584,849 active members*
3,919 visitors online*
Register for free
Login
Results 1 to 8 of 8
  1. #1
    Join Date
    Jan 2008
    Posts
    90

    Tooling Paste/Putty over Foam

    What is everyone using as a tooling paste these days? I am trying to make some molds with my machine by under cutting extruded polystyrene coating it with an epoxy paste and then doing a final machine pass on it to get it ready for sanding and polishing. Most of the pastes I have found are either only available overseas at a very high shipping cost (easy composites), polyester based and will melt the foam (bondo), or seem to be only sold to large volume folks (pretty much every decent looking one I have seen in my Google searches). I did find the Fasco Fasfair and the West Systems 105 system. Neither say that they are machinable, but I am guessing if they are sandable, they should also be machinable, right? I am not a fan of the very slow cure time of the west system. Seems like I would have to let the pieces sit to cure over night before being able to machine them. It does allow me to play with the thickness of the epoxy so I can do more of a pour and brush on deal for flatter surfaces. Does anyone have any other recommendations out there?

    Thanks!

  2. #2
    Join Date
    Nov 2018
    Posts
    4

    Re: Tooling Paste/Putty over Foam

    If you could change your foam to polyurethane it would open up the polyester products. Epoxy tends to not polish well compared to polyester.
    I've made several epoxy molds from polished plugs and you can never replicate the gloss of the initial surface if you have to polish it.
    Heat softens epoxy and if the polishing process generates heat you will never get a good high gloss finish.

    This place is almost local to me and they have a good selection and prices aren't too bad.
    https://compositeenvisions.com/

    I have used this for the surface coat of some of my molds. https://compositeenvisions.com/rdr-1...coat-1834.html it's epoxy.
    It clings to vertical surfaces well but don't expect an 1/8" build in a single layer.
    The MSDS shows it's made of epoxy and some basic fillers. You can use regular epoxy and mix some up your self (which I've done) but you end up with lots of air in the mix which needs to be degassed or you end up with tons of pinholes.
    Better to buy a product like this and avoid the pinholes. A warning, this surface coat is very hard and therefor brittle. If there is flex in your mold it will crack.

    I can't speak about the other products you mention but West 105 resin is very soft (relatively speaking).
    From the same manufacture as West is ProSet Epoxy. https://compositeenvisions.com/pro-s...esin-1776.html
    I use this thin laminating resin a lot. It cures very hard and can be post cured with heat to raise the HDT (heat deflection temperature). A little more expensive but worth it.
    A little further up the price scale would be MGS Epoxy. This is certified for aircraft use and therefor has lots of technical data about its properties and can be found here https://www.aircraftspruce.com/catal...s/mgsresin.php and here MGS Epoxy System On Wicks Aircraft Supply
    Those places also have blocks of foam.
    You could use pour foam, cast in place two part polyurethane. I've use this as well. Cool stuff but you can end up with large bubbles inside the foam. Might not be an issue if you're coating the foam to then be machined.
    This pour foam is resistant to polyester.

    This Youtube channel show them building a real plane using the technique you're talking about. https://www.youtube.com/channel/UCyE...G1Cwt8-YEAOxbg
    They are using it to create plugs which they then create a mold from. The foam looks to be white bead foam which wouldn't be polyester safe so they might be using an epoxy product.
    I don't know if they mention what product they spray on their foam but you could ask.

    Good luck.
    I'm in the beginning stages of designing a CNC router to make molds from Corian.
    davidk

  3. #3
    Join Date
    Nov 2018
    Posts
    4

    Re: Tooling Paste/Putty over Foam

    One more thing to mention, this aluminum filled surface coat is described as "highly polishable" .
    https://compositeenvisions.com/rdr-1...a3539f759fda61
    I've not used it but will next time I make a mold if I don't have my CNC done by then.

    Good luck and post your progress.

    edit..my first post is being approved by the admin so this will make more sense once it's posted.

    p.s.- rereading your post about the cure time...epoxy will always be an overnight cure at a minimum. Only polyester has a speedy cure.
    In fact, you are better off letting epoxy cure at least 7 days and at an elevated temperature. My epoxy molds were still soft after a couple days. They seemed hard but the clamps left impressions.
    Prior to the full 7 day cure the molds must be kept fully supported, i.e don't let one end hang off the table or set it on a surface with a twist. The epoxy will deflect and finish its cure leaving you will a mold that's not true.

  4. #4
    Join Date
    Jan 2008
    Posts
    90

    Re: Tooling Paste/Putty over Foam

    When I was reading your second post, my thoughts echoed yours of using polyurethane foam instead of the polystyrene foam. The polystyrene is just so convenient to pick up at the hardware store, and throw on the machine instead of ordering it, making a mold, pouring it etc, but sounds like I will end up with a cheaper product in the end. I wasn't aware that epoxy takes that long to cure. I figured the full cure time was listed on their website. Good to know!

