Saturday, April 21, 2012

A Typical Gunsmithing Problem

About a 18 months ago, I bought a couple of Savage 64F, semiauto .22 rifles.  They're fine, modern rifles, and similar to the same price class ($150-ish retail) rifles from other sellers. 
Like many other rifles in its class, the stock has to be removed to clean it, and some disassembly is required.  This is where the problem starts.  This picture shows the barrel, trigger assembly, magazine holder - pretty much everything besides the stock, upside down in a gun vise:
To the left of the magazine holder (sticking up with a "keystone" shape opening) is a screw with lockwasher, and an open hole to its left.  What goes in that hole is a round piece of steel: one end of this is an external threaded stud to screw into that hole, and a tapped hole on the other.  The internal threaded hole receives a screw that holds on the stock - there are two screws and the other one goes in that tall hex-nut on the right.  Somehow, that threaded hole on the left in the rifle got barfed up.  

This is the piece that goes in that hole.  It's about 3/4 inch long and .450 diameter (the round part).  It doesn't appear to be any sort of high-zoot alloy, and is finished in "something black".  I was able to get a replacement from Savage, but that didn't solve my problem (I didn't know threads in the rifle upper were damaged until I got this).  The threaded stud on the top of the piece is 10-32.  The internal thread is an odd one: #12-32. 

When the threads in a hole get barfed, there's not much you can do except tap it for a larger hole or weld some filler into it and try to drill and tap it again.  Since I don't have welding stuff, adding filler is out.

On the other hand, I do have a micro lathe, so I decided to make another one of these threaded pieces, and make the 10-32 stud into 12-32 as well.  Then I'll tap the rifle for 12-32 and see if I can get it back together.  My local Grainger didn't have any 12-32 taps, but Midway did.  If 12-32 doesn't hold, I either will go to 1/4", or it's time to scrap it. 

And that's how I spent my Saturday.  I have a few feet of steel bar - 12L14 a general purpose alloy that machines easily.   First, I cut a long enough bar to machine what you see there, then turned the large and small diameters.  Next, I cut the threads on the stud portion with single point threading on the lathe.  I used the replacement from Savage to test the 12-32 threads I cut - they thread together fine (I don't have any other 12-32 hardware, and it's always reassuring to check threads you've cut).  The only things left to do in the morning are thread the internal hole in the steel with the Midway tap, and put a screw driver slot in it (visible bottom left in that picture).  I'll have more info tomorrow. 

13 comments:

drjim said...

Why not use a Heli-Coil or a Keensert?

http://www.emhart.com/brands/heli-coil

http://www.newmantools.com/kee.htm

Ownerus said...

That was my first thought too. 10-32 helicoils can probably be picked up at your local auto parts store, including the tap and installation tool. That way the other standard parts still fit too. FWIW

Graybeard said...

I'm not sure how much room there is in this piece and how much a Heli-Coil needs. It feels like there's only a couple of threads engaging in the hole and it's a thin piece, maybe 1/8" at most. Hard to see in that picture.

Either way, the hole in the rifle gets bigger, so the impact is the same. From the outside, it's looks like the stock rifle: the screws that hold the stock on are the same. My threaded standoff is not standard, and it might look different inside, but I'm looking at finishing options.

They used a lock washer under this piece, which clearly didn't lock it in place. I think I'm going to use Lock-Tite in there.

Diogenes said...

And that is, if not the sole reason, one at the top of the list, Why I will NEVER get rid of my lathe (unless its in an upgrade)

Graybeard said...

Absolutely.

This may sound strange to some, but one of the reasons for doing it this way was to ask how I'd do it if the supply chain was down or seriously disrupted and I was pretty much on my own.

RegT said...

SG,

For someone without a lathe and the knowledge of how to use it, is the stress on that piece low enough that you could fill the hole with JB Weld or a similar epoxy and then drill and tap? I know that wouldn't be a good choice, that an insert would be better, but would that possibly work?

Ownerus said...

A perfectly good reason. I've fixed more things than I can count just because I could when most would have just thrown it away. And why you need TWO lathes and TWO mills...in case one needs repair... ;^)

Graybeard said...

I wish I could answer that...

I don't know enough about the properties of JB Weld to say.

Theredneckengineer said...

Just now saw a reference on my sitemeter of your blog. I'm glad I saw it, it appears that you've got a lot of good stuff to read about here. You've been blogrolled, and I'll be back to do some more reading and a bit of learning.

Graybeard said...

You might have noticed I blogrolled you last night. We have a lot of interests that overlap, and read some of the same people. Plus, I was studying to be a chemist (biochemist) before I eventually ended up as an electrical engineer.

Theredneckengineer said...

How ironic. It does indeed seem we have much in common, though I would wager I could learn a lot more from you rather than the other way around.

I was originally going to work on a degree in chemical engineering before settling on the degree in M.E. that I am currently working on.

How did you find my blog, if you don't mind me asking?

Graybeard said...

I read Borepatch and Smallest Minority all the time. They posted a link to your post about it, and your .50 cal. I know I've been there before, so figured I'd add yours to the list to check on.

Theredneckengineer said...

Ah. I see.
They are both great people to meet and shoot with. I felt kinda embarrassed to bring my .50 out given its homebuilt status and rather roughshod, homely appearance, but they were very complimentary of it.
I'll have to check back on your projects here. It is encouraging to see that there are others who are preparing for the inevitable rebuild after the collapse.