|Grinding Cutting Torch Slag|
|Drill bit grinding|
No lathe set up is complete without a tool post grinder. The dump grit all over the place making clean up very important, but they do somethings that you can't do with an ordinary cutter--like work hard things. They are also good for tool making and the like. A big lathe, of course, calls for a real tool post grinder, and this one will not disappoint. It is a 2 HP, 3 phase grinder, and it is quite effective. It is shown here (3rd photo down on left)working on a steel bushing that was otherwise unmachinable.
The most common tool post grinders are Dumores. It seems that Dumore has almost a corner on the tool post grinder market. They are very expensive and usually conside of a motor which is belt driven to a spindle. This allows a bit more flexibility in configuration than the direct coupled model shown here. For example the separate spindle allows for speed changes and for small stones to do inside work (which, of course, need a speed change as compared to the 8" stones used outside.
The fact that ours has a 3 phase motor can be a pain, but we have handled that with a phase converter. So the thing is portable---we put a plug in on it--- the same style 50 amp plug in present on our Lincoln Vantage welder thus allowing us to power it either from the welder or the phase converter. I'm uncertain what sort of a lathe this grinder was intended for, but Dumore recommends greater than 20" swing lathes for their grinders of 1 Hp and above, and I think with cause. This things weighs around 100 lbs and hangs out on the side of the compound. This one clearly like big lathes. As I write this I have been using it to reshape some large drill bits (1" to 3") that have had bad things happen to them (broken/ends burned off etc). Having a gap bed lathe is nice as well, as most of the crap from the grinding operation lands in the gap reducing the abuse of the ways. I've mounted it on my London Machine Tool lathe which has 30" of swing over the bed and 48" in the gap and it seems happy on such a lathe size. As a gap bed lathe it has a bit extra travel on the cross feed to manage the extra diameter that can turn in the gap and this comes in handy positioning a grinder that is as big as this one is.
On the right photo sequence you can see the grinder at work on a bit and see a before and after view of a large bit that had been broken. I set a 30 degree angle on them and rotated the bit slowly in the lathe and ground it to the angle required by advancing the compound. To be sure this doesn't put the relief in needed for the bit to actually drill anything, but it gets it to the basic shape. We will grind in the relief's later. On larger bits we often free hand the grinding as we don't have a bit sharpener for large bits, but when they get all screwed up, broken or badly chipped it is very difficult to get them back in good form. This process gets the bits in form with the flutes of even height and properly tapered.