Four Facet or Six Facet drill grinding

old toolmaker

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I have ground a few twist drills using the four facet method (11 degrees primary relief and 25 degrees secondary relief). Upon testing a 3/8" drill I was pleased with the quality of the hole. The hole had a much better finish than that left by a conventionally sharpened drill except at the breakout end it was not quite as good. The drill required more feed pressure probably due to the point, but it started without the need for a punch mark and did not wander.
I have not tested different angles etc. yet, but, I have two questions before I do go at it: Would a six facet drill having a secondary point angle leave a better finish at the exit end? Would a split point work to advantage here?
I have a tool grinder so I can grind under controlled conditions to get an exact centered grind.

Dick
 
A split point will reduce force required to advance the drill and heat generation.
Since the web gets thicker towards the the shank, a bit that's been sharpened many times really needs to be split.
The standard 59deg works well for HSS but not so well if it's to be split. 118deg is a better angle for harder metals and preforms well in mild steels and is easyer to splt with a dremel.

I split points of my drills, under 1/2", with a dremel tool. It's hard to get them perfectly centered but one of these days I'll get serious and build a drill grinder.
 
I've found using a 1" belt sander it's fairly easy to split the web. In fact I have a older 1"x 42" Foley belt sander with a lower table I made to mount one of those general drill bit sharpener , a good belt and it does a better job then a grinding wheel. Plus it's settable for different angles . It uses the roll method no facets but it can be done with it.
 
I have been using the stubby 135° split point drill bits lately for about 99% of my hole making. I could not be happier:)…Dave
 
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I have been using the stubby 135° split point drill bits lately for about 99% of my hole making. I could not be happier…Dave
If I ever find a set I can afford ill be getting them too. I have several individual ones and like them .
 
I have been using the stubby 135° split point drill bits lately for about 99% of my hole making. I could not be happier:)…Dave
I just ordered 9 or 10 of those this morning before heading off to work. Cobalt, 1/8" - 15/32". Never used 135* split point before so kinda looking forward trying them out.
 
I have two new sets of the short screw machine length 135 degree drill bits. One is a number set and the other is a letter set. I like them both and I could put the same grind on my jobbers length drill sets also.

But has anyone tried a six facet drill? I'm going to grind one tonight and see how well they work.

Dick
 
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