    Watching some of their videos now. Man this is a rabbit hole of awesome videos. On the November 6th update, it looks like they coat the foam with a layer of fiberglass first, which could be done with epoxy and strengthen the piece to use a weaker filler and I guess create that barrier to allow . I found someone else had asked the same question in this video: https://www.youtube.com/watch?v=ZCtyUla6pFA. Their response was Inspire Composites Spraycore?, but my google searches didn't return anything. It looks like they may now be ITW Adhesives? That spray rig though is much, much larger than what I need and can afford. Something more for a portable spray gun and a quart size hopper would be amazing though! That was originally what I was looking for, but all of the stuff I found thickness was measured in mils. I was hoping for closer to a .125" thickness to be able to mill back down to a smooth 1/16-1/32". This doesn't exist does it?

    I am going to have to dig into your materials more. They definitely seem more affordable than the west systems stuff. This stuff seems extremely cheap and similar to the West Systems epoxy I was looking at: https://compositeenvisions.com/thin-...4a43617e0.html.

    Lots more research to do...

    Good luck with your machine design! Looks like we are doing things backwards from each other. I finally got mine running happily along so now its time to start testing this stuff out to make some molds!

  5. #5
    Join Date
    Nov 2018
    Posts
    4

    Re: Tooling Paste/Putty over Foam

    That epoxy is their 'in-store' brand. It's really just common epoxy many other manufactures put their name on. Better than West in my opinion but not as good as ProSet.
    I've used 3 or 4 gallons of it in some of my molds using the slow hardener to avoid exothermic runaway.
    Using the faster hardeners will shorten the initial cure, still overnight though. Curing in a hotbox will speed the cure and, with ProSet or MGS, give a harder more heat resistant product.
    West and the one you linked don't benefit much from post curing but will still reach their final properties quicker.
    Using polystyrene foam you want to keep the hotbox temps below 120f. An overnight cure in the hotbox will give you something you can use right away.
    Hotter than that and you can experience off-gassing from the foam.

    If you lay down glass over the foam you have to be careful of any sharp radius. The glass will spring away from the foam and cause a void. If you can do it use a vacuum. A thin plastic 1 or 2 mil directly over the glass, then a layer of smooth paper towel (no embossed texture), the the final layer of plastic to form the vacuum bag. The foam can either be place inside the bag or the bag sealed to the board the foam is on using cheap latex caulk. The 'bag' is made from plastic sheet folded over like a taco and sealed with the cheap caulk.

    Hardware store foam, usually 15 or 25psi, doesn't like high vacuum. Keep it below 10" of mercury. I use 60 and 100psi foam for much of my stuff. Look for an insulation supply company, they usually care the 60psi pink or blue which will mill better and hold detail better than the 15psi stuff. Even with the higher psi stuff you don't need super high vacuum to accomplish what you want.

    Vacuum - an aquarium pump can work or the compressor from a fridg/freezer. To regulate the level of vacuum you can simply make a small slit in the hose and bend it into a U using tape to hold the bend.
    Adjusting the radius of the bend will allow more or less air to be sucked in thereby regulating the vacuum on the part. You don't care about actual numbers, just don't crush the foam.

  6. #6
    Join Date
    Jan 2008
    Posts
    90

    Re: Tooling Paste/Putty over Foam

    Ahh fair enough.

    That is a lot of great info, I am going to have to look into a bunch more things and figure out how I really want to proceed!

  7. #7
    Join Date
    Nov 2018
    Posts
    4

    Re: Tooling Paste/Putty over Foam

    One more suggestion, ditch the foam and mill some MDF. Before the finish pass, brush on thin epoxy letting it soak in to harden the surface.
    You can use a heat gun as you brush to thin the resin so it soaks in more. Let it cure then do your final pass with the router.

  8. #8
    Join Date
    Jan 2008
    Posts
    90

    Re: Tooling Paste/Putty over Foam

    Hmm, that could work for smaller pieces and be a lot firmer, but boy that would be a heavy mold for larger pieces! I really like the cheap vacuum bagging idea you mentioned. I may give that a try.

Similar Threads

  1. Replies: 0
    Last Post: 11-26-2015, 10:54 PM
  2. Replies: 0
    Last Post: 11-26-2015, 10:34 PM
  3. 700 Density super low cost tooling foam! Need people to trial!
    By Protoconcepts in forum Australia, New Zealand Club House
    Replies: 12
    Last Post: 07-08-2013, 03:16 AM
  4. Best tooling for PE foam...
    By Andychip in forum Material Machining Solutions
    Replies: 0
    Last Post: 04-28-2012, 01:19 AM
  5. Need custom foam machining tooling
    By mccafferty in forum CNC Tooling
    Replies: 2
    Last Post: 09-01-2011, 11:12 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •