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Setting-Up and Using a Bench Top Drill/Mill for Firearms Applications
by Roy Seifert

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Disclaimer:  This article is for entertainment only and is not to be used in lieu of a qualified gunsmith.  Please defer all firearms work to a qualified gunsmith.  Any loads mentioned in this article are my loads for my guns and have been carefully worked up using established guidelines and special tools.  The author assumes no responsibility or liability for use of these loads, or use or misuse of this article.  Please note that I am not a professional gunsmith, just a shooting enthusiast and hobbyist, as well as a tinkerer.  This article explains work that I performed to my guns without the assistance of a qualified gunsmith.  Some procedures described in this article require special tools and cannot/should not be performed without them.

Warning:  Disassembling and tinkering with your firearm may void the warranty.  I claim no responsibility for use or misuse of this article.  Again, this article is for entertainment purposes only!

Tools and firearms are the trademark/service mark or registered trademark of their respective manufacturers.

I’ve always wanted to do light-duty milling work to my own firearms.  This includes cutting front and rear sight dovetails, milling the rear of a 1911 slide to accept a low-mount rear sight, and cutting front cocking grooves on the front of a 1911 slide.  After completing this project, all my shooting buddies now want me to mill dovetails and front cocking grooves in their pistols!  So far I’m doing it for free under the agreement that I won’t charge them if they’re willing to accept mistakes while I’m learning.  Although this article is a bit lengthy, it explains everything I did to get the results I wanted.

I didn’t have the money for a heavy-duty floor-stand milling machine, nor did I think this was necessary.  I also felt some of the mini/micro-mills on the market weren’t stable or heavy-duty enough for the kind of work I wanted to do.  After some additional research I settled on the 12 Speed Drill/Mill Machine (item number 42976-3VGA) from Harbor Freight Tools.  Unfortunately, they no longer sell this model, but they have other similar models available.

This machine is a combination drill press and vertical milling machine with a swivel head that fit my budget, but seemed heavy-duty enough for the stability I needed for my firearms applications.  The head also raises and lowers on a column to adjust for different sizes of work stock.  I have found that most multi-purpose devices such as this perform each function almost, but not quite as well as a dedicated machine, but more about this later.  

Tool Stand
Before the machine arrived, I wanted to have a place to mount it.  My local Lowes hardware center had a Kobalt 4-drawer workbench with pegboard back (item # 47106) that I decided to use.  After I unpacked the workbench, I discovered that the bench top was made of fiberboard.  Fiberboard has a tendency to dissolve when it gets wet, and I knew that milling required using cutting oil, so I decided to laminate the top and edges.  There are plenty of how-to instructions on the Internet for laminating so I won’t go into it here.  However, having carbide-tipped laminate trimming bits for my router really made the job easy and professional.

Unpacking and Clean-UP
The drill/mill machine arrived by truck packaged in a wooden crate.  It took about 30 minutes to unpack it from the crate.  After removing the plastic cover, I found the machine was liberally coated with gooey rust preventative oil (RPO).  It took two cans of brake parts cleaner and numerous paper towels to get it clean (although I can still put my hand in places and come away covered with RPO)!

The machine came with a tray used to catch chips and oil.  It had four holes for the mounting bolts, so I used it as a template to drill the mounting holes in the bench top.  To prevent the tray from moving while positioning the machine, I drilled and countersunk two holes on either side of the tray for a #8 wood screw.  This machine is heavy so I had three other people help to lift it onto the workbench and get it positioned.  Once in position I bolted it in place.

In the process of mounting the machine, I discovered the tool board on the back of the workbench interfered with the machine and prevented me from mounting it on the bench top.  So I cut the horizontal bracket and shelf and repositioned one vertical bracket to open up one half of the back of the bench to accommodate the rear of the machine.  I had to add an angle bracket to support the vertical bracket I moved.

First Trial and Problems
I had ordered some cheap high-speed steel (HSS) milling bits so now I wanted to try out my machine.  I mounted the machinist vice on the milling table, and using the metric draw bar, installed the taper and 3-jaw chuck.  I tightened the draw bar fairly tight; having no experience or knowledge, which turned out to be a big mistake!  My neighbor, Brad, is a machinist so after helping me install the machine; he gave me an assignment to make a drill drift.  A drill drift is a piece of steel bar, about one inch wide that tapers towards the end.  It is designed to remove a taper from the mill spindle.  I clamped two pieces of steel bar in the vice, chucked my 1/2” HSS square end mill bit in the 3-jaw chuck, set the speed to 540, and proceeded to try to mill.  

