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variant22
6th Apr 2013, 07:28 PM
Today I spent some time building up a wood square box, making some green sand, and pouring some "machinist wax" (OK straight Paraffin - but I intend on using Machinist Wax). I can't find much information on people making wax casts using sand (except candles). My first attempt was a bit of a disaster, in that I ended up with a clump of waxy sand instead of the shape of my pattern. Any ideas on what I should use to stop the wax seeping into the sand?

PS: I hope this thread is moved after a few people have a chance to see it? The foundry can be a bit quiet..

ian
6th Apr 2013, 07:42 PM
Hi

are you trying to setup for a lost wax csast?
If so, I always understood that the idea was to carve/create/build the shape you want in wax, pack the wax in sand and then pour the melt into the mould.
The molten metal melts the wax and your cast ends up the same shape as the wax was, just a little smaller due to shrinkage

variant22
6th Apr 2013, 07:53 PM
What I am trying to do is make a wax copy of a rare 70's supercharger mount. The mount needs quite a few modifications and fitting to suit my application. I figured if I could make a sand mould of the part, cast it in machinist wax (harder than normal wax), then cut and machine to size. From there I would cast again to make a master pattern out of wax that I can then have cast in aluminium.

The issue is that the wax seeps into the sand and does not keep the shape of the pattern.

Michael G
6th Apr 2013, 09:35 PM
If you coat the mount with a film of vaseline or similar (as a release agent) you should be able to make a mould with plaster of paris which you could then pour wax into. I think the problem might be temperature difference - the wax is not chilling off quickly enough and so can seep into the voids between the sand grains. Whether putting your mould in the freezer for a while before pouring wax might help?:unsure:

Michael

ian
7th Apr 2013, 12:27 AM
What I am trying to do is make a wax copy of a rare 70's supercharger mount. The mount needs quite a few modifications and fitting to suit my application. I figured if I could make a sand mould of the part, cast it in machinist wax (harder than normal wax), then cut and machine to size. From there I would cast again to make a master pattern out of wax that I can then have cast in aluminium.

The issue is that the wax seeps into the sand and does not keep the shape of the pattern.
I agree with Michael

Make a female mould of the mount using plaster
then make the wax male mould using the plaster

The wax mould after machining can then be used to make the aluminium casting

the only caverat I have is if you go down this route the final part will be smaller than the original due to shrinkage

Of course, if you have access to a 3-D printer (try your local high school) you might be able to print the shape you need without bothering with moulds and wax and if the 3-D shape is inflated by the right percentage, after casting it will be the right size.

variant22
8th Apr 2013, 09:24 AM
Michael and Ian,

Thanks for your input. I tried plaster of paris yesterday and a liberal amount of vaseline on the mount. I let it set for a fair while (after the warm stage). It was firm to touch, so I removed the mount. I had the expected break-away and crumbling in areas. All in all it was a failure. It seems like the mount is too complicated to easily cast in plaster or sand. Even though I had vaseline everywhere, the mount was very hard to get out. I had to chip out some internal pockets of plaster from the mount even though underneath it was greasy with vaseline.

I guess the next step may well be looking at rubber moulds. Either that or I get my CNC setup and cut it from a solid piece of wax. It is probably more realistic however in the short term to investigate rubber and some of those "smooth on" products.

I think the mould will need to be 3 pieces. It has an extruded section that sticks out a good 80mm from the base to hold an alternator. All adds to the complexity of this part. I did read however that another fellow tried to make one and invested 15k of his own time and months of work to get it cast. So that makes me feel slightly better.

ian
8th Apr 2013, 06:54 PM
Michael and Ian,

Thanks for your input. I tried plaster of paris yesterday and a liberal amount of vaseline on the mount. I let it set for a fair while (after the warm stage). It was firm to touch, so I removed the mount. I had the expected break-away and crumbling in areas. All in all it was a failure. It seems like the mount is too complicated to easily cast in plaster or sand. Even though I had vaseline everywhere, the mount was very hard to get out. I had to chip out some internal pockets of plaster from the mount even though underneath it was greasy with vaseline.

I guess the next step may well be looking at rubber moulds. Either that or I get my CNC setup and cut it from a solid piece of wax. It is probably more realistic however in the short term to investigate rubber and some of those "smooth on" products.

I think the mould will need to be 3 pieces. It has an extruded section that sticks out a good 80mm from the base to hold an alternator. All adds to the complexity of this part. I did read however that another fellow tried to make one and invested 15k of his own time and months of work to get it cast. So that makes me feel slightly better.can you post a picture of the part you are trying to copy?

