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Author Topic: 1977 BMW R100/7 Sarcoplasmic Cow Hellride  (Read 44861 times)

Offline doc_rot

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Re: 1977 BMW R100/7 Sarcoplasmic Cow Hellride
« Reply #380 on: Dec 11, 2018, 02:25:19 »
plaster is such an underrated material. its so versatile

Offline pacomotorstuff

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Re: 1977 BMW R100/7 Sarcoplasmic Cow Hellride
« Reply #381 on: Dec 11, 2018, 08:13:01 »
Not wishing to be a thread robber, but just wanted to say +1 on using plaster for your mould.
It's perfect for the hobbyist - non-toxic, cheap, quick cure, little or no odor but just watch the exotherm (heat of hydration) during the plaster hardening process with some types of plaster.
Back in the '70's, I used a US Gypsum product called Hydrocal to make a couple of racing seat moulds.  The plaster provided a pretty smooth finish - the seats I made, the racers ran them in the white gelcoat I laid them up with.  I got about 6 seats from each mould and could have kept using them, but the job ended so the moulds got scrapped.
About 5 years ago I got back into plaster moulds again - for prototypes and one-offs - switched it up to another US Gypsum product called Ultracal.
I used Pam oven spray for the mould release on the part - didn't harm the paint on the race bike gas tank cover I was cloning - brushed a thick coat of mixed Ultracal on the tank, then "laid up" layers of burlap cloth soaked in Ultracal as the first layer was just setting up.  After the plaster had become hard, I popped off the mould, sprayed the inside with clear varathane, let it cure for a couple of days, applied 6 coats of mould release wax and sprayed PVA on top of that, much like a regular fiberglass mould.
Haven't tried the "Super Seal" product you mentioned, but if I can find some, maybe on the next mould I make...
Hope this kickstarts some of the other members to try plaster moulding.
BTW, neat looking ride.
Pat
PS really like the photo of the Triumph desert sled you have in your thread.

Offline irk miller

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Re: 1977 BMW R100/7 Sarcoplasmic Cow Hellride
« Reply #382 on: Dec 11, 2018, 09:47:15 »
Not wishing to be a thread robber, but just wanted to say +1 on using plaster for your mould.
It's perfect for the hobbyist - non-toxic, cheap, quick cure, little or no odor but just watch the exotherm (heat of hydration) during the plaster hardening process with some types of plaster.
Back in the '70's, I used a US Gypsum product called Hydrocal to make a couple of racing seat moulds.  The plaster provided a pretty smooth finish - the seats I made, the racers ran them in the white gelcoat I laid them up with.  I got about 6 seats from each mould and could have kept using them, but the job ended so the moulds got scrapped.
About 5 years ago I got back into plaster moulds again - for prototypes and one-offs - switched it up to another US Gypsum product called Ultracal.
I used Pam oven spray for the mould release on the part - didn't harm the paint on the race bike gas tank cover I was cloning - brushed a thick coat of mixed Ultracal on the tank, then "laid up" layers of burlap cloth soaked in Ultracal as the first layer was just setting up.  After the plaster had become hard, I popped off the mould, sprayed the inside with clear varathane, let it cure for a couple of days, applied 6 coats of mould release wax and sprayed PVA on top of that, much like a regular fiberglass mould.
Haven't tried the "Super Seal" product you mentioned, but if I can find some, maybe on the next mould I make...
Hope this kickstarts some of the other members to try plaster moulding.
BTW, neat looking ride.
Pat
PS really like the photo of the Triumph desert sled you have in your thread.
Thanks, Pat.  We use Hydracal and Ultracal in ceramics when durability is needed for the mold, but the release times are extended because they have a slower absorption rate.  For high quantity production of wet cast ceramics, they are less desirable.  But for Ram press casting, which is a dry casting method, they do most of their duty.  I'm using #1 Pottery plaster, which is 74% water to cast,  so it's much less dense.  It's nice for this because it dries quicker.  Instead of using burlap, you can use a material called Aquaglass, which is a fiberglass that comes in matt and chopped strands, but is formulated to work with water applications like plaster, hydrocal, ultracal, fgr-95, forton mg and matrix g.  It's from a company that produces a material called Aqua-resin that you may want to try out for prototyping.  It's a water-based plaster-like non-toxic resin that, when used with the Aquaglass, is nearly as durable as standard epoxy fiberglass.  It has a hardening cure time similar to plaster, but with much more durability.  Plus, it can be laid like fiberglass, or poured like resin.  It's only downside is expense at $4 - $6/lb.

