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I just turned one of my HS spars into complete scrap. *sigh*

The countersink cutter walked on me, even in the friggin drill press. Hmm, ok, guess the spar walked that time. I find it so hard to get it perpendicular to the surface being cut into (especially on the spar flanges that arent perpendicular to the spar web). I was feeling good about this project. *sigh*

Ill post some pictures when I get them uploaded.


-- (Dejected) Spike

Heres my luscious little hole, err .. trench...




The good news was that I figured out what I was doing wrong and considering that I wrecked the part, I figured I would just go for it and practice practice practice. In the end I got good consistent results. Its a shame that I messed up my part in the process though.



-- John

Spike!

Don't you have the type of countersink with the little probe thingy that slides down into the pilot hole?? With those babies, the countersink can never walk anywhere.

Cheers, Pete

And where do you get those? I want one. I think spike does to. Don't worry spike. I think that I will be doing my fair share of mistakes.

The rest look nice though.

Spike, could you please post a picture of this rascal countersink? I know you have done this once before on the practice project and I am having a hard time thinking that it is all your fault.

Also, the part may not be trash. You may want to increase the size of that one fastener. Do you think that is a possibility?

CJ

mustang wrote: Don't you have the type of countersink with the little probe thingy that slides down into the pilot hole??

You mean one of these?

With those babies, the countersink can never walk anywhere.

Want to bet your tail kit on that? These absolutely WILL walk on you, especially if you dont do it right as I did. If you look at those flutes its not hard to imagine that they will turn into side cutters especially if you have the depth a tad too deep. My problem was that I didnt realise when the cutter was finished and I continued to hold it in the plunged position. Occassionally my hand would move just a bit (that I couldnt detect) and it would cut sideways.

You can also screw up your part if you go in not perpendicular to the surface and then correct it. The countersink will happily cut its way around as it traces an arc while you correct. And note Im not talking much movement at all. Put that thing on the end of a drill and youve got a nice lever. It was hard to tell I was screwing up the part at all. And the last bit of advice is to make sure the tool is fully seated before you pull the trigger. I would just barely engage the tip and then start it allowing me to wiggle on the way down.

The new technique that worked very well was to seat it fully and press down. Pull the trigger and stop the second the air motor on the drill started to unload. That worked out well.

Good thing I never said I was a good builder. Maybe I can help save someone else from replacing a part though.

Also, the part may not be trash. You may want to increase the size of that one fastener. Do you think that is a possibility?

Thats why Im taking it to the local EAA meeting tonight. We have some patriarchs that have been A&P's and Tech Counseors for 20+. Ill see if they think its salvageable. Im not holding my breath because the one hole is enlongated towards the spar web. The others I think I could probably fix with "oops" rivets.

-- John

Don't machine countersink that stuff. Dimple it.

Thats pretty thick material to dimple. Even the manaul specifically calls out for countersinking.

Spike, if it makes you feel any better, you are helping newbies like me learn from mistakes like this. Sorry it had to be you teaching us.

Bill Murrish

Great Bill and welcome to the group! That is exactly why we are here. To help each other out, have fun, and make some good friends. Stick around make yourself at home.

Spike, this is the kind of thing I've been paid to fix for 20 years; do not despair! A few points:

1. Your countersink cutter moved because once it cut completely through the material (a "knife-edge" condition), there was not enough material remaining to hold the pilot (the little protrusion on the end). Watch those countersink depths carefully!

2. It sounds as though you got your technique down so that you can avoid this problem in the future, but for insurance, you can take a small piece of material, at least as thick as the part you're countersinking, and drill a hole in it same diameter as the one you're working on. Clamp this to the underside, centering the holes, and countersink. It cannot walk very easily now. A bit tedious, but it can save your part.

3. Speaking of which, if you only have a few holes so afflicted, you can install a repair plate on the underside. Pick up the problem hole and one to each side of it, and you'll be fine. Just make sure that this repair strap won't interfere with any parts that get installed later.

4. I personally feel that cold-dimpling material the thickness of your spar is not advisable. Too much possibility of inducing micro-cracks, which can turn into not-so-micro cracks. There is a process called hot-dimpling that will work without such risk, but it requires equipment the average home-builder won't have, and it's a hassle.

Don't be too hard on yourself; that's why these are called amateur-built airplanes. A&P mechanics do this sort of thing too (thank goodness; otherwise I wouldn't have a job!).

nightflyer wrote: 3. Speaking of which, if you only have a few holes so afflicted, you can install a repair plate on the underside. Pick up the problem hole and one to each side of it, and you'll be fine. Just make sure that this repair strap won't interfere with any parts that get installed later.

Umm, well, ya see I have about 4 holes that might be good candidates for "oops" rivets. However Ive got two that walked enough that make me a bit cautious about spar strength considering that they take up a good part of the flange. The good thing though is that they are towards the outside of the spars. Ive looked at fabbing straps for the back but I might have an interferance with a rib for one of them. Ill see what my chapter A&P people say tonight. Ive already ordered a new spar from Vans though since they have a long lead time on orders. If I dont need it Ill just cancel the order tomorrow.

dcheckoway wrote:Don't machine countersink that stuff. Dimple it.

Dan, I think we are looking at the HS610 Forward spar Aluminum Angles. They need to be countersunk for the dimpled spars to be flush on the mounting side.

Spike, maybe putting some hockey tape on the urethane cushion will keep it from gliding so easily? This would mitigate any operator error.

CJ

Excellent idea John I like it!!!

Actually we are looking at the HS-901 front spars. We are countersinking the flanges to accept the dimpled HS skins. Its a thick spar. Im getting the feeling that its quite different from the 6/7/8 series.

dcheckoway wrote:Don't machine countersink that stuff. Dimple it.

Spike,

Aren't those the forward spars? Looking at it again, I think Dan may be correct. If those are less than .040 then they should be dimpled.

CJ

Sorry, I am editing and thinking and subsequently changing my answer while you are reading and posting replies.

How think are those HS Spars anyways?

More than .040" needs countersinking less than is "usually" dimpled as per section 5 in the manual.

CJ

I never had any luck with that countersink tool that fits in the end of your drill. I used a hand hole deburrer from start to finish. It did take longer and get very tiring but boy you should have seen my forearms when I finished my RV-4!

This is all really good stuff. Good to know about it all. MORE MORE MORE!!!!!!!!!!!

Anything that helps us in the future is good in my book. Saying that though, please don't do it again. You might start going broke

Speaking of going broke. Last night at my chapter meeting I showed some friends that spar and they all agreed that it was the right decision to order a new one from Vans. Whats funny though is that one of them asked how much the new spar was. I told him $22 US and he offered to pay $11 of it if I were to stop whining ... DOH

Did you take his eleven bux?

CJ