Cutting threads on a lathe

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Has anyone cut threads on a lathe? I havent messed with the one much but I have access to one. I was in need of cutting some 3/4NF threads externally on a piece of rod. Could someone maybe give me some tips on how to get started? I know someone offered to help but I figure if i can get a little head start that would be great. ThanksHTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:Search "Thread cutting on a lathe" in Google, and you will find some info.  If ya don't find what ya need I'll try to type out the method for you. when i get back in from work if someone else doesn'tI'm a Lover, Fighter, Wild horse Rider, and a pretty good welding man......
Reply:well first do you have a lathe? dose it have a compound slide?ChuckASME Pressure Vessel welder
Reply:Some where I've got an adapter that fits in the tailstock. It will hold regular threading dies. You basically get it started and it runs like a powered pipe threader. I got it for doing 1 1/8" threads for a job where I used to work. This may be simpler solution at learning to cut threads the "old fashiond way", but will be more expensive. One day I hope to get a machine I can play with and learn to cut real threads.
Reply:3/4 Fine threads..The minor diameter should be .688 or so..Its nice to have a guage also for when you grind your threading tool..Some use the compound..I just "plunge cut" everything..Getting the tool ground right and set right to the piece is the biggest part..I usually take .004  .006 each pass..There is a very fine line between "It still don't fit" to "Damn! Now it's too loose "Just like anything else..Patience and Practice.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Here is the lathe in the background of this picture. I dont really know much about it like I said. Someone said they would help me out I just want a good idea of what to expect.. I am threading some strut rods on my mustang to accept a female 3/4" heim joint. They need to get good tight threads!!  I thought you could see more of the pic but I guess not? Ill try and get more info on the machine today. I googled it already but there was ALOT of reading and I got confused. Partyl the terminology I guessHTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:I guess the important question is Do you want to cut with single point? Or with a die?I have a pdf on single point threading. Let me know where and I willemail it to you (disclaimer: I found the document on the webages ago. Not sure of the origin)
Reply:Very easy if you've done it before...........Set the compound over to 29 degrees.........Set lathe speed at 90rpm (+/-)Bring carriage to work piece and using cross slide, just touch the work. Set cross slide dials (or DRO) to zero.Back carriage away from work piece.Set threading gears to proper TPIDial in .004" on compound, not on cross slide. If you simply go "straight in" you'll have huge loads on a very small cutter and not get good threads.Depending on your TPI and your lathe's thread indicator, drop the half nuts at the proper number on the treading dialBe prepared to stop the carriage before the cutter slams into a shoulder on the workpiece or the chuck on the lathe.Back out the cross slide a few turns. Move carriage back to start. Bring cross slide back to zero. Dial in another .004" and drop the half nuts at the appropriate number ...............repeat until your threads fit the nut you will be using or use "thread wires" and measure threads for a perfect fit....EASY!Roy BDartmouth, Mahttp://www.rvbprecision.comMM 185 MIGDiversion 165Purox W200 O/AGrizzly 9957 MillGrizzly 4030 Metal Band SawGrizzly 1050 Knife Belt SanderJet 1236 Metal LatheCM 14" Metal Band SawTP Blast Cabinet
Reply:maybe a real machinist  will step in here and  straighten me out on how  you will center your  work properly?if you are  going to  cut  a thread  dont  you usually need to start with your  rod oversize so you can  "true" the  workpiece to round to your lathe before you  begin your threading? i am  thinking  you will cut  deeper on one  side than the other if  not??
Reply:Originally Posted by rbertalottoVery easy if you've done it before...........Set the compound over to 29 degrees.........Set lathe speed at 90rpm (+/-)Bring carriage to work piece and using cross slide, just touch the work. Set cross slide dials (or DRO) to zero.Back carriage away from work piece.Set threading gears to proper TPIDial in .004" on compound, not on cross slide. If you simply go "straight in" you'll have huge loads on a very small cutter and not get good threads.Depending on your TPI and your lathe's thread indicator, drop the half nuts at the proper number on the treading dialBe prepared to stop the carriage before the cutter slams into a shoulder on the workpiece or the chuck on the lathe.Back out the cross slide a few turns. Move carriage back to start. Bring cross slide back to zero. Dial in another .004" and drop the half nuts at the appropriate number ...............repeat until your threads fit the nut you will be using or use "thread wires" and measure threads for a perfect fit....EASY!
Reply:Normally you center using dial indicators. That was the way I was taught anyhow, but I have never attempted to cut threads on the lathe (I don't consider myself to be a machinist, but I have watched threads cut). If you aren't a good lathe hand I would recommend finding someone who is to give you lessons on thread cutting as you can make a mess of things real quick.The difference between art and craft is the quality of the workmanship. I am an artist.
Reply:Steering and suspension work isn't really the best place to learn how to thread, but if you insist, good advise has come by.I;ll add a bit to it, noting that I am not a great machinist, but can thread like a banshee when I must, and some of the better machinists here will cringe at this. One off jobs are often based on knowing how to cheat, and I learned from some pretty effective cheaters.So, to add to what has been said, there are a bunch of ways to cut the thread. The standard single point method (already covered) is easiest using the proper insert tool with an insert suitable for the thread pitch and diameter you are cutting. On the end of a rod, It can be cut four basic ways: a) groove where the thread will stop to the root depth (a nice U-groove works well) so you have a place to disengage the carriage without making a mess; b)Stop the spindle on spot at the end of the thread (REALLY hard to do. It is one  of those things I was always told about in school, but have never seen); c) roll the cross slide out at the end of the thread by hand (takes a little practice, but not too hard, and leave a nice run-out), stopping the spindle as the tool comes clear; and thread from the back side with the lathe in reverse. Threading from the back lets you run of the end off the material (no risk of crashing the carriage or overrunning the thread and chomping the tool), and is easiest with a groove to start in. Now, how to cheat: Easiest cheat is how I passed threading in school. Single point about half of the thread depth, then finish with a die. The die will run easily and track well with little force once it has a partial thread to follow (I waited until the instructor had seen my partial single point job and turned his back, then finished the job with the die when he wasn't looking... Got an 'A'. The statute of limitations on this ran out sometime during Regan's first term, so I can talk about it now  )Next easiest is to use a cutter from a die (the type with replacable cutters, of course) mounted to the tool post.  Even a fairly light lathe can run a full thread in two passes this way. The root and depth can be dead perfect with little effort. It can be done in a single pass, but two is better in terms of getting the thread depth dead on. This still requires setting the feed fort he proper pitch, of course.
Reply:Well I am not going to use anything until I am totally comfortable with the work. I got a small lesson today and its really cool. I dont think I have the correct cutter so I need to get that. The machine has a bunch of levers you just dial in for TPI (dont know if thats standard) and you just work the depth. I dont get how to reverse out of the threads, because the guy showing me how to do it did something and reversed the machine and the cutter went right down where the threads were and didnt chew up any metal. I am just gonna keep practicing until I get the hang of it.HTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:Originally Posted by rbertalottoVery easy if you've done it before...........Set the compound over to 29 degrees.........Set lathe speed at 90rpm (+/-)Bring carriage to work piece and using cross slide, just touch the work. Set cross slide dials (or DRO) to zero.Back carriage away from work piece.Set threading gears to proper TPIDial in .004" on compound, not on cross slide. If you simply go "straight in" you'll have huge loads on a very small cutter and not get good threads.Depending on your TPI and your lathe's thread indicator, drop the half nuts at the proper number on the treading dialBe prepared to stop the carriage before the cutter slams into a shoulder on the workpiece or the chuck on the lathe.Back out the cross slide a few turns. Move carriage back to start. Bring cross slide back to zero. Dial in another .004" and drop the half nuts at the appropriate number ...............repeat until your threads fit the nut you will be using or use "thread wires" and measure threads for a perfect fit....EASY!
Reply:Ditto, rbertalotto said it best!DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:WHat are the half nuts? See someone told me about reversing the lathe instead of backing it out and resetting it. WHat works better?HTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:In school, we cut a notch where the thread would end.The long acme screw drives the thread cutting portion of your lathe. The half nut clamps on to the screw.  There should be a gauge with #s 1-4 on it.  It keeps track of where you lock on the half nuts to make more cuts in the thread.Don't forget to back out the tool before you crank it back or you will have a left handed thread of undetermined pitch David RReal world weldin.  When I grow up I want to be a tig weldor.
Reply:The half-nut is just a counter that keeps track of where the carriage is so the bit re-engages the previously cut thread correctly.  It was designed for threading.Fordman, for a critical part of your suspension, let a pro do it.  Otherwise, practice on a non-critical part first!  You can practice on nylon or aluminum rod, etc. and it won't wear out your bits.America Needs AMERICA'S Oil!!!"Global warming is the greatest scam in history ...There is no run away climate change. The impact of humans on climate is not catastrophic. Our planet is not in peril."--John Coleman, Founder of The Weather Channel
Reply:Not all lathes have a 1-2-3-4 dial for threading..Mine don't..You set the gearbox on what thread you want..Engage the threading lever..And there is another handle that makes the tranny go from forward to reverse so you never dis-engage the lead screw untill your done..Never a "screw up" or having to wait for whatever number you need to "come around".....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:I am not afraid of trying things myself. Obviously I am not going to just do some booger threads and run it. If I cant figure it out I will get help but I will do it myself.HTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:Enlpck - I tried your "Cheat #1" when I took metal cutting #1 in engineering college in '92.  We had to make a bottle jack, with had a 1 1/4" acme thread.  I cut the male threads all with single point tooling, but my dad (who runs a toolroom at a big machine shop) got me the correct tap.  I roughed the female threads out then ran the tap through to clean it up.I got a B on the project with the only points reduction being "thread appearance" on the internal threads.  I asked the teacher why he took points off and he advised me to drop it before he took any more off.  He also said that I needed to not let the tap show up in his shop or he might have to keep it.  He was actually cool about it all - and was impressed that I'd been able to find the tap.Fordman - you definitely need to start out with some scraps and practice a few times before trying your actual parts.  Like others have mentioned above the starting and stopping is you most likely place to mess up.  I usually try to have a relief groove to stop in, but have also done quite a few things where I had to back the tool off as the thread ended.  I have had the most trouble with lathes that the pointer was not dead on.  When you'd go to engage the half nut it would be a hair off and the carriage would move enough one way or the other to engage - and not always the same way.  No big deal unless your tool is already almost on the part and then you might not have enough time to react to disengage before running over the top of your threads!Here is a picture of some threads where I had to back the tool off because I couldn't have a relief groove.  It's a crankshaft from a 1906 Cadillac 1 cylinder car.  The threads hold the clutch together and were completely missing.  I had to build it up with weld, turn it back down, then thread it.  It turned out well. Attached Images
Reply:Too bad the threading gage isn't clear to illustrate the lead starting numbers like mentioned above.  Its the round dial in the bottom right corner of the pic.  You can see the 29 degree angle on the compound, though, and my nice insert style trhreading tool.Here is a closeup of the threads after adding the vee grooves that a pointed setscrew locks into.  I wish I had a before - when I got the engine they were only relying on the secscrews, which were worn in about 1/4" deep!  The threads are 1" OD, and I had to turn the shaft down to 5/8" to get good, clean metal.  The rest is TIG buildup. Attached ImagesLast edited by TubularFab; 03-17-2008 at 10:42 AM.
Reply:TubularFab: Jobs like that are why I (in my mediocre skill) prefer to thread in reverse (threading tool behind the part, rotation reverse, thread off the end). I can feed in on the start much more smoothly than I can feed out on the stop
Reply:fordmanis that franks from gottrikes.com's bender your building?if so, how do you like it?im building mine right now, looks like a nice simple design.
Reply:The lathe I use can be a pain in the butt. It has two gears that you can actually change out. One gear does not match the threads per inch as marked on the gear box. So you have to change the internal gears that drive the shaft that pulls and pushes the carriage to the one that matches the threading gear box. I use the threading dial marked 1-4, I use it to engage the carriage in sync with the threads already made. Make sure you tighten your stock very well. If you have multiple key ports tighten the chuck from all of them. And do it one more time just for fun. Because if it slips, either by rotating, or if it just walks in or out, you get a messed up thread. Unless it just happens to screw out of the chuck at the same threads per inch you are cutting. Ha-ha. It can happen though. The threads can actually hold the cutter and work piece in harmony even though the part has walked out a bit. I was surprised.        Sincerely,             William McCormick        Sincerely,             William McCormickThere is two ways you can make threads on a lathe.You can just buy a die/tap and do it manually.Then there is the way where you cut the threads with a cutter. Thats the way your asking about.First think , you should get one of those cutter gauges , not sure what they are called. It has 60 degree angles on it. Cut your cutter so it matches up with the gauge. Then next think you do is set your compound rest (i think thats what its called) to 29-30 degrees. Make sure its the right way. Then line up your cutter so its square with the stock. Since your compound rest is at 30% you will use that hand wheel to bring it in around 0.005" each pass. Don't forget to make a cut at the end of your thread before you start, also add a chamfer at the beginning of the thread. Do you have a thread lever? That has like 1-2-3-4 numbers on it?I think the rest of what you need to do is already been posted , but that is how i do it. Make sure to have a nut around so you can check how nice the fit is. Also make sure you use lots of oil when cutting , or cutting fluid.
Reply:Yeah it has one of those number dials on it. I am unsure what you mean by setting the compound to 29 degrees? Everything looks pretty straight to me, I dont know. I also ordered a few 60 degree cutters from mc master carr to test out so we will see. I am going to practice for a while obviously!! And I love the got trikes bender I built, works great. All I bend is 1.75" .120. I dont have an 1.5 die yet but I could use one, and maybe a smaller 1" die or something but thats laterHTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:The idea behind setting the compound (the part of the carriage that will let you move the tool in on an angle) is to make it so most of the cutting is done with one side of the tool bit.  If you simply feed it straight in you increase the cutter load and make it more prone to chatter.  If you feed it in at 29 degrees (just a shade under 1/2 the included angle of the cutting bit) you cut almost entirely with one side of the bit and barely clean up with the other side.  I do not know a better way to explain it...
