Counterbore versus countersink

[mountainman]

So far I have always used a counter sink on my building projects, but it seems like lately I'm having trouble with it not lining up properly, maybe it's time for a set of new ones.

I never tried using what I believe is called counter bore, would it work to use one of those for butt plate screws?

Although this photo is not my actual set, but this is a picture of exactly the kind I had been using for at least the last ten years.

[whetrock]

I recently asked a good friend who is a professional gunsmith about this same problem, and he said he had made several piloted countersinks. Turned it on a lathe and then hand filed the teeth, kind of like the teeth on a ball mold cherry. I haven't gotten around to making one myself, but it sounds like a good idea. Maybe someone on here has made one and has a photo?

If you haven't already, you might want to do a search on "counterbore" and "piloted countersink", to see the difference. The counterbore bores a secondary hole in line with the axis of the first hole. The piloted countersink just chamfers the hole, with the pilot keeping it on center.  (Added: Or as Jim K notes below, some are a combination.)

[smylee grouch]

When I have trouble getting screws to " line up properly " its because I didn't get the pilot hole drilled center and perpendicular . I've done it a lot.

[JBJ]

I purchased a cheap set of fluteless countersinks some years ago and got exactly what I paid for. Only one of the countersinks in the set was properly ground and did a great job, making a very even and smooth countersink. The others were hopeless and the resulting countersinks were anything but smooth, centered and symetrical. Somewhere along the way, I acquired two or three individual Weldon brand fluteless countersinks. The difference between the Weldon brand and the mystery brand set was night and day. Flueless countersinks can do a wonderfull job but, like like we all know when buying tools , buy as much quality as your circumstances permit. Same applies to the fluted variety of countersinks.

J.B.

[Pukka Bundook]

Whetrock,
My old countersinks are fluted multi-cut like the cherry mold  cutter you mention, but they will at times chatter a bit.
The single cut  like in the photo up the page seem to cut smoother.
I reckon if angles are a bit off, start with a very big screw head and file it to the profile!

[Jim Kibler]

You'll see some original work with basically a combination of a countersink and counterbore.  Think of basically a recessed countersink.  This is useful where the bolt or screw isn't necessarily exactly perpendicular to the surface or the surface is heavily curved.  We employ this process on most of our tang and buttplate screws.

Jim

[Scota4570]

I make my own.  Some have a pilot some do not.  I find that filing a bunch of cutting flutes is not necessary.  The chances of getting the cutting edges same enough to all cut is unlikely.  Just grind away half the diameter.  That will cut well.  Run it slow to prevent chatter. 

[mountainman]

You'll see some original work with basically a combination of a countersink and counterbore.  Think of basically a recessed countersink.  This is useful where the bolt or screw isn't necessarily exactly perpendicular to the surface or the surface is heavily curved.  We employ this process on most of our tang and buttplate screws.

Jim

Hi Jim do you have a picture of what that recessed countersink looks like?

[coopersdad]

Mm, I'd like to see what Jim uses as well.  I've been using a center drill that is 82 degrees, same as the screws, rather than the usual 60 degrees.  Its large diameter is 5/16", so I turn my screw heads to 5/16" for a bit less than 1/16".  Then I use this to countersink, and then let it bore 5/16" for the same depth.  I haven't used it on buttplate screws, I need to get a 3/8 one for that.   

When using it the initial hole has to be the same or smaller than the 1/8" pilot drill on this. For tang screws, I drill a pilot hole smaller than 1/8", and if it's off center some I can move the hole with a needle file and still be able to use this.  After it's bored, then drill the hole to finished size. 

[Blacksmoke]

 Richard:  If your counter sink chatters - use a small piece of paper towel between the hole and the counter sink. Hold down with steady pressure - no chatter!  Hugh

[Daryl]

Paper towel would likely work, but Dad taught us to use a couple layers of denim cloth to stop chattering.

[Dan Herda]

They make and sell commercially, piloted counter sinks in the style of original post.

[bobw]

You'll see some original work with basically a combination of a countersink and counterbore.  Think of basically a recessed countersink.  This is useful where the bolt or screw isn't necessarily exactly perpendicular to the surface or the surface is heavily curved.  We employ this process on most of our tang and buttplate screws.

Jim

Hi Jim do you have a picture of what that recessed countersink looks like?

Here’s what I do for a recessed counter sink.  The counter sink on this one is fairly shallow but works and I also make all my screws so can modify them to work. The steel thickness has some bearing on what can be done.

[Jim Kibler]

Yeah, that picture shows what I was trying to describe.  There are a bunch of ways to make it.  Probably the easiest is to just get a countersink of the right diameter and sink it below the surface.  I have some five flute ones that I probably got from McMaster Carr that work pretty well.

[flatsguide]

Nice work Bob! The nice thing about a counterbored hole is that a screw fitted will have a short straight section instead of having a razor thin and sharp edge. If the hole is already drilled you will need a piloted bit to do the c’bore.
Richard

[JH Ehlers]

This is one that works well, ma ford 6 flute, no chatter. Countersink down until you have a counterbored section for a screwdriver slot.

[Pukka Bundook]

Thank you Hugh  &Daryl, on the paper or denim for anti chatter !

Very nice shell, BobW.

[bobw]

I realize most everyone is doing these countersinks in a drill press.  I also use to do these the same way and always had chatter.  But, I can say that the more rigid the machine and setup the less likely this will occur.  I now use a mill and have no issues with chatter.  I could get into a dissertation on how I make holes, and related screw, for different screws on guns.
Bob

[Martin S.]

I had problems with chatter on a drill press.

I switched to a brace and bit, and went slowly.  No more issues with chatter.

[Jim Kibler]

Use good quality multi-flute countersinks and chatter shouldn't be a problem.  I've used hand drills and had no problem.  I've also not found the need for pilots.

[mountainman]

Thanks Jim, and all those who responded with valuable information.
Much appreciated!!