Threading between centers.

[Brandon1]

I have a few AK74's that I want to thread so I can add a suppressor quick disconnect. The barrels are already populated.

The bore through the headstock is too small to run the barrel through. So I am going to have to thread between centers. This will be a first for me. I will be turning the front sight base/muzzle break mount that is threaded 24x 1.5mm down and thread part of it 1/2x28.

Does anyone have any pointers or things that I should watch out for?
I have practiced cutting threads and am confident in my threading abilities.
Here is the fsb for a visual reference. As I said earlier the fsb is already pressed on and pinned.

 

[darkzero]

I don't do gunsmithing work but turning/threading between centers isn't much different than anything else. The nicest thing about threading between centers is that you can remove the workpiece from the lathe & test fitment if needed, then retrun it back to the lathe & continue threading without loosing your index.

The most import thing to check when threading between centers, if your faceplate has more than one slot & you need to remove the work from the lathe, be sure to place it back in the lathe with the dog drive in the same slot it came out of.

When tunring between centers, be sure your tailstock has enough pressure on the work so that the dog drive does not flop around in the drive plate slot. It's should have just enough pressure/friction where you can still move it by hand but not flop around in the slot.

 

[Andre]

Use some sort of crownsaver, Brownells carries them or you can make them from aluminum brass or bronze. AK barrel material is probably horrible machining, so use a sharp tool with back rake.

 

[kkcalvin]

According to Green Mountain barrel print for AK-74 front of the barrel is .568 in diameter. I would remove the front sight, mill off the threaded area and then turn the front of the barrel without the front sight installed. There would be a lot more room/access without the front sight flying around.

http://www.gmriflebarrel.com/ak47-10gm-16-3-russian-5-45x39mm-1-8-ak47-1974-barrel/

 

[chuckorlando]

Not a gun guy but you maybe could use a steady rest as well and just over hang where your working?

 

[Brandon1]

Use some sort of crownsaver, Brownells carries them or you can make them from aluminum brass or bronze. AK barrel material is probably horrible machining, so use a sharp tool with back rake.

The barrels are us made 4140 so they should machine fine.

According to Green Mountain barrel print for AK-74 front of the barrel is .568 in diameter. I would remove the front sight, mill off the threaded area and then turn the front of the barrel without the front sight installed. There would be a lot more room/access without the front sight flying around.

http://www.gmriflebarrel.com/ak47-10gm-16-3-russian-5-45x39mm-1-8-ak47-1974-barrel/

I had thought about that. My concern was that the shoulder that I will have to turn on the FSB will have to be at 90° to the bore centerline. The quick disconnect will have to bottom out on the FSB shoulder not the muzzle.So keeping everything together made sense to me. That and getting it pressed back to the exact same place as well as making sure that it is timed correctly with the other barrel components can be challenging sometimes.

Thanks for the replies keep them coming I am still learning.

 

[zmotorsports]

I don't do gunsmithing work but turning/threading between centers isn't much different than anything else. The nicest thing about threading between centers is that you can remove the workpiece from the lathe & test fitment if needed, then retrun it back to the lathe & continue threading without loosing your index.

The most import thing to check when threading between centers, if your faceplate has more than one slot & you need to remove the work from the lathe, be sure to place it back in the lathe with the dog drive in the same slot it came out of.

When tunring between centers, be sure your tailstock has enough pressure on the work so that the dog drive does not flop around in the drive plate slot. It's should have just enough pressure/friction where you can still move it by hand but not flop around in the slot.

This is the way I would do it, which is why I just ordered a faceplate to be able to drive a lathe dog as well as work hold. On my previous lathe I would either use a marker or a piece of tape to mark the slot that I was driving the work with. I also had a cheap/inexpensive lathe dog which has quite a lot of play/slop in the faceplace slot. I welded up the arm so it fit more precisely in the slot to eliminate the play, it did help.

 

[darkzero]

I just ordered a faceplate to be able to drive a lathe dog as well as work hold.

I wonder why it seems like dog plates aren't made anymore. I've searched & searched & have not seen any new lathes these days come with dog plates, only faceplates. I suppose turning between centers is not common anymore with collet systems & high accuracy chucks but IMO turning between centers is still very useful. I'm not a long time experienced machinist or by trade & even I turn between centers every so often.

I was just going to use my faceplate for driving dogs also but I was lucky to find a NOS D1-4 drive plate a while back for cheap.

 

[Brandon1]

One other thought I had.

I was thinking about turning two pieces of brass one would fit into the chamber. It would extend outside the chamber and widen out and be center drilled for the dead center to mate to. The other would be for the muzzle end and be made to be inserted into the muzzle, and center drilled for the live center to mate too.

My thought is that by doing it this way the threads would have no choice but to be in line with the bore of the barrel.Any thoughts?

 

[challenger]

A couple of comments the them as you wish.
I support your effort but I'd be very concerned about posting this questions on a public forum. I'd bet big $ there are computers searching a very corner of the wwwfor keywords that include the topic you posted. I know laws vary state to state but the feds are always looking for a reason to take away our rights IMO and this type of modification is taboo in many areas.
As for the work you are doing I can only offer my very limited knowledge. I put a dead center in a three jaw and turn it new every time. I leave it in there and I use a homemade lathe dog. Look these up as they are super easy to make with two pieces of steel, two clamp bolts and another bolt the threads into one side/end of the clamp. This bolt hits one of the jaws as the chuck turns and drives the work. Threading on centers is the same operation as threading in the chuck.