The Shop > Tools
How are four facet drills shapened on a tool and cutter grinder?
b4dyc:
This is the style of sharpener.
The drill and grinding wheel are all on the same axis (when built correctly) so when you have ground secondary angle the table is dropped so that the primary angle is ground with no further trial.
If you read the page, John suggests that you contact him for plans if you do not have them already. He has in fact posted the files to me.
Metalman:
sparky961
In answer to your question about the time to sharpen a 3/8" drill by the four facet method, I would say 10 minutes if you did it enough to come to terms with the method. Less of course, if you had equipment permanently set up for the task. For me, sharpening drills by any method is a rare task, particularly in recent years as other pastimes have taken priority.
You mention creeping up to a point being difficult, but leaving a short length of the original chisel is quite acceptable. However, percentage wise, the acceptable error becomes smaller as the drill size becomes smaller making it very much more critical, and therefore more difficult at smaller sizes.
Therefore, I consider there is a minimum size at which it ceases to be practical, unless time taken is of no importance. For me that would be 1/4”, but above that size it becomes progressively more worthwhile as the cost of a new drill escalates. Certainly, 3/8” and above it becomes, financially, the approach to take, not necessarily using the four facet method but equally by any other method, cheap DIY methods excluded.
I mention cheap DIY methods, as for me using a drill set in increments of 0.1mm, there is no purpose in sharpening a 11.2mm drill if it then drills a hole 11. 4mm diameter.
I must try to find time to visit the gadgitbuilder web site
Harold
Fergus OMore:
--- Quote from: Metalman on March 14, 2017, 07:17:17 AM ---
I must try to find time to visit the GadgetBuilder web site
Harold
--- End quote ---
John Moran is quite practical and not just for his thoughts on tool grinding.
Kind Regards
Norman
sparky961:
It's a very clever idea to use a dished wheel and stick one of the fixture's hinges inside the wheel. I have to admit that I never thought of that when trying to get the pivot point of the horizontal plane to match with the drill's point. Though, for the sake of accuracy, he's not using a T&C grinder like I had asked about. But I did include "other" machines in my question too... so it's all good. ;)
Now, if you've been following any of my other recent posts you'll be aware that I'm actually focusing my efforts on a fixture for a surface grinder. This is for no other reason than I have one readily available and it seemed the better way to go.
In considering John's (Gadget Builder) fixture, I would be hesitant to use it on a surface grinder due to a safety concern. As clever as the idea is to tuck that hinge into the wheel, this is just asking for trouble when you have a lot of table travel and it's easy to travel right into the wheel. Perhaps this problem is negated through the judicious use of table stops/dogs, but I'm not sure I'd ever be quite comfortable with it. It also limits the wheel selection to a dished/cup type of wheel, where otherwise you could use a standard wheel that has the face relieved for side grinding.
I'm a little surprised (disappointed even?) that no one has commented on the other fixture I presented for feedback. I just checked and there have been 80 views but no replies. What does this mean? Got lost? No interest? Nothing to add? It's a piece of Rube Goldberg crap but I don't want to hurt your feelings?
Let's see if I can't drum up some replies though a link here...
http://madmodder.net/index.php/topic,12011.msg142291.html#msg142291
sparky961:
--- Quote from: Metalman on March 14, 2017, 07:17:17 AM ---sparky961
You mention creeping up to a point being difficult, but leaving a short length of the original chisel is quite acceptable. However, percentage wise, the acceptable error becomes smaller as the drill size becomes smaller making it very much more critical, and therefore more difficult at smaller sizes.
--- End quote ---
Perhaps it will still drill an acceptable hole, but if the point isn't near perfect doesn't this negate the benefit of the drill being self-centering? You end up with a chisel point that isn't any better than the "standard" conical grind. Maybe you re-gain the advantage after splitting the point (on the four facet grind)? But of course, the centering of the split is very critical as well.
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