They work well on Mild Steel and softer steels. There are positive rake insert ranges, usually for Aluminium and plastics.
The top rake is around 5 deg and only a very small tip radius stoned on if nessesary. I tend to make them pointed with clearance so that I can face the bottom of the hole as well as bore.
The one's on the right will go down very small holes but not so deep and others with piece of tool steel held by a grub screw. Here is a selection of tools that I have made. How deep and what diamiter do you want to bore Robin. Hss tools will bore quite well without any top rake It’s then very easy to see which tool will be suitable for a particular bore before it goes onto the machine the clearance of the tool or lack of it will be obvious Each has a line scribed by the tool across it to indicate the centre line. I use a set of penny washers, bored at 3 then 5 mm intervals up to 30 mm. This is a recipe fir disaster as the tool again will foul In addition some think it is just a matter of dropping the height of the bar then rotating it upwards to put the tool back on centre height. Hss tools cut differently and can have a little rake, Too much will weaken the tool but they can also be set a little above centre height to enable better clearance, which unlike an external tool will improve things Without this they would be very delicate. This means they would foul the bore unless it was very large. In addition, the tips have small rake angles seen easily by examining one. Inserted tools tend to be mounted high with the tip angled down enabling a larger dia bar or the ability to be used in a smaller bore. The tool I want to make will be used to bore mild steel. Is this something specific to carbide inserts or does boring in general require a different top rake from external turning? I've always used carbide insert boring tools but haven't got one small enough for what I want to do now, so I want to grind one from HSS.Īll my carbide tip holders set the tip with a negative top rake - I don't know why, but they work.
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