I discovered a number of problems with this setup.  First, the chuck had 0.003” run out, so I wouldn’t be using it to mill gun parts.  Second, if I cut too deeply in the steel, the bit would chatter which caused the swivel head and column to rotate and the chuck to fall off the taper!  Hmmm, this is not good and would need to be fixed!  Finally, since I tightened the drawbar so tightly I couldn’t get the taper out of the spindle!  So much for sending an amateur out to do a professional’s job!

Preventing Head and Column Swivel
My solution to preventing the head and column swivel was to install some setscrews.  The machine head is mounded on a hardened steel column that allows it to swivel.  It is held in place with a handle that squeezes the head casting around the column to keep it from moving.  The base of the column has a bar with teeth mounted on the side to allow the head to be raised or lowered.  This is also locked by a handle that squeezes the base casting around the column.  When my milling bit chattered in the steel, the head was rotating on the column, and the column was rotating in the base, even though the handles were locked.


I swiveled the head all the way to the left, a position I felt I would not be using, and drilled a hole completely through the head casting and column of appropriate diameter for tapping a 3/8”–16 thread.  The column was only surface hardened, so after breaking through the hard surface the drill bit cut easily.  I then tapped the 3/8”–16 threads through the casting and column.  I positioned the head to where I felt I would do most of my milling work and drilled a detent in the column through the threaded hole, being careful not to damage the threads.  Then I installed a 3/8”–16 allen-head setscrew to hold the head in place.  This plus the handle prevents the head from rotating.

I then raised the head all the way up as far as it would go, and drilled a hole through the base casting and column.  I also threaded this hole for a 3/8”–16 set screw.  I lowered the head and drilled a detent in the column for the height at which I would be doing most of my milling work and installed the setscrew.  The setscrew and handle now keep the column from rotating in the base. 

Bigger Problem
My next problem was not being able to remove the taper with the 3-jaw chuck.  My over-tightening of the draw bar caused this.  I enlisted Brad's help and we pounded on the draw bar trying to get the taper out of the spindle.  All we succeeded in doing was to remove the spindle from the machine, bearings and all!  The spindle had an opening for the drill drift, but that was filled with the draw bar.  I decided I could sacrifice the draw bar and order another one if necessary, so I installed a 1/4“ HSS milling bit in my small bench top drill press and milled through the draw bar through the drill drift opening.  I left just enough of the draw bar showing so that we could get a drill drift in there, and after some radical pounding with a heavy ball peen hammer, we succeeded in breaking loose the taper from the spindle. 

It was easy enough to press the spindle back in place by pulling down on the drill press handle with the spindle resting flat against a piece of wood.  To keep the spindle from coming out again I degreased the outside of the bottom bearing and inside of the casting and reinstalled it with a little Loctite 609 green.  609 is used for press-fit assemblies.

My First Milling Instruction
Brad sat me down and we spoke of milling things.  He patiently explained how the taper worked, and what the draw bar was for.  The spindle has a taper, which is used to install cutting attachments such as the 3-jaw chuck. There are different types of tapers; this machine has a Morris #2 (M2) taper.  The 3-jaw chuck and taper should be installed by quickly “popping” the assembly in place in the spindle.  It should NOT be installed with the draw bar.  The chuck is used for drilling, not milling, and the downward pressure of the drilling action holds the taper in place.  To remove the taper, lower the spindle until the drill drift opening is visible, insert the drill drift and hit it with a mallet.  The chuck and taper assembly should drop in your hand after only a moderate tap on the drill drift.

Milling bits should be attached to the spindle using a collet.  A collet is a split cone with a hole in the middle to accept a milling bit.  The angle of the cone matches the taper in the spindle.  The rear of the collet is threaded to accept the draw bar.  The collet is threaded onto the draw bar, the shank of the bit is inserted into the bottom of the collet, and the entire assembly is inserted into the spindle.  A nut and washer is then attached to the top of the draw bar.  When this nut is gently tightened it “draws” the collet up into the taper, which squeezes the fingers of the collet to hold the bit tightly in place.  The draw bar should be snug, not tight, so that loosening the nut and rapping the top with a mallet can easily remove it.

