ON TOPIC: Need some suggestions for a lathe set-up

Need some collective wisdom from the group. Here is all the information I can give.
The Part: Imagine a aluminum part with an open-center Figure 8 (figure 8 with the
center connector erased) shape (similar). Wall thickness is 3.5 mm for the entire shape. Overall dia (top-bottom) is 102 mm, inside distance at the narrow point is 30 mm At 4 points along the sides projecting toward you from the page, are some ~15 mm long projections that vary in height from 5 mm to 25 mm (same wall thickness).
The machine: Gang-tooled CNC lathe. 105 mm between tool pockets. Part is held in a collet, with approximately 42 mm finished height protruding from the collet.
The tooling: Tool 1: Iscar PCD tipped parting tool. Tool 2: PCD tipped 35 finishing tool, 0.8 R (35 is required because the face of the part needs profiling - some somewhat large radii- anything larger backcuts during the profiling...i.e. the backside of the tool cuts out what it isn't supposed to) R is fixed by the part print. There is ~40mm between the inside of the parting tool, and the tip of the finishing tool, in the Z axis direction, can't go any more because the parting tool would hit the collet when the finishing tool was cutting. Due to the amount of X axis travel, the finish tool tip is about 90 mm radially from the tip of the parting tool in X.
The Task: Taking our modified figure 8 shape as above, and assuming it is in plane with your monitor, the projections toward you, we want to part off about 8 mm into the monitor. Since the parting tool is 4 mm wide, this leaves a ring of about 4mm thickness, plus the projections. Then we must profile the face of the part left in the collet.
The Process Specs: Initial RPM for cut-off: 2500 Part to within 2.5 mm of the ring being parted, slow spindle to 200 RPM, decrease feed. After piece parts, ramp back up to finish cut RPM. (not really relevant)
The Problem: Every so often, you get a chipped finish tool, apparently from impact with the parted ring as it was parted. Watching the machine, it looks like it almost always falls pretty much straight down when it parts off, but apparently not *every time*. Does anyone have any suggestions as to how to protect the finish tool from the departed ring, and still be able to machine with the finish tool? This is an automated process, so stopping the machine between the two tools is not an option. I've tried facing with a normal tool, but the wall thickness is so thin it breaks chunks out below the finished machined surface and that is not acceptable. (seriously interupted cut here folks...) The process we have works great as far as machining goes, it's just dinging a very expensive tool way too often. Any thoughts would be appreciated.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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Anthony wrote:

Anthony:
    If I'm understanding this correctly, is the tool chipping/failing due to compressive loads on it from the part moving "toward" the tool rather than "away" from it? If so, perhaps some movement limiting device/roller/strap/wedge could be implemented to make sure the part moves "away" from the tool every time.     Maybe a tool with more side relief?
--
BottleBob
http://home.earthlink.net/~bottlbob
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When the ring comes off the part, my theory is it's coming off and hitting the finish tool, which is sitting 40mm Z+ and 90 mm X- from spindle centerline. It's a fairly fragile finish tool. Personally, I'm thinking a piece of sheet metal between the tools (on the tool post/slide) on a short-stroke pneumatic cylinder activated by M code....but I don't know if we have any outputs available on this machine, we already use a bunch for other automation. I can't put anything on the headstock end of the lathe, or above, or sides of the spindle due to the automation.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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Anthony wrote:

Try jogging the part off tool right at the end of that operation. You might get the parted material to move in a particular direction every time that way. Maybe.
--
John R. Carroll
Machining Solution Software, Inc.
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A deflector like that would be your best bet. I use one on light parts that tend to miss the part chute, they seem to fly up at the last of the cutoff. But like you only once in a while. Watch it for 20 mins & all parts fall in the chute, come back 10 mins later & many in the chips.
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Why wrote:

Sometimes its easier to use an air blast to direct the path of the part.
John
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wrote:

Any chance of reversing the spindel rotation for the whole operation? Perhaps the part would take off in another direction. <g> --
-JN-
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Thought about that also, but I'm using about 99% of the X axis travel now, and I don't have a holder for the finish tool to flip it over.
--
Anthony

