02 November 2012

diy reverse drawbar

End mill holder with my "reverse drawbar" arrangement

A common question on machining forums across the internet is about making a drill press into a milling machine. The consensus answer is "don't try it, don't even ask".

From what I can see, the most common reason not to do it is that there's no drawbar and the side loads put on the endmill do not allow whatever taper is used on the drill press to hold well enough. Eventually the chuck or whatever holder you have will fly out of the spindle.

The second most common reason I see is that the drill press is not beefy enough to provide a stable platform.

Read on for my version of the infamous "drill press mill".



My solutions

1. Stability - In my case, the drill press is massive relative to the objects I intend to mill, so I'm calling this one not really a problem. Here's the specs on the drill press:




2. Drawbar - Unfortunately the spindle is not drilled for one, and at almost a couple feet long, I have no hope of actually drilling it myself.

So, after a few failed attempts to rig up a holder that fit within the #3 Morse taper drift opening I came up with something that works(yes, that little block of steel on the left started life as a Uni-Strut nut).
End mill holder with reverse drawbar arrangement

Basically I started with an endmill holder with 3/8-16 drawbar hole in the top. I cut about an inch of 3/8-16 stainless all-thread and drilled a hole down through the center of it to allow a 8-32 SHCS to fit through.

Endmill holder inserted with SHCS  sticking up through


Then I made up a little block of steel to fit inside the drift insertion area above the Morse taper inside the spindle. The block is made to just fit in there and remain upright, with a 8-32 hole threaded into the bottom facing down at the endmill holder.
Endmill holder inserted with SHCS  just engaging threads in  "little steel block"


The end result is that you can tighten the 8-32 SHCS into the little bock of steel, which pulls the block down against the bottom of the drift insertion "window" in the spindle. As you tighten it, you're also pulling the endmill holder up into the taper, because you can't pull that little block of steel down any farther than the bottom of the drift insertion "window".
Endmill holder inserted, SHCS tightened  with "little steel block"
 seated at bottom of drift insertion "window" in spindle


The little block of steel is trimmed on the ends to not extend out past the spindle diameter, so it misses the quill with plenty of room to spare, so the spindle shaft turns fine.
Endmill holder and reverse drawbar all seated
 and spindle turning inside quill

I had to cut a common screwdriver groove into the 3/8 all thread so I could screw it into the endmill holder. Also I mangled up the threads a little so that it would get a little more "stick" down inside the endmill holder. There was a tendency for the all thread to turn with the SHCS as you tightened down. That's gone with a washer and just a couple threads on the all thread crimped up.

All in all, it works fine and I'm not worried about the endmill holder flying out of the taper and making a mess.
first quick test mill

2 comments:

  1. I have a really heavy duty Clausing 20" Drill press (700 lbs.) I'm trying to do something like that..

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