All - I have been working on something with some help from the R7 group. Now I need your help as well.
This is for all the DIY CNC guys. How often have you tried a feeds and speeds calculator only to find that the results were less than desirable?
I want to create charts for those of us, a reference if you will that will get us a little closer to where we need to be feeds and speeds wise on our DIY hobby grade machines. The best place to start I believe is with feed back from you guys. Please provide as many references as you can in the google sheet linked here. At the end of the study I will release all the results on a blog with charts and graphs and hopefully we can help ourselves and the future guys get as close to that perfect cut as possible.
Been trying to figure this out myself. Chip formation plays a big part as i have found out from reading the following links.
Router Bit Diameter Maximum Speed
Up to 1" 22,000 - 24,000 rpm
1" to 2" 18,000 - 22,000 rpm
2" to 2-1/2" 12,000 - 16,000 rpm
2-1/2" to 3-1/2" 8,000 - 12,000 rpm
@J.P_Saini track back a few of my post and there will be a post about feeds and speeds for DIY machines.
I also use Bridgeports, Tormach products, and a few lathes of varying sizes. Companied by an engineering degree and a love for making, I quite enjoy hobby grade machines.
Standard feeds and speeds do not typically directly relate to those for commercial machines that have mass to damper resonances and firm anchors to the ground. Instead the hobby grade machine is typically pretty light, held down under its own weight, and has some flex to it. Yet, see a guy pull off a beautiful work piece on a machine he built himself…
My attempt, as I do not know that it has been done before, is to to make a correlation between what our formulas tell us and what the guys here are seeing. Plus, any veteran machinist I know has feeds and speeds in his head, not on the Internet or in a formula. Hopefully the community can make a nice reference to get any maker a little closer.
I really respect you guys that build a CNC router from raw materials, some machines I’ve seen built from wood or steel C channel and 608 bearings earn mass respect.
The approach is much like you are hinting at here, and what I was alluding to above. Commercial machines F&S simply don’t directly relate to our machines for all the reasons you list above. If we could get enough input perhaps there is a more appropriate “guess” we could make at the proper feeds and speeds although doubtful linear. My hope is for the guy that just built his machine to have a starting point. The feeds and speeds I use are after multiple broken and wore bits… If I had a dollar for every end mill I have broken over the years… I’d buy more endmills to break.
Steel. I believe the reason most of us have issues with this is the lowered RPM range needed and available torque from our spindles. The torque curve on even a VFD driven spindle is not a straight line from 1 RPM to max. I have successfully pulled a few cuts off but not enough experience to back feed it into something usable.
Man, you hit the nail on the head there. We are constantly requested to make larger format machines. So much so I wrote out a long blog about deflection (of course static situations only) to give the guys that get upset we won’t make the 1500mm pined at two ends, 4 lb Z gantry, extruder aluminum X. It simply creates a machine much more deflective than the material itself. You’ve been at this for a while, your experience shows it.
I use a shopbot buddy, and what you’re saying is true even there. When cutting aluminum what a calculation tells you will work rarely does, I generally speed up the spindle and slow the feedrate down to ensure no loading up of the flutes.