Kerry's Bug Cart...part 1 - the buck

[Kerry Pinkerton]

FINALLY we start!

Gene Olsen did a great job on drawing buck sections for the downsized Bugatti based on Alex's drawing. The plan was to work on them last weekend at the Dixleland MetalMeet but the weather and crowd didn't allow that. I was determined to get started though and as soon as the shop was cleaned up I got on it.

First thing was to get some contact cement and test the idea of gluing the pattern paper directly to the 7 ply 1/2" plywood. This will mean the full size drawings that Gene did would not be reusable but I paid for them and if anyone else wants to do it this way they can contact Gene for their own copies. I'll have the buck at MM06 for folks to play with and once I've finished my cart, I'll loan the buck out.

OK, I found some spray contact cement at Home Depot. It's 3M General Purpose Spray Adhesive #45. As a test, I sprayed a piece of lauan and put a piece of graph paper on it.



A new blade in my saber saw and tried to follow the lines drawn on the graph paper. Worked GREAT!!!!



The paper stayed down as I cut it and it was pretty easy to follow the lines.

Next I got the first of the 5 pieces of 1/2" 7 ply sandeply plywood (Home Depot $27) and sprayed about 12" along one long side. Then I carefully laid the paper down and lined up the reference line with the edge. The glue gives you time to move the paper around before it sets. I then pulled the unglued paper back and sprayed the remaining area, smoothed the paper down, and did the overlapping piece which was trimmed after the overlap was all done.



Here is a shot of the kind of detail that Gene put into the drawings.



Now for the fun stuff...cutting out all that detail. I had no idea how long this would take. Turns out I could do a long piece in about 25 minutes and section slices in about the same. I didn't start until about 6:30 and stopped at 8:20 with 4 long pieces and 2 of the section bucks done.



I'm going to try and do a 4x8 sheet per day so hopefully this will get all cut out this week. Gene put in a TON of ribs and to start I'm only going to do half of them. It will be easy to do the others if I need more detail.

I've never shaped from a buck before, only from a flexible pattern and I'm nervous about it. I'm seriously thinking about lining the exterior with blue foamboard (one side only) and doing a true surface to pull flexible shape patterns, then removing the foam/surface for the rest of the build. At least on the complex pieces. I'll know more after I see the buck put together.

For a true surface, is there any reason I couldn't use plaster of paris for the final surface instead of bondo? I want to take it apart and I'm afraid removing all the bondo will be a pain.

[BarryA]

Hey Kerry, looks like you've got your work cut out for you!:wink: (OK it's weak I know, but I couldn't resist)
I think once you try working off the buck you'll find it quite easy to read, but having both a buck and a flexible pattern will be great.
The plaster will be easier (and cheaper) than bondo. I have used it quite a bit for prototypes in my day job. The two biggest drawbacks are:
You need to lay down all you need in one go - any attempt to add more on top will give you areas with different hardness, which become near impossible to shape/sand evenly. Try to split the area up evenly with straight joints, and make sure you get enough thickness on each with one batch.
It is an excellent rust promoter - so no steel reinforcing. You can shape it pretty nicely when it is "green" with a cheese grater file, just clean up the tools immediately.
You will need to get some thickness for it to be strong enough, and can use something like hessian soaked in wet plaster for reinforcement from behind.
Like bondo, there will be dust everywhere when you sand, so you might want to do that outdoors!
Great to see something finally happening with the Bug build - albeit in a slightly different form to the original idea.
Barry

[Boogiemanz1]

Kerry there is quite a bit of shrinkage to p of p isn't there? I think you need to take a small trial buck and fill it and see how it works. I told you about the tank I'm working on, I have been thinking about paper mache' (sp?). That is how Roth started some of his early cars....spitwads. Easy to fill in with P-M' and then top with P of P I would think. On a project as masive as one whole side of the cycle kart, I would think that could add up to a lot of foam, it would have to cost more than water, flour and paper. You can always go around and pick up all the free trader papers, and real estate guides..........someone can get use out of them.......:grin: ...........I may try that in the next day or so..........john

[Tisdelski]

hi kerry,

i`m thinking bondo is the way to go, plaster of paris is a pain to fix if you make a mistake.

bondo is real easy to work with.

i`m not clear as to what you need the bondo for ?

gary

[Gene_Olson]

Kerry, make one side by checking clearance from the back and pull your flex pattern from that.

fit, fit, fit, fit

It will give you fit's but it will take less time and a lot less money than bondo.

