[Paul B]

I guess I thought machine counter sinking with a cage and appropriate bit was a no brainer. My first attempt using these tools (other than a few practice holes) was on the rear spar of the horizontal stabilizer (RV-9). I never got two holes in a row to be the same. I had to clean off the bit about every 3rd hole or the tool wouldn't remove any material from the next hole. So is my problem: (a) technique, (b) dull or bad bit, (c) bad cage, or something else. The tools are the ones sold by Avery and I was using them in my small air drill with the spar clamped to my workbench.

A half dozen or so of the holes are much deeper than I wanted them to be. Do I need to trash my spar? Thanks for any help!!

 

[rvbuilder2002]

I recommend you ditch the air drill (when machine countersinking) and try a cordless battery drill. Use medium pressure with full RPM of the battery drill (usually about 600 RPM).

 

[terry_georgia]

Countersinking

Also be careful around the corners. If the cage does not sit squarely on material on top/bottom/left and right, you can get a deeper hole than intended. I find that just a slight wiggle of the cage as you finish the CS helps with the consistancy of the depth. I am going to guess that you have it set too deep because if it is set to the proper depth, and you are not on a corner, there should be no way to get it to drill too deep a hole no matter what you do to it. Find some thick scrap or go to home depot and buy a cheep piece of aluminum angle and practice a bunch of holes until you are comfortable. Not really much to it, but if you have never used one before it does take some getting used to.

 

[Brantel]

Practice on some scrap, sneak up on the proper depth....

As the CS cage heats up, you might need to make some tweaks to the setting.

I also use the wiggle technique to get that last little bit of depth.

Keep the bit clear of chips, keep the area under the cage clear of chips. This is just part of the process.....

Can we see a pic with the rivets in the countersink?

I guess I thought machine counter sinking with a cage and appropriate bit was a no brainer. My first attempt using these tools (other than a few practice holes) was on the rear spar of the horizontal stabilizer (RV-9). I never got two holes in a row to be the same. I had to clean off the bit about every 3rd hole or the tool wouldn't remove any material from the next hole. So is my problem: (a) technique, (b) dull or bad bit, (c) bad cage, or something else. The tools are the ones sold by Avery and I was using them in my small air drill with the spar clamped to my workbench.

A half dozen or so of the holes are much deeper than I wanted them to be. Do I need to trash my spar? Thanks for any help!!

 

[borislav]

I never got two holes in a row to be the same. I had to clean off the bit about every 3rd hole or the tool wouldn't remove any material from the next hole. So is my problem: (a) technique, (b) dull or bad bit, (c) bad cage, or something else.

Probably technique. There are a number of reasons why you might not have achieved the full depth on your first hole (when you adjusted the microstop), resulting in deeper than expected countersink on some of the other holes:
-The base of the cage might not have been flat against the material (this can be difficult on a narrow spar flange). Rock the cage a bit back and forth to make sure it's sitting flat, then hold it down firmly while drilling.
- Shavings stuck in the cage might prevent the bit from extending fully. I'd clean the bit on every hole (or at least shake out the majority of the shavings).
- Shavings on the work might prevent the cage from sitting flush on the material. Brush them all off before starting each hole.

On your calibration countersink, try redoing it after cleaning out all shavings from the bit and the work. If you see any additional shavings, your first countersink did not achieve full depth.

Good luck,
Boris

 

[G-force]

Turn it really slow, low speed on a cordless drill slow. You can't go too slow. Even at 100 rpm it will take the same amount of time to countersink it, and wont chatter. The flutes on these countersinks are tiny and wont hold much swarf so cleaning it out every hole or 2 is normal.

 

[miyu1975]

whatever you do...Don't try to use the cage in the drill press. Bad idea...ask me why I know.

 

[FlyerJumper]

whatever you do...Don't try to use the cage in the drill press. Bad idea...ask me why I know.

I've used this technique numerous times. Use a slow speed and make sure to stop the cage before touching it to your work I've found its quicker for me on things like the trailing edge wedges.

