User Panel
[#2]
I recommend not using "PH" in conjunction with 4140 or other carbon steels as it has a specific meaning in metallurgy.
PH means precipitation hardening. Not "pre hardened". |
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[#3]
Quoted:
I recommend not using "PH" in conjunction with 4140 or other carbon steels as it has a specific meaning in metallurgy. PH means precipitation hardening. Not "pre hardened". View Quote Yeah, yeah. And I suppose you think this --> .1 is a tenth, too. We all know it's "HT". But everyone calls it pre heat treated. |
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[#4]
Quoted:
Yeah, yeah. And I suppose you think this --> .1 is a tenth, too. We all know it's "HT". But everyone calls it pre heat treated. View Quote View All Quotes View All Quotes Quoted:
Quoted:
I recommend not using "PH" in conjunction with 4140 or other carbon steels as it has a specific meaning in metallurgy. PH means precipitation hardening. Not "pre hardened". Yeah, yeah. And I suppose you think this --> .1 is a tenth, too. We all know it's "HT". But everyone calls it pre heat treated. That's a thousand tenths, and even the machinists I've been around don't talk that way! What I really like are advertisements for "1000 millionths accuracy", or some such nonsense. On the heat treating, I'm referring to writing the condition as 4140 PH, instead of 4140 HT (HT to what?!). PH13-8M0 is a proper use of "PH", and it's even part of the alloys name in this case. Something interesting I ran across this spring was whining about heat treat of carbon steel splines and gears with the usual process, and a guarantee of mechanical properties over a 20 ksi span. I don't know if the guy ever got it, maybe they plan to reject every part that didn't harden to the upper end of the range for the heat treat condition specified. |
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[#6]
I think I would wait until the inner bore was all there and make something that rides in there. Then you would be fairly sure everything lines up.
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[#7]
Quoted:
<a href="http://s107.photobucket.com/user/rahimiiii/media/002_zpsaz0rw5av.jpg.html" target="_blank">http://i107.photobucket.com/albums/m320/rahimiiii/002_zpsaz0rw5av.jpg</a> I finished boring the barrel shank. I bored it to exactly 1.002" or so. I'm waiting for the tap to arrive. Will worry about what's behind that later on. I will need to find some way to lap or level the shoulder in the receiver, any suggestions? I will post a pic of the EDM blank as soon as it arrives. I can do the same to the EDM blank as well. View Quote Your working it backwards. Start with the barrel in a lathe since IIRQ, your going to be using one already threaded, and see what needs to be cleaned up on the barrels threads and shoulder to get them concentric to the bore/chamber line on the barrel. Once you have that cleaned up, then you know what to threaded the receiver and set the threaded depth to get you close for the barrel isntall . Also, until you get the bolt channel completed, you have nothing to square the receiver to, to start truing the barrel channel and receiver lugs to center line of the bolt channel. As for running a threading tap on anything, short of say the scope mount threaded channel, the barrel channel needs to single point lathe cut to keep the threaded channel square with the bolt channel. Hence on a production action to clean it up, you are first squaring the receiver up against the bolt channel on the lathe, then you are squaring the threads (ending up with them over sized), facing the end of the receiver to the center line of the bolt channel, and them squaring the face of the receiver locking lugs up to the bolt channel. This now sets what the new barrel will need to be threaded (to match the new threads on the receiver), and even if the bolt handle will need to be removed and re-brazed back on (if the receiver bolt lugs had to be faced way back to get them squared to the bolt channel center line, and now the handle no longer fits correctly to the bolt handle slot in the receiver). As for a receiver from scratch, you really never want to start with your round stock at final OD. Hence when the bolt channel is created, it not always going to be concentric to the OD of the stock piece, and with it being over sized in OD, this allow you to center the piece on the bolt channel in the lathe, then turn the OD down to the final dimensions so the OD of the receiver is square to the bolt channel. Again, on a production 700 receiver, 99.9% the bolt channel is not square to the OD of the receiver, so that is why you never, never trying center the piece in a lathe off the OD of the receiver (center line of bolt channel always driving the bus). |
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[#8]
Quoted:
That's a thousand tenths, and even the machinists I've been around don't talk that way! What I really like are advertisements for "1000 millionths accuracy", or some such nonsense. On the heat treating, I'm referring to writing the condition as 4140 PH, instead of 4140 HT (HT to what?!). PH13-8M0 is a proper use of "PH", and it's even part of the alloys name in this case. Something interesting I ran across this spring was whining about heat treat of carbon steel splines and gears with the usual process, and a guarantee of mechanical properties over a 20 ksi span. I don't know if the guy ever got it, maybe they plan to reject every part that didn't harden to the upper end of the range for the heat treat condition specified. View Quote Every toolmaker in every shop I've ever been in, when they said a "tenth" they meant a "tenth of a thousandth" aka one ten thousandth of an inch. The old joke is "Have you ever worked in tenths?" but the "tenths" is slurred in to "tents". The pat answer is "Well, I've worked in a couple alley shops before but never in a tent". It's funny, when I first started the trade, my aunt worked at Fischer Body as a die grinder. I mentioned that I was holding tenths on the grinder that day. She said she holds tenths every day and it's no big deal. Measures with a scale. I said, "No, tenths of a thousandth. .0001". "Oh". I've worked with 17 and 15- 4- PH quite a bit in the aerospace field. Spec on 4140 HT is 28-32 Rc C scale. There are other pre hardened steels. NAK 50 is about 40 Rc and is an extremely good (Japanese iirc) steel. Very stress free and great for emergency jobs where there's no time for HT. |
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[#9]
I think my point about "tenths" blew right past; I know how it's used in the shop.
