Mold grade material

[performancenut]

I will be doing some low volume vacuum molds using ABS or polystyrene (1-2mm). The molds I am creating range in depth from just over 2" all the way up to 6". The pieces have intricate details.

MDF was recommended; however, I'm concerned that the vacuum mold process will pick up on the individual layers of MDF and create "lines". I looked at other solutions for alternate solutions (Tooling boards (http://curbellplastics.com/prototyping-tooling/tooling-boards.html) and RenShape boards).

Are there other solutions out there? I expect the tooling boards and RenShape boards to be quite expensive when compared to the MDF. Since this will be low volume, I'm wondering if there is a less expensive material I can use that holds good detail and goes up to 6" in thickness. My pieces vary in size up to 24" long and 36" wide.

I appreciate any help. Thanks.

[steve_g]

Denis...
There's MDF and then there's MDF! If you are buying from a big box store you're just getting lightly compacted hay... Try to see if you can find a supplier of "Plumb Creek" , Medex or better yet Extira!

SG

[harold_weber]

Freemansupply dot com

Their web site will show you what folks use.

I tried using mahogany, but it was wearing at around 75 parts, so it will depend upon how "low" your "low volume" is. :)

[performancenut]

Thanks guys. Freeman supply has 2" and 4" MDF; however, shipping costs almost 5x of the product cost. I have been calling local distributors all day but the thickest pieces they have is 1". I have also been looking for foam that can be milled as well.

As far as volume goes, less than 10. I revisited my shapes and have been able to redesign with a shorter Z distance but it is still more than 1" in quite a few places.

I read an article where someone "laminated" MDF sheets my sanding one side of each piece and using wood glue. This method was able to stand up to the milling process. Anyone every do this, can't always trust the internet :-P

[knight_toolworks]

You need a vacuum bag to glue mdf face to face. it works great and pretty much makes one piece. without that you won't really get a good glue joint on it.

[harold_weber]

The thickest MDF I've found within 100 miles is also 1 inch. I made a couple of model airplane fuselage molds for some serious competition free flight modelers, and I laminated two pieces of the 1 inch MDF using West System Epoxy. I did no sanding on the MDF faces, the epoxy penetrated fine.

Like Knight_toolworks, I used a vacuum bag. I'm able to pull around 20 inches of mercury vacuum.

There are different densities of MDF and I was using the "lightweight" density.

Both customers were happy with the molds.

[steve_g]

Denis...
One reason I suggested Plum Creek, Medex and Exteria was because you stated that your molds have "intricate details". I'm not aware of any "lightweight" MDF that will hold details... I've laminated MDF for small short run vacuum forming molds using lots of paint cans, bricks and whatever else I had to hold them down... I did have to use bondo in a few places however.

SG

[performancenut]

Thanks guys, I do appreciate all the feedback. The shipping for any sort of wood long distance is cost prohibitive, so I will have to use local materials to make this work.

The thickest MDF around these parts is 1". Unfortunately, I don't have anything that can draw anywhere close to 20" Hg. The best I can do is using those space saver bags and my house vacuum.

I did find something interesting though. Foamular insulation (http://foamular.com/foam/products/foamular-400.aspx) by Owens Corning. They have it in 15lb, 25lb, 40lb, 60lb, and 100lb densities. I'm thinking the 40lb would be good but is very difficult to find in these parts. I could probably get 25lb from Home Depot but I'm unsure if it is stiff enough.

At this point I may have to sacrifice some detail and make due with what I have. BTW, thanks for the input guys, it is awesome.

[steve_g]

Denis...
You had me excited! however the numbers you gave as densities are its weight bearing capacity. The 40lb material has a density of 1.8 lbs per cubic foot...Not likely to be suitable.

SG

[billp]

Have you considered anything that you MAKE yourself? You could probably try things such as Winterstone, or even plaster of Paris. There are numerous powdery mixes that would give you a dense piece when hardened. Just pour your block, and carve it !

[performancenut]

Denis...
You had me excited! however the numbers you gave as densities are its weight bearing capacity. The 40lb material has a density of 1.8 lbs per cubic foot...Not likely to be suitable.

SG

I saw that too but so far this is the best thing I have found. The 40lb weight bearing may be sufficient to hold form under the vacuum mold were my thoughts. Whether that is true or not, I'm not certain. If I can find somewhere that will sell me a single sheet, I'm out $20 if it doesn't work.

