Taps & Dies.
I’ve just finished reading my Workshop Practice Series: Drills, Taps & Dies, so I’ve got a reasonable grasp on the subject.
I’m assuming the AF rifles are all in UNF, including the bottle.
Question on dies:
I assume a “die-nut” is a fixed-size die without a split, whereas a “split-die” allows the diameter of the cut to be varied slightly so a thread can be cut in stages? I further assume therefore that a special wrench is needed that can compress the split-die in stages to produce different depths of cut (shallow to deep).
The thread in the bottle, that would be UNF 1/2″ x 20 TPI?
I’ve been looking for places to buy taps & dies, I found one that offers good looking sets, but they’re made from “HQS” as opposed to HSS or Carbon-steel. They claim HQS is superior to HSS, but I’m thinking “yeah, right…”. HQS = High Quality Steel? Probably straight out of china.
I know, threads should be cut on the lathe, but my lathe requires changing loads of cogs to get particular threads, plus it’s a metric lathe. And the manual is about as much use as yesterday’s newspaper, so I’m about as inclined to get into thread-cutting with the lathe as I am with using my teeth.
TIA for any advice chaps. 🙂
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Langasen, good to see you’re coming along with your lathe. The learning curve during the first few months is steep. If you are lucky you’ll only ruin a few tools beyond repair.
I’ve often thought of builidng a die holder like that link to Enco shows, but I’ve always been too lazy. The difference between a lathe cut external thread and a die cut external thread is this: The lathe cut thread takes you FOREVER to cut, but it will be SUPER accurately aligned axially to your workpiece. The rub is this: that not many pieces of work require that kind of axial precision. Most things do not. For guns, threading barrels is a very critical application, especially with something like a small ring Mauser (’91-96), which have only a few threads actually engaged with the receiver and thus full engagement become critical to strength and safety. But due to the time required to cut the threads with a lathe, in every instance that does NOT require perfect axial alignment, I always choose the dies if possible because they are so much faster. Cutting a thread with a lathe takes 30 or 40 passes, depending on the size of thread you are cutting. In the beginning you take a deep bite because the cutting tool is V shaped and the work is still flat, so only the point bites. As you get deeper, the work conforms more and more to the V, so the cutting area increases and the strain on the tool also increases so you have to back off; mid thread you are usually cutting only 1 or 2 thousands at a pass and by the end of the cut, you are only taking 1/2 a thousandth at a pass and on the final cut you will go 3 or more times without changing the depth of cut at all, to ‘clean up’ the cut.
A good compromise is to take the deep cuts with the lathe until the thread is almost finished; then for the finishing, you run on the die and use a wrench. Becuase the thread is already there, the die has little to actually cut, and the groove will be nearly perfectly concentric and axially aligned. This is much faster than finishing with the lathe, and the quality of cut is actually very good. But even when finshing with the lathe, you’ll find that, depending on the quality of your machine, how stiff it is, the thread may not be 100% perfect; you’ll find that some areas are higher than others by a tiny bit, but enough to make spinning on a nut difficult until it seasons a bit by spinning on and off 50 times or so.
So, good rule of thumb is to select dies in all cases that do not require perfect axial alignment. If you have to thread using the lathe, make use of the cross slide stops. The cross is set to zero and stopped there. Use it to back out of the cut at the end of the thread and then move it back into the cut at the start, watching your thread dial. Use your compound to feed in. Compound should be set 29 degrees from left right axis. Use the slowest speed your lathe is capable of. Back gear or ‘granny gear’ if you have a Southbend.
I have just started a new job so do not have much time nowdays… my order of end mills and other stuff just arrived from enco a couple days ago, though. Ouch, this stuff costs an arm and a leg… and I still have not welded up a stand to put everything into. My mill is still sitting on the ground 🙁 I have to move my arbor press off my bench first to make room, so will be welding up a stand for the press and another for my anvil which is also sadly sitting on the ground.
Good luck,
walt
I’m getting the feeling this thread-measuring malarkey with wires is for lathe-cut threads. My Workshop Practice Series ‘Screw-cutting in the Lathe’ has a whole section devoted to it, whereas the tap & die book has nada. Tap & die is a fixed value, apart from the slight variation possible with the split.
The poor mans version it buy some piano wire for like 50 cents, and use some tape on the ends to hold it in place.
