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Countersinking and the Depths of Madness

V

vsavatar

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So, I got my RV-10 emp kit, but I've been doing practice projects trying to perfect my techniques before cutting my teeth on the actual plane. I have the Cleaveland Tool Microstop Countersink Cage with the nylon footing.

The problem is this: I cannot get consistent countersunk holes. It either takes too much material, too little material, the hole is lopsided, or it enlarges the hole. I tried switching from the air drill to the Ryobi cordless, and it helped a little bit. Now I'm not enlarging holes anymore, unless I tilt the drill, but I'm still having depth and hole symmetry issues.

I cannot figure out what I'm doing wrong, but it's getting very frustrating. Can anyone maybe tell me what I might be doing wrong?
 
#1 Use a drill press
#2 If using a hand drill, use the slowest speed possible. Wiggle the drill in two planes prior to pulling the trigger to ensure the foot of the countersink cage is flush with the material.
#3 The pilot hole drilled in the material must be the same size as the pilot on the cutter (#30, #40). If the material is thin and the countersink depth results in cutting away the pilot hole, then you must provide additional (removable) backup material so the pilot hole is there to the full depth of the countersink. Use a clamp or double sided tape for the removable backup material.
 
I found I had trouble if I didn’t keep the jam nut on the micro countersink tool real tight. I also use two hands. One to run the drill, the second to hold the countersink from spinning and ensuring that the foot stayed flat against the surface that I was countersinking.
 
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I use Cleaveland's single-flute deburring bit in a screw gun instead of the micro-stop cage. In my experience the microstop is quite sensitive to pressure and the countersink recesses aren't particularly repeatable. The deburring bit needs attention but for me is easier to use.

Dave
 
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Just adding a bit more to what the others have said... Not sure what thickness material you're working on, but if it's thinner than 0.032" (and sometimes that thickness as well), the countersink is likely eating into the guide hole to be able to sit flush with a standard rivet. Once it loses its pilot hole, all bets are off.

While it's a little tedious, I found that sometimes using a 1/8" thick brass flat bar with a guide hole for the countersink bit to center up on worked well. You can use Cleco clamps to hold the brass bar in place underneath the material you're countersinking after you've centered the guide hole. I think I did all the tank mounting holes on the spar like this, as I really didn't want to get chatter marks in the spar.

Be sure to keep the drill perpendicular to the work and don't tilt it or wobble it around. If all else fails and you're still not getting consistent quality, see if you can borrow another countersink and try it out. That will rule out a defective tool.

And if you haven't already attended one of the RV sheet metal classes that are sponsored by EAA (or others), it's a really good idea to attend one and well worth the modest fee. You'll learn a lot about tools & techniques, and will likely save yourself a lot of frustration and replacement parts.
 
Anything thinner than .050 I would recommend a wood or metal backing plate in order to stop the pilot from walking. Make sure the hole in the backing plate is deep enough to let the pilot sit fully in. I always kept the speed slow for the majority of the work, but once most of the cutting is done, I went full speed on the drill and used quite a bit of force for 3-5 seconds to make sure everything was fully bottomed out. The high speed portion would take another .010" out of the metal, but it became consistent so I could set the countersink correctly.
 
vsavatar said:
So, I got my RV-10 emp kit, but I've been doing practice projects trying to perfect my techniques before cutting my teeth on the actual plane. I have the Cleaveland Tool Microstop Countersink Cage with the nylon footing.
Click to expand...

You don't say what actual countersink you are using, only the microstop cage. You must have a (usually) 3 flute countersink cutter with a #30 or #40 pilot. As you are practicing, set the microstop for a MINIMUM countersink. Then test with an AN426 rivet head or with a digital caliper to measure the diameter. Then loosen the locknut and advance the cutter say 10 clicks, lock the locknut and countersink the same hole noting the difference in diameter. When it is the right diameter, do a succession of holes in a row. They should all be the same diameter and circular if using the tips noted above.
 
terrye said:
You don't say what actual countersink you are using, only the microstop cage. You must have a (usually) 3 flute countersink cutter with a #30 or #40 pilot. As you are practicing, set the microstop for a MINIMUM countersink. Then test with an AN426 rivet head or with a digital caliper to measure the diameter. Then loosen the locknut and advance the cutter say 10 clicks, lock the locknut and countersink the same hole noting the difference in diameter. When it is the right diameter, do a succession of holes in a row. They should all be the same diameter and circular if using the tips noted above.
Click to expand...
I'd also leave that microstop set and buy a different one for each size that's commonly used.
 
Microstop

I have three. I don't trust a single one.
I use a drill press
I keep test material and rivets nearby and always test before cutting, and during.
I would swear there's an elf that thinks it's funny to adjust my cages randomly.
Typically, I use an undersized hole, undersize the countersink then dress with a hand deburring tool with a cutter.
Did I mention I don't trust cages?
:D
 
One thing I've noticed is if you're countersinking near an edge, where part of the cage is hanging off, it's very difficult to not get an oblong countersink. Make sure the cage is totally supported. I also had a lot of problems with countersinking and I found the two hand method works the best. Use one hand to hold the countersink cage down solidly on the material, and the other hand to operate the drill. Start spinning it slowly, then speed up as you near the bottom of the countersink. Also, use some cutting oil. That really helps, especially on thicker material like the wing spars.