[performancenut]

Have you considered anything that you MAKE yourself? You could probably try things such as Winterstone, or even plaster of Paris. There are numerous powdery mixes that would give you a dense piece when hardened. Just pour your block, and carve it !

You give me way too much credit. Machine is way more talented than I am.:D

[Sk8MFG]

I will be doing some low volume vacuum molds using ABS or polystyrene (1-2mm). ~

MDF was recommended; however, I'm concerned that the vacuum mold process will pick up on the individual layers of MDF and create "lines". ~

Are there other solutions out there?

*edit, Denis already pointed this out. Consider this post confirmation. Very common method in the indie skateboard builder world.

Finally, a topic in which I can contribute.

Best solution for low volume one sided vacuum moulds, Foamular (Dow pink/blue etc) rigid insulation.

Comes in many densities, grab one of the higher ratings. Vacuum bags are pretty low pressure, theoretical maximum is only 1atm (barring autoclave). I've used common junk MDF to a large extent in my big production presses, only had compression issues with very drastic bends. Depending on material the layer lines may transfer, but using a thin piece of rubber will eliminate that (shower liner). An example, my 1/16" maple layups do not transfer layer lines when vacuum bagged, not near enough pressure. Don't get transfer till I get into my 15+ ton presses.

Even the run of the mill extruded polystyrene from home depot and others works well for very low production or one off. After a half dozen pressings, there will be some compression especially if you're dealing with sharp bends and a stiff material (wood). I'm sure there are other brands of extruded poly which may fit your needs.

[performancenut]

*edit, Denis already pointed this out. Consider this post confirmation. Very common method in the indie skateboard builder world.

Finally, a topic in which I can contribute.

Best solution for low volume one sided vacuum moulds, Foamular (Dow pink/blue etc) rigid insulation.

Comes in many densities, grab one of the higher ratings. Vacuum bags are pretty low pressure, theoretical maximum is only 1atm (barring autoclave). I've used common junk MDF to a large extent in my big production presses, only had compression issues with very drastic bends. Depending on material the layer lines may transfer, but using a thin piece of rubber will eliminate that (shower liner). An example, my 1/16" maple layups do not transfer layer lines when vacuum bagged, not near enough pressure. Don't get transfer till I get into my 15+ ton presses.

Even the run of the mill extruded polystyrene from home depot and others works well for very low production or one off. After a half dozen pressings, there will be some compression especially if you're dealing with sharp bends and a stiff material (wood). I'm sure there are other brands of extruded poly which may fit your needs.

Alright! Someone has used the foamular insulation after all. Unfortunately, foamular 150 is the only insulation they stock out here. In a previous post, I was leaning toward Foamular 400 to make a mold from. Do you remember which version of Foamular you used?

[Brady Watson]

You will have good success with regular MDF (premium Plum Creek brand preferred, but not absolute) and several coats of epoxy, like the kind you'd use to laminate woven fiberglass cloth.

If you really want a nice plasticized surface, I would recommend Duratec. It is downright awesome for thermoforming and fiberglass molds: http://www.duratec1.com/Application_Guides/ag3.pdf

-B

[Sk8MFG]

Alright! Someone has used the foamular insulation after all. Unfortunately, foamular 150 is the only insulation they stock out here. In a previous post, I was leaning toward Foamular 400 to make a mold from. Do you remember which version of Foamular you used?

I believe it is the C200 (20psi), honestly never bothered to check as any flavor of XPS has worked for me. Plus, since I got my bot I no longer hand carve molds. Foam sure is easy to work with.

If you are looking for a semi permanent option, Fomular 1000 has a compressive rating of 100psi!! No idea on prices of the heavier duty stuff, would love to hear what you find if you happen to price some sheets.

The data sheet for the 150 shows a compressive strength of 15psi. Theoretically, a flat sheet wouldn't compress under a vacuum (14.7psi at sea level) any pressure points may crush a bit. Depending on how close to spec the parts need to be, may work.

Related:
Take a look at these guys, Roarockit (http://www.roarockit.com/index.php). Located out of Toronto, work with them regularly, developing skateboard manufacturing techniques and technology.

Their main business is vacuum bags, foam molds and 1/16" hard maple. Can't say enough good things about these guys, really give back to the skateboard community. Plus his products are top notch, squeezed more than 100 boards out of one of his bags. And I did not treat it well.

