Renshape alternative

[flyboypete]

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

[composites]

Here are a few places to check out.

http://www.elliottfoam.com/features.html

http://www.generalplastics.com/produ...8e466ea4a0f988

http://www.goldenwestmfg.com/html/foam_boards.html

http://www.precisionboard.com/Ind/products.htm

[XYZADave]

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????

[flyboypete]

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

[XYZADave]

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,,,,

[jallitt]

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.