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Pt1: An Endmill Flute Grinding Fixture (EMFGF) for the Cheezy Surface Grinder (CSG)

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  • Pt1: An Endmill Flute Grinding Fixture (EMFGF) for the Cheezy Surface Grinder (CSG)

    Aka: The (will it end?) story of the sow's ear and the silk purse MacGyver.
    Aka: "Air Bearings? We don' need no stinkin air bearings."


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    ¿Qué es? An ER32 collet spindle, a flat spring housing on the other end, and a flute guide finger cobbled onto one of the ubiquitous Taiwan/China cheezy surface grinder castings of the 70's-80's (whose progeny still appear, as in the Tormach Personal SG, and at MSC, Grizzly et. al.) Yeah, fixturing cheeze on top of cheeze, but it actually worked pretty well once all was said and done. Worth it? Nah. Not unless you got lots of The 'Rona Time.


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    Procedure:
    a) Indicate fixture parallel to grinder spindle. Adjust finger rest to just clear plane of grinding wheel, on center with the spindle axis.
    b) Set the finger height into the down-facing flute gullet of a 2,3,4,n-flute end mill.
    c) Position CSG longitudinal table to yield desired flute primary land relief angle. Lock table!
    d) Wind EMFGF spring cartridge 3/4 to 1 turn and engage a flute.
    e) Downfeed grinding wheel, contacting the up-facing flute. Traverse CSG crossfeed out once (grinds endmill tip towards shank). Downfeed 'til happy with result. Do a traverse for remaining flutes, re-clocking spring to same wind tension so grinding forces/deflections tend to replicate for each flute. (Helps to mark/number flutes to keep from getting lost.)
    f) Re-position CSG table for desired secondary relief angle, and Lock. (And raise finger a bit back into flute gullet for small endmills.) Repeat d,e) 'till you narrow the primary land width to what you like.

    The #&%! Spindle Part:
    Made from junk, not counting two automobile tapered roller bearings, ER collets & nut. This idea began with a store-bought ER32/MT3 chuck lying around unused. The bearings were originally picked to hold a battered MT4-MT3 adapter in a housing made of drill stem and a 3/8" plate base, with the rash assumption that the ER32 chuck could be inserted to make an adequate rotating spindle. But the end result was rubbish .006" run-out, so the MT3 adapter was re-ground in-situ (with a Dremel flex shaft grinder attached to the CSG arm). But this still gave poor repeatability; an internal MT3 is a long taper to grind with rubbish methods. And the whole mess had way too much tool extension. (An MT3 shank gives no thru-hole in which to recess the endmill.) With too much time already invested, the (il)logical thing to do was blunder on to Round 2!


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    Salvaged the housing and bearings by making a straight-shank ER32 chuck to fit, out of scrap hydraulic rod, through-bored larger than largest collet. Roughed in ER taper and threaded on lathe. A lawn mower rope starter flat spring was coiled inside a VCR head, along with another VCR head to make a belt pulley (for use as motorized spin fixture) and came up with a hack to adjust bearing preload. The spring cartridge can be captured via a thumb screw so that it will a rotational force to the spindle. When un-captured, the spindle and spring cartridge free-wheel. [A second round of spring cartridge design employed a lighter chainsaw starter spring.] The spring can be flipped over to reverse the rotation for left-handed endmills. But you also have to diddle with the finger rest.

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    Continues Pt 2.
    Last edited by wbc; 03-29-2021, 02:33 AM.
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