I fully expect that the plaster cast will need to be in 3, 4 or even 5 pieces
Not being critical, but what you are trying to do is sidestep the need to construct the wax "master" entirely from scratch. Nothing wrong with that, but it has limitations. Perhaps for the next try plug the cavities in the original before making the next cast. If the cavities only exist to reduce the weight of and material used for the mount, perhaps their absolute dimensions are not critical and they can be machined out later.

another technique to try is to cast the external mold in stages, with a separator like waxed paper placed between each stage.

as a woodworking project what you want to make doesn't sound too difficult to create from solid wood using drills, a few rasps, chisels and possibly a dremel
However, your picture could easily prove me wrong :)

variant22
8th Apr 2013, 10:31 PM
can you post a picture of the part you are trying to copy?

I fully expect that the plaster cast will need to be in 3, 4 or even 5 pieces
Not being critical, but what you are trying to do is sidestep the need to construct the wax "master" entirely from scratch. Nothing wrong with that, but it has limitations. Perhaps for the next try plug the cavities in the original before making the next cast. If the cavities only exist to reduce the weight of and material used for the mount, perhaps their absolute dimensions are not critical and they can be machined out later.

another technique to try is to cast the external mold in stages, with a separator like waxed paper placed between each stage.

as a woodworking project what you want to make doesn't sound too difficult to create from solid wood using drills, a few rasps, chisels and possibly a dremel
However, your picture could easily prove me wrong :)

Ian, you may well be right. I was thinking it would be a 3 part mould. I am sure a master craftsman/pattern maker could make this easily enough. That said, I really wanted to have a stab at it. I am however hitting a wall with the amount of time things take. I spent a few days on the sand casting and plaster. It was a bit of a frustrating exercise to see both fail. I know I could get the plaster better, but I am not sure I can get it good enough. Below are some photos of the mount (note one is in Plaster as taken on the weekend). Front, back and side view..

262086 262087 262088

PS: I plugged the holes before I did the plaster cast. The only exception is the back cavity as I wanted to keep the dimensions the same. In hindsight I should have done this separately from the main mould as the plaster got stuck, although it did not adhere to the vaseline.

variant22
9th Apr 2013, 12:01 AM
I should also make a note that I intend on cutting off the side piece covered in green masking tape. I won't cut the cast iron mount as these are rare. I will however cut it off the first wax cast.

ian
9th Apr 2013, 12:13 AM
For what it's worth, can I suggest you get some thin steel, aluminium plate or 3mm MDF to use as dividers for your next attempt at casting a plaster mould. Use a grinder and files to shape the dividers to match the shape of the part where it appears it will be easiest to separate pieces of the mold once the plaster has set. Drill each divider for at least two alignment rods. Coat both sides of each divider and the alignment rods with a release agent, vasilene appears to work on metal, I'm not sure if it is as effective on MDF.
Before the plaster sets, be sure to check that the alignment rods can be rotated in the hardening plaster. I'm not sure, but threaded rod may be better than plain rod for this application as it may be easier to remove once the plaster has set. Perhaps experiment first?
Once the plaster has set, you should be able to remove the alignment rods to separate the mould at the dividers freeing the original. Dividers placed strategicly around any cavity you wish to copy should allow a separate piece to be cast for the cavity -- straight sided cavities, or ones that are bigger inside than their throat may need to be copied using expanding foam and with a wedge of some sort

reinserting the alignment rods should allow you to accurately reassemble the mould to cast the wax master.

clear out
10th Apr 2013, 11:43 PM
There's a possibility that the original casting can be used as a pattern.
You could superglue some ply on the faces of any bosses to add machining and if these are offset out wards and then filled with bog it would make up for any contraction.Lino and sheet lead is also useful for enlarging curved areas to allow for shrinkage.
The main problem is the cavities and these may not be castable without resorting to cores. You may be able to modify the internal sides with bog or similar so they have draft.
When doing this always use generous fillets and keep the metal thickness as uniform as possible.
If this is not practical it's easy enough to add the prints and the core boxes would be a straightforward thing to make.
Only problem with this approach is that foundrys are notorious for losing or damaging rare original bits of kit.
If you plan to cast it yourself this doesn't come into it.
Where abouts are you? If in Sydney you'd be welcome to drop over and I could be a bit more specific.
H.

variant22
26th Apr 2013, 02:50 PM
Apologies, I missed the last couple of responses. I ended up going with some Smooth-on OOmOO 30 silicon molding compound. I have become a bit of an expert at using plasticine of all things! Trying to block off areas and making a mold half. I poured my first half and it appears to have gone well, except I have not removed it yet. I need a bit more OOmOO to make the next piece. It does not go far and it is very expensive stuff @ about $50 a liter once shipping is factored. I am going direct to the US to buy some more at around $25 per liter, which makes it somewhat more palatable.

Thanks for the offer to discuss in person clear out but unfortunately I am in a different state (Tas).

I will post back to this thread once I have laid my second piece. Hopefully it all goes well!

MWP
27th May 2013, 01:35 PM
Hi,

I had a similar problem when trying the lost wax process in green sand. The wax (candle wax) just melted into a sticky blob and the Aluminium pooled on the top of the sprue.
I'm thinking that the clay in the green sand combined with the wax and stopped the aluminium forming a cast.
Casts made from styrofoam work well in green sand.
Should I have be using clean, dry, fine sand with no clay additive for lost wax casting?

