing super high precision work). It's an inexpensive tool that fits into the spindle and will show you where the edge of the part is to within a thousandth or so. You then set the graduated collar on your mill to zero (minus the radius of the end of the edge finder) and use the graduated collar to move over to the desired offset. It's always good to use layout fluid to mark the location of the hole so that you don't miss it by a revolution of the leadscrew. Always approach your coordinate from the same direction, to take out the backlash in your leadscrew. And you should come in moving the same direction that you used with the edge finder. That is, if you used the edge finder to locate the left side of the part (by moving the table to the left), then you should always move the table left to the desired location. If you over shoot your reading, back up by about 1/2 turn of the crank and come in again. You use the same process to locate the hole on both axes.

    Here's a YouTube video that shows how an edge finder works:
    After you drill the hole in one side of the part, just flip it over and repeat the process, making sure that you use the same side of the part to zero off of. As long as you don't move the Y-axis, you should only need to use the center finder on the right (or left) side of the part for the "bottom" hole.

    You want to use a center drill (aka combined counter-sink and drill) to start all holes, so that the drill doesn't walk on you and change the hole location. Hold the center drill in a collet for maximum accuracy. I would also drill the hole on the back side, one drill size under the desired size, so that you can later drill all the way through the part (perhaps on a drill press) to ensure exact alignment of the holes. If it's a hole that needs to be to an exact size, you want to drill the larger hole under size and ream the hole to final diameter, again going all the way through from one side with the reamer.

    There is also a wobbler-type center/edge finder that can be used to locate a scribed or center-punched mark and works much the same way as the edge finder.

    Cal

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    Quote Originally Posted by Cal Haines View Post
    There is also a wobbler-type center/edge finder that can be used to locate a scribed or center-punched mark and works much the same way as the edge finder.
    I have a combination center/edge finder but it never occurred to me to use the center finder for anything but small holes (those too small to locate using the edge finder in each of the two axis of movement). It makes perfect sense it could locate a punched mark, though!

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    Quote Originally Posted by Ohio Mike View Post
    Not a title I was familiar with... Published multiple times by McGraw-Hill it was coauthored by Clarence Goodrich of Pratt & Whitney and Frank Stanley of American Machinist.

    Accurate tool work (198 edition) | Open Library
    for the cheapskates among us

    Accurate Tool Work : Clarence Leon Goodrich, Frank Arthur Stanley : Free Download & Streaming : Internet Archive

    dee
    ;-D

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    OK- edge finder, subtract radius to find zero, approach work from same direction as edgefinder, and use a center drill.
    Is it best to switch from from center drill to through drill and stay over the same hole center, then reinstal the center drill and move to the next hole,
    or is it best to spot in all the holes with the center drill, change out to the size drill and relocate over each hole and drill?

    -

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    Quote Originally Posted by stoneaxe View Post
    ...Is it best to switch from from center drill to through drill and stay over the same hole center, then reinstal the center drill and move to the next hole,
    or is it best to spot in all the holes with the center drill, change out to the size drill and relocate over each hole and drill?

    -
    Think about the problem yourself: What would be the error introduced with changing the drill bit or switching from a collet holding the center-drill to a Morse taper collet or drill chuck holding the drill bit versus the (possibility of introducing) error in moving to a different location and enlarge an existing hole?
    More importantly, try to quantify the risks on one side and the benefits on the other. Do you think there is a unique, categorical answer to your question?

    Paolo

    Paolo

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    Quote Originally Posted by Paolo_MD View Post
    Think about the problem yourself: What would be the error introduced with changing the drill bit or switching from a collet holding the center-drill to a Morse taper collet or drill chuck holding the drill bit versus the (possibility of introducing) error in moving to a different location and enlarge an existing hole?
    More importantly, try to quantify the risks on one side and the benefits on the other. Do you think there is a unique, categorical answer to your question?

    Paolo
    Good advice from Paolo. Horses for courses:

    -If you only need to work to loose tolerances (.01" or so - lining up bolt holes for example), spotting on the mill and drilling on the drill press is a quick way to get reasonably precise work. Twist drills are so flexible they will center themselves and unless the hole is deep, a minute angular error shouldn't matter. You're essentially using the mill for layout and it may be easier for simple tasks to scribe and center punch holes, though that may be less precise.
    -If you need to work to tighter tolerances, I would spot and then drill without moving the work, ideally holding both the center drill and the twist drill in collets (ER collets are good here with their wide closing range). If you must use a drill chuck for speed of tool changes, get a good quality one and save it for fine work like this so it has the least runout possible.
    -If you need to work to tight *location* tolerances, spot and drill the hole undersize to remove most of the stock and then bore it to size to establish the exact location.
    -If you need to work to tight location and hole size tolerances, spot and drill the hole undersize to remove stock, bore it *just* undersize to establish the exact location, and ream to establish the exact size.

    I find it easy to remember this way: drill for stock removal, bore for location, ream for size. Since each project/job has different requirements, choose the fastest method to produce acceptable results.

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    Quote Originally Posted by Paolo_MD View Post
    Think about the problem yourself: What would be the error introduced with changing the drill bit or switching from a collet holding the center-drill to a Morse taper collet or drill chuck holding the drill bit versus the (possibility of introducing) error in moving to a different location and enlarge an existing hole?
    More importantly, try to quantify the risks on one side and the benefits on the other. Do you think there is a unique, categorical answer to your question?

    Paolo

    Paolo
    Thank you for forcing me to think.
    Maybe no "best" way every time, but I am so new at this I do not know what might be accepted standard practice ie, I don't know what I don't know.

