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#11
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On Mon, 09 May 2005 11:21:48 -0700, in ?? Abrasha wrote:
A Taig LATHE and a Sherline MILL are two very different tools! True enough. I was confusing what you were discussing, as I thought it was you who were suggesting that one needed the fully equipped mill, not a lathe. But I'd have made the same comment substitutine my Unimat lathe, which is also vastly underpowered. Cutting deep contours with it is indeed a pain in the ass, which I assume it shares with the Taig. But you CAN do it. What you cannot do is use a shaped cutting too that forms the entire shape of the groove at the same time. That would of course be the usual method with things like threads, and many other types of contoured cuts like radius forming, or the like. Can't generally do that with this small lathes And no, you cannot cut a helical groove on your Sherline mill, unless you have one with an indexing head (dividing head), which is coupled to the automatic power feed of the table. This is only possible on the Sherline, if it is equipped with stepper motors. Which means a CNC interface. And even if you have all of this, how are you going to hold the 15 mm silver rod. You have to have an indexing head on one end and a tail stock on the other end. Given that the table of the Sherline mill in only 13" long, that won't leave you much length and room to maneuver for the rod. nor is my little old unimat lathe. Your little old unimat lathe is good only for the most basic of tasks. It not useful for the task that the original poster asked about. Cutting a helix on a 10-15 mm diameter silver rod. Didn't say you could. I was responding only to what i'd thought you'd said, which was that the low power and flimsy drive belt of the Taig, and others of these small machines, was the stopper. I fully agree with you that the real stopper is the needed coupled index head and longitudinal feed, and that a mill so equipped is by far the best way to do it.. But for a faster helix, at what point does one stop calling it a "thread" and start calling it just a helix? Often, the distincition is the shape of the groove, which is generally precisly defined for a thread. Some few lathes set up for thread cutting may have the ability to cut a low enough pitch thread, as to qualify for the type of shape the poster desires. That lathe I mentioned using in grad school for that time I did a similar helical form was cutting the thread at 2 tpi, on a rod with a diameter of about 3/4 of an inch, if I recall. And it did not resemble a normal machine thread because the cutting tool I was using was not the usual 60 degree thread cutting tool, but somewhat similar to a standard cuttoff tool, with the side relief greatly increased to accomodate the helix. The result was a straight walled, flat bottomed groove, pretty much just as the poster is requesting. However, I'll easily admit that this radical a tpi setting is not the norm for most lathes, even pricey ones. Nor is the nifty taper cutting attachment that lathe also was equipped with, or the headstock thrust bearings that made it usable as a decent metal spinning lathe as well. And it's price was WAY out of the bounds of the poster's request. When I did that piece, the choice of the lathe was simply because that tool was able to do it. The bridgeport mill we also had there could not do it, simply because we didn't have any sort of index head or rotary table that could be tied to the table feed to generate the helix. "The enlightened machinist will not erroneously use the word spiral or helix as is almost universally done even by some writers. To correct such error is almost hopeless and perhaps nothing can be done about it. However: I humbly thank you for correcting our linguistic error. Brought a grin to my face, recalling a few other times I've heard widely misused terms in the english language corrected by those who, ironically, learned english as a second language. Sometimes, that way to learn a language results in someone with a better use of proper grammar than we native abusers thereof... Fortunatly, I suspect that most readers of this thread did not misunderstand the intent of the post due to the misuse of the words.. At least i hope so. When you are cutting a helix, the feed rate is determined by the pitch of the spiral. You cannot just set your feed rate "slow". Again, no doubt my own incorrect terminology. I'm not referring to the transverse feed rate, which is indeed set by the machine, and determines the pitch of the thread or helix. I was referring to the rate at which one manually feeds the cross slide into the work to advance the cutting tool farther with each additional pass. If you take a very small "bite each pass, removing less metal, there is less stress on the motor, and less bending force on the workpiece, so long as you also limit the width of the cut as well as the depth. This is, frankly, a major bother and potential cause of innacuracy, since intead of letting the geometry of the grove be generated by the shape of the cutting tool, as is normally done in thread cutting, one might need to use a narrower included angle on the tool, or otherwise take small bites adjusting not just the cross slide feed into the work to increase the depth of the cut, but also it's transverse position, so the full width of the groove is arrived at with multiple narrower and smaller bites. A properly sized and powered lathe, of course, does not normally require such tom foolery, though in this case, a narrow rod of softer material might still require it to avoid bending the rod during cutting. Besides, both the Taig and the Sherline do not have lead screws, so what feed rate are you talking about? Unless you have a lead screw and change gears, you cannot set a feed rate. Your feedrate in only manual on both machines. Not very useful when you are cutting a helix in any set up. Agreed, though my unimat does have a lead screw. Only for finish cuts, not adjustable much for threading, so equally useless for this application. Unimat does make a thread cutting adjustment, and odd kludge of an affair that uses a thread form and follower to generate the transverse tool feed. I dont' own one of those, so don't know how well it works, but it too, likely does not generate the degree of pitch this poster needs. 