Making a square mortise chisel attachment for the PM935 mill

[davidpbest]

I am primarily a woodworker, and needed a way to make square mortise holes in hardwood for a new project coming up. I decided to turn my PM935 mill into a square mortise machine for this project. This is the story of how I designed and made the adapter that would mount the square chisel on the mill.

This is what the chisel looks like - it's basically a precision ground square chisel that's hollow and an auger bit inside that does most of the work:

What I needed was a way to securely hold the square chisel on the nose of the mill. Similar adapters are made for conventional drill press equipment, but none of those would fit or work on a milling machine. I came up with this design:

It's a two piece adapter - one piece clamps onto the nose of the quill, the other is a donut-shaped adapter bored to hold the 19mm OD of the square chisel. The auger component of the chisel would be secured into the spindle with a conventional R8 collet.

I started with two drops of 4041 steel I found on eBay for about $40 delivered:

I then set about machining the two components on the PM1340GT lathe and the PM935 mill. Here are couple shots of how that progressed. Here's the main housing that will attach to the nose of the quill after rough sizing and boring:

Here's the donut-ring after rough sizing and boring:

And a test fit of all the components:

Back to the mill with the rotary table, I machined away large sections of the main housing to essentially produce three fingers to hold the donut-ring:

Then I refined the donut-ring to reduce weight:

And after drilling and tapping for the mounting screws, this is what I ended up with:

And here it is on the PM935 under test.

This was a fun project and the thing works great.

If anyone is interested in the complete build log with lots of video and photos, here's the link: Square Chisel Attachment

Thanks for viewing. Comments/questions welcomed.



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[zjtr10]

Good job as always!

 

[Illinoyance]

wow

 

[Illinoyance]

How are you holding the drill? I don't see room enough for a chucl.

 

[davidpbest]

The drill is held in an R8 collet.

 

[T Bredehoft]

Very nice job, I just hung mine on my drill press. But then perhaps you don't have one.

 

[davidpbest]

Very nice job, I just hung mine on my drill press. But then perhaps you don't have one.

You are correct. My mill serves as my drill press. It's a better quality machine than any DP I've seen, and the floor space saved is invaluable. Plus the mill DRO and XY table movement is often handy for woodworking DP applications as well. I've adapted a woodworkers DP table that drops into the Kurt vise and rests on the XY table. The holes for dowel pins on each side of the table register the fence coplanar to the X-axis.

This has served me much better than a clunky conventional drill press.

 

[Boxster9]

Thank you David for an outstanding documented video of your Mortise Drill attachment for a mill. This is definitely an improvement to my stand alone Powermatic Mortiser and a space saver as well. Thanks for the idea.

 

[FOMOGO]

Very nice piece of work there David. Cheers, Mike

 

[T Bredehoft]

You are correct. My mill serves as my drill press.

I must admit, when I last used the hollow chisel mortising tool I didn't have a mill. I made do with my sloppy Craftsman drill press.