Smooth countersinks

cjensen · #1 02-20-2006, 10:29 PM

just finished countersinking for the #8 screw dimples on the spars, and they came out pretty good, but they are not PERFECTLY smooth. it's like there are tiny little particles on the countersink cutter that are preventing a nice silky smooth finish. they are the right size, but i wondered if i should get a new cutter to smooth these out, or just leave 'em.

http://www.rivetbangers.com//cgi-php...serialNumber=2

http://www.rivetbangers.com//cgi-php...serialNumber=2

http://www.rivetbangers.com//cgi-php...serialNumber=2

these are all the same countersink hole. whatcha think?

szicree · #2 02-20-2006, 10:52 PM

It looks to me like there was nothing behind the material for the pilot to ride in. If you look at the perimeter of the machined area it is not round, but kinda squared off here and there. This happens when the cutter starts to chatter around in the hole. I'm not sure what, if anything, needs to be done to correct it though. If it were me I'd probably run the countersink around the hole a couple of turns by hand to smooth it out and call it a day.

rv8pilot · #3 02-21-2006, 03:23 AM

Steve is right,you could clamp a soft 2X4 under so the pilot steers in the wood,I had the same problem on my 8 wings and orther places but the soft wood solves the problem

J?rn m?ller
RV8 205hours

TShort · #4 02-21-2006, 03:32 AM

Chad-
Mine looked pretty similar ... are you using a single fluted cutter or one with 3 blades?
I chose not to worry about it.

Thomas
-8 wings

Captain_John · #5 02-21-2006, 05:44 AM

Chad,

Your picture shows a fine countersink:

I found that my cutter prefer low speeds. I use a cordless electric drill on slow speed. It seems to come out well.

Tell me, what did you use? How fast were you turning the cutter? Many people prefer high speeds. It probably doesn't change the end product, though. It is just user preference.

CJ

TShort · #6 02-21-2006, 06:36 AM

I'm wondering if some of the perceived distortion is due to the angle at which the photo was taken - it is not directly above the hole.

I agree about the single flute cutters - you have to make sure the hole is clean, if it clogs with shavings then it won't cut deep enough and sometimes even digs a groove in the surrounding material (ask me how I know this!)

Thomas
-8 wings

Rick6a · #7 02-21-2006, 06:42 AM

Quote:

Originally Posted by cjensen

...................are not PERFECTLY smooth. it's like there are tiny little particles on the countersink cutter that are preventing a nice silky smooth finish...............whatcha think?

Often times, an open non-piloted countersink as typically used on composites or plexiglass, even a deburring bit such as the one illustrated will not only polish out minor surface imperfections in the countersink, but can sometimes enhance the "roundness" of the hole.

Rick Galati RV-6A "Darla"

cjensen · #8 02-21-2006, 07:59 AM

thanks for the responses so far guys...

to answer a couple of questions about the pics...shoulda clarified a little better in the original post-

i used the vans method to the "T" by installing nutplates first, then running a new #30 cutter into the hole using the nutplate as a guide.

the cutter is a 3 fluted from ATS. they actually started out very nice and smooth, then as i got to the second spar, they started looking like this. that's why i'm wondering if these things dull...but after such short use?

i didn't think to use boelube on the cutter-that would help i'm sure!

i was using my air drill at full pull of 1800 rpm and smooth application of pressure.

there a few distortions here and there, but most are round.

i'll splash some boelube on the cutter and run a few. i just wanted to make sure it doesn't look like i'm dealing with potential problems down the road...

TShort · #9 02-21-2006, 08:35 AM

I think they do dull reasonably quickly - I noticed a pretty significant difference just in doing the spar. Plus, that anodized spar is harder than untreated Al.

Thomas
-8 wings

rzbill · #10 02-21-2006, 10:47 AM

FYI,
If you get a new piloted c'sink bit to replace a suspected dull one, take a look at the pilot. I got one that caused me a problem before I recognized what was going on and did a little edge stoning to fix the bit. The details are at the link below.

http://websites.expercraft.com/rzbil...ry&log_id=6819