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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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turning a narrow slot
Walter Harley wrote:
I have a Sherline! Finally broke down and got myself a lathe. Now I am trying to learn to use it. I want to turn a rectangular-profile slot approximately 1/32" wide, into an acetal (moderately hard plastic) shaft with an OD of 1/2". The slot wants to be maybe 3/32" deep; that is, OD of the inside of the slot is 5/16". (In case this description is unclear, imagine making a grommet.) What kind of tool should I use to do this? Should I use a parting tool? Should I try to grind something more or less like a parting tool? My concern with doing it with a parting tool is that, although it might work for this particular problem, I think I'm limited to cutting a slot exactly the width of the parting tool. It would be nice to learn how to make slots of various widths, including fairly skinny ones. You can take the parting tool out, and make another cut to the correct depth - if it's rigid enough, to add. For skim cuts this probably won't work, but if you've got over 50% of the tool in the work, it may work well enough. |
#2
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turning a narrow slot
"Walter Harley" wrote in message ... I have a Sherline! Finally broke down and got myself a lathe. Now I am trying to learn to use it. I want to turn a rectangular-profile slot approximately 1/32" wide, into an acetal (moderately hard plastic) shaft with an OD of 1/2". The slot wants to be maybe 3/32" deep; that is, OD of the inside of the slot is 5/16". (In case this description is unclear, imagine making a grommet.) What kind of tool should I use to do this? Should I use a parting tool? Should I try to grind something more or less like a parting tool? My concern with doing it with a parting tool is that, although it might work for this particular problem, I think I'm limited to cutting a slot exactly the width of the parting tool. It would be nice to learn how to make slots of various widths, including fairly skinny ones. Thanks in advance! Piece of cake, Walter. Acetal machines beautifully so there should be no problem with the cut. Grind yourself a parting tool that has relief top to bottom on the sides and front of the tool, and a slight taper front to back, then put the radius of the wheel on top, making sure it starts at the cutting edge and goes positive towards the rear. Finish the tool by honing, keeping the corners sharp and the front square. The top grind of which I spoke means the grind will be deeper at the shank than at the tip, where it cuts, and will give you a small amount of positive rake. That makes the tool cut quite well and promotes chip flow. I've been grinding parting and grooving tools that way for years with outstanding results. Make sure the cutting end is square, not ground to the side, and not grooved like Tim suggested. He'll come to understand that's not a good idea as soon as he starts grinding parting tools. The width of your parting (or grooving) tool should be no wider than the desired width (duh!), and if it's a little narrower all you have to do is mike the tool so you know the width, then cut your groove on location and move over the prescribed amount, using a dial indicator (long travel) the amount necessary to achieve the desired width. That's how one cuts snap ring or O ring grooves and other undercuts when you don't have the exact size tool on hand. With a square ground end you can move from one side to the other when you're to depth and end up with a very nice bottom cut. This will all make complete sense to you the first time you try it. Speed doesn't matter with acetal. The faster the better. You won't hurt the tool and you damned sure won't have any trouble with the plastic melting. The faster you run it, the better it machines. One word of caution. Grinding a parting tool that thin requires a wheel that has no bounce in it, so make sure your grinding wheel is running very smoothly. The thin section of tool likes to break off at the shank when it bounces. You'd also not want to make it very long so it has rigidity in keeping with machining steel. If you're lost on my description, I'd be pleased to send you a scan of a tool so ground. Contact me on the side if you're interested. Harold |
#3
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turning a narrow slot
Grind a 1/4" HSS bit to 1/32" width for about 1/4" of length to
form a parting/grooving tool. A bit of relief front-to-back and top-to-bottom doesn't hurt, but very little is required. Once it's made well, stay away from the grinder thereafter. You can dress it up when it needs it with a few strokes of a diamond hone. I have a couple of such bits I've been using for a decade, will admit that I've also broken a few, It only takes about 10 minutes to grind a new one. You'll find a lot of other uses for that bit as well. With the skinny part that short, it's no problem to skin a slot to wider width if the cutting corner is sharp. This is one place where you don't want a radiused edge. Such a tool won't deflect in acetyl or even reasonably free-machining metal. I've recently used such a tool on 303 stainless. Just a couple of days ago I was making cylindrical bushings of steel, OD of .205", ID of .165 or so. I drilled barstock for ID, machined to OD for half an inch, parted off bushing of various lengths in the region of .015 to .030 with such a tool. The experiment was a flop but the machining went OK.... I've made many narrow slots in acetyl, most a lot deeper than 3/32" when making high-voltage high-frequency pi-wound coil bobbins. For deeper cuts (some .750 deep, .032 wide) I used a cutter made by silver-brazing material from a broken HSS slitting saw to a 1/4" square of mild steel and grinding to shape. No relief on the sides of that tool but it runs straight and true. On 1 Aug 2004 00:23:31 GMT, "Walter Harley" wrote: I have a Sherline! Finally broke down and got myself a lathe. Now I am trying to learn to use it. I want to turn a rectangular-profile slot approximately 1/32" wide, into an acetal (moderately hard plastic) shaft with an OD of 1/2". The slot wants to be maybe 3/32" deep; that is, OD of the inside of the slot is 5/16". (In case this description is unclear, imagine making a grommet.) What kind of tool should I use to do this? Should I use a parting tool? Should I try to grind something more or less like a parting tool? My concern with doing it with a parting tool is that, although it might work for this particular problem, I think I'm limited to cutting a slot exactly the width of the parting tool. It would be nice to learn how to make slots of various widths, including fairly skinny ones. Thanks in advance! |
#4
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turning a narrow slot
In article ,
My concern with doing it with a parting tool is that, although it might work for this particular problem, I think I'm limited to cutting a slot exactly the width of the parting tool. Basically you just use a parting (well, in this case it would be called 'grooving') tool that is *narrower* than the groove you want to cut. If you want a 0.100 wide groove, you can use a .093 wide tool and plunge at one side, and then shift over seven thou to make it the correct width. Just be aware that parting tools are not terribly rigid in the side-to-side direction. So you either need to plunge into solid material, like the first cut, or take a fairly small cut on the side. Minimize the tool overhang and of course use the widest tool you can. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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