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If you put an F feed on all the Z plunges to slow them down you also need to put an F feed on the next X or Y move following the each Z move to get the feed back up.
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This question could maybe be posted to Mach 3 or BobCAD but this seems like a good place to start!
I am fairly new to 3D NC milling - so far my 3D milling feed rates have been often constrained by the need for slow Z feed as often the cutter (eg ball noze) needs a slower down feed than X or Y feed.
I am probably missing something obvious but have yet to discover how to slow the Z to say 40 mm per min yet have the X and y at say 400 mm per min. I have edited the G code with all Z to say Z40 - but then the whole code inc x and Y goes to F40s.
Welcome your thoughts!
If you put an F feed on all the Z plunges to slow them down you also need to put an F feed on the next X or Y move following the each Z move to get the feed back up.
Hi Andre' B
I have tried that using 'find and replace' in my BCC G code editing - but I can't see how to avoid getting more than one F on some lines - which shows as a fault. Do you know if it is normal practice to repeatedly slow down the Z feed like this? Cheers
We have someone who can help you at www.cadcamtrainer.com/forums/index.php
That is Sorin's forum and we have someone who supports your machine helping there. (Sorin does training seminars for Bobcad)
BTW what version do you use?
Thanks - BCC V21 - cheers
keen, I think it is more usual to make the first move into the material a ramp, rather than plunging Z straight down. SheetCam works this way. Well, you can specify the ramp angle from vertical to almost horizontal. I typically specify 10 degrees (from horizontal). SheetCam compensates for this by recutting the ramped section when it is to full depth, so the resulting cut is flat-bottomed.Originally Posted by keen
MeshCam doesn't ramp the initial cut, but allows you to specify the plunge speed for the initial move separately from the normal cutting speed.
Best regards,
Randy
hi Randy - I mean on the 3D work I am milling the z in going up and down all the time - so the X and Y's are too slow if I set the Z for max safe feed.
Sorry keen, for 3D you don't really have a choice because the X, Y and Z are in a specific ratio to move the cutter in a specific direction. You can't adjust the speed of Z independently, or else your surface would be wrong (like a relief globe with exaggerated elevations, or in your case it would be squashed elevations!) You can only set the ipm or mm/min for the overall movement that the cutter will bear.
What cutter size and RPM are you talking about here? And what material are you cutting? And how much material are you taking off in one bite?
I have the Proxxon auxiliary spindle on my Tormach. With a .020"(.5mm) ball mill I will turn it at 20,000rpm and set the cutting speed at 2 ipm (50mm/min) in brass for 3D. But I initially rough the shape with a much larger cutter (say .125"/3mm) and only leave .005"(.13mm) for the small ball mill to remove.
In acrylic, I can use speeds at least double that.
Best regards,
Randy
Thanks for your time on this Randy! Yes I had imagined that during Z and X/Y simultanious movements the speeds would have to be in sync to keep the form! sure ....but I thought maybe the X/Y feeds could be faster when the Z is not moving? for me that is often eg - a big surface area shallow electrode in copper maybe with a 6mm ball nose HSS cutter running at say 4,000 RPM and a Z feed of 100 mm per min max - then a 3mm ball nose Carbide cutter (yes copper wears!) at max revs and 80 mm per min - it a lot of slow travelling on the X and Y ! Wish I was in your area and I could see your work! if you are ever in New Zealand let me know!
Maybe part of my problem is that being isolated and self taught I assumed (perhaps wrongly) the way to rough out is to pass over the part with a series of fairly shallow Z step downs. This method means that the Z axis as rapidly as the X/Y jumps down the short plunge of the step down cut...........maybe I should be roughing with a deeper and so more sweeping cut with a shallower 'width' of cut - if that makes sense!
keen, if I'm ever in NZ (a beautiful place from pictures/video I've seen) I'll give you a shout.
Machinist Mate software I use for determining feeds and speeds (I'm an engineer and have no intuitive feel for them nor enough experience yet to develop the feel) says that for a 6mm-dia 2-flute HSS endmill in copper to use 1617 rpm and 68 mm/min, and 3234 rpm and 68 mm/min for 3mm dia. It does not give any recommendations for depth or width of cut, and I've never machined copper so I don't know there either. But in brass I never go more than 1/2 the cutter diameter in depth, nor step over more than 1/2 the cutter diameter either. I do know second-hand that different coppers machine differently, and I remember OFHC (oxygen-free hard copper) as being one of the better grades to machine.
Best regards,
Randy
Hey Thanks! I think I have been pushing it! At that feed rate the Z should be fine! Just doing a code for my monday job now so will amend - cheers. yes look me up one day!
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