Micro Drilling

Discussion in 'Watch Repair' started by Jerry Kieffer, Mar 28, 2020.

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  1. Jerry Kieffer

    Jerry Kieffer Registered User
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    At some point, I have probably suggested that some exact scale model engineering parts can be half the size of the smallest Horological parts. While I share examples with Micro machining students, occasionally someone asks to see photo examples. Again while home because of the virus cleaning the shop area, I came across a couple of photo examples from years ago. Again, while not Horological, the procedure and resources info may be of interest to someone.


    In this particular case, a handicapped person requested a lathe setup capable of drilling 1/8th scale fuel injection nozzles for experimental purposes. The nozzles were to be inserted into the tip of the injector assembly to inject fuel directly into a 12mm cylinder 4 stroke combustion area,


    The Lathe setup per first photo included a lathe mounted Microscope designed to track the machining process while remaining perfectly focused at all times.

    The second photo shows an example of a nozzle/drill compared to a fine ball point pen ball of .015” or .38mm diameter. The nozzle body is .003” or .075mm diameter and .008” or .2mm long with a .006” or .16mm head diameter to be parted off. The drill is .001” or .025mm diameter and was supplied by National Jet.

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    The drill was ground square or diamond shape similar to Armor drills designed to drill out broken taps.

    Armor Drill Tool Machines And Drills Granite, Armorplate, Stone, High Speed Steel, Hardened Steel, Drill Out Broken Taps


    In use, factory tailstock alignment along with collet/ drill mounting regardless of brand or type, is generally inadequate for consistent success at this scale. Thus it must be created. In this particular case, stock was mounted in the tailstock chuck and was spot drilled, drilled and reamed for a slip fit to the drill shank. This procedure compensates for all inaccuracies except bearing runout. Due to the small size of the drill and lack of load, the slip fit is more than adequate to hold the drill from spinning. However, as an additional resistance and safety method, the rear of the drill shank is ground to a chisel point. Third photo.


    When drilling at this scale, the drill must be be very precisely controlled. In this case the standard tailstock hand wheel was replaced with a larger version shown on the lathe bed in the first photo. For each degree that the larger hand wheel moves, it advances the drill .00014” or .0034mm about 1/7th of drill diameter. For each degree of movement the OD of the hand wheel travels about .026” or .66mm. In order to achieve this control, all backlash must be removed from from the tailstock spindle hand wheel. If not, any unwanted spindle movement from backlash could overload and bust the drill. This was accomplished by spring loading the spindle per fourth attached photo. One additional advantage of this was the ability to safely clear chips when drilling.

    Probably the unsafest part of drilling at this scale is the unknown reengagement point of the drill after retracting to clear chips. With no backlash in either direction, one can note the hand wheel setting upon retracting and return to that exact setting to reengage.

    At this scale, drilling is accomplished by very lightly and slowly advancing the drill one or two hand wheel degrees at a time until drilling is complete.

    Jerry Kieffer

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  2. pocketsrforwatches

    pocketsrforwatches Registered User
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    Does National Jet sell these drills? Looking at their website seems like they are primarily a service company but I may be missing something.
    Thanks for the post. Very interesting!
     
  3. Jerry Kieffer

    Jerry Kieffer Registered User
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    National jet provides a service to industry for those in need of micro drilling solutions. They not only provide contract service work, but manufacture drilling machines per a customers required specification as well as tooling for those machines.

    My first contact with this company was after purchasing one of their earlier 7A drilling machines (used) per attached first photo. The last I knew, they still produced this machine.
    The second photo shows the specifications of this machine and its drilling range from .0001" or .0025mm to .015" or. .375mm. Since they supply tooling including drills for this machine and others, I have been able to purchase drills from them from time to time. You have to call and discuss your needs.

    The third photo shows the 8" diameter calibrated depth control wheel on the 7A machine. If you note the depth control markings , they are about 10 times more sensitive than the lathe setup in the original post. However, they are also designed for drills 1/10th the diameter.

    While several machine tool supply sources sell micro drills, the following link is another example.

    Harvey Tool - Carbide Miniature Drills


    Jerry Kieffer

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  4. Uhralt

    Uhralt Registered User
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    Interesting. Looks like a very small mill. I wonder why they use such a big motor for such tiny drills....

    Uhralt
     
  5. Jerry Kieffer

    Jerry Kieffer Registered User
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    Uhralt
    The motor is extremely quiet, stable and perfectly balanced with no vibration.
    I suspect that may have had something to do with the selection.

    jerry Kieffer
     

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