How to drill a counterbore to a precise depth and width

[Juan Hovey]

I've been making infill planes from scratch lately and need help with a particular problem. Take a look at the steel rivets with brass sleeves fixing the front bun and the rear tote and infill to the inside of the plane in this photo.
IMG_1928.jpg
To place these sleeved rivets, I clamped the plane to my drill press table and, using a drill bit that matched the diameter of the rivet plus sleeve, I drilled all the way through from one side of the plane to the other.

Then I counter-bored the hole on each side, eye-balling it in an effort to make it not too big, not too small, in hopes that when I peened and filed the sleeved rivets, they would fill in the counter-bore perfectly.

But as the small gap around the rivet and sleeve through the bun shows, eye-balling it doesn't get the job done.

Can anyone suggest a jig or a technique that will enable me to drill a perfectly sized counter-bore repeatedly? It's very frustrating to get this far into a project like this only to mar it, and I'd greatly appreciate some input.

My drill press, FYI, is a Craftsman with runout and an imprecise, screw-type gizmo limiting quill travel. Some months back I bought new bearings in hopes that they would solve the runout problem, but I haven't had time to take the machine apart and install them. But it's not the runout that's the problem, in any case. It's the fact that every time I counter-bore the holes for my sleeved rivets, I end up with a different opening. What's the solution?

[Bruce Page]

What are you using to c'bore the hole?
Spindle runout is a killer in situations like this. A decent minimill (RF-30, RF-45, G0704) etc. might be a worthwhile investment.
Beautiful work, BTW.

[Adam Neat]

For repeatable depth attaching a dial indicator somewhere where your depth stop is would work.

So when you say counterbored do you mean cosink? as in an angled hole? Or cobored, a flat bottomed hole?

[Ryan Baker]

You could start by buying a real counterbore in the proper size with the proper size pilot. That should give you consistent diameters. Something like Adam's dial indicator trick would work if you can do all the holes without changing the indicator setup (zero point). As Adam asked, is this really a counterbore or a countersink?

It would seem like getting the counterbores completely filled has more to do with peening enough to fill the existing hole. It can be hard to tell until after you file it down. More peening with a lighter hammer may help.

[Juan Hovey]

I have three countersinks - a 3/8-incher, a 1/2-incher, and a 5/8-incher. I used the 1/2-incher. Which should I use?

Adam: Can't picture how I would attach a dial indicator near the depth stop indicator. Please tell me more.

Ryan: I peen, file, peen, file repeatedly to make sure that I get the metal to flow into the gaps, and then roughly finish the sides and sole against a belt sander. I switch to sandpaper in a flat block to finish the sides, and I flatten and polish the sole with sandpaper on a granite slab. I peen, file, peen, file in similar fashion when working on the rivets holding the infill in, but as I think about it, maybe I'm not being as careful with the rivets as I am with the dovetail joints holding the sides and sole together.IMG_1966.jpg

[Bruce Page]

There’s a big difference between a counter-bore and a counter-sink. That said, I still think you problem is being caused by spindle runout.

[Adam Neat]

I had a plunger type dial indicator on my drill press years ago but I cant track down any pics. (I moved up to a Bridgeport Mill)

Here is a good article on a craftsman drill press with a set of digital calipers mounted up http://www.instructables.com/id/Accu...n-Drill-Press/

[Ryan Mooney]

What Mr Baker was referring to was something like vaguely this:

http://www.icscuttingtools.com/Cntbores.htm

No affiliation yadda yadda, if you search for "piloted counter bore" you'll find lots more. I have no idea which are any good. You can also make custom ones, but I'm not smart enough to do that so no advice there.

I also suspect that a drill bit with a different tip geometry wouldn't wander as bad, or perhaps even just better quality twist drills. Wandering is usually when the drill is cutting unevenly for some reason and "pulls" to the side. It could be that you aren't centering carefully enough which would also cause it.

Personally I've had better luck with things being centered by drilling a small pilot hole, then the counter bore then the through hole, but I'm not a good machinist (by any stretch) so don't take that as advice.

I would also agree that you aren't peening enough before you start filing close. Take your time and really peen that sucker in there good before you file it flush, you can hide a myriad of sins with careful peening. Personally I find it easiest if the pin starts just the right height above the hole before I start peening as you can spread the metal easier the closer you are to it (but you have to leave enough to have enough to peen down..). I'm not so good at actually figuring out the height before hand, but afterwards its usually pretty obvious that I got is wrong

[Ryan Baker]

I can't tell from the picture -- are the gaps all around evenly or just in certain spots (like on one side)?

These rivets go all the way through, right? Maybe turning it over to peen the other side is driving it a little back on the first side?

The reason I suggested a lighter hammer is because that helps fatten the rivet out in the hole (making it tighter), and peen the end over nicely, whereas smashing with a heavy hit will tend to drive the rivet in or bend it over more than spreading it out.

