Removing a damaged or broken screw can be a difficult task. Sometimes just the head breaks off and if you’re lucky, some exposed screw shank is left behind that you can grab with pliers. Other-times, you end up with a screw that breaks flush with the surface. Removal is possible with the right techniques and a careful setup.
For this job I ordered the following tools from Brownells:
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The gun shown here is a stainless steel Remington 700 with the front scope base screw sheared off flush with the top of the receiver. Just a sheared screw can be a difficult job, but this one is compounded by an unsuccessful attempt to remove it by drilling a hole that turned out to be off-center. Unlike the other screws on the top of a Remington 700, the front screw hole is blind, it bottoms out on the barrel threads; like the off-center hole, this makes removal more difficult.
As with most screw removal tasks, I always start by soaking the area in Kroil penetrating oil. While I plan on cutting out the screw threads, the Kroil will hopefully eliminate any extra sticking which is common in stainless steel parts.
I plan on cutting out the sheared screw on the milling machine. The 700 has a round action, to hold it in the vise, I need to hold it in a v-block fixture.
I’m going to use a 3mm 4-flute center-cutting carbide end mill. These have a diameter of .118″, the tap drill size for a 6-48 screw is .120″, so alignment has to be perfect before you drill a hole. .002″ off center in any direction and you’ll end up cutting threads. A center-cutting end mill will cut on the downward plunge and leave a flat surface. Traditional drill bits have a pointed-tip which would likely walk on an irregular surface like this broken screw.
I located the centerline of the action on the mill. Then I dial in the location of the hole along the x-axis using the shank of the 3mm end mill (I grab it gently by the flutes). Once I located this, I zero the DRO.
Front hole spacing on a 700 is typically around .8625″, I move the action over and check alignment.
Now with my mill’s spindle-speed turned all the way up (3,000 rpm on my Bridgeport), I make a slow plunge cut, retracting often to clear the chips. I’m cautious not to drill into the barrel. The 700’s action diameter is around 1.350″, the major diameter on a factory barrel shank is 1.0625; this means I can drill down to about .143″ deep without messing anything up. The end mill worked so well it evacuated the old screw’s threads from the hole with nothing left to clean up after the cut.
The sheared off screw is fixed. Note the damage to the front hole from the unsuccessful removal that was attempted before it was brought into the shop. Fortunately, it will be hidden by the rail.
The rifle is ready to go!