Center Ribs

Submitted by Papakeith on Thu, 08/31/2006 - 17:03
August 1-3  
 
  The past few nights have been spent studying the plans and cleaning the workspace in preparation of cutting the center ribs.  As usual I'm probably over-thinking the process.  Oh well, when I'm satisfied that I won't be screwing something up too badly, I'll start cutting.
August 4,5  
main_spar_caps.jpg (57625 bytes) What a great build weekend.   I ended up having to draw out in and exploded parts type view the way the spar caps were assembled on the spar.  I finally got the proper rib sizes figured out in my head.  Once that was figured out I could spend some quality time sanding
   
center_rib_formblock_no_spacer.jpg (64818 bytes)

I am going to use the same router method that I used on the nose ribs.  The first step is to make a template with the 9/16 flange.

I made the template 1/4 inch short on the main spar side and 1/8 short on the rear spar side.  I'll describe why in a couple of minutes.  Once the main center rib template is complete I need to make a duplicate of the template so I can sandwich the rib black between the two.  The simplest way I know of to make an exact copy is to use the laminate bit and simply route it to size.
center_rib_formblock_spacer.jpg (74431 bytes) The reason for cutting the ribs short by 1/4 inch on the main spar side is to accommodate the varying thicknesses of the spar cap.  I borrowed a chapter from Russ Erb and got some 1/8 thick aluminum stock and made two inserts for the end of the rib template.  I made the center hole off center so that I can only put the spacers on one way.
Center_rib_spacer_mounted.jpg (83224 bytes) With these two inserts I can make the template be full thickness, 1/8 short or 1/4 inch short.  In this picture I've got the spacer clamped into place while I inserted the screws.

center_rib_spacer_install.jpg (81726 bytes)

 I managed two minor screw ups in this process.  

One:  I sanded the rear of the template 1/16 too much.  The solution was to sand another 1/16 too much and add a 1/8 insert to the rear spar side of the template.  Problem solved.

Two:  I got in a rush when I was drilling the pilot holes for the wood screws I used to hold the inserts in place.  I neglected to check my drill bit size.  The result was a pilot hole that was wider than the thread of the screw.  The solution?  I dripped some gorilla glue into the holes, inserted the  screws and clamped them in place for the night.  The insert on this end doesn't need to be changed out, so gluing it in place isn't a problem.
August 6center_rib_router_jig.jpg (65798 bytes) After letting the glue set overnight, I was ready to start cutting my rib blanks.  The same process that I used for the nose ribs would be used here.

center_rib_jig_loaded.jpg (69496 bytes)
  1. cut the blank slightly oversized
  2. place the blank in the master form block to get jig pin holes drilled 
  3. clamp the blank in the routing jig.  
  4. route the blank to size
  5. debur the edges.  I don't debur the holes at this point, since all of the holes will be drilled out to be the lightening holes later.
025_center_ribs_routed.jpg (65409 bytes) The only difference in production from the nose ribs was that this time I labeled and kept score of which ribs (different length) had been made.
025_center_ribs_routed.jpg (65409 bytes)

In retrospect, I kind of wish I had cut the nose ribs to size when I was making them.  Time will tell if it will make much difference.

With all of the .025 center ribs cut it was time to start hammering flanges.  I made two piles of ribs.  I checked and double checked to make sure that I had the proper ribs in the proper piles.  Once I was confident that I had my left and right wings fairly represented I started hammering the flange.
   
center_rib_rivet_spacing_mark.jpg (68611 bytes) I placed the routed rib into the master formblock.  Using 5 of the 1/4 inch holes I had already drilled I secured the blank in an MDF sandwich.  Once secured, I marked off the general rivet spacing.  This will ensure that I don't place any flutes where  a rivet might be placed later.
center_rib_hammer_flange.jpg (72045 bytes) Once I had both flanges marked I laid the whole formblock down on my bench with one side overhanging the edge.  I have a note on the backer block to make sure that I'm hammering the correct direction.
center_rib_flanged.jpg (73805 bytes)  It was a good day of work.  I got all but four of the .025 center ribs flanged.
August 7  
  Tonight I hammered the flange on the remaining .025 center ribs.  I seamed and fluted two ribs after that and called it a night.
August 8  
center_rib_first_hole.jpg (87102 bytes) I got 5 more ribs squared up tonight.  That completes the job for one wing. Well, it completes it for the .025 center ribs anyway ;) .

 I decided to start in on the lightening holes just to mix it up a bit.  I got three cut and called it quits for the night.

About the only other thing I did tonight was to install a cheapo wall mount fan. 