1: You didn't cut a spiral, but a helix. yeah, yeah. thanks again :-) :-) 2: You cut a certain very special kind of helix, i.e. a screw thread, which is not what the poster is after I think. Well, no. See above. While the lathe may have thought it was cutting a thread, the use of a differently shaped cutting tool created a flat bottomed, straight sided thread, which is more or less what the poster is trying for. What may not have matched is the pitch of my thread to his desire, but mine was unusually low (2 tpi, if I recall) Screw threads are cut on lathes equipped with leadscrews. Helices are cut on milling machines, in a manner I have now described in several posts. Agreed, though the two forms are essentially similar geometry. At what point does a thread pitch become so low as to be called only a helix? Certainly the typical shape of a twist drill is not something one cuts on a lathe, but the division where one becomes the better tool is mostly based on what your machinery is capable of. And you are correct that the mill is no doubt the better tool for this job. Just a thought, though. I recall seeing wood workers setups used with a router, intended for doing the helical forms for things like twisted shape table legs or railings, or whatever. A form much like a coarse twisted rope. Those jigs use a premade form with the needed helix. Moving the router along the workpiece causes a form much like a half nut on a threading lathe to follow the preform, and the preform is linked to the workpiece, so the preform rotates and the workpiece follows along, resulting in a similar helical cut on the workpiece. It might take some ingenuity, but I'm wondering if our poster could construct a similar, smaller scale cutting jig to cut his helical grooves. I see lots of mechanical problems in getting a precise enough device to work well in metal, but the basic geometry of how those router jigs work might be applicable here if the fellow is inventive enough. The principal is not that different from what the thread cutting attachment for the Unimat does, with a form and follower defining the cutting tools path Peter |
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#12
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On Mon, 09 May 2005 11:21:52 -0700, in ¸õ Abrasha wrote:
Carl 1 Lucky Texan wrote: Like Peter said, plus, if the piece were not too large, perhaps it could be done in wax and then cast? Carl To cut a helix in wax you would need the exact same setup as for metal. Abrasha http://www.abrasha.com But if the need for precision is less, one could reasonably consider whether one might simply hand cut the form in wax. Would take some very careful layout, and careful wax carving, but it's possible. No doubt not as accurate as a machine generated and cut helix, but perhaps that degree of accuracy is not needed. Peter |
#13
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"Abrasha" wrote in message ... Andrew Werby wrote: "norwick" wrote in message ... I need to cut a spiral onto a silver rod. The sides of the cut can be at 90 degrees/and/or inclined. I envisage this to be done by a lathe (milling machine?). Diameter of rod could be 10-15mm, spacing between edge of the next groove ca 3mm, groove width & depth ca 2mm (ideally there should be some scope for visual considerations). Non electric system would be acceptable (or very slow speed lathe), machine size should not be more than 1m, weight under 50kg. Cost should not be more than $1000-1500, but this assumes that it can be used for other applications, eg cutting tool steel etc. [You could do this on a miniature CNC milling machine (like the Taig mills I sell) equipped with a rotary table, chuck, and tailstock. You'd need to program the toolpath to advance the tool along the X (long) axis while rotating the A axis (the rotary table) so that the grooves were properly spaced. A ball-end tool would give you a round-bottomed groove; a regular endmill would give a flat-bottomed groove. The weight and size of this machine would be about what you're asking for above, but the price would be higher - about $3k, with the accessories you'd need. These machines can be used for many other things, but for best results with tool steel anneal it first, and use carbide cutters.] The motor that typically cames with the Taig does not have enough power to cut a 2 mm deep groove in a 15 mm diameter silver rod. The cutting force would stop the spindle dead in it's track, or the rubber band (the drive belt that comes with the Taig is no more than a big rubber band) would just slip. Abrasha http://www.abrasha.com [Want to bet? Taig recently started providing a bigger motor with their mills than previously. The 1/4 hp Franklin motor now standard would have no problem cutting a 2mm groove in a piece of silver - or a piece of steel, for that matter, in one pass, if one went at an appropriate speed using a 2mm 2-flute cutter. It could also make multiple faster cuts at shallower depths. The Gates drive belt, while it may superficially resemble a "big rubber band" is actually quite resistant to slipping, when tensioned correctly. The pulley settings can be changed to provide more torque, or more speed, as needed. Have you ever actually used one of these mills?] Andrew Werby www.computersculpture.com |
#14
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Possibly not the same power requirement, hobby lathe might be OK.
