Building a fiberglass bumper

[wayne petty]

tony... is not the point to put the first layer of the mold over the form or plug to be exactally the shape of the plug...

when you brush on the first layer of resin through the web it should fill out smoothly over the mold release you have applied...

you can fill and modify the inter face of  the mold just like you would do any fiberglass bodywork...

you might want to coat the plug with a layer of resin first...this would limit the amount of cloth penatration next to the plug...

are there any vacuum formers in your area... they could probably vacuum form a piece of plastic over it much faster to make the mold.

vacuum forming takes a piece of plastic in a frame. holds it above the part.  heats it to til it's soft and drops it over the part and vacuums it down... if you build a backing out of blue board or some kind of rigid foam to fill any gaps behind the curve so it will sit flat on a table it will be really easy for them... think of bedliner material...

in fact.. you might even be able to cut out the vacuum form.. prime it wil plastic primer and use that...


just a few thoughts....

[WZ JUNK]

Not sure how to finish / smooth off the interior of the mold once I have that built.[/quote]

Make the part you are going to draw the mold off of as smooth and flaw free as possible.  It will be easier to get the plug right than to work on the mold.  One time molds do not need to be very fancy.  Modeling clay will fix many flaws, also masking tape, cardboard, and foam can be used to modify the shape so that you can make a mold.

When it comes time to release the part from the mold,  I use plastic wedges that I make from cutting up bondo spreaders.  Drive the wedges in along the edge of the mold between the part and the mold.

I made the tail light housing for the #974 this way.  There may be some pictures on Sumners site.

John

[enjenjo]

You can take some resin in a cup, and mix in enough  polyester glazing putty to give it some body so it won't run off, and the catalyze it as normal and brush it on the part. this will be the surface of the mold, use a mold release agent on the part first, a good heavy coat of wax works. then a couple layers of matt over that will make your mold. you might want to glass in some ribs to keep it from warping.

[DrJ]

I have fairly straight bumper (chromed steel)....  Making a mold off this seems fairly straight forward from items I have read on this forum.

Not sure how to finish / smooth off the interior of the mold once I have that built.

(Mold making is on my professional resume.)

You don't want to "smooth off" the mold after making it, you want to do that to the pattern first.

Your mold will reproduce even fingerprints on the pattern/bumper.
If it's only fairly straight it 's actually fairly crooked and so will the mold and part be.

Your material$ will be better $pent making the SURFACE of the bumper PERFECT before making the mold.

You should definitely straighten any twists or bends out of it and fill dents with Bondo just like you would a fender then paint it and seal it as already suggested.

If you are only making one part, you could make the mold out of plaster to save money, but it must be bone dry (or polyester resin won't cure at all and Epoxy will foam, and painted or sealed with wax or the part resin will soak in and not come out.)
I have pulled 8 fiberglass parts put of a plaster mold and it was still useable.

I reinforce a wide mold like that with a piece or two of rebar or even a wood 2x4 to keep it from warping once off the pattern.

Generally, molds should be at least twice as thick as the intended part. otherwise you run the risk of the part warping the mold as it is curing.
That's why I suggested the plaster, because the mold is going to cost you twice as much material as the part.

Also, the longer you leave the part in the mold, the less it will warp, or change shape after pulling it.
Production shops sometimes have curing cradles, that may just be old molds, that pulled parts are rested in for curing, sometimes for days or even weeks.

Gat any particular Qs, post them.












And
I agree, leave Britney alone, please...
The media is going to kill her like they did Diana and I'm tired of her being more important than global news!

[Bugpac]

Well good resin is upwards of 40 bux per gallon, I agree, make it prom plaster, get the bondo out and shape the bumper, wax the licing bejesus out of it and plaster away, add some reinforcment before you pull it off the bumper.....

[DrJ]

I had not thought about the use of plaster. This may be the ticket for me.  

It works well.
The best part of it is it doesn't shrink, at all, like resin molds do.

I cant emphasize enough that the plaster be dry though.
You know when it is dry when it is room temperature to touch.
If it feels cold then it still has water evaporating out of it.
On small molds I have melted wax, parafin candle wax whatever, into the plaster and saturated the plaster with it with a propane torch.
There are also spray mold sealers made just for this which are basically lacquer, then you must wax that three or four times with mold wax.
and spray a release on that, for good measure.

Another thing you might consider if yuor bumper is too bent is pull a plaster mold off it, pull a plaster bumper out of that, cherry out the finish of it. Then pull another plaster mold off that plaster bumper.
I buy plaster, USG#1 from a ceramics pottery supply store in 100 lb bags for around $20 last time I bought it.
DON'T put out what they want for a 4lb"Plaster of Paris" at an art supply or Home Depot box
You can reinforce the mold with sisel fiber or cut up coffee bean or potato sacks. I get them from a bait shop for a dollar here. you might need two at the most.

Mix your plaster by sprinkling itby hand into a container 1/3 full of water untill it starts to make an "island" on the surface.
Then mix it up.
It should be about the consistency of waffle batter.

I use 1/2 a drinking straw to gently bow on and pop air bubbles in the first surface coat as it's applied by hand with a controlled "fling" being concerned with not trapping air pockets.
The first plaster batch should be enough to cover the whole patter with one thin coat.
I use gallon or 1/2 gallon plastic milk bottles cut off for mixing bowls. If you use half a dozen of then you can let the empty but coated used ones "set" and then just crack the left overs out and reuse them.
Don't ever wash unset plaster down a drain because it will set in the traps in the plumbing!

More "lecture" if needed... I usta teach this class!

[btrc]

Tony,
 Have you had the bumper off the Falcon yet.  I just had bumpers for my '63 comet rechromed and they were pretty lightweight.  Your falcon bumper looks smaller than the comet one so it is probably lighter yet.
 Years ago I made a fiberglass trunk lid for my Mazda RX2 drag car.  It ended up heavier than the stock lid and I took it to the dump.

Bob