Super Seal is a waxed based sealer from Smooth-On.   As far as exotherm reactions during cure, I have a lot of experience with that and some great stories to go with it.  I taught all the mouldmaking and casting classes for Temple University while i was there.  Students loved to cast things they buy at the grocery store, especially when project requirements get into multiple part molds.  Well, with college students you get some whacky stuff.  Someone always cooks a chicken or fish in their mold.  Freezing before casting helps, but it still comes out nasty and slimy as shit. 

As far as mold release for plaster, you can also consider Murphy's oil soap.  If you buy mold soap for plaster from a vendor, you get a concentrated gel version of Murphy's oil soap.  I just buy the gallon jugs of Murphy's from Costco, so I don't have to dilute that gel.  You coat it, let it dry, re coat, let it dry and smooth any bubbles if you need to.  You can get some extremely precise castings with Murphy's oil soap and your part just needs a light rinse when it's de-molded.

Offline irk miller

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Re: 1977 BMW R100/7 Sarcoplasmic Cow Hellride
« Reply #383 on: Dec 11, 2018, 14:44:06 »
Seat foam is done. Cast with Smooth-on Flex Foam-iT 7FR. It’s the mid range of their densities and fire resistant. Next up is a leather cover...




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Offline advCo

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Re: 1977 BMW R100/7 Sarcoplasmic Cow Hellride
« Reply #384 on: Dec 11, 2018, 14:53:10 »
Seat foam is done. Cast with Smooth-on Flex Foam-iT 7FR. It’s the mid range of their densities and fire resistant. Next up is a leather cover...

I had no idea you could cast foam like that. That's killer.

Offline 1fasgsxr

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Re: 1977 BMW R100/7 Sarcoplasmic Cow Hellride
« Reply #385 on: Dec 11, 2018, 15:06:36 »
Im loving all this mold info! I have been wanting to try making my seat and tail out of fiberglass.
http://www.dotheton.com/forum/index.php?topic=41083.0

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Offline pacomotorstuff

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Re: 1977 BMW R100/7 Sarcoplasmic Cow Hellride
« Reply #386 on: Dec 11, 2018, 15:17:16 »
Exceptionally nice work and good on you to spread the info around - particularly about the foam casting. An educated fabricator is a better fabricator IMHO.
If any of the DTT'ers in the Toronto area want to try using plaster or mouldable foams, go to Sculpture Supply Canada (345 Munster Avenue) for the casting plasters, foams and the miscellaneous other materials discussed in the last few posts.
Their catalog is online and they also ship (most of) their products.  The problem I have with them is ordering one or two things and then buying a bunch of other stuff that's really neat to use as well.
Pat




Offline doc_rot

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Re: 1977 BMW R100/7 Sarcoplasmic Cow Hellride
« Reply #387 on: Dec 11, 2018, 16:05:04 »
  Someone always cooks a chicken or fish in their mold.  Freezing before casting helps, but it still comes out nasty and slimy as shit. 

when i was an undergrad and just getting into casting I got a whole cows head from the local butcher shop, which i then cast in plaster. The worst part was because of my school schedule i didn't get around to remolding it for a couple days. I had de mold it it outside and I was retching the whole time.

hahaha sorry to continue the thread jack.

Seat looks great. I have thought about casting seat foam before but i was always concerned about stiffness and longevity. It will be interesting to see how it feels and ages.

Offline irk miller

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Re: 1977 BMW R100/7 Sarcoplasmic Cow Hellride
« Reply #388 on: Dec 11, 2018, 17:04:10 »
Seat looks great. I have thought about casting seat foam before but i was always concerned about stiffness and longevity. It will be interesting to see how it feels and ages.
This particular foam seems to have virtually identical stiffness to the stock foam, but it has more rebound if that makes sense.  It's a springier foam.  Aging is obviously TBD, but it's 7lb/ft^3 density when fresh.

Oh, and I should mention that this foam requires a mold release called Mann Ease Release 2831.  There may be others, but it's what Smooth-On markets as a match.

Offline trek97

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Re: 1977 BMW R100/7 Sarcoplasmic Cow Hellride
« Reply #389 on: Dec 12, 2018, 20:17:58 »
That is very cool.