I’ve been having a look, do you know how much that shizzle costs?! 😯 There are shed-loads of different wire gauges and on one site they’re $200 per set (that’s three wires for one specific thread size, designed to go into a measuring jig). I haven’t been able to find any in the UK, probably because nobody can afford to buy it.
I’m seeing what you mean, but how do hobbyists afford it? Or is there a poor-man’s version?
Accurately laying out and measuring your work is a good habit to get into whether the piece requires it or not.
I’ll eyeball stuff and fit things together without measuring – But I’m not starting out at this and neither was the guy who wrote that book.
I’d recommend taking the extra steps (which more often than not don’t take much time or effort) and using “uneccessary” levels of accuracy.
You’ll need a surface grinder. You need to buy one of those too. And you are going to need a tool post grinder and a few other goodies. Oh and dont forget to get a left handed sky hook 😛
I’ve got a box of wet & dry already, thanks.
Lang,
You’ll need a surface grinder. You need to buy one of those too. And you are going to need a tool post grinder and a few other goodies. Oh and dont forget to get a left handed sky hook 😛
We do not know who let you play with those things. But somehow we feel a kinship with them 😛
Damn, I thought I’d got rid of all those pictures of me re-filling my lighter. 😳
http://www.use-enco.com/CGI/INSRIT?PMAKA=318-2031&PMPXNO=944247&PARTPG=INLMK3
It goes into the tailstock chuck, and keeps the die streight.
I built my own with a morse taper to go directly into the tailstock taper.
if you can use a die for your threading job, it makes it MUCH faster job. Professional machinests do it that way.
Mark
Now there’s an idea. 😀
I guess the work could be put into the chuck and rotated by hand, though I’m guessing a considerable amount of torque would be required for an 18mm diameter cut. I’ve also seen a jig, a bit like a drill-press. A drill-press/milling-machine can also be used apparently.
Well, it’s all fun. Learning new stuff etc. 🙂
We do not know who let you play with those things. But somehow we feel a kinship with them 😛
If you are cutting threads for High Pressure Applications you better be spot on and not eyeballing it.
You will kill someone.
I’ll check the existing threads (internal and external) against the tap and die to start with, see if they match up as they should. Also go over them with a pitch-gauge. Then I’ll cut in gradual stages and check between each cut to see how it feels (once the cuts are deep enough for the threads to bite of course). Considering the existing threads and the tools cutting the new threads are known quantities there shouldn’t be any issues, but I’m mindful of the 3000psi. They used to let me play with hand-grenades and rifles and machine-guns too. Who would have thought one day I’d be allowed to run amok with a lathe. 😯 😉 😆
This die holder is the way to go on a lathe:
http://www.use-enco.com/CGI/INSRIT?PMAKA=318-2031&PMPXNO=944247&PARTPG=INLMK3
It goes into the tailstock chuck, and keeps the die streight.
I built my own with a morse taper to go directly into the tailstock taper.
if you can use a die for your threading job, it makes it MUCH faster job. Professional machinests do it that way.
Mark
I use a hand plane on bamboo and get .001″ accuracy. I think you can get the same accuracy with your mill and lathe with some experience.
If you are cutting threads for High Pressure Applications you better be spot on and not eyeballing it.
You will kill someone.
How about take a wee cut and try the thread for size, adjust accordingly?
Eyeballing is okay for some things but you really need to learn precision work. Or you might as well stick to a dremel tool and hacksaw.
Come along Adam, there’s a wide space of ground between measuring threads with bits of wire and cutting them with a Dremel and a hacksaw. 😆
A particular application may or may not require that level of precision, and there’s no point applying it where it’s not required. The chap I’ve been reading has over thirty years experience and even he indicates a wide latitude in choice between precise and loose, depending on the application and how many taps you want to break (drill-size vs tap-size vs finished thread tolerance). Anywhere between 50% and 85% tolerance is acceptable, according to the particular application. For sure, he can get it bang-on first cut. A gonzo like me would take it slowly and build up to it by taking multiple shallow cuts and having a feel between each one. There’s more than one route to precision.
If I was completely clueless that wire-measuring jazz would put me right off and I’d run a mile. In fact I have a feeling it was stuff like that in school that led to me frying plastic tanks and soldiers in the metal-shop furnace. 😆
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Walt, after reading all that I almost feel like I’ve been cutting threads myself for a good few years. Thanks for taking the time, it was most instructive and much appreciated. 😀