Parting tool question

[Chuck in E. TN]

 I have been busy making aluminum QCTP tool holders for those once in a while tools that we hate to take another tool out of its holder to use.
Last night I was making the knurled wheels (mat’l aluminum) for setting tool height. I drilled a piece of al bar and tapped for the height screw, sectioned off 4 wheels, chamfered the edges, and finished parting them off. The picture shows the burr left by parting. My question is, can I grind a parting blade with a slight angle on the tip to cut the parted piece clean? How much angle?
Chuck

[andyf]

You can put a slight angle on the end, Chuck, but I find the item I'm parting off still breaks away when almost there, leaving a bit of a burr. Also, with a thinnish parting blade, the angle can cause the blade to flex and steer off course as it gets deeper in so it tries to follow a curved track into the material and jams up. That's just my experience, though.

Andy

[Lew_Merrick_PE]

Chuck,

I have several parting tool holders -- and several parting tools.  My ultra-thin (1.25 mm X 6 mm) parting tools have a holder for aluminum that presents the tip as a 5° angle to the horizontal plane.  Just about everything else (I have a -2.5° holder for titanium) is set to present on a dead level plane.  The key attribute of all of my parting tool holders is to match the (vertical) taper such that the parting tool seats firmly in the holder.  I have a (screw-adjustable) guide that fits on my (large table) bench grinder to assure that the tip of the parting tool is ground perpendicular to the face of the holder.  I then carefully hand stone the resulting edge to dead sharp.

However, the fact is that a parting tool will tear through one side or the other of the part being parted.  The bore to which you are parting is rarely truly round (especially a part with internal threads).  Exceptionally slight vibration will cause the "tear" to start at one edge or another and leave a burr.  And, of course, if the face of the parting tool is not exactly parallel to the CL of the part, you will get a burr.

[Jonny]

Problematic and striving for an answer for last 13 years.

I have decent parting blades and holders from likes of Arno, Iscar, Manchester, Sandvik and some others. Have selection of tips with different angles, rakes, grades and neutral, left or right handed. All at best leave a minor burr. Some neutral tips leave full width of tip as a long burr. That's with a  bored hole to break in to using 6082 aluminium with coolant.

One thing I haven't tried is speeding spindle up massively from 540rpm but suffer start issues at higher speeds. Most of the tips I have are used on 5 axis machines running up to 4000rpm.

To get rid of the burrs I usually use a knife as a deburrer, works wonders.

[Chuck in E. TN]

I came to that same conclusion, Johnny. I've tried all the suggestions on 6 different forums. I debur with a fine file.
Chuck

[John Swift]

Hi Chuck

once you part off the last piece you could screw a stud / grub screw into the end of the bar
the knurled wheel can be mounted on the stock and wheel faced off to remove the burr

how about using a countersink ?


several years ago I repaired a EMI-MEC Sprint capstan lathe

I noticed one of the other machines used something that looked like a boring tool to cut a v groove in side of the bore in the part being made

when parted off the remains of the v grove broke the edge of the bore saving a second operation

one thing I noticed was the part off tool was very thin ( approx  0.05")
compared with the tools supplied for my  C2 mini lathe

   John

[picclock]

Hi Chuck

I tried the angle on the end to get a clean finish on the part after I saw a youtube video (Tubal Cain ?). As always his stuff came out fine, but I had other issues. The parted surface was no longer flat, but slightly concave, and even worse I still had the burr. I think it may have to do with the blade bending sideways, although this was with a 3mm blade. The bending may be due to the edges of the tool cutting at different speeds.I just have them straight now. I think the angle was 5-10 degrees. i copied it from what I could see of the video.

If you succeed I would be interested to know how.

Best Regards

picclock

[mcostello]

Excessive stickout of Your parting blade could also do that. In a previous occupation I was told something like 10% more stickout led to 33% more deflection, or something like that.

[Jonny]

The only time I currently see concave is when using supposedly decent Eclipse 1/16" blades with ground relief and either ground right hand or neutral cut. No amount of sticking out will cure and highly visible the tool deflecting off right even 1/16" plunged in.

Never seen it on any other left, neutral or right hand tipped cutters but there again they are respectable brands like Iscar mainly.