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1911 80% Tactical Machining Build, Part 5: Cutting the Slide Rail

Finally got the Tactical Machining 1911 Jig in the mail so I threw the 80% in there and got ready to cut the slide rails.

This is probably the hardest cut so I figured I’d do it first in case I messed up.  Disclaimer again.


You’ll also need the bits, drill press, sliding vise, calipers, & Dykem I mentioned in Part 2.  Tighten everything down and make sure you can smoothly move the main axis of the sliding vise.

1911 Slide Cutting Setup
1911 Slide Cutting Setup


Double check your resources and measure your slide with a good caliper.  For me, I am going to cut down .105″ from the top, and go .05″ deep.  The 3/32″ keyseat cutter comes out to be .09375″ while the slide’s thickness is .12″, so there will be some filing.  The square file in the file set tapers from around .09″ to .011″ so it should be good to go.

Dykem & Marking

Before you put the 80% into the jig, paint some Dykem on it.  I got excited and put it into the jig first before painting so you’ll see blue all over the jig in the pictures.  I would put it thicker next time too.  Do it in some well-ventilated place and let it dry.  Measure off .105″ on your caliper and lock it.  I put the edge of the caliper on the top of the paperweight and let the sharp edge cut into the Dykem.  Perfect!

Tactical Machining 1911 80%, Jig, and Dykem
Tactical Machining 1911 80%, Jig, and Dykem


Put the jig with the 80% into your vise.  Make sure you’ll have enough space to move everything around.  Last thing you want to do is reset halfway through when your jig hits the drill press.  I’m definitely guilty…

Get into Position

The TM jig fits well but you cannot expect it to hold the 80% perfectly level.  Use your level and if needed, move the jig around.

Leveling 1911 80%
Leveling 1911 80%

Move everything closer to each other so you can change the height of the bit.  I prefer to move the bit up and down rather than the platform.


Measure twice…or ten times, then get ready to cut.  I went for something around .04″ deep for the first cut.  Make sure you hold the jig steady and not yank it…you can see my deeper cut about half an inch from the right side.  Then just go nice and slow while holding the line you cut into the Dykem with the caliper.

Cutting 1911 Rails
Cutting 1911 Rails

Watch out when you near the end since I had the bit jump.  Nothing a little filing can’t fix!

1911 Rail Cutting Booboo
1911 Rail Cutting Booboo

I measured and everything was good, with just some variations from .04″ to .045,” so I went ahead with a second pass to get the proper end depth.

I setup the other side and did the same thing.

1911 Rail Cutting Opposite Side
1911 Rail Cutting Opposite Side

Keep the jig as is so you can do the barrel seating cut next.  You’ll have plenty of time to file and lap the slide to fit the frame.

Next Lesson

Part 1: Intro (Finding the 80%)

Part 2: Tools

Part 3: Parts List

Part 4: Basic Fitting

Part 5: Cutting the Slide Rail

Part 6: Barrel Seating

Part 7: Hammer & Sear Pin Holes

Part 8: Fitting the Slide

Part 9: Assembly & Fitting

Part 10: GunKote Application

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8 Leave a Reply

  • Commenter Avatar
    Bruce Henderson

    I was going over your article about building an 80% M1911 and, in part 4, I think, you note certain measurements as below. It would seem you mean that 0.09375 < 0.12, not 0.012 as stated. I am wrong about that?
    Thanks Bruce

    The 3/32″ keyseat cutter comes out to be .09375″ while the slide’s thickness is .012″, so there will be some filing.

    November 23, 2016 4:13 am
    • ehung

      Hi Bruce, I believe you are correct. Thanks for catching the mistake!

      November 24, 2016 10:29 am
  • Commenter Avatar

    What did you use to clamp the vise to the drill press?

    October 26, 2014 1:35 am
    • Eric Hung

      I used a couple bolts/nuts/washers I had lying around and aligned the vise to the base of the drill press the best I could.

      October 26, 2014 6:36 am
  • Commenter Avatar

    what rpm/speed did you set your press at? also how long to just cut the rails on the press(not file too)? did your bit stay sharp?
    thanks, thats a clean build

    September 7, 2014 4:38 pm
    • Eric Hung

      Thanks! I set my drill press to the fastest rpm. The actual cutting was very quick, probably a few minutes each side. I spent a lot longer just double-checking the positioning of everything. I also found no problem with the bit staying sharp for a couple passes on each side.

      September 8, 2014 1:13 am
  • Commenter Avatar

    Hi Eric,
    Where did you get specs for cutting the rails?

    Thank you

    July 24, 2014 8:49 pm
    • Eric Hung

      I got them from my Kuhnhausen book, but there's this link (choose 1911-A1 blueprints).

      But the best is to start there and measure your actual slide since that is what has to fit onto the receiver.

      July 25, 2014 12:11 am