Ok, back to the Internet to find the appropriate collets for my M2 taper.  My search engine brought up the Little Machine Shop, which specializes in providing tools for mini/micro/bench top machines.  I purchased their set of M2 Collets (item #1752).  This set comes with seven collets in sizes 1/8", 3/16", 1/4", 5/16", 3/8", 7/16", and 1/2", which I felt would be all that I needed for my work.

Draw Bar
Remember that I damaged the original metric draw bar that came with the machine while removing my over-tightened taper.  The new collets required a 3/8”-16 draw bar, so I really didn’t have to replace the metric one.  The original draw bar had an M10 threaded end about 1/2” long attached to a narrow shank about 11” long.  The end of the shank was threaded to accept a nut.  The M10 end was threaded into the taper; the shank went through the length of the spindle, and a metric nut was affixed to the top of the draw bar on top of the spindle.

I fabricated a new drawbar by cutting off 1/2“ of threaded end from a 3/8”-16 bolt, then drilling out the center to accept a 12” piece of 1/4“-20 threaded rod.  I tack welded the threaded rod into the bolt end, and viola I had an acceptable draw bar.  The threaded rod wasn’t exactly perfectly centered or straight, but the hole in the spindle was wide enough to accommodate my sloppy work.  I also discovered that a standard 1/4“ flat washer was too wide to use with my homemade draw bar.  When I pulled down on the chuck feed lever the washer got caught on the pulley.  So I reduced the diameter of the washer so it would fit inside the pulley when the chuck was lowered.

To remove the draw bar and collet from the taper, I took a 2” x 2” square piece of oak and drilled a hole halfway through just wide enough for the draw bar nut.  To remove the draw bar, I first fix the chuck with the chuck fixing lever; this prevents the spindle from moving down when I hit the piece of wood.  I unscrew the draw bar nut until it is all the way to the top of the draw bar and covering the top threads.  I place the wooden block over the nut and rap it with a rubber mallet.  It should only take a moderate hit to loosen the taper.  I make sure to hold my hand under the bit to prevent it from falling out and striking the table.  This can damage both the table and the bit.


Dial Indicators
Milling is a precise operation that requires exact measurements, especially when working on firearms.  As well as being able to take precise measurements, you also need to be able to “do the math.”  The math I’m talking about is adding and subtracting of fractions, converting fractions to decimals, and some basic geometry of angles.  My first set of precision tools included a dial indicator, travel indicator, and adjustable magnetic base.  These are available from Little Machine Shop for a very reasonable price.  You can also find these items on ebay.  Using the dial indicators is easy if you remember that you need a fixed, non-moveable point of reference, and a moveable point of reference.


Another tool I needed was a set of parallels.  These bars are milled perfectly flat and square and are used to ensure the work is mounted in the vice perfectly square and level.

Measuring Level and Run Out
The first thing I wanted to measure was the accuracy of the setup of the machine.  First I measured run out on both the chuck and collets.  The chuck had 0.003” run out (± 0.0015”), but the collets had 0.0” of run out.  This will be great for milling!  I measured this by placing the magnetic base on the cross-slide table and touching the dial indicator to a bit mounted in either the chuck or collet, then I rotated the spindle to read the indicator.

Next I measured how level the cross-slide table was.  I mounted the magnetic base to the non-moveable base of the machine and touched the tip of the dial indicator to the tabletop.  I moved the table back and forth and side to side and the dial indicator stayed at 0.  Well, everything is setup correctly, but I’m still not ready to mill yet.

Machinist’s Swivel Vice
The machine came with a 70o machinist’s swivel vice, which means I can rotate it ±70o from center.  The jaws of a machinist’s vice are supposed to be perfectly flat and parallel, and the base between the jaws is also supposed to be flat and square to the jaws.  I mounted the vice to the cross-slide table using the T-bolts provided.  In order to accurately mill a sight dovetail the vice needs to be perfectly square to the direction of travel of the cross-slide table.  To measure this I cut a 3” piece of 3/8” steel rod which I mounted in the 3/8” collet and put in the spindle.  I then attached the dial indicator to this rod using the attachment from the magnetic base.  The tip of the dial indicator rides along the inside edge of the fixed side of the vice.  I moved the cross-slide table parallel with the vice jaws and rotated the vice until the dial indicator read 0 for the entire width of the vice.

