The Hobbyist's Machine Shop – Blog

"One Perfect Part at a Time"

Machining in the 4th Dimension

The fourth dimension is often mentioned in science fiction as a dimension beyond the human senses. Today, real scientists (if there are such people) claim the fourth dimension does exist. But there are IMHO plenty of pseudoscience, especially promoted as video “entertainment.”  Material for a future rant…

In machining there really IS a fourth dimension. Usually called the 4thaxis. The Hobbyist Machine Shop (THMS) has a fourth axis for use on the Taig micro mill. It’s been on both the mill used for metal machining as well as the wax milling machine. Currently it is on the Taig micro-mill used for wax carving

THMS has (owns) four software CAM software packages that can create g-code for the 4thaxis machining. I’ll list them but will not (here) get into the fine details of using them.

Two types of 4thaxis operations are most common.

First is indexing. The material to be machined is held in the 4thaxis rotational device. Standard X, Y, Z three axis machining is performed on the surface facing the Z axis. 3 axis machining is paused, and Z axis is raised to clear all dimensions of the material. The 4thaxis rotates (indexes) the material to another face. This can be 180, or 90, or 45, or any equal or non-equal rotation. Then 3 axis machining operation resumes on the new surface plain presented. Repeat as necessary.

The second process (A axis rotation) requires setting Z axis Y position perpendicular to the center rotational axis and A axis assumes the movements of the Y motion vectors by rotating. Where A axis was stationary in the first method, the actual Y axis is stationary in the second.… Continue reading

Fanning the Coals

It’s no secret one of my lusts is machining in metal and wax. Actually, machining any material is fine with me. Wax became my favored material because it machines so well, especially with very small tool bits. Primarily, jewelry CNC carving for lost wax casting (LWC).

But I have also machined wax for LWC casting in brass, and that also works very well. I am not involved with casting large objects. At least not yet. But I don’t have an interest in doing large scale sand mold type casting. That’s a whole ‘nother sideline.

My light weight Taig equipment is perfect for machining wax. Taig tools also do an admirable job on small metal cutting as well. I have milled everything from stainless steel to cast iron. I have had no problems with brass, at least the types I have machined. Like most metals, there are many alloys. I choose the easy to machine.

I recently viewed a railroading model project (a hand-car)* made by an old friend Ed Hume. It got me re-considering my old lust for live steam engines and locomotives. They are machined directly from metal. That fanned the embers again and created a bit of remorse that my metal shop hasn’t been productive as was intended, except for the LWC silver work.

*Don’t know how long this link will last.

I designed my shop and machine equipment size specifically to create model train and model engine components. Not (what I consider) full size, or real life-size components. The term often used is “Model-Engineering” workshop.  

I recently dusted off one of the machines, the Proxxon PD400 mini-lathe and turned down some leaded steel stock into a mandrel and cap for my wax carving. That effort really felt good, experiencing those perfect cuts and… Continue reading

Ring Carved on 4th Axis

Everything came together for the first real use of the forth axis mandrel for ring carving. It’s nice when the plan comes together and everything works as intended. There was of course far more than just making the mandrel. There is the CAD design stage and the CAM (Desk Proto) for generating the G-code for the 4th axis. Then running the G-code on the micro-mill. I use LinuxCNC and I had to write my own metric post processor for Desk Proto. Not all that hard, actually. I made a USC (inch) version too. One tiny code change.

The first picture is the carved ring blank on the mandrel. I can accommodate a wide range of wax sizes. There will be much more experimentation and determination of the correct wax width for a project. This example worked fine.

The second photo is after the wax master model was hand finished and at this point is ready for casting. Sprue’s were added the ring put into a flask and the investment added. This post is not about the lost wax process. However, I thought it was interesting to show the wax carving and the final result the mandrel helps create.

The last picture is the finished Sterling silver ring shown on my hand (size 11). It really looks great. I will be doing a lot more wax carving on the 4th axis of the Taig micro-mill.

Wax Carving Mandrel

Wax Carving Mandrel

Plastic prototype and machined steel wax carving mandrels.

This is the finished mandrel turned from 12L14 steel as well as the prototype that was 3D printed. The steel mandrel will hold the green wax (in the photo) that will be machined into a ring on the rotary 4th axis of the Taig CNC micro mill. A 1/4-20 thumb screw will be fitted into the end for drawing down the cap, acting as a clamp for the wax.

The wax is purchased in a tube with the center hole existing. The wax will be sliced in widths greater than the ring design I will be milling. Then the hole will be manually (by hand) increased to the proper ring size after carving.

That’s the plan. It should work well for thin rings that don’t need side machining detail. Such as wedding bands or rings with engraved designs just on the top surface.

I am now contemplating wax holder designs for other styles of rings, pendants, and charms. Perhaps small LWC figurines. I can utilize the 4th axis on the mill for indexed flip rotation as well as continuous 360 degree rotation.

View of cap

Steel end cap bored out

DeskProto stopped producing their 123WaxRing system. So I may borrow some ideas from that process. Seems the problem may have been the special wax shapes required were expensive to produce in low volume. I will design around standard available wax shapes, or as I do now, utilize slices off larger stock (bulk) wax. I have already been doing that for years using Freemen Waxes.

DeskProto for 4th Axis

Using 4 axis milling, requires a CAM software system to create the necessary CNC G-code. It’s not something one can easily hand code when doing 3D designs. Simple level surfacing could be hand-coded on a 4thaxis, but probably lathe turning would be far easier.

Aspire, a three-dimensional CAD/CAM produced by Vectric can produce G-code for the 4thaxis. It is one of my go-to programs. However, I don’t design everything in Aspire CAD. Fusion 360 and RhinoCAD are also programs I use for design.

Both these programs have 4 axis CAM built in. Fusion 360 has a built in CAM, and with Rhino5 I have a plugin RhinoCAM 2012 w/4axis.  In Fusion the 4thaxis CAM is 2.5D and cannot produce 3-dimensional 4thaxis G-code. I added 4thaxis 3D CAM to RhinoCAM 2012 but find it extremely difficult to produce quality cut pathing. It seems to contain some very strange algorithms producing highly fragmented pathing.

This has led me to another 3rdparty CAM software (from the Netherlands) called DeskProto. It can take input (in the proper format) from any CAD software. (I won’t be getting into describing the process here.)

DeskProto’s claim is that it is CAM software for creative people and not the die-hard machinist. I find agreement to that statement. I find details missing with some lack of particular seldom-needed features perhaps needed by a high powered VMC machinist. For the rest of us common users, making things (on up to 5 axis milling systems), DeskProto gets the job done without micro-managing every single minor detail.

Having made that (limiting) statement, there remains plenty of useful variables that will insure getting the results a user like myself desires.

I will admit I put off choosing this program,… Continue reading

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