If you pull your pattern from the buck it will be just a bit small anyway as it won't have the skin thickness info

[Jeff Parker]

Kerry-

I just had an idea that MAY be useful.

Lay a piece of saran wrap over the buck. Tack the edges
Lay some fleece fabric over the saran. Tack edges
Use resin (for fiberglass) to wet the fleece. The fleece will flatten and add maybe 1/16" over the ribs??
Bondo over the valleys between the ribs.

I know the resin works over fleece. Fleece is cheaper than fiberglass cloth, and follows all sorts of contours. Its what the high end automotive audio guys use to build custom cases for speakers. And I know the bondo will stick.

My only concern would be the resin vs the saran vs the wood. Don't know if it would melt through the saran, and stick to the buck.
And the 1/16" build up for the resin. You could always reinforce the inside of the pattern after you removed it from the buck if you felt the need.

[Boogiemanz1]

When I have to make a custom seat pan I lay saran wrap on the frame of the bike and use strips of cloth and resin on top of it. I usually use a few layers but have never had a leak....john

[BarryA]

The saran wrap (assume this is what we call cling film?) won't be affected by polyester resin. If it is the same stuff I'm thinking, it is polyethylene so it will be self releasing too. Just don't melt it by adding too much catalyst! (Seen fires started a few times by someone over catalysing and leaving it in the bucket)
And look out for holes - tacking it to the wood might not be a great idea. I would use some kind of release agent on the buck just for peace of mind.
Barry

[JD in SoCal]

Kerry,

I think you will find that shaping parts over a buck is not as difficult as you may be thinking. As you know, lots of parts are made without a solid surface to pattern from. You can take rough paper patterns from the buck, then refine the shape by fitting the panel to the buck. It seems to me that you would be adding a large amount of unnecessary work and weight if you cover the buck with plaster, bondo, or anything else.

I also have a question on a related topic, and please excuse me if you have already answered this. Did you look into having the buck parts cut out locally on a CNC cutter/router? I have not done this (yet) but a furniture-manufacturing friend of mine tells me that the service is readily available and relatively cheap around this neighborhood. I'm curious if you checked into this or just decided to go with the manual cut-out method?

Either way, its great that you are tackling this. I'm very interested in the process and am toying with undertaking one myself.

JD

[Kerry Pinkerton]

Originally Posted by JD in SoCal

... I'm curious if you checked into this or just decided to go with the manual cut-out method?

Either way, its great that you are tackling this. I'm very interested in the process and am toying with undertaking one myself.

JD

I didn't check into it. Doing it again I might. It looks like the buck will take about 12 hours to cut out. I ran out of spray adhesive and need to go to THD to get 3 more cans. Hopefully by tomorrow night, I'll have everything cut that I'm going to and can try and get the buck put together.

In retrospect, I wish we had spent a little more time talking about scale. At 8' long and over 3' wide, it's probably a little bigger than it needs to be. I don't know if Gene can easily scale up/down at this point or not.

I was remis last night when I was only thanking Gene for his work on the buck. There are LOTS of folks who put a LOT of effort into this including Wray, Anders, Todd, John, Alex, Gene, Tim, Mike, Ralph, Dick, and many, many more including Richard Crees although he's now deleted all his posts in the thread for some reason. Everyone who has an interest in this owes these folks a vote of thanks.