Ted (owner), has put together a number of tutorials regarding vacuum bagging woodwork, skateboards and otherwise. Who knows, may find it
interesting.
Roarockit - Ministry of Wood tutorials (http://ministryofwood.com/764-2/)

[performancenut]

I'll have to check them out and see if I can learn something, thank you!

BTW, do you remember any of your settings (feed rate, spindle speed, etc) when you were using the insulation? I found someone who will sell me a couple of sheets of Dow highload 60 and I'm new to ShopBot (may be a topic for another section of the forum).

[khaos]

I cut foam 10,000rpm and 4-5 inches a second without any issues. I have used tapered 0.125", 0.25", 0.5, and 1.5" bits with great success. I do a rough cut though many here do not. :eek: I have less production pressures than some.

I cut the pink and blue 3" foam from the Home Desperate. You should test from 3" a second with a conservative pass depth.

hth

[performancenut]

I cut foam 10,000rpm and 4-5 inches a second without any issues. I have used tapered 0.125", 0.25", 0.5, and 1.5" bits with great success. I do a rough cut though many here do not. :eek: I have less production pressures than some.

I cut the pink and blue 3" foam from the Home Desperate. You should test from 3" a second with a conservative pass depth.

hth

Tapered probably won't work for me since I have vertical portions on my molds. What size taper are you using?

At 3in/sec, is that your roughing pass or your finishing pass? Roughing pass seems definitely doable, finishing pass I'd be afraid it would miss details. And what do you consider "conservative" pass depth? 0.25", 0.5"?

[khaos]

Tapered probably won't work for me since I have vertical portions on my molds. What size taper are you using?

At 3in/sec, is that your roughing pass or your finishing pass? Roughing pass seems definitely doable, finishing pass I'd be afraid it would miss details. And what do you consider "conservative" pass depth? 0.25", 0.5"?

Sorry about that. I use a tapered 0.125 the others are end mills, radiused end mills and cove cutters.

I cut 3 to 4" a second for the finish cut. In most foam I take .5" off for rough and .25" off for finish. The only caveat being if I am using dense foam like #12 or greater precision board, which is heaven, I take .2 off in the rough and between 0.1 and 0.15 for the finish.

Remember that the ramping speeds handled by the shopbot control software take over your cut speed is the optimal cut speed for your part. Tight turns and changes in direction are preceded by decelerations defined.

Quote from Brady hits the nail squarely:
She'll go as fast as she'll let you go...Every relief is different & tweaking ramps will let you gain some speed, but not gobs more.

Three areas are going to influence your 3D cutting more than anything else:

1. Slow Corner Speed; simply explained, the percentage of your move speed that sets how fast it will go around a corner, in XY OR YZ OR XZ (and XYZ) - so if your SCS is at 30, it will slowly climb over details. Jack it back up to the stock 65 setting, unless you are getting rough movement or 'banging' - think of SCS as a cushion. The higher it is, the harder it is.

2. 3D Ramp Rate, this reduces the sensitivity of ramping in the Z axis. Stock is 100, I like 150 for most things, up to 300 is useful, more than this is a diminishing return. If Z bangs, pull it back.

3. Often overlooked, one of the most important things is machining at a 'good speed'. The XY to Z speed ratio is important, so go check out the speeds I posted in the article and try running at one of those. On that relief, it isn't that detailed, so you should be able to run maybe 3,2 or 3,3. I don't like running the Z faster than 3 because it will result in a poor finish...it is asking an awful lot from the Z motor to move that fast while lifting a 20-35 pound gyroscope. Running at the speeds I recommended will make tuning the other 2 settings easier.

-B [Brady Watson]

The link to article is here (http://www.shopbotblog.com/index.php/2008/03/a-ramping-the-vr-command-and-how-to-tune-your-tool-for-maximum-performance/).

I hope this helps.

[Sk8MFG]

BTW, do you remember any of your settings (feed rate, spindle speed, etc) when you were using the insulation? I found someone who will sell me a couple of sheets of Dow highload 60 and I'm new to ShopBot (may be a topic for another section of the forum).


Hmmm, don't recall exactly.. but fast
I use 1/2" ball nose for roughing and finishing. Roughing was at 10 or 11 ips at .5" depth. Finish I believe was 8 ips with a 15% step. A bit of sanding and the mill marks are gone.

But, every job is different. My molds are typically long smooth curves, really lets me crank up the speed.

[RichardG]

Renshape 460 is exactly what your looking for