I admit, he seems to need to do longer pieces than might be practical to cast though. And certainly they wouldn't have comparable finish/precision, etc. Just a thought. Carl Abrasha wrote: Carl 1 Lucky Texan wrote: Like Peter said, plus, if the piece were not too large, perhaps it could be done in wax and then cast? Carl To cut a helix in wax you would need the exact same setup as for metal. Abrasha http://www.abrasha.com -- to reply, change ( .not) to ( .net) |
#15
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Peter writes:
"Just a thought, though. I recall seeing wood workers setups used with a router, intended for doing the helical forms for things like twisted shape table legs or railings, or whatever. A form much like a coarse twisted rope. Those jigs use a premade form with the needed helix. Moving the router along the workpiece causes a form much like a half nut on a threading lathe to follow the preform, and the preform is linked to the workpiece, so the preform rotates and the workpiece follows along, resulting in a similar helical cut on the workpiece. " Peter -- That is a reasonable approach to doing it on these small, underpowered lathes -- using active tooling, such as a dremel motor mounted in a toolholder on the cross-slide. A ball-nose end mill cuts nice flutes. Then, as Abrasha points out, to cut really slow pitches, you need either a full cnc setup, or one of these: http://www.avatartools.com/ The Frog, in threading mode, syncs the lead screw advance to the lathe spindle using a hall-effect sensor, and is only limited in pitch by spindle speed and maximum slew rate of the stepper motor on the lathe leadscrew. As the pitch gets coarser, you reach a point where the cutter can't slew fast enough to keep up with the spindle. But with the variable speed motor on a Sherline lathe, you could cut some very coarse pitches. I have this setup on my Toyo (Sakai) lathe, and have cut helical flutes with it in wax and soft metals. A follower rest on the toolpost helps control workpiece deflection. You are limited to a single helix, however. I haven't found a way to cut multiple starting point threads with the Frog. That's my machine, btw, at http://www.avatartools.com/Merchant2...ory_Code=Sakai I've since added a third stepper on the mill Z-axis. Regards, Bob |
#16
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Peter W.. Rowe, wrote:
I was referring to the rate at which one manually feeds the cross slide into the work to advance the cutting tool farther with each additional pass. That's called the "depth of cut" Abrasha http://www.abrasha.com |
#17
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On Mon, 09 May 2005 20:52:12 -0700, in ¸õ Abrasha wrote:
Peter W.. Rowe, wrote: I was referring to the rate at which one manually feeds the cross slide into the work to advance the cutting tool farther with each additional pass. That's called the "depth of cut" Abrasha http://www.abrasha.com thanks again, for the correction. once, I seem to recall knowing all those correct terms. wonder what happened... (grin) Peter |
#18
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Peter W.. Rowe, wrote:
On Mon, 09 May 2005 20:52:12 -0700, in ¸õ Abrasha wrote: Peter W.. Rowe, wrote: I was referring to the rate at which one manually feeds the cross slide into the work to advance the cutting tool farther with each additional pass. That's called the "depth of cut" Abrasha http://www.abrasha.com thanks again, for the correction. once, I seem to recall knowing all those correct terms. wonder what happened... (grin) Peter You probably stopped using the lathe and mill, and your need to know disappeared. I use my lathe and mill almost daily. Abrasha http://www.abrasha.com |
#19
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norwick wrote:
I need to cut a spiral onto a silver rod. The sides of the cut can be at 90 degrees/and/or inclined. I envisage ... Any suggestions? In one of the Foxfire books there is an article about how to rifle a gun barrel 'by hand'. It would be some work to make the rig, but you could modify their design, turn the cutter "inside-out" and make it work for what you need. The tool itself would require no electricity to use, but it wouldn't be fast. -- Carl West http://carl.west.home.comcast.net change the 'DOT' to '.' to email me "Clutter"? This is an object-rich environment. |
#20
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Andrew Werby wrote:
[Want to bet? No. However your reply seems to indicate your need to be right by trying to bluff me into a bet. So I challenge you to produce the helix, the original poster asked about, on your mighty Taig mill. I say, it can't be done. Go ahead, prove me wrong. You've got the Taig. If you succeed, (which I know you won't), you have a strong selling point. If I am not mistaken, you are after all trying to sell these things, which seems to make you a bit biased. I find that rather amusing. Don't get me wrong. The Taig is a very valid and verstile tool and a useful one at that. And it cannot do what the original poster asked. You can try to bluff me all you want, it can't be done. You can't do it. Taig recently started providing a bigger motor with their mills than previously. The 1/4 hp Franklin motor now standard would have no problem cutting a 2mm groove in a piece of silver - or a piece of steel, for that matter, in one pass, if one went at an appropriate speed using a 2mm 2-flute cutter. We weren't talking about a groove. We were talking about a helix! That's what the original poster wanted. Something very different. However, you claim that the Taig, does a 2 mm depth of cut cut in steel, on a 15 mm diameter (original poster's measurement) in one pass? Prove it! SNIP Have you ever actually used one of these mills?] No, I have no need to. I have a real mill, with a 3/4 HP, 3 phase motor. Actually, it is a rather wimpy mill as far as true power is concerned. I'm ready for something more powerful, like a Bridgeport. But a Taig, gimme a break, why would I ever want to use one of those when I have a Clausing 8520? Now go and make that helix, you claim you can make on it. I say, you can't do it! Abrasha http://www.abrasha.com |
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