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Gang tools don't have much X axis. Deflector if you can rig it is still the best bet. I guess you are cutting on the back side. If it was on the front side like I do, you could just put a sheet metal deflector on your turning tool front side so the cutoff tool would not let the part hit the turning insert.
But then if I knew what I was doing I wouldn't have started a machine shop, been a lie'er, dope dealer, anything else <Grin>.
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BottleBob wrote:

Bob, We discussed this on the IRC chat server. The piece that Anthony is parting off is hitting another tool and nicking it. It's a gang tool setup. Anthony has tried different speeds and feeds and has tried to direct the cutoff piece with coolant also.
It's a gang tool setup so the tools are very close together.
--
Regards,
Steve Saling
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On Sat, 12 Aug 2006 06:19:52 -0700, Garlicdude
<snip>

<snip> Unka George (George McDuffee)
...and at the end of the fight is a tombstone white with the name of the late deceased, and the epitaph drear: A Fool lies here, who tried to hustle the East.
Rudyard Kipling The Naulahka, ch. 5, heading (1892).
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sorry about the earlier partial post ....
On Sat, 12 Aug 2006 06:19:52 -0700, Garlicdude
<snip>

<snip> I don't know how practical this is, but consider some sort of shop vac with a small nozzle just over/above (or under?) the cutoff tool. You should be able to do this with a gang turn setup. If available use an m-code/relay to turn the vac on only when the part is almost cut through. You may need to pad the inside of the vac and/or some sort of baffles to avoid part on part damage.
Unka George (George McDuffee)
...and at the end of the fight is a tombstone white with the name of the late deceased, and the epitaph drear: A Fool lies here, who tried to hustle the East.
Rudyard Kipling The Naulahka, ch. 5, heading (1892).
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On Fri, 11 Aug 2006 23:27:20 GMT, Anthony

====================Kind of difficult to make suggestions w/o having seen the process so the following may totally off the wall.
Could you try a high pressure/volume air or coolant blast only during the last part of cutoff to make sure the slug or part goes the correct way? An air surge tank and solenoid valve should not be that hard to rig. If you have "spare" M codes/relays available [option on some controllers] extra coolant pump may be the way to go. Cheap enough from Harbor Freight.
You may want to rig some sort of catcher/strainer for the flying part so you don't have to sift the chips looking for the money....
Unka George (George McDuffee)
...and at the end of the fight is a tombstone white with the name of the late deceased, and the epitaph drear: A Fool lies here, who tried to hustle the East.
Rudyard Kipling The Naulahka, ch. 5, heading (1892).
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wrote:

On my gang lathe, so that I don't have to constantly switch spindle rotation, tools that cut on the front (operator side) of the part, are face up, and tools that cut on the back side are upside down. I usually turn on the back side (with the tool upside down) so that the chips fall down into the chip pan. Since the only place to put a parts pan is at the front of the machine, the cut-off tool/ parts chute is also at the front of the machine (table).
99.9 % of the time, mostly because of the limited table space, the distance between my cut-off and first turning tool (which I also use for a bar stop - pneumatic bar feeder) is only slightly more than the diameter of the bar. My right hand cut-off tool is face up, sometimes causing the parts to lift up slightly (and jump forward towards the first turning tool) when parting off, and have, in fact, chipped many a turning tool because of this.
How about using a left hand cut-off tool, and reversing the spindle? You'll simply have to put a 1/2" (or whatever the centerline is on your machine) riser under the tool holder. That way the ring will fall down and away from your finish tool.
Matt
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On Sat, 12 Aug 2006 17:39:49 GMT, Matt Stawicki

Should have said - Left hand cut-off tool, *upside down*, and reversing the spindle.
Matt
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A couple of thoughts; If you have the table space use a Watkins saw instead of a part off tool. <http://www.saw-lutions.com/
On a screw machine, I might use a piece of stiff springy wire bent so that it force the part down after part off. Being that the part is aluminum and not round, that would likely scratch it up. So my next thought is to use the same idea but with a soft bristle nylon brush. The twisted wire shank ones are usually fairly springy. Or maybe something as simple as a paint brush could be rigged to the C/O holder so that the part is trapped in the bristles as it's being parted.
--

Dan

Scopulus est usquequaque nefas
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That is a really good concept there.
--
Anthony

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