Nomad 883 Pro for Mold-Making?


(Greg) #1

I’m looking to make some of my own molds for casting buckshot and shotgun slugs from lead. Generally these molds are made from brass or aluminum (either of which is acceptable to me) however I’m curious if anyone here has ever used the Nomad 883 Pro to do this or for similar mold-making efforts?

On a somewhat-unrelated note, can anyone walk me through how the the 883 Pro is configured to know the dimensions of the stock placed on it? I have read all the tutorials I could find, and while most mention zeroing the Z position as well as the tool height measurement, I haven’t seen any yet that mention how you tell the machine the dimensions of the work surface in terms of X and Y.

I’m chomping at the bit to buy my 883 Pro and get started but want to make sure I know everything I need to before taking the plunge on it.

Any help/advice/experiences would be appreciated.


#2

The stock size is something you specify when you generate the G-code in your CAM package (Fusion360, Inventor/HSM, Carbide Create, MeshCAM, etc)

Summary of the workflow:

When you set up to generate the G-code, you specify the stock size, position of the part in the stock, and where the origin should be set.

When you mount the stock in the machine, you position it wherever it needs to be (based on how you are mounting it and access. For example, you may be mounting the stock in a vise that is in a fixed position on the machine bed), with the orientation as specified when you produced the G-gode.

You then zero the machine so the machine zero matches the appropriate point on the stock, wherever that point is.

I try to specify Z=0 at the top of the stock, and have my Y=0 at the front so I can see it during setup. X=0 is usually one end or the other, unless I have a good reason to put it in the middle. There are a few fixtures I use where I can zero on the fixture before mounting stock, so the origin is set to a point on the fixture, instead. I need to account for that when generating the G-code.


(MachineHeadLabs) #3

This is more detail than what you asked for, so excuse me, but if you start with something like this:

you could do away with having to square the stock or add alignment pins.
You could then model up your part, add cylindrical gates and spew, and place that model inside a geometry matching the dimensions of the total of both mold blanks. Then, using a shell or Boolean operation (s) in your CAD/CAM software, you create the negative cavity and split the mold in two, leaving you with two perfectly fitting mold halves. You may even be able to get a CAD file from the vendor which would make it very easy to begin. Another option would be to make a “positive” from which a silicone mold is then made. This would be preferred if there are any undercuts that would prevent the part from being released from mold.
Jerry


(Greg) #4

Thanks for the explanation, this helps a lot. I did a fair bit of machining in my younger years but very little CNC so I appreciate the information. That’s interesting about zeroing from the fixture vs the stock; I was actually wondering if that was something that could be done with the vice you can buy from Carbide3D and that maybe it was already programmed into the system. Very cool.


(Greg) #5

I was planning to purchase pre-fabricated aluminum/brass blocks from a local metal shop here but I see what you mean about the blank molds. For alignment pins I was toying with the idea of actually building them into the shape of the surface of the mold itself (male one side, female opposing) to avoid having to press in any steel pins. I’ve seen it done with some brass molds before but they were circular vs rectangular.

That’s a very interesting idea about creating the negative cavity and splitting it; I had been planning to build one ‘half’ and just mill out two of them but actually modeling the bullet or roundball and splitting it would probably work much better.

I doubt silicon would work for me just because I’m working with molten lead as a casting material but who knows. Things have advanced so much in terms of materials.

Thanks for the great info and advice.


(MachineHeadLabs) #6

Your welcome. Building alignment pins into mold blanks is common practice, but relys on accurate fixturing. Same concept actually. Steel pins are used because they wear better being hardened as opposed to aluminum and are replaceable. It may not matter depending on how many runs you are aiming for (no pun intended.) Modern industrial silicone will withstand molten lead, but may stretch over time.
Jerry


(MachineHeadLabs) #7

I don’t remember who, but a member here modeled up the Carbide3D vise in Fusion360. If using that software, it “knows” to avoid crashing the spindle into the vise on retracts and rapid moves. I’m not sure how other CAM programs handle this. I would ALWAYS run a simulation first. Another thing to be aware of is that even with using the low profile vise you lose about 1/2" or so of Z on the Nomad that needs to be accounted for. It’s not a problem for most mold blanks though.
Jerry