Smooth countersinks

[cjensen]

a few of you have already helped me with this, but i want to get as many responses as i can...

i finished countersinking for the #8 screw dimple last night on my wing spars, but when i got to the second spar, my countersinks started looking a little rough (still nice and round, but rough on the inside). they started out nice and smooth. i used the vans method of installing the platenut first, then countersink with the #30 cutter. didn't use boelube (should've). do these need to be smoothed out, or do they look like yours??







the cutter is a 3 flute from ATS, and was used for the first time on the spars.

[prestwich]

Hey Chad,

If you're using the exact technique on your second spar that you were on your first, and since you aren't using lube, I'd chalk it up to a dull cutter. Cutters without coolant and lubricant get dull pretty fast.

As far as technique, I know it's been discussed before, but most machinists, I believe, will tell you: Single flute for aluminum, three flute for steel, and *slow* on the RPM to avoid chatter.

As far as cleaning up the countersinks you've got, I don't know whether chatter marks will cause stress risers, but I'd also be wary, naturally, of going too deep in an effort to clean them up.

Jon

[Spike]

Im leaning with Jon. Id say leave them as your more likely to damage cleaning them up. Use the lube next time and move on.

-- John

[tshort]

Chad-

Something I did do was take the swivel deburrer (that yellow handled thing from Avery) and use it to take the edge off the deep part of the c'sink - these are deep enough that the edge nearest the nutplate is razor sharp since the c'sink goes about all the way thru. I just spun it in there quickly to take the edge down without altering the countersink itself.

I didn't try lube ... sounds like a good idea, but I was worried that it would make cleaning up all the chips a nightmare - i.e. if they get down in the nutplate, etc. I didn't try it so I don't know for sure...?

Thomas
-8 wings

[cjensen]

well, i used my hand deburring tool to smooth out the c-sinks a bit. they look better and i didn't remove enough material to make a measurable difference. i just made one or two very light revolutions, and that's it. made small difference...

[deltazulu]

I had the same problem when doing test pieces with a three flute bit. Get a single flute pilot bit from Avery...or somewhere else. Below is a pic of my countersinks using a single flute bit. I use my pneumatic drill at full speed with light to medium pressure until the cut is just about complete and finish with heavy pressure before pulling the microstop off. Works great!!



Dalton

[deltazulu]

Can't seem to get the pic to post ??

[tshort]

Try this:



(the % was left out of your url: http://www.deltazulu.net/Post%20Pics/CS1.JPG)

T.

p.s. I second the single flute cutter - just gotta be careful when a chip gets caught in it!

[deltazulu]

Thanks for the assist T!!

Agreed on the chips. I experienced a problem with a chip when I was countersinking my VS803PP and it left a groove in the CS. When doing my spars I clear the bit completely of chips before I move to the next hole, and using light to medium pressure takes small amounts off which are easily ejected. When I check the bit it is usually empty once the CS is done. I also wear a leather glove on my left hand and hold the Microstop level on the surface while drilling. I position the window in the Microstop so I can see exactly what is going on. Hope this helps anyone else who is facing the CS of their wing spars. I found it to be pretty nerve racking the first time I started cutting on mine.

[TomNativeNewYorker]

Looks like chips are scarring the countersink.

I strictly is three flute piloted counterssink cutters in a countersink cage. 400-500 RPM for aluminum is all you need. I start with light pressure and increasing it as I get towards the final depth. Approx every .020" depth of the cut, I will take pressure OFF the countersink cutter in order to help clear chips from the hole being countersinked. You should get a 4 RMS surface finish easily if you have a good cutter and follow the above.

[LooseNut]

Hey delta,

I was looking for the single-flute pilot countersink bit you mentioned, but can't seem to find it. Looking at Avery, Brown, The Yard, they all seem to have three-flute pilot bits. Do you remember where you found yours?

Maybe you already have this figured out, but, here's my thoughts for what it's worth. I also used the Vans method (install nutplate and use that to guide the pilot).

I found that the countersink starts with some guidance from the original hole. Then as the countersink gets deeper, the pilot has nothing to guide it and the cutter starts getting a bit loose. Finally at the end of the cut, the pilot finds the nutplate and guides it home and all is good.

I found it's that middle part of the cut where you have to have a steady hand. It doesn't have to be perfect to the micro-thousands of a nat's whisker, because the end of the cut, which has the nutplate guiding it again, will clean up a little wobble. But, if you get too sloppy in the middle, and let the cutter move sideways or at an angle then the cutter can put in ripples that are too deep.

Once I figured out what to pay attention to, it was pretty easy. Just grab a hold of the micro-stop with your free hand to keep it from moving sideways and to keep it square ... watch what you're doing through the micro-stop's window ... make a slow-turning steady cut ... keep in mind you're free-handing it in the middle of the cut.

[tshort]

I got mine from Cleaveland:



http://cleavelandtoolstore.com/prodinfo.asp?number=CCSF

(The single flute cutters, that is...)

Thomas
-8 wings

[LooseNut]

Thomas,

Thanks for the link. I was a little confused about the name of these "single flute" cutters. I saw cutters like this ... that is, cutters with the diagonal hole ... called "zero flute" in one of the catalogs. I think I also saw this style cutter going by some other name too ...

I've been using the three-flute pilot cutters to do countersinks. Hmm, maybe I should try these single-fluties.

I have a single-flute cutter without the pilot that I've been using to debur with. Highly recomended! It chatters much less and cleans up burrs without taking as much of a cut into the "good material". Using the three-flute cutter, I thought the de-burred holes looked too much like a little counter sink!

Harold

[Mike Balzer]

I use an 1/8 piece of angle aluminum to guide the pilot of the countersink and drill the spar with a #19 drill for the -8 screws and use a #20 piloted counter sink.

With the new pre-punched holes you can use the drilled angle for the oppisite holes on the other spar.

After each counter sink if you use a single flute you will need to clean the burrs out of it.

I found it better to use the 3 flute #20 counter sink with perfict results when using a #19 drill.

After counter sinking the spar hole and cleaning the chips away re-countersink that same hole to make sure the holes are all uniform.


Hope this helps any one