Sharpening a thin parting tool

[sparkie54]

Hi all
Could I get some help please.
I just purchased a thin parting tool (as per photo) and was wondering if the angle needs changing as it tends to catch a bit during use. I have (dare I say) a tormek system where I can establish the angle on a dry grinder and sharpen on a wet grinder.
Any help will be greatly appreciated
Regards
Chris

[Skew ChiDAMN!!]

Hmmm... how are you using it?

To me, in that picture it is upside down and will be prone to catching whatever the angle if used like that!

This is because the cutting edge would be the width of the tool away from the tool-rest and, while centered over the rest when held perfectly vertical, any minor deviation from vertical will cause it to want to twist & probably catch.

I use a very similar parting tool myself, made from an old carpet-layers knife. Not only do I rest the long end on the rest - so the bevel is facing up - I also tend to round over both long edges of the bevelled side, so that if the tool rolls a smidgin during a deep cut it's less prone to digging in.

Apart from that, I've found that the angle doesn't really matter much; it all depends on how you use it... and how deep a parting cut you're making. In use, it's just a matter of adjusting the presentation of the tool. If you find you need to angle the handle up or down too much to get it to cut smoothly, then regrind the bevel to a more suitable angle.

Just my 2cents. :;

[Paul39]

If your tool is not wedge shaped with the thick part on the top, it will be grabby as you go deeper.

Set your tool rest close up to your spindle at a height that the top of the parting tool is pointing at the middle of the spindle.

Stick the point into the rotating spindle just a bit below the center, and after it enters bring the tip up a bit. It will really start cutting.

When you feel it pulling or dragging the slightest bit pull out and start another cut half to 3/4 of the blade toward the waste side almost as deep as the first cut.

Go back to the first cut and deepen that until a drag is felt, go back to the second cut and deepen that.

Alternate until you are through.

My favorite thin parting tool is a 12 inch bread knife with a wedge shaped blade I bought for 50 cents in a junk store.

I ground about 1/8 of an inch off the sharp edge and rounded it a bit with sandpaper. I grind the tip at about 80 degrees upside down on the spark grinder so I have a burr sticking up. I line it up vertically and give it about a 1/2 second contact and it is sharp.

I also have a couple of diamond shaped parting tools, and one I made from a stout flat bladed screw driver. I use the home made ones more than the proper ones.

About any angle will do from what you have to almost 90 degrees. As long as the tip is cutting and the area below has enough relief to keep going in, it will work.

A longer handle might give you more control. If you are parting off thick pieces, 4 to 6 inches, a diamond shaped parting tool with a long handle might serve you better.

I am sure there will be many more favorite methods and grinding angles proposed. Look at them all and do what you are most comfortable with.

[sparkie54]

So I should be presenting it with the long side on the tool rest

[brendan stemp]

I'd agree with both Skew and Paul but would add:

I reckon a parting tool like that is not designed to part large diameter splindles which is why it hasn't got a long handle. I use this width of parting tool a lot but only on spindles of max diameter of 40mm. Even then I am inclined to initially widen the cut, usually with an extra half cut, on this size diameter which kinda defeats the purpose of a narrow PT.

And, yes, definitely use the tool with long edge on tool rest where the fulcrum point is closest to the cutting edge.

[sparkie54]

Thanks for all that - all seems to be working ok now