Material to cut plug from?

[sco]

Hello, and thanks for reading, Ive been here before, but had to reregister for some reason...
I was wondering if sombody might be able to point me in the direction of some materials that I may be able to use for cutting a plug to make a mold from.
We are making a mold for a composite model aircraft and this will be our first 'proper' CNC router cut. I know of a fellow in melbourne who used 'Jellutong' to make a plug, but was wondering if there was anything 'better', or is this good stuff to use?

Thanks for your time
cheers
sco

[pmpjohn]

sco

Never heard of "jellutong" over here but a have built a lot of patterns using Basswood and Mahogany. The wood will need to be jelcoated, wet sanded, polished and waxed before starting to layup the mold.

John

[RoGuE_StreaK]

I don't have too much knowledge on the subject, but I've definitely heard of jellutong being recommended for mould plugs, a brief search found some basic info like this, which says it's excellent for turning and machining, and used for pattern making and carving.
I get the impression it would be easier to machine than mahogony?

I have looked into it a little bit in the past, definitely remember jellutong being recommended, but I think another recommendation as far as ease of carving was concerned is butterwood(?), if I recall correctly it's good for surface finish etc., but inversely more susceptible to damage. Depends on how durable you need it, I guess.

(PS. I'm also in Aus, so that explains hearing about jellutong; apparently it's an Indonesian wood, probably doesn't make it to the US, other areas probably have their on localised equivalent that's cheaper than importing)

[High Seas]

[EDIT ADDED -- seems like plastic worker gave a much better description than I did -- for some reason I didn't have but 2 posts showing when I wrote the following -- go figure] And yes use the vacuum technique!


It sounds like you want to make a female mould. Then do your product layup inside?

Have you considered using the cnc to route out 2 FEMALE halves of the fuse and layup inside that? You could use foam for fast speeds and many passes to get a good surface -- then finish it off with gelcoat or similar product for a "perfect finish." You could then use the foam as a trial or "proof mould"- but it might not hold up to many mouldings.
BUT you could take a resin and fiberglass mold off the first product, -- gelcoat it, and then multi layer fiberglass, and supporting bits and resin for a bullet proof mould.

This approach adds a step or two -- but gives you a "proof" model at low entry cost. You can then tweak it" to get the final parts to mold from.

[NOTE:You asked for plug materials - and the same approach could be done using foam for the plug.]

Best of luck - Welcome aboard, and
Jim

[adixon]

Here in the US a product called Renshape is available. It is a great material for plugs. It cuts really well with carbide or highspeed steel cutters.

It is a polyurethane material that is made specifically for pattern and mold making. Since it is man made, there are no voids within the material that require attention after cutting.

http://www.freemansupply.com/RenShape5169Foundr.htm

will link you to a suppliers page for more information.

I have made small and very large plug/patterns from this material and the only annoyance is cleaning the machine after cutting. The chips have a lot of static and cling to everything. So if you can keep a vacuum near the cutter will machining cleanup is a lot easier.

After cutting gelcoat or seal as you would anyother material for the use you intend.

-Al

[Me2]

G’Day Sco,
I use jellutong all the time for my patterns and core boxes. I cut it on the CNC, it has a very fine grain and machines very easily in all directions on the grain giving a smooth finish. When finished lightly sand and spray with Spay Putty to give a hard surface. I purchase my jellutong from a local pattern maker, 30mm thk x 300mm wide x 1.2M lg at around $40AU.
The patterns on the back of the table where all done with jellutong. Check out
http://www.cnczone.com/forums/attach...9&d=1212671963

Cam

[Eclipze]

Given your in Melbourne, there are two places which may be able to provide both advise and material.

Australian Wax Co... www.australianwaxco.com.au in Clayton South.
They have machinable wax.

There is also Solid Solution in Bentleigh, www.solidsolutions.com.au
They have quite a lot of materials that could be used for mold making.

Suggestion you give one of them a call and have a chat about your requirements and what solutions they have ;-)

[PlasticWorker]

G'day Mate ( sorry I couldn't resist )

If this is a typical composite layup I assume the plug is an exact model of the part to be made from which you will layup a mould that the real parts will be vacuum bagged into.

If you are going to use foam as has been suggested, we use joint compound to skim coat the surface. Fills all the little voids and is easily sandable. Then you can prime and paint. We use auto paint because of the easily obtainable class a finish.

Renshape is a good material but it's very expensive.

One of the problems with large wood patterns is expansion and contraction due to humidity, so the glue joints have a tendancy to show if there is any change in the air. And you have the end grain vs long grain sealing to deal with.

As an additional suggestion consider MDF. I don't know if you call it MDF down under, it's that cheap brown board made from that appears to be cardboard. (not particle board) It has a pretty consistant grain structure. You can make thicker sections by gluing sheets together with aliphatic resin glue ( yellow carpenters glue). If you have a really large (and heavy) piece to make you can cut hollow layer sections on the router and glue them together and then remount on the router and finish to final shape.

By hollow layers I mean:
Take a 3d computer half model and slice it into "layers" the same thickness as your MDF ( here in the states 2" or 50 mm is the thickest ). If you look at the bottom one of these sections you will have a solid shape with the outside profile of your object. Add a suitable amount to the outside for remachining. 15 mm should be enough. Now draw a line, about 100 mm smaller than the outside of the next smaller layer, inside the new outside line. This gives you a hollow layer. You need to make the inside small enough to overlap the outside of the next layer. Do the same for the next smaller layer. After all the layers are cut stack them and glue into one shape that will have a stair step outside shape slightly larger than your finished model. Mount on CNC and cut to final shape. With MDF it's easy to sand off the scallops left from the toolpath.

I know this sounds slightly confusing but it's really easy once you get the technique down. Depending on the shape we usually put some alignment feature in the pieces. If there is a place, a hole that will fit an available wood dowel works well. Obviously all the dowel holes should not change spacing from layer to layer. Three or four dowels work well to align the pieces for assembly. Sometimes you can use the piece cut from the insides to make the smaller layers.

Hope this helps

[sco]

Thank you gents!
I don't think that I have ever experienced such helpfull and direct answers to a question. I hope that I may be able to return the favour some time.
Thanks again
cheers
sco

[flyboypete]

Hi There
I use MDF machine to shape and then paint with epoxy resin and then heat with a heat gun so the epoxysoaks in.
I then remachine about 0.2mm lower into the mdf/epoxy mix and use this as my plug. Takes paint well no fluff and easy to get a good surface.

Best regards
Peter Williams

[appicnc]

Hello SCO

I have been using blue foam to do what you are describing, here is a first trial cut on one I have just done, I used the densest ( heaviest ) foam ( from a Co. in Wetherill Park in Syd ) I had Carbi-Tool make up a solid carbide cutter that in a 1/2" Triton router will do a full depth ( 87mm ) cut at 6000mm per min', then .5mm stepover, I am not fiberglassing them ( cut for a friend ) but I think you would need to protect the foam if using polyester, the foam was in a 2.5m by .6m by .1m block, from memory I think it was < $90.00 for the block, if you are interested I'll check tomorrow.

Ed

[sco]

Thanks again.
I got myself some Jellutong...2.1 X 300 X 50. I am not sure of the price yet, but it will be just under the $100 mark.
I have some Dow hi-load 50 blue foam and some MDF that I might give a go to, thanks to those suggestions.
I will repot back after the first cut, to tell how it goes.
cheers
rosco