Parting and Cutoff Issue

Pmedic828

Pmedic828

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I know that there are problems with using a parting cut off tool on a lathe - I have a cut off tool that uses a blade that looks kinda like a trapezoid. It is slightly larger across the top tapering in on both sides down to the base - it's the one that is sent when you purchase an AXA-100 QCTP and tools. I hate to use this because it never works like it should. I make sure that the insert is parallel with the chuck by using a 1 inch parallel between the chuck face and the insert. I also use lubricant on a brush constantly while plunging the bit into the work. I have made sure that it on center, have ground a slight chip breaker into the blade, and after cutting a groove about .001, move over a slight bit and re-insert the tool to provide clearance if the tool blade were to rub the sides of the cut portion. Then widen this cut until it part it off but it always fails before the parting off portion!
It always seems to work to a depth of about .300 then, unexpectedly, grabs the work, pulling it from the chuck and flinging the work off the table - I have a variable speed lathe and am only turning about 30 rpm. (I have tried to vary this from ultra slow to about 100 rpm - seems to make no difference. My question is I think that I remember reading about some type of "T" type of blade which would provide clearance for the cut but cannot find anything like that in the Grizzly, Victornet, ENCO, or other tool bit providers. I'm not sure if I am not looking in the right spot, or that they are really expensive and I am not looking at those pages.
Can anyone provide any information as to what I am doing wrong? Another post suggested a carbide cut off tool with a carbide insert that was sold by SHARS tool company. Should I think about purchasing one like this. I would reason that the carbide would fracture when the tool grabs and self destruct the insert? Does anyone have one and do ya'll like it? Suggestions please as this is getting rather frustrating:whiteflag:, not being to part anything off - Sometimes it's just inconvenient to cut stock on a band saw .. My Horrible freight doesn't cut straight either after numerous calibration attempts. H E L P ?
 
I have the same size tool post and parting blade as yourself.
On my 9x20 I had exactly the same problems as well.
It was very hit or miss as to whether it parted successfully or not.
I think you will find it is possibly a problem with flex somewhere in the cross slide/top slide/tool post assembly.
I cured my parting woes by making a better fixing to the cross slide (pitkin donut)
http://www.hobby-machinist.com/showthread.php/28057-9x20-tool-post-flex?p=254826#post254826
I am actually astounded at how easy it parts now.
You dont mention what lathe you are using but something similar should be possible for it.
 
As you get closer to the center, the SFM decreases. Dropping the spindle speed is going the wrong direction. Without sufficient surface footage, the blade isn't cutting, it is pushing the piece off.

CNC lathes and turning centers automatically wind the spindle up to maintain proper SFM. My Mazaks would hit 6,000 rpm at the center of the nub.
 
Make sure your tooltip is exactly at center. Make sure you use plenty of lube. More flood then brush. Make sure you get the oil right down at the cutting edge. The chips should be ejecting as you plunge. Make sure they are not getting caught in the slot preventing oil from reaching the cutting tip.Don't push too hard but make sure you keep constant pressure on the tool
 
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I've found it much easier to cut with the power feed instead of manual feed. But you may have other issues as others have pointed out.
 
I am with Micke. I used to manual feed and very low SFM but have found better luck with a normal speed and power cross feed.
With steel or stainless, still lots of lube.
Jim
 
I had started a thread cussing about my parting woes a while back. A few people had suggested that I try an Iscar style parting tool that uses carbide inserts. I bought one and tried it...loved it. I'll never go back to those old style parting tools.
 
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