Cutting straight with a die

I have spent a very long and unproductive day trying to cut a 5/16-24 thread on a cut-off piece of 5/16 bolt. I knew things were not going to go well when I could not get the
*never-previously-used* die to even bite. I chamfered, then chamfered again, nothing. eventually I made the tip almost conical. I got some purchase but a) the effort to cut was disproportionate and b) the end result was a thread which was skewed - and not subtly! I tried again with another piece of 5/16 rod - same result.
I hit the books to see if I omitted something glaring. Most of the texts I have are big on starting *taps* straight but they did not stress the dies so much.
In the end I borrowed the tap technique: I gripped the rod in the chuck of my drill press. I clamped the die in my drill press vise (there is a little shoulder that allows it to rest flat). I raised the table and centered and clamped the vise with the rod touching. I turned the rod with a pair of vise-grips while simultaneously feeding the spindle (it would be really nice to have three hands!). After the first turn the feed took care of itself. This way I cut a reasonably straight thread but the effort was much harder than I expected. Also, the vise-grips make a mess of the rod.
I tried it again with the cut-off bolt. This time I turned the spindle of the drill press directly by a makeshift lever improvised from the same stock and inserted into the chuck key holes. It was even harder to cut this time (I checked the diameter etc. - all identical).
I should mention that the whole workshop was swimming in Rapid Tap at the end - no dry cutting here.
I suspect that the die is crap and I will go and get another one but the whole process brought up some interesting questions. The most important of them is: How does everyone manage to get a straight thread when die cutting?
I think the method I use is OK provided the workpiece *can* be held in a chuck but if not, I am stumped.
BTW, if using a drill press to start a tap in a hole how do you turn the tap? Do you grind flat spots on your taps to get a better wrench purchase?
--
Michael Koblic,
Campbell River, BC
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Some dies and some die stocks have adjustable or replaceable guides to hold everything square. Some dies and taps are of poor quality, are hard to start, and require a lot of torque to operate. A two piece tap wrench (or the clamp from a tubing flaring set) can be clamped tightly around the tap to turn it in the drill press. I can generally get a tap up to 1/2" started by tightening the chuck three times, once in each key hole. Once I get the thread started, I generally remove the job from the drill press and finish tapping by hand. A purpose built die holder or tap holder seems desireable to hold everything straight and make it easier to turn. I have a set of Snap-On dies that have double hex outsides (12 pointed like a box wrench or socket) and I use these butted against the lathe tailstock to start threads on work held in the lathe.
Don Young
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Michael Koblic wrote:

