G0704 conversion - feeds and speeds questions for 0704 users

Hi all,

I've converted a G0704 clone (AMA25LV) to CNC using some 4nm steppers, chinese ballscrews, homemade bearing supports and nut adapters and a BOB/linuxcnc. It's all working pretty well - I managed to get it down to 30 microns backlash in all axes except the Z which sees 70 microns. This has been pretty adequately removed in soft compensation and I can see 50 micron repeatability over 100mm moves and zero backlash registered on a 0.01mm resolution DTI. Chuffed! I then found Hoss's pages and wondered whether I should have gone that route - ah well!

That said, I'm pretty new to the CNC process and I'm doing a lot of learning off-line - my first few forays into using it in anger have been OK but recommended feeds and speeds have needed some significant tweaking. Due to the lower spindle speed limit (2Krpm), small diameter cutters fed into a few online F&S calculators yield a very very high feed rate (like metres a minute at times for aluminium!).

As the motors I have can snap a cutter at the drop of a hat (and have, and boy do they make a hell of a vibration when not microstepping!) can anyone throw out some approximate feeds/DOC they've used with say 3mm/5mm/10mm endmills when slotting in 6082-T6? I found that in order to not feel like I was breaking things I had to drop the feed rate down to a point where I was more or less smudging the tool along the part (new HSS, ti coated tools). I'm sure this can't be right but I've not found a sweet spot yet so I'd appreciate some guidance if anyone can spare the time or point me to a link? I see so many folk claiming nuts values. I can move all axes at 2500mm/min no worries when rapiding and I'm tempted to start running microstepping (at the cost of torque/speed) to reduce the vibration through the table which seems to show up in the cuts at times.

Cheers!

I have never used 6082 aluminum so I do not have any number for that. I want to make 2 recomendations.

1. I am fairly certain you want to turn on the microstepping. I know you loose some torque at the max RPM of the motors but you actually gain some at low speed (from the charts I have looked at). It will smooth out your movements and you will get a better surface finish

2. If you have a smart phone check for "feeds and speeds" apps. I had one a while ago that was free and seemed fairly good. You would enter your spindle HP and RPM, and your machines max feed rate capability, cutter and material info and it would spit out a RPM and feedrate that was idea for the cutter and material or the best that could be done within the limits of your machine.

Hmmm FS wizard suggests 378mm/min with a 5mm cutter in 6061 (similar IIRC) which seems much more sane.

I use FS Wizard too and it does a good job. You can set the max rpm to whatever your machine can do. The only recommendation I have, as a newbie as well, is if you don't have flood coolant and you're slotting take shallow passes. I use .05 inches and have a little handheld blower to keep the chips out. If the slot is deep I use my shop vac blowing to keep the chips clear.