UJK Parf Guide Mark 2 blowout on bottom of holes

[jcrowe1950]

Hi All,

    I have finally gotten around to using the Parf Guide Mark 2 to create a couple of MFT/3 tops one traditional and one isometric. I used Osmo Polyx over a high grade of MDF prior to drilling the holes. I had some blowout issues on the underside when drilling the 20mm holes....otherwise it was a fantastically useful experience. FWIW, I did use my CXS which was not really challenged per se, but could have been a bit stronger. Anybody have any suggestions?
[jawdrop]

 

[MikeGE]

I used the same guide to drill 200 holes in a 1x2 meter piece of 19mm Valcrhomat top (denser than MDF).  I used the "tap-tap-tap" method Peter recommends, and I had blowout on over half of the holes.  The blowout wasn't too bad and was never more than 1mm, but it was still annoying.  If I make another top using this material, I will put it on a sacrificial sheet of normal MDF and make sure the 3mm pilot hole goes far enough into the MDF to make room for the pilot point on the 20mm cutter.

I made a few practice holes on 18mm MDF, and didn't see any blowout.  Assuming you applied the Osmo Polyx to both sides, maybe the problem you had was due to the bottom surface being too hard (brittle).  The brittle nature of Valchromat seems to be the reason for the blowout on my workbench top.

 

[woodferret]

Once the 3mm holes are drilled, flip the top and just by hand run the forstner bit lightly around to score the surface.  I tried backing blocks to no avail and this was the only thing that worked.

 

[Rick Herrick]

I did the same method, only with the 20mm bit that came with the UJK kit.  Just broke the surface.  Wasn't perfect but very acceptable.