Jayhawk adds a spacer in between the base and the colum to get enough height for the bit mount into the speed chuck and clear the ball. This is with the Tri-Oval Jig.
I know this from experience I bought a Mill Drill separately and added the Tri-Oval Jig to it. Bought a JMD-18 from Jet but it ended up being a hybrid of the JMD-18 and the larger model. So I had to create a custom spacer for mine. It was quite a bit of work but have a great machine now. I can't thank Russ Wilson from Jayhawk enough for his help.
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Rick Guined
Owner/Operator: New Millennium Proshop:
http://s239.photobucket.com/albums/ff183/Guined/Vise PBA Regional Staff Player
IBPSIA Certified Technician
USBC Bronze Certified Instructor
www.viseinserts.com