Countersinking problems

msmst25 · #1 06-30-2020, 04:39 PM

I feel like I have more trouble with countersinking than anything else. This is my second part that I have to replace due to a countersinking error. I have a dedicated microstop cage for my 3/32 bit, and I always do a few test holes in scrap, but I still seem to get inconsistent results. Fortunately, this was only an $18 part. I've been using my cordless drill for the countersink. Would it be any better to use the pneumatic drill? Any advice appreciated.

Another countersinking error by Matt McCoy, on Flickr

ryankhallcpa@yahoo.com · #2 06-30-2020, 04:46 PM

I've found that I get good results with my old, heavy Dewalt cordless turning very slowly while applying lots of down pressure on the part. Of course, the part must be supported. So, I usually have a small hole drilled into particle board that is supporting/backing the part which allows the pilot from the countersink to go into. That hole is only necessary if the part is rather thin and the pilot must protrude somewhat through the other side.

Hope this helps!

Ryan

flion · #3 06-30-2020, 05:15 PM

When countersinking in thin aluminum, always be sure there is a backup piece to guide the pilot. When the countersink creates a 'knife edge' around the hole, the pilot can wander. If there is not structure to countersink into in assembly, I usually drill the piece onto some wood, clecoing as I go, and then use the holes in the wood to guide the pilot. The key is that whatever you use as a guide for the pilot cannot wander, so if you are just doing a single hole, you must clamp the guide material behind it, drill the guide hole, and countersink before unclamping the guide.

wirejock · #4 06-30-2020, 05:16 PM

I have one dedicated to 3/32 as well. I don't trust any cage as far as I can throw it.
Typically I test on scrap and leave it shy then dress the hole by hand. I don't know why they do that. Murphy's law.

Louavul · #5 06-30-2020, 05:18 PM

What Ryan said only I would use a scrap of .064 +/- as backup to keep the countersink from rattling. You'll use it often and it's unlikely to wallow out as anything other than metal will eventually do.

koupster · #6 06-30-2020, 05:26 PM

I see radial scuffing around the holes. Are you holding the cage steady with the hand that's not holding the drill? Agree with the need for a backup for the pilot hole.

Cheers, David
RV-6A KBTF

Taltruda · #7 06-30-2020, 05:43 PM

Are you sure that you are supposed to countersunk that part and not dimple it? I don't know what that part is, but it looks too thin to countersink. I agree with others that you need to clamp either a piece of wood or thicker aluminum to hold the pilot of the countersink cutter. Be careful reading the plans. .it's easy to confuse countersink with dimple sometimes

msmst25 · #8 07-01-2020, 01:22 AM

Thanks for the suggestions. It is definitely supposed to be countersunk in order to attach the hinge underneath for trim tabs. I will definitely start attaching a piece behind it for support.

msmst25 · #9 07-01-2020, 01:23 AM

Quote:

Originally Posted by koupster

I see radial scuffing around the holes. Are you holding the cage steady with the hand that's not holding the drill? Agree with the need for a backup for the pilot hole.

Cheers, David
RV-6A KBTF

The scuffing happened after the mistake. I went over it with scotch brite to see how bad it was.

Karetaker · #10 07-01-2020, 08:23 AM

If I may...

As mentioned before, the wondering of the countersink is due to the material being thin and the cutter enlarging the hole . The guide nub on the countersink then wonders around in the large hole. If I need to countersink rather thin material; as you stated, to fit a hinge underneath, I choose to fit and match drill the two parts together as one. I then leave the parts clekoed/clamped and then proceed with countersinking with everything in place.