 

[rzbill]

Why?

whatever you do...Don't try to use the cage in the drill press. Bad idea...ask me why I know.

Drill press is an excellent place for using countersink cages. Slow speed and blow the chips away every hole.

 

[Flyer68]

Countersink

From all the advice above, (all very good by the way), I've found the best way for me to get decent results is to use the electric drill, drill slowly, wiggle the cage, and keep a rivet the size you are countersinking for and test the hole as you go. You can't go too slow, and after a few tests, you get the hang of it and only test on every third or forth countersink.
I am the epitome of KLUTZ and have made my share of screw ups, and then some, and this method works for me.

Flyer68

 

[Crossbow]

My approach is a bit labor intensive, but I like the results.

For thick material, use the cage with a slow cordless drill to make a shallow counter-sink, then use the hand tool to get the counter-sink to the correct depth.

And in the case of thin material to be counter-sunk, only use the hand tool.

Like I said, labor intensive, but it prevents me from making counter-sinks that are too big.

 

[roee]

My technique, FWIW

- Adjust the cage depth by countersinking some scrap before you do any real parts.

- Re-check the adjustment after the first few holes because the countersink bit can tend to tighten and settle a little deeper into the cage.

- Secure the part you'll be countersinking in a vise or using clamps. A secure part reduces the chance of bit chatter.

- Make sure that the holes are drilled (or preferably reamed) to the correct size for the countersink pilot, and are free of burrs.

- Make sure that the part is thick enough for your countersink depth. Material that's too thin will lead to a razor edge hole and/or chattering of the countersink bit, both of which are not good. If the material is too thin, then dimple instead of machine-countersinking.

- When countersinking, hold down the cage with your left hand to ensure that it is firmly seated level on the part, and is not rotating (letting it rotate can scuff the part).

- For an aluminum part, use medium speed (~600RPM is good) and moderate pressure to reduce the chance of chattering.

- When it feels like the cage has bottomed out and the countersink bit is no longer cutting, increase the pressure for a second just to make sure, then release. I would advise against "wiggling" as this could enlarge the hole or alter the geometry of the countersink. Better to keep everything concentric and square.

- This technique works great with a drill press, air drill (at much less than full RPM), or cordless drill. The drill press is actually the best option where possible, because it inherently ensures that everything stays concentric and square and also has the least chance of chattering. (miyu1975- what problems have you had?)

- Clean out the chips from the countersink bit & cage between every hole.

YMMV, but this has worked well for me.

 

[Paul B]

Thanks for the advice!

I will try out some of the suggestions tonight (on some scrap to start with). Specifically: 1. Use a slower turning cordless drill. 2. Clean the shavings out of the tool before every hole (if needed). 3. Take my time on each hole, make sure the tool is flat and check depth often with a rivet.

I have not decided if my spar is ruined or not. If I can figure out how to post pictures, I might do that and ask for some more advice. Thanks again to everyone who responded.

 

[Bernie RV7]

Cordless Drill for Countersinking

I'm going to buy a new cordless drill tomorrow specifically for countersinking..
the one I have in mind is a Bosch Lithium powered 10.8 volt 410 RPM and 25 NM Torque. Will it do the job or do I need more speed ?

 

[longranger]

I sprang for Avery's countersink tool with the ball bearing cage and polished metal (non-nylon) foot.

http://www.averytools.com/p-452-polished-foot-heavy-duty-ball-bearing-countersink-cage.aspx

It works great in my air drill. It's a bit more expensive, but worth it, IMHO. It's my belief that the ball bearings and solid metal foot provide for a much more stable tool. I've NEVER had it to "chatter", and it doesn't heat up while doing successive holes.

 

[David Paule]

Good Countersinks With 3-Flute Cutter

I've found that at least in .040 material, two things help chattering of a three-flute countersink.

1. Use a slow speed, as people have mentioned.

2. Make a back-up piece of aluminum. I'm using a piece of scrap from the spar bars on the tail that's about 3/16" thick - definitely more than necessary.

Together I get good countersinks.

Dave