1001001
Well Known Member
This has been driving me nuts for a day or so. There are some odd instructions regarding rivets connecting the Firewall Bulkhead F100A and the Forward Floor Ribs, F-1049x. I can understand sometimes the plans don't specify dimpling when flush rivets are used, leaving it up to the builder to know that of course flush rivets need dimpled or countersunk holes.
But the specificity of some of the steps here is confusing.
On Page 27-2, Step 6, the plans say "Dimple (flush head on forward side) all rivet holes in the web of the F-1001A Firewall Bulkhead..."
OK, that's fine, but there are some rivet holes in the web of the firewall that have not yet been match drilled to their joining parts, which are the F-1049A, B, C, and D Floor Ribs. Most of the time we want to match drill before dimpling/countersinking holes, but this instruction says do them "All." But, this doesn't seem right to me. Step 6 also says to "Machine countersink all parts that lay against the web of the firewall bulhead for the dimples..." One could take this as an instruction to read ahead and see that the F-1049 ribs join the firewall, and should be dimpled. But they are not otherwise mentioned on this page, so maybe it would be a good idea to find them in the instructions! So, reading a bit further:
Page 28-5 is where we start to work with the Floor Ribs. On Page 28-7, we start to interface these ribs to the Firewall Bulkhead. Here, in Step 1, we are told to "Final drill #30 the holes common to the ... Firewall Bulkhead and the forward tabs of the F-1049A... Floor Ribs. See Page 28-5, Figure 2. Sure enough, Page 28-5, Figure 2 calls these out as AN426 flush rivets.
At this point, we've been told to dimple the firewall bulkhead rivet holes and then to final drill these holes to their corresponding ribs. This is not usual practice, in my experience with any of the prior instructions.
On Page 28-10, Step 11 says "Dimple all #30 holes in the fwd fuselage floor ribs EXCEPT the holes in the forward and aft tabs and the most forward hole in the upper flange. See Page 28-5, Figure 2."
OK, that's pretty specific. These are not supposed to be dimpled here, and probably not supposed to be already countersunk.
Then, on Page 28-11, it says in Step 6,"Dimple the forward tabs of the fwd fuselage floor ribs." This page says nothing else about these ribs other than to rivet them to the F-1072 fuselage bottom skin. Not sure why it's important to do that now, rather than earlier, other than that dimpling them earlier might cause fit problems for other parts?
Then on Page 28-13 toward the end of Step2, we are finally instructed to rivet the forward tabs of the F-1049 Floor Ribs to the Firewall Bulkhead. I can't find any language in between 28-11 and 28-13 that says to dimple the corresponding holes in the Firewall Bulkhead.
So, I'm confused. I can understand waiting to dimple the floor ribs' forward flanges if doing so too early can cause fitment problems with other parts, but why suggest that the corresponding holes in the Firewall Bulkhead should be dimpled much further back in the process? Is it impossible or extremely difficult to dimple these holes in the Firewall Bulkhead this late in the game?
Why would the plans have us final drilling a dimpled hole and an undimpled hole together?
Please help, I'm going a bit nuts over this, and I'm concerned that if I don't follow the rather Byzantine instructions regarding this that I'll have a serious problem fitting parts together, but it also seems really odd to match holes for flush rivets after one of them has already been dimpled (which opens up the hole quite a bit and can't achieve a very good match if done in this sequence).
But the specificity of some of the steps here is confusing.
On Page 27-2, Step 6, the plans say "Dimple (flush head on forward side) all rivet holes in the web of the F-1001A Firewall Bulkhead..."
OK, that's fine, but there are some rivet holes in the web of the firewall that have not yet been match drilled to their joining parts, which are the F-1049A, B, C, and D Floor Ribs. Most of the time we want to match drill before dimpling/countersinking holes, but this instruction says do them "All." But, this doesn't seem right to me. Step 6 also says to "Machine countersink all parts that lay against the web of the firewall bulhead for the dimples..." One could take this as an instruction to read ahead and see that the F-1049 ribs join the firewall, and should be dimpled. But they are not otherwise mentioned on this page, so maybe it would be a good idea to find them in the instructions! So, reading a bit further:
Page 28-5 is where we start to work with the Floor Ribs. On Page 28-7, we start to interface these ribs to the Firewall Bulkhead. Here, in Step 1, we are told to "Final drill #30 the holes common to the ... Firewall Bulkhead and the forward tabs of the F-1049A... Floor Ribs. See Page 28-5, Figure 2. Sure enough, Page 28-5, Figure 2 calls these out as AN426 flush rivets.
At this point, we've been told to dimple the firewall bulkhead rivet holes and then to final drill these holes to their corresponding ribs. This is not usual practice, in my experience with any of the prior instructions.
On Page 28-10, Step 11 says "Dimple all #30 holes in the fwd fuselage floor ribs EXCEPT the holes in the forward and aft tabs and the most forward hole in the upper flange. See Page 28-5, Figure 2."
OK, that's pretty specific. These are not supposed to be dimpled here, and probably not supposed to be already countersunk.
Then, on Page 28-11, it says in Step 6,"Dimple the forward tabs of the fwd fuselage floor ribs." This page says nothing else about these ribs other than to rivet them to the F-1072 fuselage bottom skin. Not sure why it's important to do that now, rather than earlier, other than that dimpling them earlier might cause fit problems for other parts?
Then on Page 28-13 toward the end of Step2, we are finally instructed to rivet the forward tabs of the F-1049 Floor Ribs to the Firewall Bulkhead. I can't find any language in between 28-11 and 28-13 that says to dimple the corresponding holes in the Firewall Bulkhead.
So, I'm confused. I can understand waiting to dimple the floor ribs' forward flanges if doing so too early can cause fitment problems with other parts, but why suggest that the corresponding holes in the Firewall Bulkhead should be dimpled much further back in the process? Is it impossible or extremely difficult to dimple these holes in the Firewall Bulkhead this late in the game?
Why would the plans have us final drilling a dimpled hole and an undimpled hole together?
Please help, I'm going a bit nuts over this, and I'm concerned that if I don't follow the rather Byzantine instructions regarding this that I'll have a serious problem fitting parts together, but it also seems really odd to match holes for flush rivets after one of them has already been dimpled (which opens up the hole quite a bit and can't achieve a very good match if done in this sequence).
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