Here is the way to hold a tap in a chuck.
http://s233.photobucket.com/albums/ee238/LewHartswick/?action=view&current=9-Tapholders.jpg http://s233.photobucket.com/albums/ee238/LewHartswick/?action=view&current «unchofholders.jpg http://s233.photobucket.com/albums/ee238/LewHartswick/?action=view&current «unchofholders.jpg
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Re: dies A lot of the dies out there are only suitable for rethreading, particularly if you got them at a hardware store and they're hex in shape. If it's Chinese, you've now got a nice paperweight. Round split-button dies can be adjusted over- or undersize to fit the female threads. About the only kind I have. You can order good ones from MSC or the like.
5/16" bolt shanks aren't necessarily the right size for threading with dies. They roll threads these days and cheap hardware store bolts aren't necessarily precision stuff. Sure you didn't have a hardened bolt?
Get a good die stock. The ones I use for freehand threading have an "iris", a set of fingers that can be adjusted to the workpiece diameter. I've seen these at True Value and Ace, the ones I use most I bought at Sears decades back, before they peddled junk.
Most of my threading with a die is done in the lathe with a die holder, ditto tapping.
Tap shanks are hard and will slip in a drill chuck, not recommended to do it that way. You can buy/make a tap wrench with an extension that can be chucked and slides up and down, a relatively cheap item, Enco had them at one time. Another way is to get a decent T-handle tap wrench with an accurately centered center hole, Starrett made the ones I use, then put a center in the drill press to start the thing straight. I do it this way in the lathe. Or you can make/buy a tapping block to start things square. Get decent tap wrenches, the T- handles with spring fingers made from the body should be junked, the best sort have spring-loaded hardened jaws. Dog-bones are handy to have on hand, too.
Stan
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wrote: A lot of the dies out there are only suitable for rethreading, particularly if you got them at a hardware store and they're hex in shape. If it's Chinese, you've now got a nice paperweight. Round split-button dies can be adjusted over- or undersize to fit the female threads. About the only kind I have. You can order good ones from MSC or the like.
*****Is this true of *all* hexagonal dies? I was looking at some Irwin dies in the House fo Tools yesterday. They are hexagonal but nothing on the package says "for re-threading only".
5/16" bolt shanks aren't necessarily the right size for threading with dies. They roll threads these days and cheap hardware store bolts aren't necessarily precision stuff. Sure you didn't have a hardened bolt?
*****That I cannot tell. However, the rod I switched to I am pretty sure was not, yet the result was much the same. If I absolutely had to use the bolt, what would heating it up (annealing) do?
Get a good die stock. The ones I use for freehand threading have an "iris", a set of fingers that can be adjusted to the workpiece diameter. I've seen these at True Value and Ace, the ones I use most I bought at Sears decades back, before they peddled junk.
*****Mine has just that. But...the iris is exactly concentric, the die in the stock, when the screws are tightened, is not. This renders the arrangement useless in this case. The openings are not lined-up.
Most of my threading with a die is done in the lathe with a die holder, ditto tapping.
Tap shanks are hard and will slip in a drill chuck, not recommended to do it that way. You can buy/make a tap wrench with an extension that can be chucked and slides up and down, a relatively cheap item, Enco had them at one time. Another way is to get a decent T-handle tap wrench with an accurately centered center hole, Starrett made the ones I use, then put a center in the drill press to start the thing straight. I do it this way in the lathe. Or you can make/buy a tapping block to start things square. Get decent tap wrenches, the T- handles with spring fingers made from the body should be junked, the best sort have spring-loaded hardened jaws. Dog-bones are handy to have on hand, too.
*****Thanks. Food for thought.
--
Michael Koblic,
Campbell River, BC
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<Big Snip>
The best method that I have used is to hold the die in a lathe. Make or buy a die holder for the cross slide. Set up the lathe for screw cutting, at the same pitch as the die. The die can be set square by running it up to a face plate, and of course it must be at centre height. Mount the workpiece in the chuck. Engage the leadscrew, and crank the lathe by hand. Very often, you can just grasp the chuck to do this. with a good hefty chuck, the key can be used as a handle. Use plenty of cutting oil, and don't forget to back off every quarter turn to clear the swarf. The steel in most bolts is intended for rolled threads, and may not be good for threading with a die or screwcutting. Better to find some better stuff to practice on.
Steve R.
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Are you sure you don't have a hardened bolt? If the die won't get a bite on the rod/bolt with a good chamfer, either the bolt is hard or the die is soft.
Michael Koblic wrote:

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Michael Koblic writes:

Chuck work in lathe. Position die in holder by hand at the end of the work. Push up against opposite side of die with tip of closed drill chuck in the tailstock, so it keeps the die "normal" to the work. Turn die handles back and forth by hand while feeding tailstock.
This holds the die in two angular degrees of freedom, "pitch" and "yaw", if you will, and in the Z axis. Does not constrain the "roll" (which you want to spin by hand anyway), nor the X and Y, which are roughly constrained by the self-centering tendency of the die around the work.
Reality is always 6 degrees of freedom that must submit to your will via tools.
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Because external threads are so much easier to cut on a lathe.

It isn't easy, and so-called 'drunken' threads were common way back when threads were cut by hand. Your drill press technique or some variation on it helps. If you can turn or file down the end enough that the die slides on or at least cuts easily it's more likely to start straight, though not always concentric. I've used a vee block to square the die and line up the shank of a cut-off headed bolt that was too big for the chuck.
You might be able to sharpen the die by grinding the holes with a Dremel. Most of my larger taps and dies came from second-hand stores and I resharpened them until they cut satisfactorily. Carefully hand- grinding the front face of a cutting edge, where the chips flow, shouldn't affect the geometry of the edge enough to matter for home use. Take a small equal cut off all edges and check, then repeat, rather than trying to do each one completely, so they stay about the same size. A sharp edge doesn't reflect light.
The dies sold in hardware stores are good for cleaning rust and dings off old threads, not so good for cutting them from round stock. As others have written, dies from an industrial supplier are much better.
See why we buy a lathe? I cut the thread part way on mine and finish with a die, using the tailstock to start it square.