The piloted counterbore (I think you can also find piloted countersinks if you look around a bit) will help control the runout problems with the drill press, which can be a real problem on a lot of presses these days (like mine). It's not the cheapest solution, but it may be good if you do a lot of rivets the same size.

Any sort of reliable depth stop should give you consistent size countersinks, aside from runout issues.

Maybe George Wilson will chime in here. I'm wondering whether the countersink shape you are using is the best shape to use. It seems to me that it would be difficult to get the material to peen down cleanly along that straight tapered surface. You may be bottoming out at some points along the taper, then exposing some gaps when you file it down. My inclination is that a more concave surface would be easier to fill, but I have no evidence of that. Just a thought that you might have different results using, say, a square counterbore. I bet George knows.

[George Carlson]

Like someone else was saying, there is a big difference between counter bore and countersink. A counterbore is a straight sided hole, e.g. the process used to provide the recessed hole for a socket-head cap screw. A countersink is an cone shaped hole. Usually 82 degrees.
If you're using a countersink, try using a single flute or zero-flute countersink in 60 degree. The 60 degree would not be as sensitive to depth, the single flut tool will follow the hole without chatter.
A counterbore, since it's straight sided, should be rather insensitive to depth. You will need a piloted counterbore. Trying to use an endmill in a drill prees is a disaster.
In either case, run the drill press as slow as you can and allow the workpiece to "float". Allow the tool to follow the original hole, and runout should not be a problem.

[Juan Hovey]

Good stuff, folks. Many thanks to all.

Ryan Mooney: It's very possible that the rivet was too long before I started peening. I will experiment on a plane in the scrap pile to get a better sense of this. I will also experiment with pilot holes and a counterbore.

Ryan Baker: The rivets do pass all the way through the plane, from side to side, and since they are only 1/8 inch in diameter, plus the sleeve, it's possible that the rivet shown in the photo bent over as I peened it. I use an 8-oz hammer and thought I was getting the hang of it as I worked on this, my tenth plane, but it's clear I have a way to go.

Also, the gap in the rivet in the photo is irregular and mostly on the near side, so the good bet is that the countersink didn't drill into the side of the plane at a true 90 degrees. If I can find a piloted countersink - better yet a concave countersink - I'll experiment with that, too.

George Carlson: I will look around for a 60-degree countersink.

[george wilson]

Your drillpress runout is more likely caused by an Asian chuck if it is a recent(or not so recent make). My 1963 Craftsman drill press has a genuine Jacobs chuck,and has always run true. It still has the original bearings,too.

Since Jacobs has also become Asian in the last few years,I'm not sure if they are still true running or not. Mine has a #33 Jacobs taper and a collar that screws onto the spindle above the #33 taper,so the chuck cannot fly off when using it at high speed.

If you got a mill drill,and used a 1/4" R8 collet in it to hold the shank of your countersinks,it would run true and you'd get more consistent results using a depth stop. Also,I like single flute counter sinks because they do not chatter like multiple flute ones do. They can suddenly decide to make a 6 sided job for you. I have only had 1 Asian R8 collet that did not run true,and it was WAY out. I am pretty sure you'd be safe using a mill drill and collet. You could definitely use a mill if you're going to keep making planes.

If you want better results from your drill press,Albrecht chucks are still high quality,though a 1/2" chuck will run you a few hundred dollars+. You can buy them from Enco(I think),and for certain from MSC. Make sure you get the real brand and not an Asian look alike. Stay away from Grizzly chucks. They offer absolutely NO information on how concentric their chucks run,including their lathe chucks. I don't like buying stuff that has no specifications laid out.

You may want to test the runout of your drill press #33 taper. Take the chuck off and mount a dial indicator with a magnetic base(clamped by the magnet to the drill press table). Put the indicator against the side of the taper,and run the drill press slowly. If the taper itself is off,it won't do any good to buy an expensive chuck. I'll say that .001" runout is the maximum runout I'd tolerate,and I'd like less than that myself.

[Dave Verstraete]

Juan
We use Weldon countersinks in my metalworking shop. They hardly every chatter and stay sharp for a long time. They are 60 degrees.

[Ryan Mooney]

One more idea to consider for counterboring, do it in one pass:
http://www.wlfuller.com/html/special_drills.html

You couldn't do through holes in each piece in one pass, but you could clamp the pieces together and drill small pilot holes through then use something like this to do the main hole and countersink in one pass.

I also have no idea what that would cost

I would second Georges suggestion for measuring the runout of the various pieces.

[Juan Hovey]

George- The runout is a hair more than .002, measured as you suggest. I mentioned earlier that I might overhaul the drill press and install new bearings, and it looks like that's the next step.

Also, I installed a digital caliper some days back and, using one of my earlier planes which now rests comfortably on my reject pile, began practicing countersinks. Middling results so far.