Renshape alternative

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Thread: Renshape alternative

  1. #1
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    Default Renshape alternative

    Hi Listers

    I ahve a cnc router for making molds and plugs formodel aircraft.
    I am looking for a cheaper alternative to Renshape. ( Renshape is a polyurethane tooling board that is used for making prototypes and general cnc machine work, stable n=machines well no grain etc.

    I can get it in Auckland from Nuplex but at over $1000 for four small sheets am looking for something cheaper. Currently I am machining in MDF and plan to soak this in epoxy and post machine .....time will tell.

    I know Styrotech ( CNC Firm in Auckland) use uniform MDF, I don't know how much better it is than the garden variety that we get in the hardware stores, does anyone have any experience with uniform MDF. (UMDF will cost me about $400 from Styrotech I understand).

    I have machined in Armour (sort of like mdf but much tougher and probably made with a better resin and it is much heavier), this was quite good and held a good surface finish and takes paint well etcbut this is no longer available according to Laminex.......does anyone have any other ideas?

    Best
    Peter Williams
    Paraparaumu NZ

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    Flyboypete,how about mixing up a gallon of body filler ( bondo ) dump into a bread pan, vibrate or evacuate to remove bubbles, let cure and machine. Unless i'm mistaken the filler is talc so there shouldn't be any toolware problems. To increase volume or or vary
    density, glass microbeads can be added, ( free machinig as well ) Once fully cured the dimentional stability should be fairly good ulthough the strength would be very limited.
    Haven't tried it myself but should hold fairly high detail baring undercuts????



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    Default Renshape alternative

    Hi XYZADave

    Great idea. I will try this as you are correct it machines like butter. I do have a vacuume degassing chamber ( actually a plastic container that an old fridge compressor sucks down to a fairly good vacuume). I will use this to try and remove the bubbles first before pouring into a block!

    I did machine my part in MDF and then poured epoxy resin over it and heated it so that the epoxy soaked in. After it had cured, I remachined the part 0.1mm lower in Z and I am quite pleased with the results. It will stay bolted to the bed until I pull a mold from it at a later stage.

    But I do like the bondo idea and will do a trial batch over the next couple of days and report back.

    Best regards
    Peter Williams



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    Hi Flyboypete,, I don't know how much work you have
    done with this stuff or the size you require,,, A few tips you may want to consider. Work Fast, this material is quite sensitive to heat and humidity. If high, you may have a working time of less than a minute. Mix thoroughly, sorry I don't have any recommended mix ratios to work with,,,pour
    then degass. At least you will have the block shape if it starts to go into the rubbery stage before it is degassed completely. All else I can offer is.. floor wax, paste type, is a good mold release. Several coats, heated with a hot air gun, (good for porus substrates) as you have done with your resin and MDF, and bondo and fiberglass resins won't stick. ( been a while since working with this stuff )......Good Luck!! . Keep us posted,,,,



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    Everytime I try emailing nuplex I get no response to my queries.

    Flyboypete, do you recall what sizes you were quoted. The last single 1500x500x50mm sheet of renshape I got from another supplier was $950 - ouch!

    For smaller pieces I pour unfilled polyurethane resin (5 minute cure time) into a square plastic container which probably works out more expensive but it means I can adjust the amount of resin based on the thickness of the part. But for 2-10mm thick parts I've started machining acrylic sheet - works pretty well but you (obviously) need a slower feedrate than renshape.

    Last edited by jallitt; 02-11-2008 at 06:33 PM.


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    Jallit,

    Maybe I can make your day.

    I have been looking and trying many materials because Renshape and other name brands are just not available here in Peru, and who can afford to pay $100 for a 20 x 300 x 300 board of it. So I tried some experiments.

    My experimenting took me down all paths, MDF, to Fiberglass resins (epoxy, polyester or vinylester) waxes and different timbres.

    Obviously the Epoxy resins are far too brittle to be going through a CNC router so I experimented a bit more with them.

    Through all my practice I had a lot of Dust from the MDF (very dangerous stuff BTW, take great care) so I mixed it into some resin, set it into a block and routed it. It produced a lot of gas, so even after a stint in the decompressor (to remove bubbles) it still formed bubbles there was something going on there on a chemical level...

    To cut a long story short, because all up I tried over 500 different recipes over a few months and I finally came up with something that machines very well and is easy to make.

    I take measurements by volume (but when adding hardener you need to know your resin weight, so take care to take note).

    Take a cup of corn flour, or corn starch what ever you call it. A cup of resin ( I use a polyester resin), mix and stir well (slowly so as to not cause too many extra air bubbles (not important as you will see in a few minutes).
    Their is a reaction that takes place between the polyester and the corn flour. It degasses itself!!! After a bout 20 minutes the resin is degassed.
    AMAZING! Maybe an industrial chemist could tell us why.
    Now add your hardener but do not stir too much. We don't want those bubbles coming back.
    In 10 minutes your block is set, in an hour you can machine with it.
    Now because we use fifty percent volume (actually about 10 percent of the finished block (you will see what I mean) the plastic is less fragile and less prone to break outs. It is fairly soft on the tools and no louder than wood to machine.

    I pay about 10 soles ($4) for a litre of resin and 2 soles for the same volume of corn flour. That makes my 20 x 300 x 300 blocks cost about $5.

    I am now machining this material with some great results. The detail I can obtain is amazing. Obviously this is not renshape, but it is just as good for my use. I'm sure you guys will love it.



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    Is there a particular polyester resin that works better than other polyester resins?



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    Elfrench,

    I used a Fiberglass / Marine Finish Polyester. I find any other type has a tacky finish that clagged up the tools. There is a wax finish polyester available they say is machinable but I never actually got around to trying it. After my problems with the tacky resins I went straight for the marine finish. In Europe the US and America Evercoat have a vast range that I have used but find one with a non tacky finish... I am no expert on Polyester resins but I tried three different brands here in Peru before I got one that did not finish tacky.

    This type of resin is designed to be mixed with a substrate (fibreglass sheets) so don't try making a solid block of it. It will be brittle and probably crack while curing. Mix it with corn flour or as I read in the other posts Talc (rather expensive). My advice is to buy one or half liter pots of what you want to try. Buy the cheapest and work your way up to the most expensive marine (wax) grades.



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    Non sticky resin has wax in it, it needs that to dry without being sticky.

    There is also a polyester resin called "casting resin".

    They make tabletops and sinks with it and probably many other things.



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    Default Re: Renshape alternative

    Peru Dave,

    Are you still having success with your recipe? If so, can you share some ideas?



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