Wow! Homemade 'machinable wax' is a dream!

[lloydsp]

Wow!  This new DIY 'machinable wax' cuts like a dream - dry!  I've cut about five pounds out of this block, and only lost about six ounces to errant chips.

It doesn't clog the bits, either.  It does 'fill' the flutes, but with a fluff that's as soft as a new-fallen snow, and it flings itself out at about 1000 rpm in little ribbons to be vacuumed-up.  I built a special 'wax catcher' for my shop-vac, and have caught just about all the chips.

I got the whole master mold machined today.

The mixture is (by weight) 3 parts refined paraffin and 1 part 3M 3764B hot-melt adhesive granules.  It takes a while to blend, and this mold master took over 25lb to cast, so it was a BIG pot of stuff! (It all has to be done in one melt, and one pour...)

Lloyd

[tau]

Lloyd,

thx for sharing your recipe!

Not sure if will ever be in need to use this type of prototyping material (i do mainly wood or plastic as my main materials to process), but sure is useful if i ever need it.

At least your recipe is way mor afforadble than an original machinable wax! 

[pixelmaker]

Hello
especially 3M™ Scotch-Weld™ 3764 is a very expensive component. At 45€ per kg, the milling wax is quite expensive.
The Scotch-Weld™ 3764 has a softening point of 88°C and a temperature resistance of 55°C (according to the data sheet). The material should not even be left in the sun and such a mold should not be left in the car even in summer.

I use paraffin and 30% melting point booster based on polyethylene. This gives me a temperature resistance of 100°C. A kg of it costs only 15€. The 25 lbs / 11 kg cost me 8.22€ / kg for my mixture.
My mixture can be milled at high speed as it cannot melt. It can be polished to a high gloss with hot air. I like to color the milling wax blue.

[lloydsp]

The adhesive is LESS than half that price here.

I deliberately chose the lower melting temperature for purposes of 1) safety in casting such a large master, and 2) lesser cooling time.  Such a large block must be cooled slowly in order to prevent cracking due to shrinkage.  Even at its lower melting point, it took 36 hours to cool enough to demould the raw block without damaging it.

It will never be transported outside my air-conditioned workshop, so the 'hot car' comment was just snide and non-sequitur.

If I desire a higher melting point, the 3764 A offers that with increased polyethylene content, or I can add PE pellets, which I have.

Lloyd

[pixelmaker]

I realize that large blocks have to be cooled down for hours. I have an oven with time and temperature control. I can cool slowly to the temperature where it solidifies and then cool faster and faster.
Using a wax with a lower hardening temperature greatly increases the cooling times.
If I start from 130°C, where the wax and all the ingredients are liquid and the wax solidifies at 100°C, I need much less time.
From 60°C there is no more shrinkage in my mixture and there are no more cracks.
With the temperature control in the oven, I no longer need to worry about the correct cooling times.

ralf

[lloydsp]

Ralf,
Because I seldom need large blocks of wax, I took a different tack.  I built (inexpensively) an insulated box that closely shrouds my casting form with a thick layer of mineral wool all-round.  The insulation actually is in contact with the form, not just 'around' it, and several inches thick.  I also made a PVC 'box' lid for the form, similarly insulated.  But with all that, the pan is removable (which is why I didn't use 'foam' insulation).

I place the casting form in the insulated box and pour it in-situ, then just cover it, and abandon it for a day and a half.  No timing, no temperature measurements.  It cools so slowly that the shrinkage issues are mitigated without any external controls.

If I ever require these more-often, the oven sounds like a good idea.

Lloyd

[Bob La Londe]

I've got a box of commercial machinable wax on the shelf.  I thought I might use it to make negatives for making rubber stamps, but I've actually only made one rubber stamp and I machined the negative is a scrap of aluminum. 

My thought was if I did bunch of rubber stamps I could remelt and reuse 99% of the wax each time.

Years ago I did security work (alarm, video, barriers) for a jeweler who CNC machined wax for jewelry casting blanks.  He had a tiny little desktop machine that cost as much as a small VMC with a 60,000 RPM spindle.  To this day I don't think I've used any cutters as small as he was running on that thing for detail work. 

Oh, gotta go.  My RG-45 just arrived. 

[pixelmaker]

I cast blocks of 300 x 500 x 50 mm from the wax.
The wax block gets a hollow of approx. 5 mm, which I get rid of by milling it flat.
I pour PMMA into the milled molds. Without an oven, these flat blocks have become extremely warped.
As only small runs are produced here, it is not worth making silicone molds.

[lloydsp]

This one I'm doing is roughly the same dimensions horizontally, but about 115mm deep.  I get around 12mm of 'dish' in the middle which, like you, I mill flat.

In my insulated cooling box, they do not warp.

I just ran my first silicone casting last night from about 2.3Kg of that very expensive resin.  It turned out nice.  The tiny 1.4mm 'air port' I drilled (and plugged) in the bottom-most feature of the mold allowed me to eject the casting with air pressure.  It was a little bit scary, watching it 'balloon' as it did, but it came free without damage to it or the mold.

I have another 2.3Kg mixed and degassing, right now, to pour in about 20 minutes.

Lloyd

[pixelmaker]

about 2.3Kg of that very expensive resin.

You mill a part out of wax, make a silicone mold out of it and then pour a resin into this silicone mold?
Photo please

[lloydsp]

Here's the first 'pull' from that wax master.  I've already done two, and the third pour is curing now.  It looks like the master will survive several more uses.  So far it shows no damage, distortion, or surface imperfections.

The 'resin' we pour in those is a modified hot-melt / wax blend used for coating pyrotechnic items for both physical containment (to improve explosion force), and moisture protection from our high humidity.  It has to be poured at about 300F, which is why I chose silicone for the molds; that, and the easy demolding silicone offers.

They form small, individual blocks of about 125g each, for feeding a continuous-melt dipping process.  The dipping station has a 'melt pot', and a 'dipping pot', with the dipping pot situated about 30mm higher than the melt pot, and with an overflow drain back to the melt pot.  The melt pot has an 'air lift pump' (similar to an aquarium air-lift) that moves hot wax from the melt pot to the dipping pot.  It then drains back, to keep the level constant in the dipping pot.

Then by use of holding jigs, groups of the pyrotechnic items may be dipped to a constant depth, without any skill on the part of the operator.

L