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  #1  
Old 10-31-2021, 08:51 AM
missile29 missile29 is offline
 
Join Date: Oct 2020
Location: Dacula, GA
Posts: 25
Default Tips for countersinking spar flanges?

Does anyone have any tips for how to countersink the flanges of spars, specifically the horizontal stabilizer spars? I’m looking for tips or even pics of a jig or something that (ideally) allows you to run the whole shebang through a drill press. That’s probably a lofty goal, so I'd settle for some kind of clever jig or attachment that helps hold the countersink cage square to the spar flange, and keeps the whole thing from torquing over in your hand and cutting too deep.

Maybe the answer is “just do it” but the problems I’ve had on the stringers (that I DON’T want to repeat on the spares) are that I can’t hold the countersink cage square to the surface I’m cutting, and the single cutting edge bit I’m using bites hard and digs out all the material at once, making it impossible to go slow. It also, as mentioned, twists in my hand and on some of the holes on the stringers ended up going too deep. So now I'm terrified about doing the spars.

Thanks in advance!
—mgm
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  #2  
Old 10-31-2021, 09:48 AM
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Bruce Bruce is offline
 
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Location: Anywhere, USA
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Default

MGM,

E is best option.

To remedy.
Use 1x4 wood cut to size under project piece.
Use scrap piece of metal same size of piece, fasten all to table, drill in place.

Will keep all square and level end out so cage will not tilt.

Boomer
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  #3  
Old 11-02-2021, 07:03 AM
missile29 missile29 is offline
 
Join Date: Oct 2020
Location: Dacula, GA
Posts: 25
Default

Quote:
Originally Posted by Bruce View Post
MGM,

E is best option.

To remedy.
Use 1x4 wood cut to size under project piece.
Use scrap piece of metal same size of piece, fasten all to table, drill in place.

Will keep all square and level end out so cage will not tilt.

Boomer
Thanks! I followed your advice (using a piece of wood and a spacer) on a lot of the holes on the stringers and it definitely helped. For the spar, are you suggesting clamping the 1x4 so that it sticks off the end of the table (so the web and other flange of the spar can hang below? or something else?) I toyed around wit a setup like that in the shop but was too chicken to drill yet. I think it should work, but I need to get my wife to help hold everything stable. I also set up a little backer+spacer out of two pieces of HW store aluminum that I might give a try.

I'll probably also do it in multiple passes and work my way down to the depth. Sure is a lot of holes to have to make two or more passes each, but that's better than screwing up a spar.

Thanks!
--mgm
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  #4  
Old 11-04-2021, 02:49 PM
DavidP2020 DavidP2020 is offline
 
Join Date: Dec 2020
Location: Howell, MI
Posts: 37
Default

Quote:
Originally Posted by Bruce View Post
MGM,

E is best option.

To remedy.
Use 1x4 wood cut to size under project piece.
Use scrap piece of metal same size of piece, fasten all to table, drill in place.

Will keep all square and level end out so cage will not tilt.

Boomer
Bruce,

I am also approaching this point. Can you expound a little on your remedy? If I understand, the 1x4 goes on the bench, the scrap on top of that, and the flange attaches on top of that with the web approximately perpendicular to the bench. What is the purpose of the scrap piece of metal?

Thanks!
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  #5  
Old 11-04-2021, 03:29 PM
rapid_ascent rapid_ascent is offline
 
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You need to have a backup piece of some sort because the pilot of the countersink bit needs to be supported in some way. With thin material the pilot being unsupported will result in messed up countersinks. You can even use a block of wood and move it along as you go, but it will get enlarged over time. Then you need to drill another pilot hole and start over. As a result, using a scrap strip works a little better, but the main thing is for you to know the pilot needs to be supported.
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  #6  
Old 11-04-2021, 09:41 PM
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PaulvS PaulvS is offline
 
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Default Change cutter

mgm, I'm wondering if a different cutter will give you better results? I've only ever had and used the 3 flute cutters and they have worked very well with no tendency to grab or cut too fast. It's possible to shave off the tiniest amount by using light pressure. They can however chatter if the material is too thin and a backing pilot hole and steady pressure helps with this.
There's going to be many more holes to countersink in the project so I think it would be worth getting the cage to work right!
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  #7  
Old 11-18-2021, 08:28 PM
missile29 missile29 is offline
 
Join Date: Oct 2020
Location: Dacula, GA
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Totally agree, and that's exactly what I did on the spars. I was determined to come up with a workable and repeatable solution before I screwed up the (much more expensive) spar subassemblies. I switched to the 3-blade cutter and was able to go more carefully and slowly. Just to be safe, on the rear spar (which I did first) I only set the cutter to flush depth and did all the holes like that. Then I came back and went to +0.007" in a second pass. MAN was that a LOT of countersinking! My wife (who was kind enough to hold the other end of the spar for me the whole time) was about ready to jump out the window! But it turned out great and I got into a rhythm and got comfortable with the tool, which was what I really wanted.

I think the single bladed cutter can make nice cuts, but it's probably better to be used in an electric drill or drill press, where you can go very slowly with lots of low speed torque and have a lot of control over the progression of the depth. Or maybe a pneumatic drill is fine, as long as it's someone with more skill and finesse than me ;-)
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  #8  
Old 11-18-2021, 08:56 PM
Taltruda Taltruda is online now
 
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Which model are you working on? I believe the HS spar FLANGES are dimpled, while the bars that go into the WEBS are countersunk. On the wings, it is in fact the FLANGES that get countersunk, I’m just making sure you have the terminology correct, flanges vs webs..
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  #9  
Old 11-19-2021, 07:38 AM
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Bruce Bruce is offline
 
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Quote:
Originally Posted by rapid_ascent View Post
You need to have a backup piece of some sort because the pilot of the countersink bit needs to be supported in some way. With thin material the pilot being unsupported will result in messed up countersinks. You can even use a block of wood and move it along as you go, but it will get enlarged over time. Then you need to drill another pilot hole and start over. As a result, using a scrap strip works a little better, but the main thing is for you to know the pilot needs to be supported.


What Ray said.
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Bruce (BOOMER) Pauley
Kathy (KAT) Pauley

RV 7A--"MISS MARIE"--- N177WD (SOLD FLYING)72742
VAF #582-----------------EAA LIFETIME MEMBER
EX -KC-135A -------------BOOM OPERATOR #3633
VAN'S FLIGHT------------#6930

RETIRED————————-Enjoying life

See you in OSHKOSH


http://www.mykitlog.com/users/index....ley&project=84


=VAF= 2006-2022 DUES PAID
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  #10  
Old 11-24-2021, 11:40 AM
missile29 missile29 is offline
 
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Location: Dacula, GA
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Quote:
Originally Posted by Taltruda View Post
Which model are you working on? I believe the HS spar FLANGES are dimpled, while the bars that go into the WEBS are countersunk. On the wings, it is in fact the FLANGES that get countersunk, I’m just making sure you have the terminology correct, flanges vs webs..
This is for an RV-10. The HS spar flanges are countersunk to accept the dimples in the skins. Not sure what part you're referring to when you mention "bars" that go into the webs, but on the -10 there are indeed quite a few AD426 rivets that attach the spar doubler to the spar web that also require countersinking into the doubler. I don't specifically remember any countersinking done on the spar web directly, but I'm going from memory at the moment so there could be.

Thanks,
--mgm
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