Lastly, you'll probably have to accept that they aren't all going to be perfect. Like Larry said, check the depth often, especially before starting on a new piece. But understand that there is some variance in them and perfection is the enemy of progress.
 
dwollen89 said:
One thing I've noticed is if you're countersinking near an edge, where part of the cage is hanging off, it's very difficult to not get an oblong countersink. Make sure the cage is totally supported. I also had a lot of problems with countersinking and I found the two hand method works the best. Use one hand to hold the countersink cage down solidly on the material, and the other hand to operate the drill. Start spinning it slowly, then speed up as you near the bottom of the countersink. Also, use some cutting oil. That really helps, especially on thicker material like the wing spars.

Lastly, you'll probably have to accept that they aren't all going to be perfect. Like Larry said, check the depth often, especially before starting on a new piece. But understand that there is some variance in them and perfection is the enemy of progress.
Click to expand...

I actually was countersinking on an edge. It was a piece of 5/8" angle, and the cage was partly off the edge. On my test piece, which is a 2 inch angle. My results are more consistent.
 
If your doing multiple holes make sure there is no debris on the bottom of the cage or underneath your piece of material especially if using a drill press. It doesn't take much to throw it off. Jam nut must be super tight as other have said. When doing a series of holes especially in important pieces I check the dept using a rivet regularly.
 
I have found the countersink cages to be less precise and repeatable than one might think when looking at them. For quite a while, I had a #40 and #30 cage set up with torque seal on the threads, so I'd know they were set correctly, but even so, sometimes they wouldn't cut to the depth needed.

I most often use them with a cordless drill, rather than the high speed air drill. Slow and steady seems to work better for me. Yes, keep rivets handy to check the depth as you go, and sneak up on it. I haven't ever used a drill press, the parts needing countersinking always seem to be too tiny, or already part of the structure.

I envision countersinking more as a fancy sort of de-burring, rather than as some precise mechanically repeatable operation. Accept that it may take a couple attempts at each hole to get it right. You want a certain sort of edge when you're done and you don't want to remove more material than necessary when you do it. Yes, keep thick stock handy to check your set up. Pre-drill that scrap with #40's and #30's so you can check easily when you need.
 
One thing we emphasize in the Oshkosh Sheetmetal 101 class is that the pilot on the C/S cutter needs to have a place to go.
As you shave material away with the cutter the pilot will travel deeper into the hole. If you have your part on a table top the pilot will bottom out by hitting the table before you have a full cut. Make sure there is air space under the pilot.
I also tell folks to let the drill run until you don't see any more shavings, that way you know your micro-stop has stopped where you set it.
 
I prefer the three flute cutters in a micro stop cage and have three cages. This to set down to 5 thou under and the single flute to take the last bit to seven….ensuring there is a backing for the pilot to go into. The reason?….my Cleaveland single flute likes to drive in hard and grab….the three flute doesn’t…but the three flutes will leave chatter marks and the single flute cleans them up and doesn’t grab once most of the countersink is there.
 
Another thing to check, the top of the cage countersink can bottom out on the drill if it's in too far or slips after some use. You won't notice it by feel, but a previously well-adjusted countersink is suddenly not deep enough.
 
I recommend re-fitting the cage for every session, doing that I haven’t had an issue. I learned this after I did a session, marked the teeth and left it to use another time, luckily did a test first and it was off, too deep. After that I always reset the cage and work my way back to depth at the next session.
 
All the tips everyone has given were helpful, but the most helpful was to use the drill press whenever possible. I used that thing on the spar doubler, and I ended up with perfectly countersunk holes every single time. I thought I might be wasting my money on that drill press, but it has already proved invaluable more than once, especially when trying to drill through solid steel for the lower rudder hinge brackets.
 
ALWAYS make sure the collar is screwed down tight (jam nut?). If it comes loose, your countersinks will be deeper than intended and inconsistent. It may seem like it wouldn't matter, but it does. I Check it stays tight every 5 countersinks or so.

If you have a cage with a plastic ring that makes contact with the component, that plastic ring screws on and off. If you don't ensure that plastic ring is screwed on tight, your depth will be shallow and inconsistent. I check that ring is tight every 5 countersinks too.

Also, I noticed in my hand drill that if I seat the countersink cage all the way to the stop, the cage will actually contact the drill's claws (the three prongs that hold the bits, I'm not sure what they are called), preventing it from stopping at the depth you want, making the countersinks shallow and inconsistent.

FYI, there are very few places on the actual plane where a drill press will actually work for countersinks. The primary exception is trailing edge wedges, and some brackets. My point? You do need to get good at hand countersinking.

Oh yeah, and if the hole to countersink is on a piece's end where the cage will hang off the end, it is extremely easy to over-countersink. Be ridiculously careful for those holes.
 
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