Four Facet vs. Split Point

[paulsomlo]

I'm in the market for a new drill grinder and trying to assess what capability I need. I've read through about 20 minutes worth of posts here and still have questions.

My impression is that they're both self centering, but it appears that the four facet doesn't cut all the way to the center, as does the split point. Can someone who has experience with both weigh in?

 

[Booze Daily]

Sounds like a core drill. For drilling cored holes in a casting.
Split point is generally cobalt. 140 drill point angle

 

[???]

4 facets are weaker due to the flats.

 

[johansen]

A true center cutting split point, in my opinion needs to be a continuous spiral out from a zero web thickness point at the center of the drill bit.. Practically this is impossible. If you have a dremel and a 1/32” diameter electroplated diamond bit, you can create it.

Instead its a compromise where you have a sharp corner from where the helix angle and positive relief of the flutes meets a neutral angle center relief.

In comparison with a lathe cutting tool, the split point has a neutral rake angle usually but you can make it positive or negative.

The rest of the cutting edge has a positive relief of the helix.

Read here if you have not.

DRILL POINT GEOMETRY , an article by JOSEPH MAZOFF - Newman Tools

'DRILL POINT GEOMETRY' , an article by JOSEPH MAZOFF

www.newmantools.com

Its not easy to figure out, but the 4 facet grind leaves a negative relief edge that gives space for and pushes, smearing the metal out of the center and pushing it to the positive rake angle of the drills helical cavity. But it does not reduce the web thickness of the drill bit whereas thr split point does.

In theory no metal needs to be smeared and moved around with an ideal geometry. In practice there is some amount of smearing.

Also ideally the back relief of the grind would be no more than necessary to match the feed rate.

 

[???]

Instead its a compromise where you have a sharp corner from where the helix angle and positive relief of the flutes meets a neutral angle center relief.

Take a look at the high helix long series drills used by toolmakers to drill waterways. The split point is undercut to get away from the negative angle of the traditional split point. They are also incredibly difficult to regrind without the proper equipment. Still haven't sorted out my phone so I can't take a picture to share.

 

[EmGo]

A true center cutting split point, in my opinion needs to be a continuous spiral out from a zero web thickness point at the center of the drill bit.. Practically this is impossible.

Well, there is the Cincinnati spiropoint

 

[swarfless]

Don't see why you can't have four facet with split point, but it would mean a fine grain, hardish bond wheel to hold the edge necessary. Worth bearing in mind, Christen who were I think the original proponents of four facet, say in their instruction manual that four facet is only suitable for a max of 5/16th or 8mm drills.

 

[gbent]

Christen makes collet/chuck to make 10mm 4 facet.

 

[Houdini]

I found it not very cost effective to regrind drill bits.(non-carbide)
ie. the cost of a new one vs buying a machine and the time it takes to sharpen it, was a wash or a loss.
So I haven't bought a sharpener and won't.
I let them pile up and some day I will send them all in at once to have re-sharpened.
just my 2 cents.

 

[rke[pler]

The Optima drill grinders do 4 facet with split point. I split the points of screw machine drills when I grind.

 

[paulsomlo]

Read here if you have not.

DRILL POINT GEOMETRY , an article by JOSEPH MAZOFF - Newman Tools

'DRILL POINT GEOMETRY' , an article by JOSEPH MAZOFF

www.newmantools.com

Its not easy to figure out, but the 4 facet grind leaves a negative relief edge that gives space for and pushes, smearing the metal out of the center and pushing it to the positive rake angle of the drills helical cavity. But it does not reduce the web thickness of the drill bit whereas thr split point does.

In theory no metal needs to be smeared and moved around with an ideal geometry. In practice there is some amount of smearing.

Also ideally the back relief of the grind would be no more than necessary to match the feed rate.

I've read that article in the past, but just read it again - I don't think he states explicitly that his "modified split point" is a better geometry than the four facet, or even six facet.

 

[paulsomlo]

The Optima drill grinders do 4 facet with split point. I split the points of screw machine drills when I grind.

I'd love to have an Optima, but can't really justify the cost. I missed one at auction a few weeks ago, last bid would have been $823 w/fees & taxes. Kicking myself now, as it was well tooled, although I would have been bidding blind - it was 110 miles away, which made inspection difficult. Of course, you don't know how high the other bidders were willing to go.

 

[eKretz]

I've read that article in the past, but just read it again - I don't think he states explicitly that his "modified split point" is a better geometry than the four facet, or even six facet.

Modified split point is pretty damned good. One of my favorite points. Only beaten by helical (Spiropoint).

 

[paulsomlo]

Modified split point is pretty damned good. One of my favorite points. Only beaten by helical (Spiropoint).

I watched a video of the Cincinnati Spiropointer in action - quite the gadget. As far as modified split point, what type of grinder/wheel configuration does that require?

 

[John Garner]

Can't recall ever using a Spiropoint drill, but I sure did like using Winslow-pointed drills.

Are the Spiromatic and Winslow points significantly different, or are the differences subtle?

 

[paulsomlo]

A true center cutting split point, in my opinion needs to be a continuous spiral out from a zero web thickness point at the center of the drill bit.. Practically this is impossible. If you have a dremel and a 1/32” diameter electroplated diamond bit, you can create it.

Instead its a compromise where you have a sharp corner from where the helix angle and positive relief of the flutes meets a neutral angle center relief.

I took a good look at one of my split point bits and I think I understand - the area where it's notched out for the split must look like sort of a brick wall as far as the chip is concerned. There's a slight positive rake, but it doesn't look it would have nearly the same cutting action as the edge farther out from the center where the chips can flow down the flute.

 

[swarfless]

Christen makes collet/chuck to make 10mm 4 facet.

Yeah, my manual is pretty old, for an 05-8 machine, & the machine I actually have is an 03-5 .. know anyone sharpening # 80 drills? Manual says, "With larger sized drills, the flat facets backed off at 30* show a tendency to cause the chips to be jammed at the cutting edge". Maybe they later found a different combination of angles for the facets that worked? They went on to say the lips with 30* facets were too weak on drills larger than 5/16".

 

[eKretz]

Can't recall ever using a Spiropoint drill, but I sure did like using Winslow-pointed drills.

Are the Spiromatic and Winslow points significantly different, or are the differences subtle?

They are the same, as far as I know. Helical point is the generic name.

 

[eKretz]

I watched a video of the Cincinnati Spiropointer in action - quite the gadget. As far as modified split point, what type of grinder/wheel configuration does that require?

It just needs something that has some decent adjustability to the split point settings really. I'm able to do it on my Black Diamond. You change the split point chisel so that it's angled more toward parallel to the normal angle of the drill lips, rather than at near 135° like the usual split point.

 

[rimcanyon]

Grinding 4-facet drills is not difficult if you make a jig to hold the drill at a 59 degree angle to the wheel (65 degrees would be a good option also). This is one I made, designed to work with standard 5C hex collet blocks. The slide was designed to fit a carbide tool grinder and miter gauge. It handles up to 1 1/16" drills. For drills up to 1 ⅜" I use a 2J collet block.







This is with the 2J collet block, which works in the same 120 degree slide since it has 12 sides: