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Author Topic: MB's CB750 custom seat pan, battery tray and rear hoop, etc.  (Read 9532 times)

Offline The_Beave

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Hi, all! I figured I would throw up a build thread for the work I am doing for MB to his CB750. The basic plan is detabbing, welding on a new rear hoop, building a custom seat pan and battery tray, maintaining as low a profile as possible. I just finished up the rear hoop tonight, but I'll let the pics do most of the talking. Most of this is going to be cross posting specific stuff relating to MB's bike from my blog (link in sig). I hope you find something interesting, and please do ask any questions and I'll even take criticisms. =)

MB's frame as it was when I took possesion of it:


MB was kind enough to cover it in Aircraft Remover so I would be reminded at how effective that stuff is at removing/irritating skin. heh

He also kindly supplied this tank so I could properly dimension the seat pan (which is the next thing to get worked on):



I actually like the tank just as it sits. LOL!

Next up, I started a bunch of de-tabbing and smoothing:



Some of the shots are out of focus, as I only had my dang phone on me at the time, but I think you'll get the point:





This was something interesting I discovered when cleaning the ends of the frame:


It was filled with body filler. That would have to be taken care of, for sure!

To take off the tabs from the under side of frame brace, I cut most of the tab off with a cut off disc, then pried off the flat part of the tab that was spot welded in place:




This saves your time and your flap discs. Don't use regular grinding stones for most stuff. Flap discs run smoother, allow for more control and leave a much smoother surface finish than normal grinding wheels!

Comparison between times:


I also decided the front section needed some love and brushed off the slip fit joints:




There was a tab here:



Then I got some beads on the front:




Welding on old metal is always an adventure, no matter how well you clean it! LOL!

Another random view


Then I measured a bunch and drew up some plans for the seat pan and battery tray:




Mike wanted everything to be as streamlined and visually minimized as possible. I think that I'll achieve that, especially based on the templates I made (and will show soon enough).

Final shot of the frame that day:


Here's where most of these pics and more commentary can be found:

Mike's Frame
« Last Edit: May 28, 2012, 12:06:53 by The_Beave »

Offline The_Beave

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Mike stopped by and we picked up some sheet metal and a few other things, and he dropped this off:



The dimensions were actually quite good, though the ID was a bit small to match exactly with the frame. I figured I could fix that without any issues, and I did but not without some bloodshed . . . (Every project needs a bloody christening, right?)

Another piece of old metal I cleaned up to use on this project:



Speaking of cleaning, I needed to take care of this bit of choas:



I don't like working in a cluttered place. Due to my "shop" arrangement, I can't always leave things where I'd like, but that is going to get rectified soon enough. I need to invest in some lighting so I can work in the other half of the garage that I am borrowing and then I can move all my stuff semi-permanently into place and not have to fuss about where things are, since I will have a place for everything and everything in it's place. (Eventually.)

I also installed a few things for safety and convenience, the most notable of which is a bottle-pressure rated T for my Argon setup:


That is going to make backpurging so very, very much easier and more frugal!

So, as a mentioned before, the hoop that Mike bought was a bit shy on where it should be. No problem, I thought to myself, just tweak the legs out a bit since Mike wants the hoop as short as possible.


That worked OK, but the spring back on the material was a bit too much to actually tweak the legs out enough to fit. So, I shortened the legs:



I was basically using the vise as an expander, and it was working beautifully until . . . The hoop spring off the vise so fast that I didn't even see it coming! It impacted the right lens of my safety glasses and left this:



That was after it stopped bleeding profusely and after I managed to scrounge up that single butterfly to close it up. Needless to say, I didn't really do much of anything after that as my face really )(#$()*#$* hurt. The worse part was I thought I lost a tooth, as my face numbed up so fast I couldn't anything from my brow to my lower lip. The moral of this story is: ALWAYS WEAR EYE PROTECTION! If I hadn't had mine on, I would likely have damaged my eyeball, and that is no fun.

I just shut everything down and grabbed this last pic for that particular day:



As always, there are a crapload more pics and lots of text that includes tips, tricks and temper tantrums on my blog. I'll edit this post with links some time soonish, but I have to go get ready to go out to meet some of the woman's friends, which is a lot nicer than typing and cutting and pasting pics for you guys (and gals????). heh

Very much more on this found here:
Wear Your Effing Safety Glasses!
« Last Edit: May 28, 2012, 12:08:47 by The_Beave »

Offline surffly

  • Posts: 2810
Good idea welding up the slip joint on the front of the frame
I read that you should only weld the vertical portions and not connect them horizontally though

Offline MB

  • Posts: 613
MB's CB450 custom seat pan, battery tray and rear hoop, etc.
« Reply #3 on: May 28, 2012, 02:29:16 »
We should also mention this is a 73 750 project, the 450 I'm working in doesn't involve any frame mods. I'm too lazy/busy to make threads so I'm glad Matt has put up this portion. Maybe I'll get my shit together to put together one for the engine etc...

Offline The_Beave

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I think I mixed up the 450 and 750. LOL!

I'd like to find out why the horizontal parts shouldn't be welded. If that's the case, I can "fix" that easily enough.


Offline surffly

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What dont you understand?  He literally wrote a book on this stuff.
I cant understand your hatred of him, Hell he even agrees with some of the stuff that you have pointed out as far as weaknesses.  Either way it is well documented on more then one location about how to properly brace or improve on and existing frame or just build your own. 
I was wrong about the foale reference about the horizontal welds, that info came to be buy a few racers on the sohc4 board.

Offline The_Beave

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I took a few tabs off and welded the seams. That is all.

Offline The_Beave

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After taking a break waiting for my face to not feel like I came from the dentist (it was soooo numb!), I got back to work and put the rear hoop on the frame!

I trimmed back the legs on the hoop to a reasonable length that would allow for a decent matchup of widths (as I wasn't going to attempt to stretch it any more after the last time . . . ) and this is basically was I had to deal with:


To fill the damaged section of the tube, I halved some leftover trimmings from the hoop:


Used the vise to squish it a bit, then hammered it into place thusly:


Then, looking at the hoop and the width of the frame, I figured I could actually smooth the transition substantially by adding a small filler piece and welding that in the "step" on the outer side of the hoop/frame transition:



I had to tweak it a bit because of spring-back using my "adjusting tool"


Decent enough fit, I think:


Then I got creative with emplacing the hoop without having to use my hands, which are going to be busy while tacking!


If you look closely at that picture, you can more easily see the step between the frame and the hoop.

It took a bit of fitting and trimming of things to get the hoop absolutely straight, but, it sure ended up that way.

Poor closeup pic of the step:


General idea for filling the gap, though this piece is too long:


I trimmed down the above piece to maybe 3/8" and then did a lot of this:


Looks like crap mostly because I was just running bead over bead to build up areas to make the transition as nice looking as possible.

Welding done on both sides:


Because I was so thorough with welding, all it took was less than 15 minutes with a flap wheel to get to this point:


Nice and straight:


Hole? What hole? There was a hole?


Overall, I am really pleased with how the hoop installation turned out, and Mike was very happy with how short I made it, since that was another one of his must haves for the bike. =)

More commentary and some other good info here:
Hoop Install!

Offline The_Beave

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Next up is the long and drawn out process of CAD: Cardboard Aided Design! (I got the name from this article: C.A.D.)

I started off making a half-template of the battery tray from cardboard:



I started with the half for several reasons:
1. I wanted to see if Mike thought that the profile was OK with what he envisioned
2. Making the template "blind" from the drawings (that I linked to above) verifies that my measurements are correct.
3. Correcting any mistakes now by doing so checking saves much time in the future when you are working from known dimensions that fit well.
4. Start thinking of mounting solutions that are easy to access yet still secure enough to hold the weight against vibration and still out of sight so they don't impact the look of the bike.

Mike approved of what he saw so I started moving forward with the "final" template for the battery tray.
My scribbled mess of lines:


Final cardboard template:


The gap on that side is from the thickness of the cardboard hitting the tabs that are still on the frame. I really don't recommend using corrugated cardboard for templates for thin sheet, but it is what I had on hand. If you do have to use it, just be conscious of where your dimensions are taken from (either the inside or outside of the bends you make in the cardboard).

A view from the other side:


I managed to shorten the depth of the tray a bit, too, which helps in the overall look of the bike, I think, which is, again, what Mike wanted, and that's what he gets. =)

Plenty of space for whatever Mike wants to add in!


I didn't get a lot of in process pics of the next template because I was busy! heh This one wasn't too complicated, but took a few tries to get it to suit Mike's taste:


It might not look complicated from the side:


But it really is. Mike wanted a flat top, originally, but due to the tank shape, the front of the seat pan had to be raised up a little over a 1/4 inch at the front, which meant that the front support shape had to be changed, and the sides had to changed to accommodate the new height. This is all while the front section tapers to the centerline of the bike, making the angles even funkier. Also, the front section of the sides had to be trimmed back to fit around the edge of the tank and still allow room for seat material while remaining as tight to everything as possible. It was a headache, but I think I got all that stuff accomplished well, and Mike certainly was happy with minimizing the upward tilt and the low profile of the seat pan in general.

I thought the front part of the seat pan was going to be a headache, and I was right, but the front had NOTHING on the rear, mostly because of one mistake that I spent hours trying to "fix." heh

I started off with a simple mockup and support for the bracing:



I am not going to have the longitudinal brace in the final design, but since cardboard is floppy, I added it mostly to keep the rear transverse brace in place.

This next piece I added on was the killer:


It took hours to figure out WTF I was doing wrong, since nothing was matching up at all! I was a dolt and was using measurements from the centerline radius of the tube instead of the inner radius! ARG! That 1/4" difference was messing with all my math and drawings. After I "saw" my mistake, everything clicked into place.

Upper view of the proper radius fitted into place.


Once I got that figured out, I quickly moved on to the "ring" to trim the back of the seat:


I think that will be the hardest part to fit nicely without a ring roller, but I have a few tricks up my sleeve I am going to try. Worst case . . . it will be hidden by the seat cover and padding. LOL !

Rear profile:



General side view of how it should look:


Top view:


Making the templates gave me the exact measurements I need to make all the separate pieces for everything. The next step is going to be layout and triple checking measurements then cutting the pieces out of the big sheet and then using my band saw to make the final cuts. I'll actually use a hole saw to drill out the round sections that fit around the tubes. I am going to be adding "feet" to the supports to spread the force a bit and hopefully minimize paint wear, so I am going to use a 1 1/8" hole saw to accommodate the extra material. Lots of work left to do, but, the hardest parts (for me) are now done. =)

Much more located here:
Poor Man's CAD!

Offline The_Beave

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Re: MB's CB750 custom seat pan, battery tray and rear hoop, etc.
« Reply #10 on: May 28, 2012, 14:45:33 »
One good engineer's repair?

One well engineered repair?

<--- ignorant of German, forgot most of his 3 years of Latin.

Offline The_Beave

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Re: MB's CB750 custom seat pan, battery tray and rear hoop, etc.
« Reply #11 on: May 28, 2012, 18:16:33 »
Thank you for the compliment.

I am afraid my Latin has sunk to the level of "Ubi, O, Ubi est mea sububi?" heh

Offline The_Beave

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Re: MB's CB750 custom seat pan, battery tray and rear hoop, etc.
« Reply #12 on: Jun 05, 2012, 02:07:29 »
Here's something else that Mike needs to have fixed:



Closeup:


I'll be welding this in place after cutting and grinding the old stuff down to acommodate the new material:




Offline manualofman

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Re: MB's CB750 custom seat pan, battery tray and rear hoop, etc.
« Reply #13 on: Jun 05, 2012, 12:24:05 »
a meticulous and carefully planned job here. should pay out big, looking forward to following this.

Offline MB

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MB's CB750 custom seat pan, battery tray and rear hoop, etc.
« Reply #14 on: Jun 05, 2012, 20:51:35 »
I'm pretty happy to have met Matt. He is THE man to make my very particular but technically deficient aesthetic ideas real.