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More firewall imponderables

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naumuk(at)alltel.net
Guest

Posted: Mon Apr 30, 2007 2:37 pm Post subject: More firewall imponderables

All-

     If I were just risking a chunk  of .025 I wouldn't care, but we're talking .040 here. Built a 4' Dave's brake  over the weekend and this is my first job on it.

     The DL of the stiffener blank is  141mm (Top drawing), but the sum of the flanges and center of the finished piece  (Bottom drawing) is 145mm. Am I supposed to add 2mm/side to the DL to account  for the 1/8"R? Makes sense, but my question is, is this drawing the norm or an  exception so I know what to do in the future?

 Bill Naumuk

HDS Fuse/Corvair

Townville,  Pa

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craig(at)craigandjean.com
Guest

Posted: Mon Apr 30, 2007 3:14 pm Post subject: More firewall imponderables

No matter what  theoretical answer you get I would cut out a narrow 1-2 inch wide cross section  test piece, bend it and check the  results.

  

 --  Craig

   [quote][b]

naumuk(at)alltel.net
Guest

Posted: Mon Apr 30, 2007 3:45 pm Post subject: More firewall imponderables

Craig-

     I just noticed that another part  on the same print page had a DL less than the finished. Maybe the metal gets  stretched during forming. I might be overanalysing.

 Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

 [quote]   ---

n4546v(at)mindspring.com
Guest

Posted: Mon Apr 30, 2007 4:20 pm Post subject: More firewall imponderables

Hey Bill:

     The DL always seems to be less  that the total sum of the lengths.  The best example of this is the  standard "L",  The plans show each side as being 19mm (38 total) yet the DL  is 36mm.  I don't think it is the metal stretching during bending, but  in some mysterious way, once the part is formed, you are measuring the bend  radius twice, once from each direction.  I think that allows for the  missing material, right?

  

 Regards,

  

 Randy L. Thwing, Las Vegas  do not  archive/

 [quote]   ---

n4546v(at)mindspring.com
Guest

Posted: Mon Apr 30, 2007 4:35 pm Post subject: More firewall imponderables

Hey Bill:

     I forgot to mention I agree with  Craig that one should make some test bends, especially since you are usuing a  new brake.  You will find a 

"sweet" spot somewhere under the nose of  the brake tongue where when you position your stock with the bend mark, once you  bend the metal, your mark will be in the center of the radius.  I've sent  pictures before showing bending standard "L" on the TAPCO siding brake.   I've found that if I shove the metal under the tongue, so that the bend marks  are barely visible when "eyeballing" them at about a 45 degree angle from above,  puts the marks in the center of the bend radius every time.  This is not  too crucial when bending "L" etc., because if your off a little, you just wind  up with one leg of the "L" a little longer that the other.  But when you  are bending channel, where you are trying to wind up with a specific channel  width, you need to know where to locate the bend marks on YOUR brake to  accomplish the correct radius, located in the right place twice, to accomplish  the finished channel width.

  

 Regards,

  

 Randy L. Thwing, do not archive

  	  Quote: 	
		      

   Subject: Re: More firewall    imponderables

   



   Craig-

       I just noticed that another    part on the same print page had a DL less than the finished. Maybe the metal    gets stretched during forming. I might be overanalysing.

   Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

    	  Quote: 	
		        

     Subject: RE: More firewall      imponderables

     



     No matter what theoretical answer you get I would      cut out a narrow 1-2 inch wide cross section test piece, bend it and check      the results.

      

     --    Craig

craig(at)craigandjean.com
Guest

Posted: Mon Apr 30, 2007 4:39 pm Post subject: More firewall imponderables

The numbers from current XL plans (6-B-7 dated 03/06)  are the same: The flat piece measures 141 deep. The two flanges are listed  as 30 and 20. After the bend the three sides are 30, 95 and 20 with the  developed length given as 137.

  

 I've read a number of definitions of developed length and  still don't see how 137 fits in to all this. In what way (if any) do I have  to apply 137?

  

 30+95+20=145. I agree with Randy  that difference between 141 and 145 in part comes from double  counting the curve.

  

 On the other hand IMHO this is one part where the dimension  of the two legs of the "U" could end up being over a bit and not cause any harm.  I may be overlooking something but I don't see where some extra length in the  legs would interfere with another part (at least on the XL).

  

 -- Craig

   [quote][b]

planecrazydld(at)yahoo.co
Guest

Posted: Mon Apr 30, 2007 4:40 pm Post subject: More firewall imponderables

When I lay it out at 30 x 95 x 20 in 0.040" thickness, add the .125" bend radius, the outer surface DL is 141. The inner surface DL is 138. Looks like the 141 is good.



I have always made the bends then trimmed the flanges when I did not have production tooling to position and feed the workpiece...



Bill Naumuk <naumuk(at)alltel.net> wrote: 	  Quote: 	
		         All-

     If I were just risking a chunk  of .025 I wouldn't care, but we're talking .040 here. Built a 4' Dave's brake  over the weekend and this is my first job on it.

     The DL of the stiffener  blank is  141mm (Top drawing), but the sum of the flanges and center of the finished piece  (Bottom drawing) is 145mm. Am I supposed to add 2mm/side to the DL to account  for the 1/8"R? Makes sense, but my question is, is this drawing the norm or an  exception so I know what to do in the future?

