[xj5373]

Hi,
Relatively new to Bobcad and new to this forum. I am working on patterns for lost wax casting and have moved into 3d machining on my Denford Easimill with Mach 3 with the aid of Bobcad V24.
I hope I have attached a zipped version of the Bobcad file which is one half of a pattern for a steering arm - this part of the pattern is essentially a cavity 1/2 steering arm shaped.
The steering arm was modelled in Solid Edge then imported into Bobcad and then a Boolean subtraction from the stock gives the pattern 3d model.
I have made a start with a couple of 2d pockets for the two circular bosses but what would you suggest for the arm itslef. I have defined one boundary where the shape is essentially 2 1/2d (in the area of the two pockets) - then I have a second boundary for the 3d shape proper. I have overlapped the boundaries to get a good transition between the two areas which I anticipate using different strategies for.
Anyone like to suggest some tool choices and strategy choices?
Thanks
Ian

[xj5373]

Plodding on with this I have programmed a 5/16 plain slot drill to mill the round pockets as simple 2d pocketing operations - the same cutter then mills the full depth of the 2d element of the part with another 2d pocket (toolpath boundary by extracting edges from the part geometry), then a further 2d pocket mills in the shallower rib. I then go in with a .125 diameter ball nose mill and create the radius using a Z level finishing program running just over the depth of he radius by specifying top and bottom of job. This gets the 2d bit sorted reasonably efficiently I think. It certainly looks good in Predator.
Thinking now about the 3d element I am thinking advanced roughing with a 5/16 ball nose mill? Not sure about the finishing paths after this though.
Ian

[xj5373]

As I am typing this I realise that the 2 pocketing operations after the round pockets should be the other way around to avoid milling fresh air - the bigger shallow pocket first then the deeper rib up the middle.
Ian

[winaa]

I would try advanced rough for the whole job with a large flat bottomed end mill, then perhaps andother advanced rough with rest roughing enabled and a smaller ball nose to machine the fillets. After that you could use flatland's to finish the flat sections with a flat endmill. Then use Equidistant offset to finish. You may have trouble getting sharp corners in the 3D arc opposite your 2d section you could try using pencil mill and as small a ballnose as you can but that will still leave a fillet in the corners.

[xj5373]

Thanks for this,

Can I check out how rest roughing works. Am I right in thinking that following a roughing operation with a bigger cutter, selecting rest roughing causes the program to look only for material that a smaller cutter would be able to get to? Could you run a further rest roughing cut with an even smaler tool?

I had used flatlands on a previous job and must admit that I had some problems. Is it right that selecting the complete geometry it will find all the flat (constant Z) areas without setting boundaries?

Ian

[winaa]

Thanks for this,

Can I check out how rest roughing works. Am I right in thinking that following a roughing operation with a bigger cutter, selecting rest roughing causes the program to look only for material that a smaller cutter would be able to get to? Could you run a further rest roughing cut with an even smaler tool?

I had used flatlands on a previous job and must admit that I had some problems. Is it right that selecting the complete geometry it will find all the flat (constant Z) areas without setting boundaries?

Ian

Rest roughing work the other way around start with a big cutter then do another cycle with advanced rough and a smaller cutter and tick rest roughing bobcad will ask the size of the previous cutter and only machine the place the large cutter could not get to, it can be a real time saver.

For flatlands just select your entire geometery then use boundary's to control where it cuts.

Aaron.

[xj5373]

Thanks,

I guess that is pretty much what I thought - advanced rough with a bigger cutter, then rest roughing with a smaller one. I assume that this would work more than once i.e. set up a second rest roughing path with an even smaller cutter - I will give this a try this evening.

Ian

[naomi105813]

Yes,he's right.For flatlands just select your entire geometery then use boundary's to control where it cuts.

[xj5373]

Thought I would post a photo to show what happened - one photo is showing half of the lost wax pattern that was the subject of the original post, the second shows a different pattern along with a wax.

The second half of the pattern is now in the machine - I am advanced roughing with some intermediate steps which seems a good strategy to get the bulk of the material out.

Finishing is taking a while but I need to get to grips with constant velocity mode in Mach 3 to get things moving along a bit better.

Ian