Hey guys, I have been commisioned on a pair of walnut tabletops with topo maps carved in to them.
2.5" walnut slabs, roughly 19x27" engraved area, with a height of 1.25". Needless to say, cutting time is pretty long, about 40 hours.
Im looking to minimize any chance of broken bit set backs. Not worried about roughing, i’m using a 1/4 amana on conservative depth of cut.
I am worried about the 1/8 ball i’ve been using for previous finishing, cheap, buck endmills. Any recomendations on more robust ones, with the ability to cut to a depth of about 1.25" (the height setting in the 3d render, bottom to top of grand canyon essentialy)?
if you want to be gentle on your finishing bit… you can do a 2nd roughing pass but say with a 1/8th bit (but you’d want to do it in a rest-machining kind of way or it’ll take forever cutting air … depends on the software you use)
tapered ballnose gives you super fine details… IF you use a very small stepover… without such small stepover the result is generally aweful.
and also, depending on the design… the V part basically means you can’t do (near) vertical walls, something a ballnose can somewhat better.
If you do the roughing well enough the actual depth isn’t the depth you’re cutting at… the big thing is that you need enough clearance throughout the design… again that’s an issue around edges and around the steeper areas
Yup, that was my fear as some of the canyon walls are near vertical. I found a longer reach ball, I think maybe a slightly smaller stepover is in order. I tried to orient the angle of the finishing pass as such to avoid running down the vertical walls, but it kind of is what it is. I make alot of these with a height of .5 or so, way different at 1.25.
Any thoughts on how long to run the machine at a time? Ive done several 5 to 7 hour projects, this one being almost 30, not counting surfacing time, is way more. Immediately following this is another which will run about 30 as well. I generally stay with it 5 or 6 hours at a time, but I am running out of things to do around the shop!
What kind of feeds, speeds, depth of cut? I calculate with a 1/8" ball, 0.025 stepover, taking 0.020 stock left from the rough, I can go 60 IPM. That calculates out to about 6 hours. ~7 hours with a 0.020 stepover.
You could speed up roughing by using a 1/2" tool, 0.025 depth of cut but at least a 1/4" stepover. Use a Z-Level / Level based rough so you get close to the 0.020 you want to leave for finish.
Most Tapered ball mills are around 3-4° per side. Are your walls steeper than that?
Very conservative feeds and speeds. I know i could go quicker. Not neary machine at the moment, but for roughing, im runnimg .11 DOC w/ a 1/4 amana, stepover is about .11 as well. Its running at about 82 IPM, programmed to 65, but ive been running at about 130%, chips look a little better, cut is alot cleaner.
I also have it set for a slightly smaller stock to leave than i normally use (which is typically the default setting). I hope that between the stock to leave and the smaller depth ofcut durimg roughing, my finish pass will be pretty low impact. It does get steep in several spots. So far so good. Next time i go get some run time in ill check my exact setup.
Will can probably say how long one can do this, but you can pause the machine and continue the next day. It’s not good for the stepper motors to have them on “standing still” forever (stepper motors use the most power holding still under a load)… but “forever” I take as weeks and months; overnight might be not too bad.
In theory you can also turn things off and re-home and continue, but homing switch repeat accuracy is good, but not nearly as good as stepper motor steps, so you run a bit of risk doing that that things shift a little… might be ok in roughing, but I’d not do that with finishing passes
Stepper motors are weird — they work their hardest at holding position — we recommend not pausing for more than a brief break (which is probably conservative, but…) — better to shut down and resume cutting the next day after adjusting the file.
I had read that somewhere. This cut, and the next, are brutal. By adjusting the file, are you talking about removing the lines already completed? For instance, right now i am mostly through roughing, and am sitting at line 270,000 of 1,222,000. Basically shutting down, and removing the first 270k lines, then resuming?
For a 3D cut, you could estimate how much material has been removed, draw in geometry which defines the remaining area to be cut, and assign the 3D toolpath to that — or edit the G-code file itself — preserve the pre-amble, determine what line was last successfully cut, search up from there for a move down from safe/retract height and start the file at that point.
Perfect. That helps. I keep a log of what line im at every manageable bit of time. For this next one, it is a 26x19 topo map, instead of having a single 26x19 rectangle containing my tool paths, could i do 4 rectangles (13.5 x 10 or so) overlapping for roughing, then a single 26x19 finish? That way i could rough one quadrant, and come back and do the next another time. Height on these two jobs is 1.3", with tiny stepdowns since tryimg to minimize stress on my long reach 1/8 ballnose. So the rough time is long, 20-30 hours.