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Hi guys,
a friend brought over a very nice Zastava model 70 in .308Winchester but it had a broken screw in one of the holes on the receiver for securing scope bases. The top of the broken screw is flush with the top of the receiver. I would appreciate any suggestions on how best to remove this screw. If the screw can't be removed then I suppose the other option would be to have the a new set of holes drilled and tapped.
you thoughts would be appreciated.
best
atr
Take it to a good gunsmith or machine shop along with the scope base
Thread should be 6-48
They’ll put it in the mill and drill it out undersized and clean out the threads
I have removed them by using a left handed bit smaller than the hole.
I often have drilled like 1/16" hole in the broken screw.
Then I pounded an Allen wrench that fits snug into the hole.
Then just unscrew the broken screw.
You might want to warm up the receiver a little in case the screw is rusted in place or is bottomed out in the hole.
Be sure you drill the hole in the center of the broken screw.
Also.
Putting a drop of Crazy Glue on the tip of the Allen wrench helps it attach better when you drive it into the broken screw.
You can use a small prick punch to walk t out by tapping it in the right direction. If its been locktited this will be a lot harder. I have removed a lot of screws like this. You can drill it out with a solid setup, a left hand drill works best. I would start with a clay dam and soaking in kroil for a couple days
A solid drill press min better a mill, center drill and then drill keep the bits as short as possible for rigidity.
If it was my gun I would heat up the broken screw with the soldering gun and then try to walk it out with the smallest drift or an awl if it is possible to do so without skipping and damaging the bluing or scratching the receiver.
One tip I use is to put the gun under a magnification lamp, and CAREFULLY flatten the broken area of the screw PRIOR to trying to drill it or tap it out etc. I use a dental burr in a Foredom tool to do this. Go slow, flatten the piece,, the start the removal process. And as noted,, heat or soaking in Kroil is also very desirable.
If you don't want the gun all dinged up - take it to a machine shop. An automotive machine shop will work fine. Removing broken screws is bread and butter for them. Just be aware that you may be required to wait at the shop while they work on it if they are not a licensed FFL.
There is a tool called and EZ-out (SP)
https://www.harborfreight.com/screw-...a28801593589fe
You can get a cheap set from Harbor Freight or maybe better ones elsewhere.
You still have to center drill the stuck screw. Heat, pen oil, etc. help but it not locktited should come right out. Like most machining operations getting set up right is very important. Need a good vice, drill press or mill. Need to center punch and be close to level. Since you are using an undersized drill you don't have to be perfectly level (perpendicular). Like others have said, a shorty drill bit or just chokeup on it so it doesn't wobble, you are not drilling a deep hole and you don't want to hit the bottom of the hole.
Tim
This thread has convinced me to buy a set of left hand drill bits, to have around just in case. Are left hand drill bits used for anything else?
Build the broken screw up with a Tig until proud, weld a scrap of flat to this and unwind once cool.
If scrap breaks reattach. The heat will cook any locktite, the expansion and cooling also helps to break free rust etc
You can use a LH bit the same as a RH bit to drill a smooth hole. Most folks use the LH bit with a centr drill bit, to remove broken RH bolts or screws. It is quite normal process in shops. They tighten stuff, real well and some bolts or screws are defective and just snap off. But the public has no clue hen it comes to thread locker, if a little is good, a lot is better, so pour it all over everything, making a huge mess.
While on the subject, clean the screw hole and screw shank threads with acetone on a q tip. Put a toothpick's tip size drop on the screw thread only, just one little drop on one side of the shank. Screw the scope base screws in tight. No more thread locker than that.
ditto this. a fine tipped diamond abrasive or center punch to start it straight.. then drill out left. unless a red loctite was used.. usually the bit pulls the screw out before you get thru it anyway.Quote:
Originally Posted by pworley1
[QUOTE=country gent;5580122]You can use a small prick punch to walk t out by tapping it in the right direction. If its been locktited this will be a lot harder. I have removed a lot of screws like this. You can drill it out with a solid setup, a left hand drill works best. I would start with a clay dam and soaking in kroil for a couple days
This method has always worked for me also. Use patience and a steady hand, even take more than one attempt. I fussed with one for 3 days and it finally started to move.
Can't use a left hand drill bit on my drill press or lathe, they don't reverse.
Small lefty and a hand drill. Just get it centered..pin punch or a diamond bur. Slow is often better.. You pretty much WANT the bit to grab and extract the screw.
The left hand drills work great.
But finding them and spending that money for something that you probably only use once in a great moon isn't that good for the average guys.
But if you are a full time gunsmith they are well worth the cost.
And you brought up a good point.
Lots of drills or presses do not have a reverseable option.
Hand drills do.