Michael G
27th May 2013, 06:38 PM
The lost wax process is slightly different from pouring onto Styrofoam, even though they are both called lost wax processes. With the Styrofoam, the metal is hot enough and the foam light enough that the foam melts/ burns out the way.
With traditional "lost wax" however, the wax is used to make a replica of what you are wanting to cast, then is coated with something like clay or plaster. When the coating is dried, the wax is melted away, so that there is a cavity the same shape as the wax master. In goes the metal and the result is a replica of the wax.
My knowledge of casting is scant, but pouring straight onto wax is very unlikely to work as an enormous amount of heat would be needed to burn away wax.

Michael

Peterwaker58
11th Aug 2014, 12:03 PM
The lost wax process is slightly different from pouring onto Styrofoam, even though they are both called lost wax processes. With the Styrofoam, the metal is hot enough and the foam light enough that the foam melts/ burns out the way.
With traditional "lost wax" however, the wax is used to make a replica of what you are wanting to cast, then is coated with something like clay or plaster. When the coating is dried, the wax is melted away, so that there is a cavity the same shape as the wax master. In goes the metal and the result is a replica of the wax.
My knowledge of casting is scant, but pouring straight onto wax is very unlikely to work as an enormous amount of heat would be needed to burn away wax.

Michael
Hello
You can also machine casting sand ready to cast into Here is a robot doing that https://www.youtube.com/watch?v=sjMNKYAYdFE
Peter

Ueee
14th Aug 2014, 11:42 AM
How have you gone with this?

I am casting some polyurethane rubber at the moment, it is suitable for everything from mold making to floor mats, depending on the hardness.
Ew

variant22
15th Aug 2014, 10:24 PM
How have you gone with this?

I am casting some polyurethane rubber at the moment, it is suitable for everything from mold making to floor mats, depending on the hardness.
Ew
Ew, I ended up getting a bit further than the thread detailed. I poured molds, mixed wax and plastic, cast wax and did a bunch of fettling. I ended up getting stopped dead in my tracks due to three reasons. The first being that the Smooth On "OOmOO" was rediculiously expensive ($50 per liter). If I recall correctly, I needed 8 liters to do the mold pictured below. That was just to make a mold to copy the original. I made this mold as a 3 piece mold. Somewhat impressive, and fortunately it came out usable. The next issue that I had after taking a serious whack to the back pocket, was that the wax was developing porosity/air bubbles/voids when I was casting it. Sometimes parts of the mold would have air bubbles removing important features. I ended up shaking it, drilling holes, changing the wax/plastic composition and I could not nail it. I think I needed to do vacuum casting. So stuff started getting complicated and I hardly wanted to fork out another $400...

The third and final reason was that I got very lucky (rare!) and happened upon a supercharger from one of these (http://youtu.be/mXgWWNJVdYA?t=11m10s).. Which meant that the mount needed further modifications. In the end I decided to stop stuffing around and get on with my CNC. As it stands today I am one piece (rather trivial bit) away from having all the mounts done for my RF45 CNC. All the hard work is done, ballscrews are purchased, power supply and NEMA34 Servos are here from the US, and the mounts all bar one piece of AL are done. The CNC will be used to cut the template. Possibly out of wax...

322300 322301 322302 322303 322305 322309

Ueee
15th Aug 2014, 11:01 PM
The high grade polyurethane cold castable i am using is about $26+gst a kilo. There is a lower grade that is cheaper. The killer for me is the bonding agent, it is over $100 a liter.

Ew

variant22
15th Aug 2014, 11:30 PM
The high grade polyurethane cold castable i am using is about $26+gst a kilo. There is a lower grade that is cheaper. The killer for me is the bonding agent, it is over $100 a liter.

Ew
The only alternative I know is buying direct from China. I made some inquiries and It was really cheap. Unfortunately the volumes required would only work if there was a group that needed it. It really surprised me how much I needed to do the mount mold. I thought I could do it with 4 liters, but turned out that I needed 8. It was really good stuff to work with though. For small parts it would be pretty darn good. Especially plastic parts that can be poured straight in. I can see how it is really useful for plastic trim parts in cars etc. The result with wax on my large part was hit and miss due to the fact it kept developing air bubbles. It did not matter if I relieved the section with a hole, just migrated the problem elsewhere. I tried different pouring positions in the mold, high, low etc. Different wax temperatures. Different wax/plastic mixes. No matter what I tried I could not get it consistent. I reckon the way is to do it under vacuum.

How much bonding agent do you need per kilo of PU?

Ueee
15th Aug 2014, 11:59 PM
How much bonding agent do you need per kilo of PU?

Bonding agent is for sticking it to another surface, not to be mixed in, so it depends on the application at to how much. I reckon i'm going to go through 50+ kg of poly before i even start to look like using up the bonding agent.

Ew