Parallel dowels are not supposed to come out - are they?
I thought the idea was for locating, looking at the drawing the two dowels stay in the base (part). The top part comes off with the two screws, the two dowels are a good fit in the top part but stay in the base part, which enables the top part be replaced accurately. Now if one is going to "knock" them out (the dowels) then what was the point of putting them in.
Dave,
Cylindrical dowel pins are made slightly (.0005/.0002 inch) oversize to press nicely into the part to provide alignment. However, they
can be removed so long as a the
press is not too intense. You can then re-press them several times without having to go to an
oversize dowel pin.
The tool & die industry makes special
pull dowels that have (A) a groove (usually a spiral) around the OD to break the vacuum of a blind hole and (B) a tapped hole at the center such that you can use a screw and stack of washers to
pull the dowel pin. Commercial dowel pins are case hardened. So, unless you
break through the case, they are a RPITA to drill (and worse to tap).
American industry makes standard
press fit and
slip fit reamers for inch-sized dowel pins.
Slip fit reamers are usually .0015/.0010 inch oversize. If you look hard enough, you can find such reamers sized for different materials (LC steel, HC steel, aluminum, etc.) though LC steel is the most common set to find. They may have disappeared from the market, but they
used to make dowel pin reamers for hand usage (as opposed to machine usage). The difference is that they had between 2X and 1.5X the major diameter ground cylindrically before starting the back-taper (about .002/inch) that reduces friction.
I had to make my own fluted dowel pin reamers for tool steel, aluminum, and magnesium as an apprentice. It is amazing how
lessons of that variety stick with you...