Newbie learns great technique for cutting straight threads

[Larryx]

I am working on the round things which are part of the build and I finally made it to the place where I had to thread the rear barrel plate. The advice I received on this forum was spot on as far as making the carrier block in 2 pieces and using the Cutter suggested fixture on the rotary table.  All the holes had been bored and reamed and not it was time to cut the threads. I used my time honored technique of holding the tap vertical by means of the milling machine quill. WRONG!!!. I ended up with 10 holes threaded for 7/16-20  threaded barrels but 5 were vertical and 5 were \"drunk\". What to do? There is room on the rear barrel plate to drill out the 7/16 - 20 threads and re-tap for 12mm 1.75, Easy enough to say but I really did not want to repeat the error of having  non vertical threading.   I contacted a professional machinist friend  who prescribed the following technique: drill the proper size hole. Put the tap in the drill chuck medium tight. Move the quill down to the surface of the work and turn on the rotation for only a moment. As the quill is spooling down press the tap into the work. There is sufficient momentum for the tap to take several turns into the work. Release the chuck and complete the thread with the tap wrench. I got 10 perfect threads this time. It may be that everyone but me knew that trick, but as someone much wiser than me once said, \"experience is what you get right after you need it\"

[bruski]

After a while you can actually run the tap all the way through under power. What I mean is power on then off momentum tapping then reverse tap out under power and repeat several times until you are through.

bruski

[Cutter]

While all of the above works.

I would not recommend for Greenhorns.

 

Hand tap with a spring loaded center.

[gbull]

A spiral point guntap works great on thru holes. It pushes the chips ahead of it, and helps prevent chips building up in the hole. This works great on thru holes. A combination of turning off the spindle and applying the brake right away, you can control how deep you tap. Then you can clear any chips and hand tap with a bottom tap if you are threading a blind hole.

[bruski]

The spiral taps work great on through holes also with no backing off. They put out a long stringy chips just like a sharp drill bit.

 

bruski

[maccrazy2]

Agreed, I buy spiral taps for everything I do regularly. Also I stay away from Irwin brand in the hardware stores. I don’t know how they became the standard at most retailers. I guess they are cheaper since they don’t bother to make them sharp. Lol

[Bluedog]

Another recommendation for the spiral taps. That’s almost all I use now.

[Larryx]

I made another fascinating discovery today. One of the  downsides of starting a build this late in the program is that the apparent large supply of affordable used .22 cal barrels has become about as easy to find as chicken teeth. I therefor decided to follow Paul Moores suggestion and use appropriately sized DOM tubing , drill it to the appropriate size and slip in and adhese a commercially available barrel liner.  First  two steps went smoothly, and the drilling of the tubing was without incident. I used a letter P aircraft drill which gave me required diameter but kept the clearance to less than the 0.006 inches suggested for locktite.  The barrel liners were ordered from Brownells, each 26 inch liner sufficient for 2 barrels. Imagine my surprise when I completed the drilling and then attempted to slip in the liner. (The drill is supposed to follow an existing hole, and I drilled from each end after very carefully  centering the DOM tubing tn the 4 jaw chuck.) I got part of the way in and then end of party!.  After measuring, re-drilling, carefully cleaning, and similar efforts which made sense at the time, I discovered that the barrel lines ARE NOT STRAIGHT.  Am I the only person that got liners that are (not carefully measured) 0.100 curved liners?

[maccrazy2]

I watched eBay for a while and found a guy selling 14 Barrels. I offered to buy them all and asked about combining shipping. He put together a lot purchase for me and even knocked off a few bucks. The cost bet barrel was about what the liners and tube cost would be. Not counting the multiple hours of labor turning them all down.

Obviously this is no help to you know but if you decide to scrap the lined barrels I would start searching eBay as well as calling all your local gunsmiths to see if they have any laying around.

[gbull]

I bought 10 liner halves that I assumed came from Brownells from someone on this site or the other one. I drilled the tubing like you did but the liners seem straight. They slip in nicely. I’m not sure I would try straightening them if I were you. I have done a lot of straightening over the years and there seems to be a pretty steep learning curve. Can you push the liner all the way in with a little persuasion or does it stop hard halfway in? The DOM tubing should be sturdy enough to straighten the liner as it goes in. You wouldn’t have an equal distribution of the loctite, but it should hold the liner firmly in place. Does the loctite call for .006 total or per side? Is it the 640?

[Larryx]

of the 10 liners, 8 I am able to slide into place using only my hands.  There are 2 that I can push perhaps 9 inches by hand and I am sure the remainder of the way using some somewhat gentle mechanical means ( press, hammer on 2 x 4 or some similar means). I am fearful of having the tube jam up hard and then have no way to recover.  I saw somewhere where the green locktite will fill up to 0.006 inches but with 12 inches of glueing area, I believe the liner will stay in place even if some areas had a larger gap. I designed for 0.006 total, let the liner decide how to proportion it. I was looking on line at tubing straighteners and there seems to be a rather simple design using sliding door pulleys. I have just the 1 liner ( sufficient for 2 barrels)  to worry about so I think I will look into that. I can see where the non straightness is but as you commented, moving the tube just enough to counter the bend and overcome the spring e ness without overdoing it by hand is beyond my comfort zone.

[bruski]

You can always turn down the shank of your P drill bit some and braze on a extension that is drilled out to slip over your shank on the P bit. This will eliminate any step that might be in your barrels.

 

bruski

[Larryx]

probably easier that building the wheely straightener.  Thanks for the suggestion.