 Bill Naumuk

HDS Fuse/Corvair

Townville,  Pa

	


  Dave Downey

  Harleysville (SE) PA

  Zodiac 601XL/Corvair?

           Ahhh...imagining that irresistible "new car" smell?

 Check out [url=http://us.rd.yahoo.com/evt=48245/*http://autos.yahoo.com/new_cars.html;_ylc=X3oDMTE1YW1jcXJ2BF9TAzk3MTA3MDc2BHNlYwNtYWlsdGFncwRzbGsDbmV3LWNhcnM-]new cars at Yahoo! Autos.[/url]  [quote][b]

craig(at)craigandjean.com
Guest

Posted: Mon Apr 30, 2007 4:56 pm Post subject: More firewall imponderables

BTW: on the current XL  plans this piece is made of 0.063, not 0.040. Is that why the listed DL is  different: 137 on the XL vs. 141 on the  HD?

  

 --  Craig

   [quote][b]

planecrazydld(at)yahoo.co
Guest

Posted: Mon Apr 30, 2007 5:31 pm Post subject: More firewall imponderables

If fyou want to work it out for yourselves, check one of the following for the formulas: AC43.13-1B/2A, AC65-15, Tony Bingelis' books on homebuilt fabrication.



What you are seeing is the difference between the two side measurements of the .125" radius and the length of the arc swept in that corner.



"Randy L. Thwing" <n4546v(at)mindspring.com> wrote:[quote]       Hey Bill:

     The DL always seems to be less  that the total sum of the lengths.  The best example of this is the  standard "L",  The plans show each side as being 19mm (38 total) yet the DL  is 36mm.  I don't think it is the metal  stretching during bending, but  in some mysterious way, once the part is formed, you are measuring the bend  radius twice, once from each direction.  I think that allows for the  missing material, right?

  

 Regards,

  

 Randy L. Thwing, Las Vegas  do not  archive/

 [quote]   ---

rickpitcher

Joined: 27 Feb 2007
Posts: 76

Posted: Mon Apr 30, 2007 6:18 pm Post subject: More firewall imponderables

You're seeing the "setback" or "bend allowance".

http://www.engineersedge.com/bend_allow_calc.htm

 The "DL" (developed length) will always be smaller than the totals of the 

flanges because of the radius in the bend.

Don't sweat it too much, just be sure your parts nest together nicely.



Rick

601HD

---

naumuk(at)alltel.net
Guest

Posted: Mon Apr 30, 2007 6:34 pm Post subject: More firewall imponderables

All, update-

    .040 bends a lot harder than .032. Don't center on the  edges of your brake, center on the hold-down bolts. Still works acceptably well.  I wound up with 32mm, 22mm, and 95mm, which is what I was shooting  for.

                                                                            WJN

 [quote]   Tom-

       I tried a test piece and found    out two things.

       1. The DL is adequate to come    up with the finished part. Probably a combination of material stretch and a    trig compensation for the radius.

       2. Dave says you    can build the brake out of  either 3" or 4" angle. WHAT FOLLOWS IS    NOT A SLAM AT DAVE!!                Sometimes a solution is so simple    you can't believe you're so stupid. Standard 3" angle is 1/4" thick, but 4" is    3/16". I built mine out of 4", because that's what they had at the junkyard.    It never occurred to me that a larger angle would be thicker. Duh! I'm not    worried, because the additional radius makes for a stronger part, up to a    point. 1/32"R is not that point.

       The target dimensions were    20mm and 30mm flanges, with a center section of 95mm. Going right to the    flange lines, I wound up with 23mm, 33mm, and 93mm. So if I cut down on the    flange mark lines by 1mm, I'll be right on for the center section, and within    +/- 2mm for the flanges. As good or better than kit parts.

       By the way, the test piece of    .032 bent like butter using the 4" angles. I have a total outlay of $18.72 in    a 4' brake, not counting 2 rods, the electricity to weld the handle, and a 2    year old partially used can of Rust-Oleum. If there's ever a category for    "Backyard invention of the century", I'll nominate Dave's    Brake. 

       

   Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

   [quote]     ---

TxDave

Joined: 22 Jul 2006
Posts: 168
Location: Temple, TX

Posted: Mon Apr 30, 2007 9:01 pm Post subject: Re: More firewall imponderables

Thanks for the kind words, Bill. I built my brake from 3" angle and didn't realize 4" was thicker. I'll be sure to change the plans to reflect that fact.



By the way, I have a link to a great bend line calculator on my website. It was created by fellow scratch builder Larry Winger. It helps take the guess work out of figuring out multiple bends. 



Craig's advice for doing test bends, and Randy's comment on finding the "sweet spot" are right on the money. 



Dave Clay

Temple, TX

601XL from plans

http://www.daves601xl.com

naumuk(at)alltel.net
Guest

Posted: Tue May 01, 2007 2:31 pm Post subject: More firewall imponderables

Dave-

    The fact that I found 2 pieces of 3" at the junkyard and couldn't find 

another is responsible all the discrepancies. Had to go with 4" for the 

hold-down piece. I figured out a +/- 2mm correction, and I only have a 

handfull of bends left to make, so I'm not worried.

    Thanks.

Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

---

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