Parting tool blade not sitting square

[old martParticipant @oldmart]

With a milling machine, you could slightly modify the wedge in the holder so that it pulls the cutting off tool towards the vertical. It would probably only need the edge of the wedge to have a 2 degree bias where it touches the tool.

When I bought my little 7 x 12 lathe, the seller included lots of tooling and I immediately noticed that the tiny trapezoidal parting cutter was upside down in its holder, the thicker section was at the bottom. How he got it to cut, I will never know, but as the ends were cut in the wrong direction by the manufacturer I could see why he had fitted it upside down.

[peak4Participant @peak4]

This really is the last one; I just remembered I had a cut down HSS blade holder which I no longer use.
As you can see, the “vertical” face isn’t; it’s at half the included angle of a tapered HSS blade.
The bottom of the blade shows the ground angle OK, though it’s hidden at the top as it’s been sharpened to a horizontal cutting surface.

It’s only just dawned on me, that I and others, have been describing the HSS blades as trapezoidal, but I guess that’s not strictly correct, as no two sides are parallel; avoiding discussion of the ends of course.

Irregular Quadrilateral maybe? (depending on which side of the pond you reside)

Also shown is the, ex-GPO wire feeler gauge I mentioned earlier

Bill

[larry phelan 1Participant @larryphelan1]

Beware of parting off under power, lest you join me in a stripdown of your machine ! Everything was going well, too well, and then–Disaster!, and all this with a rear tool post, which usually works well.

SOD says he usually ends up using his hacksaw, wise man !

[gluhParticipant @gluh]

By way of an update, this is all very strange. A replacement holder and a replacement blade have arrived.

• New Blade c/w New Holder – everything is fine, and the blade sits vertically.
• Old Blade c/w New Holder – everything is fine, and the blade sits vertically.
• New Blade c/w Old Holder – everything is fine, and the blade sits vertically.
• Old Blade c/w Old Holder – blade rotates away from vertical.

Even with swapping the locking “wedges” over between holders & blades, the _only_ combination that always fails / rotates in the old wedge in the old holder with the old blade. All other combinations are fine. I will return the old bits to Arc and see if they can work out what is wrong.

 

[old martParticipant @oldmart]

Glad to find the replacements are better fitting, parting off is commonly fraught with problems without having tilting cutters. When parting off, it is best to lock the saddle (carriage) and make sure the gibs in the cross slide and compound are not loose. For larger diameters, I tend to chicken out after about 20mm 3/4″ of depth and finish with a hacksaw.

[gluh]

On gluh Said:

By way of an update, this is all very strange. A replacement holder and a replacement blade have arrived.

• New Blade c/w New Holder – everything is fine, and the blade sits vertically.
• Old Blade c/w New Holder – everything is fine, and the blade sits vertically.
• New Blade c/w Old Holder – everything is fine, and the blade sits vertically.
• Old Blade c/w Old Holder – blade rotates away from vertical.

Even with swapping the locking “wedges” over between holders & blades, the _only_ combination that always fails / rotates in the old wedge in the old holder with the old blade. All other combinations are fine. I will return the old bits to Arc and see if they can work out what is wrong.

 

how does the cross section of the new and old blades compare?

Bill

[Ian PParticipant @ianp]

Just adding another parting blade holder version to the ones that Bill showed. I do not know whether this is a Dickson part as it came along with other toolholders with a second hand lathe.

I have no idea what the correct blade for it should be but the ones it came with were not held correctly and had no side clearance whatsoever on the chuck facing side. I packed the top of the blade recess with a shim (two actually, one brass, folded into an angle for retention, and steel strip that sits under it, retained by grease) steel strip is displaced in lower picture.

Compared with the OP’s 250-107 this holder has the advantage of being able to part off very close to a shoulder or the chuck as the LH edge of the blade is almost flush with the face of the holder.

Ian P

P.S. The blade in the picture is ground to suit making a PolyVee pulley.

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