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Thread: Parting Off Blade/Tool Advice
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29th Jan 2018, 10:44 PM #46Member
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Hi jack620,
I had a look at my spare 1/8" SOMMA TBL832C COBALT blade this afternoon and to all intents and purposes the top of the blade appears to be flat. However, when I placed a thin straight edge across the top of the blade and held it up to the light, I saw the two outside edges of the blade kissing the straight edge with a slight concave between them. It's ground on a fairly big radius, but definitely hollow ground.
Alan
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30th Jan 2018, 07:06 AM #47Most Valued Member
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Hi Alan,
That's what the supplier said too. Here's part of his response to my email:
"The manufacturer uses a single radius for every width of blade so the curve is more noticeable on a wider blade and the ½” ones I sell are the smallest they make. The drawing they use to show the hollow grind is much more exaggerated than they actually are. From looking at the grinding marks on the blades I have it appears they use a wheel of around 6”-8” diameter held at 90 degrees to the blade so the diameter of the wheel produces the curve rather than a shaped wheel."
I question the benefit of such a flat 'concave' but it's better than nothing I suppose.Chris
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30th Jan 2018, 07:34 AM #48Senior Member
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I just ordered a GTN2 insert parting blade, hopefully I don't break this one as quickly. I usually overthink things so when I first tried parting off a few weeks ago I decided I was just going to work it out as I went without watching any videos / doing any research. Bit of a mistake!
I went for the 2mm insert as I figured it would be less stressful on the lathe (2506v)
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30th Jan 2018, 08:16 AM #49Golden Member
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jack620
Yesterday I had a little job to part of, it was made out of a piece of 1" dia bright mild steel bar of unknown grade, from memory I think this bar originally had a blue painted end on it. The usual recommended surface feet/ minute for HSS is arond 80-100 feet per minute. I parted off at 350 RPM which is around 90 feet per minute, this works out OK by controlling your feed rate, the surface finish was reasonably good. I then increased the speed to 500 RPM using a similar feed rate the surface finish improved and chip evacuation also improved. For the third cut I increased the RPM to 700 and both chip evacuation and surface finished improved again.You can hear the difference in sound and feel the difference in pressure needed. For all three cuts you need to find the sweet spot the pressure did not appear to increase. I used a brush dipped in oil held in the cut for lubrication. In my experience flood cooling produces a better finish than the brush method as it washes all of the chips out of the cut,easy to see why CNC machines use this method. The downside is it can be very messy. I just looked at the top of my blade and you would need a loupe to see any curvature, the chips do come out of the cuts without any sticking suggesting there must be a slight curve.
Bob
Bob
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30th Jan 2018, 09:29 AM #50Most Valued Member
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Bob l direct the coolant/cutting fluid onto the parting tool, it flows to the end of the tool and right where it needs to be, under the swarf.
You only need a low flow and it does not throw you coolant all over the floor. When you put the coolant on the job it is pouring on the wrong side of the chip and l think less fluid gets to the cutting edge.
Cheers, shed
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30th Jan 2018, 11:18 AM #51Most Valued Member
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2nd Feb 2018, 07:00 PM #52Diamond Member
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Well my blade and holder turned up today. Right in front of my wife! She asked what I'd bought this time, I just mumbled something or other and left it at that. Price not mentioned.
I'm making another drawbar (M12 thread) so I'll have to wait before trying it out.
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11th Feb 2018, 07:53 PM #53Diamond Member
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I've parted off a few times now with the EE tool.
I had to play around with speeds a bit and different diameters and material.
On some of the harder material (I think it might be 4140 but not sure: it was bright steel with a pink end) I had to use run the lathe at 830 rpm (or thereabouts) to clear the chips.
On leaded 1214 it was like parting butter.
I haven't tried using a power feed yet but I might later.
Ben.
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11th Feb 2018, 09:21 PM #54Most Valued Member
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According to this chart a pink end should be 1214. 4140 should be blue.
Chris
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11th Feb 2018, 09:28 PM #55Golden Member
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bwal74
Those chips look pretty good to me, you should be able to tell by the sound of the blade cutting and seeing a constant chip flow how it is cutting. A nice sharp tool, on centre with a constant lubrication flow and you hand controlling the feed you will soon master it. Try your power feed on your 1214 with the lowest feed rate and watch the chip feed for any changes means trouble.
Bob
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11th Feb 2018, 10:25 PM #56Most Valued Member
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The colour of the end is entirely up to the manufacturer and there's no standard per se unfortunately. Most seem to settle of yellow or "custard" (whatever the heck that colour is supposed to be) for 1020, pink is free machining, and blue is 4140. But again that's not to say it must be that way. You can normally tell 1214 as it will be covered in rust
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11th Feb 2018, 10:30 PM #57
Those chips are looking pretty good.
Grahame
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12th Feb 2018, 07:17 AM #58Most Valued Member
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