But drilling in the center of the small screw is a little more difficult than with a drill press.
I try to provide options that the average guy can do if needed.
thanks guys.....the only suggestion that confused me was the one about applying the hot tip of a soldering iron to the stuck screw. Wouldn't the heat EXPAND the screw making it tighter in the hole?
I can understand if the screw was place with blue lock-tight, the heat would help break that.
I am off to my cabin for the next week or so, If you want to see cabin pictures go to Outdoorsman/hiking and my "I did it" post
best and have a good safe Memorial Day.....Memorial Day means something to me.
atr
I have used a a fine pointed diamond tip in a Dremel to cut a groove in the scres for a very small screwdriver. Must be held solidly in a vise with two hands on the Dremel. Not easy, great care required.
Heating the broken screw will not expand it far enough to prevent removal.
But it will soften any rust or Locktite.
If you use that Allen wrench method.
You have to be sure you don't use a Allen Wrench that mushrooms out the hole and expands the broken screw too much.
When I use that method.
I found that it sometimes helps if you taper the tip of the Allen Wrench just a tiny bit so it starts into the hole easier.
But the corners on the Allen Wrench still dig into the broken screw for a better bite.
Square easyouts have seldom worked well for me on tiny screws, they seem to expand the whole screw before they get enough bite to work.
The Allen wrench can work, I've used it.
The even better option is a small torx bit, they seem to bite better for me.
These days it seems every tool kit comes with small torx bits that are never used, so pick one that is small enough to fit and that you have a drill bit that is a skosh smaller and give it a try.
Robert
That is what I've done. I have the HF set and with liberal penetrating oil it has worked better than expected.Quote:
Originally Posted by pworley1
If you have a socket set you can often use straight screwdriver end of the right size and after soaking in kroil or similar tap it in with a hammer and then use a socket and ratchet to get it out. I think it's 6 or 8mm for the bit?
Lags....I was thinking the same thing about the allen wrench
thanks
If an average guy can't afford 8.50$-13$ they don't need a gun. That's how much left bit sets cost.. I looked up a few suppliers..that was the range for starter sets from 1/16 thru 1/4.Quote:
Originally Posted by LAGS
As for centering.. That's easy.. Prick punch as a start or a diamond bur to grind a dimple as a center.
Any average guy can do those.. If not..they have -0- place being around a firearm...period.
As country gent said, A small drift prick would be my first try. If that doesnt work my next choice would be a small ball end mill bit. I know that most of you dont have a mill to use; but find a friendly machine shop or gun smith, that will save you a lot of headaches.
BD
My picks were ground up on drill blanks, they actually work best after they have been used a few times and are a little dull. Once you find the right angles to tap at it goes pretty good, if they havent been locktited even blue makes this much rougher.
with your punch put a dimple off center close to the edge. Angle your punch so that it pushes at the angle the thread turns and still bites into the dimple. Use a small hammer and tap the punch Use light bows and watch. I you can see a spot watch it to see the start of rotation. usually when it starts it goes fast. After 1/4 to 1/2 turn you can usually set the punch straight in the dimple and spin it out. My hammer is nothing special just a 4 ounce ball peen. This isnt a brute force process but one of finesse.
i like what soundguy said
All this pickin and drilling will go Ok if the screw itself isn't a hardened one.
Many of the scope mount base screws are hardened and will resist regular drills and a center punch.
Check first to see if it is and if the broken off stud is a hardened one,,then anneal it first before spending time setting up in a mill or drill press only to have
the bits dulled over as soon as they make contact.
If soft or you have annealed/softened up the broken screw, carefully centerpunch the stud.
Then drill out w/ progressively larger bits till there is very little left of the screw w/o touching the recv'r threads.
Choke up on the drill bits so they have max strength and won't wander.
By then the broken off stud will be weak enough to be collapsed in the hole & dug out with a wire pick, even if you are off center by a small amt.
Just don't keep drilling a larger dia hole if you start to get any of it into the recv'r thread.
I have removed a good number of broken taps using a ball end carbide mill bit. if the screw is hardened use carbide.
BD
Agreed.. Hardened bolts and studs aren't magic..just have to attack them different. I've drilled out plenty of broken hard bolts with carbide. Takes patience...but can be done. Ball end burns are extremely helpfully here.
You can turn the spindle by hand on either one, and you can reverse a drill press or lathe by twisting the belt into a figure 8. A slightly longer belt will be easier. Likewise using a round belt if you have one or can make one. And you can improvise a belt with a pair of pantyhose.Quote:
Originally Posted by dtknowles
What kind of lathe do you have that doesn't reverse? I think I remember reading that some of the import 8x lathes weren't easily reversible, but there are ways...
Bill