I'm part way through making a 4" aluminium drive wheel for a belt grinder - I'll get there eventually! I've got it bored and I'm just trying to get the keyway cut. It needs an 8mm wide key slot about 3½ - 4mm deep and 45mm long....although I don't think it'll be an issue if it goes all the way through.
I tried what I'd done with some delrin previously - essentially an 8mm square HSS bit sharpened like a chisel and held at an angle for clearance. With the scaling up of width and the harder material, the stick-out just makes it too flexible. I think I need to make a boring bar style of tool with a single tooth cutter in the end. I've seen youtube videos of similar efforts but nobody seems to agree on geometry. What sort of angles do I need on the mounting hole and the tool bit please?
I'm thinking a 20mm bar - that's what's lying around shouting "Make me into a boring bar!" - cross-drilled to 11.5mm * and with a set screw to retain the HSS at the end. One of the videos suggested slanting the hole by 7° to get some built-in relief and then grinding side relief on the tool bit so that it doesn't rub. Is this the sort of geometry that's appropriate for this and will I get away with a slightly over-size hole for the tool bit?
I guess I'm probably making this harder for myself by over-thinking it....but would appreciate some pointers to avoid going nuts!
Many thanks,
Gareth
*The 8mm square HSS should have a diagonal of 11.31mm but 11.5mm is the closest drill I have without setting up a boring head....which I could do if you think it's really necessary.
I tried what I'd done with some delrin previously - essentially an 8mm square HSS bit sharpened like a chisel and held at an angle for clearance. With the scaling up of width and the harder material, the stick-out just makes it too flexible. I think I need to make a boring bar style of tool with a single tooth cutter in the end. I've seen youtube videos of similar efforts but nobody seems to agree on geometry. What sort of angles do I need on the mounting hole and the tool bit please?
I'm thinking a 20mm bar - that's what's lying around shouting "Make me into a boring bar!" - cross-drilled to 11.5mm * and with a set screw to retain the HSS at the end. One of the videos suggested slanting the hole by 7° to get some built-in relief and then grinding side relief on the tool bit so that it doesn't rub. Is this the sort of geometry that's appropriate for this and will I get away with a slightly over-size hole for the tool bit?
I guess I'm probably making this harder for myself by over-thinking it....but would appreciate some pointers to avoid going nuts!
Many thanks,
Gareth
*The 8mm square HSS should have a diagonal of 11.31mm but 11.5mm is the closest drill I have without setting up a boring head....which I could do if you think it's really necessary.
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