Reply:I need to see it, because dont you want the cutter straight in so that you get your 60 degree thread?HTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:The tool bit has to be set square to the shaft, but the bit will be fed in at an angle.  The compound is set at 29 degrees, and the tool bit will be set square to the work using the tool post.  Just as TubularFab stated if the bit is fed in straight then Both sides will try to cut, and will cause chatter and threads that are not clean.  Feeding it in slightly to the side will make the leading edge cut, and keep the trailing edge free.I'm a Lover, Fighter, Wild horse Rider, and a pretty good welding man......
Reply:I think I know what your talking about. I need to go see an expert and have him just school me.HTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:I need to go see an expert and have him just school me
Reply:Yeah now that I think about it I have seen some guy right around the corner from me with a full on machine shop in his garage!! I need to go talk to him HTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:Originally Posted by rbertalottoWhen I decided to get involved with Gunsmithing, I didn't even know how to spell Lathe.......I found a couple of retired (bored) master machinists to come over at night and show me the "tricks of the trade"...........You can't even learn the stuff these older folks know because at vocational schools it's all about CNC machining and very little on actual engine lathes. And these older fellow just love to be in your shop messing with tooling again. I think they got more fun out of it than I did!Although I've taken many courses on specific gunsmithing procedures and technology, the basics need to be learned hands on with someone over your shoulder. If you don't, you'll develop all kinds of bad habits (of which some can be outright dangerous to you and your machines).Have a ball!
Reply:Originally Posted by Hammack_WeldingSo true.  I have hardly never seen an old timer that would not be glad to talk to you or share his trade with someone starting out.  I learned alot from my dad, but there were two mean who taught me so much about metal that it would have taken years to learn.  One was a welder, and an inspector in the ship yards during the 2nd world war, and later owned the local welding supply business.  He basically started me out in business.  The other owned a machine shop that was out of this world.  he started in the late forties by trying to borrow money from the bank to buy a lathe, and they basically laughed at him, and said no one will ever build  machine shop in the country.  some 30 years later he one of the largest shops in the southeast not to mention that he was probably the largest share holder in that same bank.Just sitting down and talking to him taught me more machining than I ever could have learned on my own.  He also gave me several pieces of machinery that he wasn't using anymore in the shop.  He would rather see someone he knew use it, and help them than see it go to waste.  I think sometimes we take for granted just how much of a resource our elders can be.   Fordman, find you someone who knows what they are doing and ask if they will give you some pointers you might be surprised at what you get in return
Reply:HELLO TO ALL,the statement about taking a cut on the rod beforeyou thread. is right on. hot rolled rod is not round,and you need to take a light true up cut to make itso. cold rolled is better, but i have seen some CR rodthat was not very round. better to take a light cutbefore you thread.good luck to all!wlbrown
Reply:Originally Posted by wlbrownHELLO TO ALL,the statement about taking a cut on the rod beforeyou thread. is right on. hot rolled rod is not round,and you need to take a light true up cut to make itso. cold rolled is better, but i have seen some CR rodthat was not very round. better to take a light cutbefore you thread.good luck to all!wlbrown
Reply:HELLO TO ALL,i have used the ground, and polished material,and it is great. i made a splined shaft from some of that material. it was also heat treated, 4140 28-32 Rc. good luck to all.wlbrown
Reply:So I played with it for a while and this is what I did. I turned down the diameter to .750 because its around .780 stock. I have a "trav a dial" on the slide, I just zero'd it where I started the cut then just went back to that same spot everytime. It worked great for me, I  finished the thread with a die. It feels great and isnt sloopy, looks good too. Is there anything wrong with using this methodHTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.
Reply:Originally Posted by fordmanSo I played with it for a while and this is what I did. I turned down the diameter to .750 because its around .780 stock. I have a "trav a dial" on the slide, I just zero'd it where I started the cut then just went back to that same spot everytime. It worked great for me, I  finished the thread with a die. It feels great and isnt sloopy, looks good too. Is there anything wrong with using this method
Reply:Agreed. It's not a bad idea to have a die available to use for a "go-no-go" test when doing a thread on the lathe. It alo helps to have a lathe that can do a nice slow speed, say 70 rpm or so but mabe this has been covered above.
Reply:Yeah mine goes to I think 45. I found that taking my time and going slow makes everything run smoother!!HTP Invertig 201Lincoln Idealarc SP250Miller 180 AC StickBy farmall:They should have held the seagull closer to the work, squeezing evenly for best deposition.