My point about "HT" is that there are many choices, I can specify heat treats of 4140 from annealed and normalized to 220 ksi condition. (Last winter I was hunting for a piece of pre heat treated plate to use on my blacksmith anvil and I was surprised by the prices, plus I would like to use a harder heat treat.) We are illustrating the different ways we think about these materials. You have a notion about what 4140HT means for your uses and needs, and I have another one. I think in terms of the strength of the material in ksi, and have to use a hardness table for translation if I'm faced with a material that is presented as having some Rockwell hardness without the rest of the story. Each heat treat specification produces material heat treated over a 20 ksi range. In other words, if I specify heat treat to 140 ksi per process spec "1", the resulting material will exhibit 120 to 140 ksi ultimate strength, or hardnesses of Rc 26 to 31. If I chose spec "2", the next one in the list without any other control, the result would be 125 ksi to 145 ksi (Rc 27 to 32.5). What I would do in real life for a part that let's say I required to be 140 ksi, is specify, "Heat treat to 140 ksi minimum (Rc 31.5) per process spec 4." , knowing that I might have to live with parts that came out of tempering at 160 ksi. As part of the analysis, I would take a look at other properties than the ultimate strength, mostly the ductility and yield strengths. I probably would not specify mid range properties without a remarkable reason that justified the scrap rate, and an expensive materials testing project to develop the allowables for that essentially unique material would be necessary to justify choosing a particular strength. That ain't gonna happen. A nice feature of working 4140 is that heat treat processes are available that produce overlapping ranges in the strength. 4340 and 6150 are two others. The rest process in steps such as 120 to 140 ksi, then 140 to 160 ksi, then 160 to 180 ksi, and so on. It's too bad carbon steels love to rust, they can be used to produce really great parts with smart choices. |
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[#10]
I think we may be talking past one another.
Yes, you can take 4140 ann and heat treat it to any Rc you wish up to about 55. If you want harder, you can nitride it in one of several different ways or carburize and harden (which I've never heard of being done with that material). But, there's a specific material called 4140 pre-heat treat. Designated 4140 HT and industry standard Rc is 28-32. OP said he had a bar of 4140HT and then said it checked 40 Rc. That is out of spec for that material designation. I don't know where he got the material. It's possible someone mistakenly sold him some NAK50 or similar. |
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[#11]
I don't know if it is truly 4140 pre hard but the eBay description says it was turned and ground to 1.5 inch, it has been hardness tested to 40rc, and he said it was used as some kind of a pin or something. Whatever it was it is heavy, strong, and hard to machine enough that I believe what it says. Standard pre hard is probably around 28-32 rc but it is clear whatever this is has been heat treated further. It could very well be stainless given how it would not rust much at all
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[#12]
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[#13]
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[#17]
It's the only room I have at the moment, so I have little choice.
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[#18]
Quoted:
It's the only room I have at the moment, so I have little choice. View Quote I welded a glider fuselage in the living room of an apartment. I put particle board with a plastic sheet on the floor to protect the carpet. That mostly works, except when a hot part bounces off the particle board onto the plastic on the carpet. I fixed it with a pocket knife and comb when I moved out. |
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[#19]
Besides, it's actually the one activity I can do. I was mostly interested in guitar building and woodworking in general but metalworking is much more easily done in the apartment, because metal doesn't create fine dusts that stay in the air for days, coating everything in the room, and in several adjacent rooms with a fine coating of dust, nor does it clog ventilation ducts with dust. Milling is also a lot quieter than cutting wood with a router, if done correctly. The metal shaving mostly stays in my room and they are easily vacuumed up or brushed off. Wood particle gets on everything, including inside your lungs and coats the entire room in dust.
Even milling wood with a mill is not all that good because the wood dust gets everywhere, and I can't use coolants to stop the dust from going everywhere (whereas on metal this is easily done). |
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[#20]
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[#21]
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[#24]
An 11/16ths' drill is more than 10 thousandths of an inch smaller in diameter than .702.
But the wobble in your set up will probably take care of that. |
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[#25]
You're doing a great service to folks showing them this can be done in an apartment. Thank you.
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[#26]
If it won't fit, I can enlarge it very slightly with a boring head.
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[#27]
A couple of articles about a rail gun built by an Australian -
http://bulletin.accurateshooter.com/tag/rail-gun/ Scroll down the page. http://www.benchrestbulletin.net/drupal/sites/bulletin/personalprojects/action%20details.htm A little light on the bloody details, but still interesting. |
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[#28]
When you said rail gun I thought you meant that thing that uses electricity to shoot projectiles at hypersonic velocities
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[#29]
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[#30]
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[#31]
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[#32]
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[#33]
Quoted:
<a href="http://s107.photobucket.com/user/rahimiiii/media/001_zpsppfyiu5q.jpg.html" target="_blank">http://i107.photobucket.com/albums/m320/rahimiiii/001_zpsppfyiu5q.jpg</a> I cut the bolt raceway. I have ordered a 3/8" broach and will use it to try to square up the corner. View Quote A large clearance and force press and a lot of shimming. |
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[#34]
I'm likely to use the broach as some kind of a saw to just shave off a tiny amount of metal around the corners... not a lot of metal will be removed so the amount of force needed is minimal. It's just a step above using a file that's all.
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[#36]
Quoted:
I'm likely to use the broach as some kind of a saw to just shave off a tiny amount of metal around the corners... not a lot of metal will be removed so the amount of force needed is minimal. It's just a step above using a file that's all. View Quote Good luck not having a lot of taper. I did find an old broach from work in my shop. It was designed to make a channel about 1/2 inch wide and 3/8 deep. We used them to allow length adjustment on some equipment at a very high altitude for antanna pointing. It is abut 48 inches long. A couple passes with different collars to control it in the bore. They lasted about four sharpenings so this one is a little worn. The press was all of two stories high. |
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