Installing and repairing 1911-type grip-screw bushings: whether you're building up a new 1911 frame or repairing stripped-out grip screws, there are a few things you need to know about those tiny little bushings.
One of the pesky little problem areas with the 1911 frame is the grip-screw bushings. Whether you're repairing a stripped or loose grip-screw bushing or installing bushings on a new-gun project, there are a few things you need to be aware of to produce a professional-looking end result and to ensure the bushings stay in place through the firing of thousands of rounds.
Grip-frame screws and bushings for the 1911 have threads that are extra fine by most standards. The screws that hold the grips in place are .150-50 (that means .150 inch in diameter and 50 threads per inch) and the bushings that fit into the grip frame and hold the grip screws are .236-60. Because fine threads such as these are quite shallow from root to crown, these extra-fine threads are easily (and often) stripped or cross-threaded. The .150-50 grip screw threads are .012 inch from root to crown and the .236-60 grip bushing threads are .009 inch from root to crown, so you can imagine how easily these threads can get over-torqued to the point they fail to do their duty. Care needs to be exercised when fitting new screws with these shallow threads, making sure they go in straight when they get started into place.
With a new frame that's being used for a new gun build-up, I take the time to clean out the shallow threads in the grip frame with isopropyl alcohol to remove any grease or other debris that may be inside the root of these fine threads. I will then run a .236-60 four-flute tap into each of the four bushing threads in the frame. This ensures the root of these threads are clear of any burrs or chips left behind from the manufacturing process, and will remove any burrs that have been rolled over into the threads from the straight-line sanding done to the frame sides.
Each of the four grip-screw bushings are then cleaned with alcohol to remove any rust preventative or grease that may be captured in the threads. Once I feel safe that the mating threads are as clean as I can get them, each bushing is dry fitted into the frame by finger turning until the grip-screw bushing bottoms out to the frame face.
Securing the Bushings
Looking into the end of the grip-screw bushings that threads into the grip frame you'll see a chamfer cut into the inside edge of this diameter. This internal chamfer is meant to be flared outward with a staking tool to keep the bushing in place and prevent its rotation when tightening or removing the grip screws. The grip-screw bushings are small and this chamfer is slight, so rather than rely completely on the staking process to keep the bushings in position, I'll add a drop or two of thread locker as added insurance. If the bushings ever need to be removed later on, it's a simple matter to warm the bushing up with a propane torch to loosen the thread locker so the bushing can be removed.
The staking tool that has served me quite well over the years was purchased from Brownells. This tool has been altered a bit on the width of the working end. The width on this end has been milled from .750 wide to .455 wide for a length of .750 inch to give a bit more side-to-side maneuverability during use. The replaceable staking tip is extremely hard and has a blind hole that will accept the front end of a 1/8-inch diameter punch. The punch, of course, is what gets whacked with the hammer during the staking process.
Another must-have tool is a bench block that will support the side of the grip frame. No attempt should be made to stake grip-screw bushings into place without a support block of some sort, as damage to the bushing and/or frame could result. Bench blocks for this purpose can be purchased ready made or one can easily be fabricated in the shop. The support block I use for this purpose is a simple little block made from 1/2-inch-thick cold-rolled steel, 2 inches by 1-3/4 inches. A letter "B" size drill was used to drill a.238-inch-diameter hole completely through this block from top to bottom. A counter-bore was cut with an altered 7mm drill to a depth of .040 inch to create a nesting place for the collar on the grip-screw bushing. The 7mm drill was altered so that the cutting tip would create a flat-bottomed shoulder. This counter-bored flat shoulder will allow the grip screw bushing to have a solid resting place while this side of the flame rests against the block for more support.
All four of the threaded holes in the frame are then cleaned with alcohol along with the threads in each grip-screw bushing. Place a drop or two of thread locker on one of the bushings and then finger thread this bushing into one of the holes in the grip frame as far in as it will go. Turn the bushing all the way with a MagnaTip bit that has been especially made to accommodate these bushings. This driver bit has a slotted end tip captured in a tube that surrounds the outside diameter of the bushing to prevent slipping and possible damage to the side of the grip frame. Insert this newly placed bushing into the nesting hole in your support block. Slip the staking tool head inside the grip frame where you would normally insert the magazine, placing the coned tip of the staking head into the grip screw bushing. A 1/8-inch flat-end punch can then be passed through the above bushing hole through the frame until it passes through the blind hole in the staking-tool head. Give the top end of the punch a couple of solid whacks with a hammer and then rotate the staking tool as far as space will allow and give the punch a couple more whacks. The idea here is to upset the chamfered inside of the grip-screw bushing enough to hold it in place.
There are gunsmiths who don't feel the thread locker is necessary when installing these grip bushings. My opinion is, it can't hurt, and I like the idea of the extra holding insurance the thread locker provides.
When you come across a grip-screw bushing thread that's badly worn to the point where it's loose and won't tighten, or if you find one where the threads have been stripped or cross-threaded, there's a very simple fix to the problem. Brownells sells a set of four grip-screw bushings with oversize threads along with a .255-60 four-flute tap to create a new thread for the bushings. The inside threads on these oversize bushings are .150-50 so the normal grip screws can still be used.
As a final tip, when cutting new bushing threads for the oversized bushings, install the tap in a tap handle that has a center hole in the top end. Then chuck a center in your drill press and use this as a guide to help get these new threads started.
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|Title Annotation:||Tools & Tooling|
|Author:||Wood, Dennis A.|
|Date:||Nov 1, 2008|
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