Need tips for keeping countersink concentric with hole.

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Electrojim
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Need tips for keeping countersink concentric with hole.

Post by Electrojim »

Historically, enclosure panels for electronic project boxes have been sheet metal, most often aluminum, and in thicknesses between 0.050 and 0.125, depending on the size of the panel and need for mechanical rigidity. For home hobbyists like myself, getting these panels fabricated at a local shop is fantastically expensive, most shops looking to do hundreds when some of us are dealing in maybe 10 of something at the most.

Recently, there's been a trend to have these made of copper-clad fiberglass printed circuit board material. There are outfits that 'panelize' circuit board projects from individuals, drilling and milling the panels to very good precision and at a price that's a fraction of their sheet metal counterparts. One thing that the board fabricators cannot provide, however (except in higher quantities to commercial customers) is installation of hardware. For example, a front panel may have flush-pressed threaded PEM studs sticking out the back to hold an LCD display or special switch. The front of the panel is covered by a plastic overlay with graphics, hiding the stud heads. A workaround is to use a flat head screw with either a nut or a threaded standoff hanging off the back, also to be covered by an overlay once the screw is tightened.

So the boards come in from the vendor with, say, 0.125 holes for a 4-40 screw, which then requires drill press setup and a 'bombsite' countersink operation. Aye, there's the rub. I found out quickly that a single-flute countersink is useless for hand-held work; it oscillates the panel in a circular pattern as it bites into the panel, making a countersink that's never quite centered on the hole. A 6-flute countersink is much smoother, and what I've tried is bringing the spinning countersink down slowly while barely hanging onto the panel, letting that action center the panel's hole under the spindle axis. Then I just bear down hard on the panel with one hand and bring down the countersink with the other until the drill press hits the stop. This works pretty well, but still no consistent results. I realize that I ought to center the hole with the countersink stopped and then clamp the panel down, but with several holes to do in multiple panels, that's really time-consuming. I hope maybe someone has a tip or two for doing this 'on the fly,' as it were. All ideas welcome, thanks!.
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rmac
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Re: Need tips for keeping countersink concentric with hole.

Post by rmac »

Sounds like you want a piloted countersink. Click here for an example of what I'm talking about. After that, Google should help you find one that fits your needs exactly.
Electrojim
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Re: Need tips for keeping countersink concentric with hole.

Post by Electrojim »

Aha! That looks perfect, Marty (woops, I mean Russ). Not only does it have a 'holefinder,' but it's carbide, so it won't dull quickly working into fiberglass, and it has two flutes to cut symmetrically and not shake the workpiece. My only question is what does that threaded shank screw into? I'll work it out, many thanks!
Last edited by Electrojim on Sun Feb 19, 2023 10:54 am, edited 1 time in total.
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Harold_V
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Re: Need tips for keeping countersink concentric with hole.

Post by Harold_V »

That's Russ who responded, not Marty. :wink:

What you're looking for is Microstop. They control diameter of the c'sink by a stop that surrounds the c'sink, not by spindle stop. Much more accurate, as part thickness plays no role in the process.

Here's a link to a source, which I am NOT promoting. There are other sources but this gives you an idea what you're looking for.

https://www.aircraftspruce.com/catalog/ ... 20Products
H
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Russ Hanscom
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Re: Need tips for keeping countersink concentric with hole.

Post by Russ Hanscom »

I bought a number of the self piloted tips from Boeing surplus in Seattle when they were active, Most of them have a 1/4-28 thread. Quite easy to make up your own shank from some 3/8" or 1/2" dia rod and a little lathe work.

Also picked up a few of the Micro stops, might be able to find one on ebay.
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rmac
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Re: Need tips for keeping countersink concentric with hole.

Post by rmac »

Harold_V wrote: Sun Feb 19, 2023 12:38 am That's Russ who responded, not Marty. :wink:
I've been called worse. :D
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GlennW
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Re: Need tips for keeping countersink concentric with hole.

Post by GlennW »

I'm a bit late here...

Both new and used countersinks and Microstops.

https://www.yardstore.com/consumables/countersinks

https://www.yardstore.com/catalogsearch ... microstops

Countersinks come in different angles as well, so be aware of that.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
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Harold_V
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Re: Need tips for keeping countersink concentric with hole.

Post by Harold_V »

GlennW wrote: Sun Feb 19, 2023 3:58 pm Countersinks come in different angles as well, so be aware of that.
Yep! As Glenn said---they are commonly found in 82°, 90° and 100° included angles. The most common one would be the 82°, which is the angle of most flat head screws.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Electrojim
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Re: Need tips for keeping countersink concentric with hole.

Post by Electrojim »

I'm countersinking into pretty thin stuff, 0.050, so I opted for 4-40 screws with a 100°head. Countersink to match, of course. Just in case the cone of the head pokes out the backside, there's a washer with a spacious ID between the panel and the standoff. Most available standoffs are countersunk a bit, but not the PEM SOS_440-10 I was able to find surplus. The 5/16 standoff and .040 #4 washer adds up to just about 9mm, the actual spacing required.

Many thanks to all for the tips and help. Quick answers, too! -Jim
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Harold_V
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Re: Need tips for keeping countersink concentric with hole.

Post by Harold_V »

Jim,
If you're not familiar with the Microstop c'sinks, you'll be well pleased to discover that the pilot will prevent any oscillations of the c'sink/part relationship, so the c'sink will be on location. The slight exception might be if the resulting cut enlarges the hole (when the cone protrudes beyond the back of the panel). Even then, if you're not ham handed and don't force the cut, it should still remain on location as it was well established originally.

The one problem that was ongoing when using the Microstop was breaking pilots. That won't be a problem for you with your thin material, but thick plates where one might back off the cutter to clear chips often caused a chip to enter the hole, binding the pilot. They're mighty fragile, just as they are with piloted counterbores with interchangeable pilots.

H
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Electrojim
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Re: Need tips for keeping countersink concentric with hole.

Post by Electrojim »

Thanks, Harold. Previous to this I wasn't at all familiar with Microstop technology. After looking at you guys' references, along with a couple of YouTube videos, I'm now actually terrified of them. I found a couple on eBay at a good price and came close to buying one to give it a try, but have had such good fortune now with my 100-degree, six-flute c'sink, that I'm really pleased with the consistent results I've been able to obtain. I get the impression that the Microstop devices come in real handy with larger holes and larger screws/rivets. Many of the online demonstrations showed hand drills doing this work, which of course doesn't allow for a spindle stop like on a drill press. When I set up to do a bunch of holes, I home-in on the first hole of the day, biting a bit deeper each try until the screw head is just even with the surface of my panel. Once the stop is set, I can sink all the rest of the holes in very short order, even without a pilot if I'm really careful. The material I'm working with is 0.050 fiberglass, copper-clad on both sides. The copper is very thin, and inevitably makes a small cone on the backside because it gets 'pushed out' by the c'sink instead of being cut. But when I tighten the screw into the standoff behind, with a flat washer in between, the cone of thin copper is pushed into the washer hole and doesn't cause a problem at all. Bottom line: I'm a happy camper now. I sure wish I'd gotten into machining and metalwork decades ago. My abilities as a machinist are best summed-up in this photo.
Machinist1.jpg
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GlennW
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Re: Need tips for keeping countersink concentric with hole.

Post by GlennW »

Electrojim wrote: Sun Feb 19, 2023 9:47 pm I'm now actually terrified of them.
??

If there was ever a correct tool for the job, and dead simple, this would be it!

Once set for your favorite screw head you won't ever need to adjust it again for the rest of it's life.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
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