I have but if they are deep enough to not slip they weaken the tap considerably. On a two-flute tap I grind shallow wrench flats into the shank end of the threads.
I chuck the tap, loosen the belt and turn the pulley by hand to start the tap straight. Just before (or when) it slips I switch to a tap wrench, being careful to apply equal pressure to both ends of the handle so the tap isn't pulled sideways until there are a few full threads to hold it straight. The long straight types of tap wrench that clamp in the center work best here because they fit in under the chuck.
Another solution is a good tee-handled tap wrench that can be guided at the upper end. The smaller ones fit into a loosened chuck, some have a center hole and you can chuck a guide pin, there is a type with a separate guide on the top. The trouble with them is they stack up so high you may have to raise the head to use them and lower it to drill, losing position.
After the Army I worked as an assembler building custom equipment for the auto industry so I got plenty of practice locating, drilling and tapping holes by hand on large machines. After a week or so I stopped breaking taps and eventually learned to tap with a reversing power drill. It just takes sharp tools and practice to learn the feel.
They made me go through all the assembly, machining, wiring and drafting positions before promoting me to project engineer. It was a very useful experience that unfortunately can't always be imposed on fresh engineering graduates.
Jim Wilkins
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wrote:> See why we buy a lathe?
The HoT 7x12 lathe just gone on sale from $999.0 to $750.0. I suspect it is too small, though. Furthermore, it would be a really big step in that I would not really know what I am buying.
I am looking at local colleges for a course on lathe/mill machine use. I have a long and relatively successful history of teaching things myself but I have feeling this would be one of those activities where time and money might be saved by learning on the actual instrument rather than from books (come think of it, there might be DVDs, too).
Of course, if my Better Half returned from Toronto and found a lathe in the garage I just might get my gonads removed.
Now here is a very basic question: I need a new drill press. Rather than buying a bigger and more expensive one, would it make sense to add to the pot and buy a mill? I.e. will mill do what drill press does as well as the milling?
--
Michael Koblic,
Campbell River, BC
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I was more or less pointed toward the Bridgeport and told to have fun with it. The kid who used it showed me how to change speeds and left. I burned and dulled the first end mill by overspeeding and overfeeding it but was OK after that. Likewise the checkout I got on a CNC Bridgie was turn it on, let it boot, home it, this is jog mode, now make some chips.
Having someone around to answer questions was very valuable, though.

Generally yes, with the exceptions that a floor drill press can drill into the end of a much longer piece, and you can clamp a bench drill press onto a large beam or plate to drill it. IMHO a drill press might be equal or slightly better for woodworking, but a vertical knee mill or mill-drill is excellent for drilling metal. I don't know enough about new equipment to suggest any of them.
Jim Wilkins
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Generally yes, with the exceptions that a floor drill press can drill into the end of a much longer piece, and you can clamp a bench drill press onto a large beam or plate to drill it. IMHO a drill press might be equal or slightly better for woodworking, but a vertical knee mill or mill-drill is excellent for drilling metal. I don't know enough about new equipment to suggest any of them.
Jim Wilkins
one comment on mills versus drill presses - some mills (mine for example) do not have a handle for lowering the quill like a drill press does so to drill things you raise the table - you have no feel for what is happening that way, so I find I like to have both.
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Is it a new machine or an antique?
One of the few things I like on the RF-31 mill drill is its 5" quill stroke. The 3" stroke on my mill is more typical, and adequate to drill a hole but when I have to use several different tools at the same place it's limiting. It helps to buy tools that are all approximately the same length, such as large 1/2" shank drill bits that are about as long as a stub-length pilot bit in a chuck. Taps are a problem. I've seen shop-made tap holders that used 4 setscrews to clamp the square end.
Jim Wilkins
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wrote:

Is it a new machine or an antique?
One of the few things I like on the RF-31 mill drill is its 5" quill stroke. The 3" stroke on my mill is more typical, and adequate to drill a hole but when I have to use several different tools at the same place it's limiting. It helps to buy tools that are all approximately the same length, such as large 1/2" shank drill bits that are about as long as a stub-length pilot bit in a chuck. Taps are a problem. I've seen shop-made tap holders that used 4 setscrews to clamp the square end.
Jim Wilkins
My machine is an Abene VHF-3 - they are still made, though this particular machine was made in 1970 - 6 hp spindle, 2 hp ways - what is good is that it's horizontal/vertical because the head rotates and it has an overarm. But the quill downfeed was optional and I've never seen an Abene mill with that option - if I saw one, they go cheaply enough I might buy the whole mill just to get it.
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One can extend the ability of the floor standing (or bench - mount 180 degrees from normal and over the bench edge... Use strong bench /metal plate...
You can use a screw up table - Z table IIRC from the floor jacking up the part.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com /
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On Fri, 6 Jun 2008 19:02:24 -0700, "Michael Koblic"

I had the identical problem with a new chinese die. 1/2 inch national coarse thread.
I persisted until I got the rod threaded. beautiful thread in the end. ....but 1.2mm under spec diameter! no wonder it wouldnt engage on the rod.
I went out and bought an australian made die and had not a problem threading the rod. and it was bang on spec diameter.
throw your die at the neighbours cats and get one made by a quality manufacturer. your die is more than likely a piece of garbage. Stealth Pilot
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