Grinding my own external grooving cutter

[Chris TickTockParticipant @christicktock]

Hi Guys,

I wish to nut a 3/8 external groove in steel which is hard to get into at an angle using my existing cutters. Jason has already posted I could use a parting tool. I have poked around on the web and have come up with grinding my own from HSS. Have I got the angles in the right places and width on the front correct at 1/8th.

Any comment as to improve this cutter

Chris

[Chris TickTockParticipant @christicktock]

[JasonBModerator @jasonb]

Make the business end half the width so you don't get chatter on your small machine.

If you are using it on brass the top can remain flat

reduce the other angles so the tool is not so thin where it meets the main body and so that there is more support below the cutting edge

[Chris TickTockParticipant @christicktock]

Posted by JasonB on 27/08/2020 18:37:49:

Make the business end half the width so you don't get chatter on your small machine.

If you are using it on brass the top can remain flat

reduce the other angles so the tool is not so thin where it meets the main body and so that there is more support below the cutting edge

Appreciated Jason

Chris

[mechman48Participant @mechman48]

'I wish to nut a 3/8 external groove in steel ' …do you mean a ' Glasgow kiss' .. I'd much prefer to give a 'knuckle sandwich'… … I'll just get my coat.

George.

[Chris TickTockParticipant @christicktock]

Posted by JasonB on 27/08/2020 18:37:49:

Make the business end half the width so you don't get chatter on your small machine.

If you are using it on brass the top can remain flat

reduce the other angles so the tool is not so thin where it meets the main body and so that there is more support below the cutting edge

Jason, Have made one it grooves and parts really well, better by far than the parting blade. The point is I take it doing the 'cutting' which edge or edges need to be sharpened here when necessary, is just the sharpness of the point/

Chris

[JasonBModerator @jasonb]

You should really only need to touch up the one marked in green, this can be done with a small diamond slip which just removes enough metal to restore the edge, should it become heavily worn then use your grinder or sander.

[Chris TickTockParticipant @christicktock]

Posted by JasonB on 28/08/2020 19:20:15:

You should really only need to touch up the one marked in green, this can be done with a small diamond slip which just removes enough metal to restore the edge, should it become heavily worn then use your grinder or sander.

Jason, is it the front surface and / or the edges of this surcace with its corners. If so front edge and its sides??

Chris

[JasonBModerator @jasonb]

Whole of that surface.

[Dave SParticipant @daves59043]

You can get away with a whole lot less side relief than shown.
As little as a quick stroke with a Diamond file will be fine.

The front face can be nearly vertical.
If you a smack on center height then a vertical face would still have “relief” by virtue of the cylindrical shape of the bar.

Dave

[Pete RimmerParticipant @peterimmer30576]

If you feel that you'll need to touch up the front edge often, grind it steep like the diagram (but not so much) and put a much shallower primary angle right under the cutting edge. That way when you do need to touch it up you'll only have a small facet to dress, not the whole face.

[Chris TickTockParticipant @christicktock]

Posted by Pete Rimmer on 30/08/2020 15:43:04:

If you feel that you'll need to touch up the front edge often, grind it steep like the diagram (but not so much) and put a much shallower primary angle right under the cutting edge. That way when you do need to touch it up you'll only have a small facet to dress, not the whole face.

Peter I have found several folk online stating that putting a groove on the tip and a shallow angle greatly improves cutting. The groove is done with a Dremel. A steady hand is required….possibly luck as well on that thin edge.

Chris

[Pete RimmerParticipant @peterimmer30576]

If the groove is shallow then you won't have any problem. If the groove is deeper or if you're parting (especially with that 1/8" tool) then you'll need to use coolant. Most of the problems that people have with parting, on machines that would otherwise not struggle, is from not using coolant. Parting generates a lot of heat which makes both the tool/tip and the swarf expand. Because the tool (and the swarf) is the exact same width as the cut you're making it takes an incredibly small amount of expansion to make the tool expand in the groove and start to bind. If the swarf backs up in the cut it'll trap heat in there and exacerbate the problem. Once that expansion starts the heat generated sky-rockets and in moments your tool is buried in the groove, the lathe stalls and if you're really unlucky something breaks.

[Author]

Posts