End Mills
We’re just about ready to begin milling, but first we need to “tool up” with the appropriate milling bits.  This machine uses end mills, which are similar to drill bits but have a different cutting edge.  Standard end mills have either a square end or a round “ball” end.  There are other end shapes available, such as dovetail, but think of an end mill as a router bit for metal.


When purchasing end mills, buy carbide.  Carbide allows you to run your machine faster, they seem to cut smoother, and they last longer.  Another search on the Internet brought me to Sun Coast Precision Tools Inc., which has a large selection of carbide end mills.  I bought a selection of end mills from 3/32” to 1/2“.  Front cocking grooves seem to be either 3/32” or 1/8” so I bought four of each.  I also purchased a selection of HSS dovetail end mills from Brownells  in order to cut front and rear sight dovetails.  Since these bits are HSS they should not turn above 700 RPM, so when I use these I set my speed to 540.

My First Dovetail Slot Cut
I really didn’t want to practice on a real gun part so Brad brought me a 5” piece of 3/4“ bar stock.  Machinists will tell you that it takes longer to set up the work than to do the cut.  Please refer to my article Milling a Front Sight Dovetail for details on how I measure and cut a dovetail.

Front Cocking Grooves
I had purchased a used Federal Ordnance 1911 .45 and wanted to practice my milling on it.  My first project I decided to be front cocking grooves.  I wanted the grooves to be vertical to match the rear serrations, and I wanted them to be narrow 3/32” instead of 1/8”.  First I leveled and squared the slide in the vice.  I used the correct height parallel to accomplish this, but checked it with the dial indicator anyway.  I set the rear of the spring tunnel against the edge of the vice as an index point.

The front cocking grooves can’t be too deep because I don’t want to weaken the slide, but the edges need to be sharp enough for the fingers to gain purchase, so I adjusted the travel limit screw accordingly.  Again, to prevent the bit from breaking I took four passes with each groove, going just a bit deeper with each pass.  Even so, I broke one bit and left a mark on one edge of one groove.  After I completed one groove, I used my travel indicator and moved the work twice the thickness of the bit to cut the next groove.  This made sure the distance between each groove was the same as the width of each groove.  (I did this to the slide of one of my friends and my travel indicator slipped without me noticing it.  The gap between two grooves was just a bit larger than the other gaps.  Lesson learned:  be very careful.  As they say, “measure twice, cut once.”)  After I cut five grooves, I flipped the slide over and again set the rear of the spring tunnel against the edge of the vice.  After ensuring the slide was square and level, I cut the grooves in the other side.  Before refinishing the gun I polished the tool marks out of the grooves with 320-grit wet/dry paper wrapped around a jeweler’s file. 

Rear Sight
After completing the front grooves, I milled the rear of the slide to accommodate a low-profile Millet adjustable sight.  I had to purchase two additional end mill bits for this job; a standard 3/8” dovetail cutter, and a 3/16” round end cutter.  The instruction sheet provided by Millet with their sight gave all the cutting dimensions.  The round end mill was used to mill a groove on either side of the slide for the rear sight.  (Yes, I refinished the gun with Dura-Coat in an Urban Camouflage pattern!  You may laugh or you may sneer, but the work is all mine!)

In spite of what so called “experts” say, you can perform firearms work with a bench-top milling machine.  The machine must be heavy and stable enough to perform the precision work necessary for firearms.  Also, you need to have the proper measuring tools to ensure your work is precisely aligned, and when necessary, moves a precise amount.  There’s nothing like the satisfaction of doing a job yourself, and doing it well. 



Web Site



Harbor Freight Tool 42976-3VGA 12 Speed Drill/Mill
Lowes 47106 Kobalt 4-Drawer Workbench
Little Machine Shop 1752 M2 Collet Set
Little Machine Shop 1249 0-30-0 Dial Indicator
Little Machine Shop 1782 0-1” Dial Indicator (Travel Indicator) with adjustable magnetic base
Sun Coast Precision Tools Inc.   End Mills
Brownells   Dovetail end mills
   © Copyright 2008 Roy Seifert.