August 9  
  I fluted the other 7 .025 center  ribs tonight.  I also finished cutting out the center lightening hole in the rest of the batch.
August 10  
  More work on the ribs last night.  I set up my high-tech flanging station and flanged half of the pile last night.  I'll probably do the other half tonight. Just so you don't think I've fallen off the planet, this will be my last update until the 21st.
August 11-16  
  The 11th through - 16th were spent camping in NH.  It was pretty nice.  No cell service, quiet, disconnected.   I wish I could have stayed.
August 17-20  
center_rib_oval.jpg (52306 bytes) I worked on and off from Thursday through Sunday.  The main hurdle I'm wrestling with is the cutting of the .025 oval lightening holes.  If I had been thinking straight, I would have cut the ovals first with a router while I still had all of my jig pin locations intact.

Instead I cut three of the five lightening holes first, leaving me with only one jig pin location to secure the rib to a form.  Not good.
back_rib_layout.jpg (49109 bytes)

I think I'm going to buy a dremel hole cutter attachment and make the ovals that way.  I'll post more detailed pictures once I get the process figured out.

I did try to make the oval with the fly cutter.  It works, but it's messy.  Lots of clanking and jamming.  It's just not the way to get the job done.  At least it isn't for me.

While I'm waiting to come to a decision on my course of action, I started laying out the lightening holes for the back ribs.
August 21  
  After weighing all of my options, I ended up taking another stab at cutting the holes with my fly cutter.  If I took it slow and cut a bit off of each circle at a time, I was able to get good results.  I'm happy to report that the oval holes are behind me.
backing_block.jpg (51524 bytes)

Here's a run down of the basic process I used. Bear in mind that if I had planned this out better, I could have saved myself a lot of aggravation and simply routed out the oval the same way I had the rib.

Since I had cut three of the five lightening holes in the ribs already, my options were a bit limited.  Most of my jig pin locations (lightening hole centers) were gone.

First I made a backing block for the operation.  I did this by placing the 2.4 under the master form block and drilling out the remaining two jig pin locations.
rib_on_backing_block.jpg (73017 bytes) Next I placed the center rib on the block with two bolts sticking up through.
master_formblock_clamped.jpg (59441 bytes) I then placed the master form block over the rib and clamped it down into position.
drilling_oval_pilot_holes.jpg (68886 bytes) Next I used a hand drill to drill the pilot holes for the two circles needed to make the oval hole
rib_secured_to_press.jpg (88520 bytes) Here is the rib after it has been screwed down to the drill press.  The screws are in the centers of the two remaining jig pin locations.  This serves two purposes:  One it keeps the rib stationary while cutting, and two it keeps the waste from the cutting process in place so I can cut both holes.
half_cut_oval.jpg (100346 bytes) Here's a picture of the process when both holes were cut half way through.  Almost there :)
oval_cut.jpg (87434 bytes)  Finally! Here's a picture of the rib after the holes have been cut.  All that is left at this point is to sand the peaks where the circles meet flat.
August 22  
  Last night was "tape the maze night" on the farm.  I spent about 20 minutes total out in the PK skunkworks facility.  I sanded down the peaks in the ovals, making them. .  . well. . . oval.
August 23  
center_rib_5_holes.jpg (83312 bytes) Tonight was another light night.  I cut the last of the lightening holes in the .025 center ribs and of course took the obligatory picture.
August 24  
  see all of those holes in the picture above?  Well tonight I broke out the Bobstick3000 and had at it.  70 holes later, I was done.  I didn't have any arm left, or I would have started in on the push tool to flatten them all out.  Maybe tomorrow I'll do that. Before I do any push tool work I need to make a push station for the center ribs.  I don't think the setup I used for the nose ribs will work quite as well for the center ribs.
August 25-30  
center_rib_push_station.jpg (94428 bytes) Friday night I set about making the new and improved push station for the center ribs.  I used another chunk of MDF (yes the same single sheet I bought when I started this whole process) and drilled the lightening hole centers just like it was a rib blank. Then I increased the size of each hole to account for the rib flange area.  Once I had all of the figuring done, I started drilling.  The result turned out pretty darned good if I do say so myself. 
The only thing I found that helped was the addition of a scrap block of mdf on the narrow side of the formblock.  you can see it in the picture above.  This helped keep the rib from sliding around as I did the pushing

center_rib_before_push.jpg (90457 bytes)

center_rib_after_push.jpg (85014 bytes)

Here are the before and after push pictures of a center rib.  The bottom picture is not quite finished, but it's the only "after" picture I have.