Drill Sharpening - 4 Facet Grinding.
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- เผยแพร่เมื่อ 8 ก.พ. 2021
- Continuing the search for the perfect drill grinding guide, I look at four facet grinding and try my hand with a low tech shop made jig. Results were surprisingly good !
- วิทยาศาสตร์และเทคโนโลยี
good description of 4 facet grind, helps me to make whats been floating around in my head for ages good stuff.
A another great video on problem solving and materials you have in the shop.
Christopher
Thanks 👍
well done Alan, cheers from the USA, Paul
Thank you.
As with the previous bought jig I believe that in this nicely built jig the feed should be done from behind the drill as well instead of from the table Y feed. By feeding the table Y feed the lip is slowly but surely diverging from being horizontal, the outer edge is dropping due to helix of the flute. The change is surely minute as in every grind only a small amount is being ground of but if you were to grind a lot of material off due to edge chipping fro example it would compound to a larger change.
Try modifying the jig to feed from behind the drill and having the flute stopping bolt in such a location that it would force the drill to twist along the flute a little as it is being fed forward so that the edge will remain horizontal throughout the grinding operation. I believe it would improve your results.
Thanks for your comment. I did consider the issue of the lip dropping as the drill length is consumed, and I started the secondary relief grind with the lip angled slightly up rather than level for just this reason. It would certainly be more correct to feed the drill past the index peg following the helix angle but it was just easier for me to use the table movement with the prototype jig. It didn't seem to have much adverse effect and I did check the horizontal alignment before starting the primary relief angle.
However, I do plan on factoring this idea into an improved version of the jig. I had this in mind when threading the adjusting screw at 20TPI as this will facilitate making a dial graduated in thousandths of an inch.
I am also contemplating a couple of other improvements aimed at getting a better surface finish from the grinding process.
@@alanshomeworkshop If had a tool/cutter grinder or a surface grinder with such a jig I would probably use the table movements as well and get around the negatives in ways such as you mentioned. It's so much easier and controllable it makes sense to use the machine's precise and smooth axis movements. After all I imagine endmill end faces which are glorified drill bits are ground by using the machine's x-y-z axis motions exclusively.
for clamping the drill bit why not put a straight shank on a jacobs chuck to go through 2 sets of bearings and put a locking indexing plate on the end, all you would need then is a reference for the existing angles of any bit and your rotation should then be spot on.
Or instead of an indexing plate you could make a protractor (with a needle somewhere) held on the shaft with a locking nut that you could zero out and have some sort of brake between the 2 bearings on the shaft (although this is liable to introduce run-out if not done with some finesse)
An interesting idea, but it would also need an adjustable height rest to support the drill tip. Without this, the drill would be gripped/clamped a long way from the grinding contact point. This would introduce a lack of rigidity and likely cause chatter problems. Might try it and see though. Cheers, Alan.
have been looking for a solution but what is your mechanism behind the correct starting orientation (rotation) of the bit and how small can your jig go with?
For correct sharpening, the drill lip must be horizontal. I set this initially by eye using a straight edge. Rotational alignment of the drill lip is then indexed by moving a peg (small bolt head) into contact with a drill flute. The drill lip is then brought into contact with the grinding wheel and fed into the wheel as its length is consumed by sharpening. By keeping the flute in contact with the peg, the drill rotates as is it moves forward and the lip remains horizontal at the point of contact with the grinding wheel. Hope this makes sense and answers your question.
I have not tried to use the jig on drills smaller than 6mm diameter. The limiting factors on minimum size are: 1. ability to see the lip clearly enough to set it horizontal and 2. whether the index peg can fit under the edge of a drill flute. My eyesight is not as good as it once was, and I now choose to consider drills under 6mm to be a consumable so do not attempt to sharpen them.
Thank you for the interest.
@@alanshomeworkshop got you but i think if the helix angle is different in that case you will get a different lip clearance angle i guess according to same setup, i have just made a grinding jig to be able to regrind very small bit from 6 and down to 1mm, please inbox my page if you are interested to talk about it more
facebook.com/GraphicManInnovations
Hi, genuine question (couldnt find a way to dm you)
Is there a reason why you dont sharpen by hand, it takes ~60 seconds to sharpen a bit. For reference im not a machinist perhaps a lathe requires a perfect centred bit?
Ive always ground my bits by hand and often change the angle/s depending on the drill and/or material at hand
Your question is perfectly valid and I know that many people are able to sharpen drills freehand. I have just never taken the trouble to learn, or perhaps more accurately practice, sharpening by hand; I have tried it a few times over the years with very indifferent results. In particular, I was not able to get the cutting lips to be of equal length. This, of course, results in an oversize hole. However, I may yet have another (more determined) try at this - it would certainly be a useful skill to have.
Cheers.
Hi, would it not have been better micing up the tip of the drill to see if it had drilled under or over size?
Possibly, but it was easier to measure the drill shank and, given my understanding of how drills are ground from a blank, the tip can never be larger than the shank. Thanks for your comment.
Cheers, Alan.
@@alanshomeworkshop the shank is meant to be smaller than the business end, so measuring the shank can be misleading but it only a few thou or so.
@@chrisstephens6673 Interesting. Thanks for sharing Chris.
WOULD THIS SET UP SHARPEN 3 AND 4 FLUTE END MILLS …
I don't think so.
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To much talking
Thank you for the feedback.
Thanks for all explanations Alan,
helps me decide to go ahead and do my own jig. I have previously made a mock up one that worked well for small drill but its time to make one like yours. Keep well, tks a lot.