# Making a square mortise chisel attachment for the PM935 mill



## davidpbest (Aug 11, 2019)

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 (Aug 11, 2019)

Good job as always!


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## Illinoyance (Aug 11, 2019)

wow


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## Illinoyance (Aug 11, 2019)

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


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## davidpbest (Aug 11, 2019)

The drill is held in an R8 collet.


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## T Bredehoft (Aug 11, 2019)

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


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## davidpbest (Aug 12, 2019)

T Bredehoft said:


> 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.


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## Boxster9 (Aug 12, 2019)

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.


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## FOMOGO (Aug 12, 2019)

Very nice piece of work there David. Cheers, Mike


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## T Bredehoft (Aug 12, 2019)

davidpbest said:


> 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.


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## 38Bill (Aug 12, 2019)

Wow! That is the nicest mortising attachment I have ever seen. I can see how that would be nice to have that with a DRO.


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## davidpbest (Aug 12, 2019)

38Bill said:


> Wow! That is the nicest mortising attachment I have ever seen. I can see how that would be nice to have that with a DRO.


Thank you.   It was a fun project, and I finally had a real project to test out the new rotary table.   I replaced my Phase II 8" rotary of 20 years with a new Vertex and the Vertex is a much nicer unit.   Some close machinist friends commented "you know, you could have made this out of aluminum and never noticed a difference" to which I replied "well, maybe you wouldn't notice the difference, but I would always know I took the lazy man's shortcut and didn't challenge myself if I didn't do it in 4041".    Excessive compulsive disorder you know.   LOL


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## stioc (Aug 13, 2019)

And you're primarily a woodworker?!


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## davidpbest (Aug 13, 2019)

stioc said:


> And you're primarily a woodworker?!


I'm not sure why this is so funny.   Enlighten me please.


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## stioc (Aug 13, 2019)

davidpbest said:


> I'm not sure why this is so funny.   Enlighten me please.



It meant that's top notch work (for someone who's not primarily a machinist).


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## davidpbest (Aug 13, 2019)

Thanks much.


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## bretthl (Sep 28, 2019)

The nice thing is you can run it as slow as you want.  I have an old Multico that will turn the bit blue if not lubricated which is not so good for a mortise and tennon joint.  I can see from your sketch your getting ready to punch a lot of those.


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## StevSmar (Oct 7, 2019)

Wonderful work David.

I find the idea of increasing the capability of an existing tool, so I don’t have the clutter of adding another tool, very satisfying.


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