Newbie- which one??

[justgary]

Huh, I have tried higher feedrates and gotten problems on corners cutting the outside of a twelve sided polygon (in aluminum). If it were inertia, it would cut too wide, but it cuts too far into the next side if I go too fast. Maybe I cut too deep and the tool load was not uniform enough at the turns. That has kept me from speeding up for a while now. In order to stay accurate, I stay slow. Maybe I should check the toolpath and do a few test cuts.

Thanks for posting that, Randy. Lately, 1/4" is a large mill for me, too. I think I'll play with higher feed rates again.

- Just Gary

[zephyr9900]

Aaah, 12-sided polygon isn't contouring, Just Gary. [Crocodile Dundee mode] This is contouring.[/Crocodile Dundee mode] You are entirely correct on angular toolpaths. Mach3 tends to take liberties in path fidelity in favor of even velocity when it is in CV mode (which Greg Jackson says it's set for).

But I must admit that for the driver (3.50" OD, X-Y finishing passes with .094" ball-end mill at .004" stepover after roughing with .250" flat-end mill at .050" stepdown, toolpaths courtesy of MeshCAM and taking about 15 hours to finish, using the Tormach primary spindle flat-out at 4500RPM) the finishing was at 12ipm due to the extreme path Z-changes. But that is an extreme case for me. Normal all-convex or all-concave shapes are fine at much higher speeds.

The Tormach is really an awesome machine. The flat surfaces on the hub and counterweight were done entirely with the ball-end mill and stepover (no facing pass at all). I could barely feel the texture with my fingernail, and a little rubbing with Scotchbrite smoothed it entirely.

Randy

[philbur]

Very, very nice work Randy. I'm sure you have said before but to save me having to look, what CAD and CAM did you use for the wheel?

Phil

Originally Posted by zephyr9900 Aaah, 12-sided polygon isn't contouring, Just Gary. [Crocodile Dundee mode] This is contouring.[/Crocodile Dundee mode] You are entirely correct on angular toolpaths. Mach3 tends to take liberties in path fidelity in favor of even velocity when it is in CV mode (which Greg Jackson says it's set for). But I must admit that for the driver (3.50" OD, X-Y finishing passes with .094" ball-end mill at .004" stepover after roughing with .250" flat-end mill at .050" stepdown, toolpaths courtesy of MeshCAM and taking about 15 hours to finish, using the Tormach primary spindle flat-out at 4500RPM) the finishing was at 12ipm due to the extreme path Z-changes. But that is an extreme case for me. Normal all-convex or all-concave shapes are fine at much higher speeds. The Tormach is really an awesome machine. The flat surfaces on the hub and counterweight were done entirely with the ball-end mill and stepover (no facing pass at all). I could barely feel the texture with my fingernail, and a little rubbing with Scotchbrite smoothed it entirely. Randy

[zephyr9900]

Thank you, Phil. The model was from SolidWorks, and the CAM was MeshCAM. I did the front and back sides as separate jobs.

I forgot entirely about the semi-finishing, which I did as a waterline move (also from MeshCAM) with a .125" ball-end with a .020" stepdown.

I did the center hole and perimeter trim after the contouring with toolpaths from SheetCam, which I use for 2.5D (pocketing and outlining)

The pictures are after roughing, after semi-finishing and during the finishing on the front side.

I did two different versions of the wheel center. They were for patterns for lost-wax casting. I did 3 or 4 acrylic trial pieces, and broke a cutter on the first brass try about halfway through the finishing pass. That's when I decided to do the semi-finishing to knock down the worst of the jaggies from roughing.

Randy

[justgary]

Randy -

That's super work, but now I'm corn-fused. You talk about N scale, but that driver has to go at least 2.5 inches in diameter, and that puts it into probably O scale. Don't tell my you are one of those crossover modellers!

The other ones you showed were smaller, and would have been close to N scale (from memory, I think they were just smaller than the dime in the picture).

I though I was crazy running programs of a few hours, and here you are letting it run for most of a day...

Regards,

- Just Gary

[zephyr9900]

Just Gary, I am modeling in N scale. These driver centers (heavy shown, also a "light" version with smaller counterweight and center boss) were for a fellow back East. They are F scale (15mm=1 foot, or 1:20.32)

And the run time just shows how much crazier I am than you... There was about 25 hours of machine time in each driver (the backside had much less depth so the finishing time was less).

The N-scale drivers I showed earlier are just 2.5D pocketing, and a final pass with a ball-end mill to "chamfer" the spokes and simulate actual oval cross-section (I turned the blanks with flange profile on my CNC lathe). You need an eye loupe (well, at least I do) to tell that the spokes have straight sides, probably even more so after they're painted grimy black.

Randy

[justgary]

Randy -

Thanks. I thought I was loosing it when I saw a driver twice the size of the collet holder. You don't hear a lot about F scale (actually, it sounds like you do, but I don't). I can't imagine the amount of detail possible at that size. We thought we were hot back in the '70s by hand laying turnouts and putting decent ladders on N scale. I imagine that everything has changed by now.

I have a box full of old N engines and rolling stock. As my friends would get out of the hobby, I would buy all of their stuff for about $100. If I ever get back to it, I'll probably scratch-build everything, and go to full digital control.

When I was young, I never understood how someone could own just one beautiful locomotive and no rolling stock or place to run it. They would come by and show it off or run it on the club track, but that was all they had. It took years, but now I completely understand.

<sigh style=heavy>Maybe some day I'll have time to build myself a steam engine, too.</sigh>

Keep up the good work, and post more pictures!

Regards,

- Just Gary