    So- the obvious advantage of staying over the same hole is positional accuracy, the only variable would be a new tool holder and any corresponding runout.
    The disadvantage would be workload- having to make multiple changes of cutting tools with the attendant raising and lowering of the table each time.

    So my best take- it depends... if the machine has a very accurate system of repeatable positioning, spotting in all the holes then going back might be a lot quicker- but changing tools over the hole does eliminate that risk for a machine that may be hard to dial in exact repeatability.

    I like the caliper suggestions for double checking for gross error- one could be set up easily on a magnetic base to use a a quick check.
    This machine seems to be fairly accurate -the dials are within .001 of actual table travel, over the range (1") the indicator has. About .005 back lash.
    Soon as I get some time I will go practice drilling accurate holes.
    Thank you all for this education!

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    On something like a Bridgeport, where it's a lot easier to change tools because of the quill, I like to do all my operations on each hole before I move. On a Van Norman, where you have to crank the table up and down to change tools, I would probably center drill all the holes with the center drill in a collet, then switch to a drill chuck, go back and drill all the holes. It's a little simpler if you have a chuck with a stub that you can use in the same collet that holds your center drill. If you're going to be doing very much hole drilling on a Van Norman, you might want to invest in a set of "screw machine" length drills, which are shorter than the "jobber" drills that you normally see.

    If you have a good drill press and a second vise for it, spotting the holes on the VN (as suggested) and moving the part to the drill press really shouldn't affect accuracy. But, in the problem at hand, where you're trying to match two holes bored from opposite sides, I would probably do everything on the mill and only open the vise one time to flip the part. Also, it would be good practice to run an indicator up and down the reference (right or left) side of the part to make sure that it's absolutely vertical; a small error there will keep the holes from lining up. As long as the fixed jaw of the vise is vertical and in good condition, you shouldn't have to worry about that axis of the part staying vertical. Pad the moving vise jaw with a piece of dense rubber or cardboard, or use a horizontal dowel between the moving jaw and the block, to make sure that the fixed jaw is in full contact and controlling the orientation of the part.

    As far as checking the rough hole location goes, put a little layout fluid where the center of each hole goes, then use the tips of your caliper to quickly scribe the locations, like this: Using a Caliper to Lay Out a Part - YouTube. Bring the table up to just touch the center drill to the part to verify that you've hit your mark.

    Just out of curiosity, what's the situation that's forcing you to try to line up holes drilled in opposite sides of the part? Normally, you would rest the part on parallels to get it up off the bottom of the vise enough that you can drill all the way through. But, if you do need to control the location of the hole on both sides, flipping it over is a valid thing to do. Twist drills can walk veer off a tiny amount, depending on how well they are sharpened, etc.. If you use the trick of drilling the hole on the back side of the part a little under size, the drill from the front will pick up the hole on the back and come out right where you want it. That's a handy trick in wood as well, where the grain of the wood can deflect your drill.

    Cal

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    Stoneaxe,
    I really like the way you think. Many times, coming from a different field is an advantage because you need indeed to think why you do in a certain way and not differently.
    One concern that many times is exaggerate is the concentricity of the various boring tools used, since they rotate around a more or less central axis.
    You've received tons of good advice from many members. I strongly suggest laying out the work every given time, since it will highlight any macroscopic mistake (e.g. being off by one revolution).
    One thing that has not been discussed explicitly so far is that, if you want your holes perpendicular to the surface, you need first to make sure that the head of the mill is trammeled correctly. On a Van Norman you can control directly only the nodding, but not any side-to-side error. However, depending upon the dimensions of the work, shimming the bottom of the vise (so that the surface where your piece rests is perpendicular to the spindle) is a viable option.

    Paolo

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    This VN 12 is pretty square, it is as good as I can measure anyway.

    The hole was in a extrusion where the inside of the hole ran against the extrusion wall and was likely to deflect the drill if drilled all the way through.

    Let's talk drill holding- I have a full set of collets for this, but they only go to 16ths. So tap size drills etc I cannot hold. So a chuck is in order.
    The options for a chuck- get one with a collet size/center drill size stub,
    make an arbor with a VN C to Jacobs taper and stick a chuck on, or make a VN- C to morse taper and use a chuck with a morse taper stub. I was going to go with a VN C to Jacobs taper, but that would mean the collet for the center drill would have to be taken out every time I switched to the chuck. So the center drill size stub chuck seems like a more user friendly option, even though it can handle less torque. And the chuck is probably the ultimate limiting factor anyway, yes?
    There was a chuck with a 1/2" stub with the VN 12 - it has a free spinning threaded collar attached to the chuck body with a internal snap ring of some type, as if it were meant to be drawn up tight onto a threaded shoulder on a 1/2" end mill holder equiped with external threads.. Hmm. Not sure what that is about. Maybe I can get the collar off, I don't like things floating around and there is nothing in the box of parts that it would screw on to.

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    the lead screws on any machine are not high precision for measuring larger dimensions to higher tolerances. a .001" error per 6" is not unusual
    .
    .002" per 12"
    .004" per 24" is not unusual
    thats what gage blocks are for. some simpler cnc the cnc dro is calibration checked yearly
    .
    1) zero test indicator on end of 4.0000" gage block against a stop
    2) zero DRO or digital readout
    3) remove gage block move so indicator reads .0000 and read DRO
    quite normal to read .001 error. many DRO or CNC the DRO might read 3.9990 and in calibration mode you tell it it is actually 4.0000 and it adjusts the scale of DRO so 4.0000 movement reads 4.0000 on DRO
    ..... usually check X and Y as each axis can be off different amount. lathe DRO same are often calibrated so it reads more accurately of dia on DRO and what you measure part dia stays same as dia reduced.


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