turning a narrow slot

Nahh, something like run it in (x-feed) to cut one side, back it out, advance the carriage to the other side and cut it. If your tool is thin and long, I bet you'll get some deflection and get either an undersized notch or chatter. I would grind a vee on the tip rather than an angle to one side or another, so you get two square corners from the same tool. It may have to be square if you don't cover a tool width after cutting the meat out.

Tim (yeah, armchair lathe instruction... tsk tsk... well it works on the lathe turning inside my head.)

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

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.

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

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.

In article ,

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

Thanks, those instructions were very clear and made sense. (And thanks to Don as well, who filled in my remaining questions, e.g., can I grind it from a 1/4" blank.) Much appreciated.