3 ms·

2 more things: 1. this isn't really printing, its subtracting. I think its important to make this distinction. 2. feed rate is REALLY important with getting g

by abakker 10y ago

2 more things: 1. this isn't really printing, its subtracting. I think its important to make this distinction. 2. feed rate is REALLY important with getting good tool life as well as good cut quality. Relying on gravity to control a 1-2 HP router is not going to counter the cut forces well except at seriously sub-optimal cut rates. e.g. A carbide 2 flute upcut end mill with .5" diameter cutting plywood works nicely with a cut depth of about .5" and a feed rate of somewhere around 200-300 inches per minute. Even that may not yield the optimal chip load to keep the bit cool. That assumes a router speed of ~20k RPMs and 3.25 peak HP (AC motor @ 110v).

hexane360 10y ago
Would 1-flute, small diameter endmills help keep the feed down? Your jobs would take a lot longer, but I think there's still room to maneuver even if you have to limit feedrate.
- abakker 10y ago
  Kind of. Routers have very limited speed control, so this is still somewhat problematic. Also, small diameter bits tend to have shorter cutting lengths and cannot cut as deep. They are also fragile. Finally, costs do not scale well with small bits because they last much less due to poorer heat dissipation and early failure.
VLM 10y ago
"Relying on gravity" I have never built one of these, I wonder why they do that. I would think 3 strong steppers would be capable of some pretty amazing forces and would be quite well constrained. Or perhaps 4 steppers or more. I've spec'd out NEMA 42 frame steppers that could quite easily start my car (under the theory that a pony engine need be a tenth size to start a larger engine and my commuter car only has 100 ft-lb torque, so 20 or so ft-lb of torque should easily be adequate to start the engine) Lets see a KollMorgan KM11 with 3750 in-oz of torque applied to a six inch pulley is 40 pounds of force. That should accelerate a ten pound router with some authority, 4 G or so. I know from experience I can push a traditional router against a jig or fence or table much longer and more comfortably than I can curl 40 lb barbells so 40 peak should be more than adequate. A stepper of that output retails qty one to end users for like $150 delivered maybe? So figure maybe $300 for three in bulk order shipped by pallet-full? Over the course of my life the prices of steppers and control electronics doesn't seem to change but the torque seems to go up an order of magnitude per decade for several decades now, so it might be a matter of waiting until 2026 to unleash something like the above.
- abakker 10y ago
  Steppers are definitely strong enough. The NEMA 42s on my machine are geared down 10:1 and work very well moving a 100ish pound gantry. The issue with gravity is not really motor strength so much as it is rigidity. There is no z axis rigidity in the setup because it only has a chain. So it can't exert pressure against the material from the axis. The lack of rigidity is the real problem. As mentioned in other parts of this thread, .01" accuracy is not going to give you great tolerance for pieces where that error can be cumulatively compounded.

by abakker 10y ago

hexane360 10y ago

Would 1-flute, small diameter endmills help keep the feed down? Your jobs would take a lot longer, but I think there's still room to maneuver even if you have to limit feedrate.

abakker 10y ago
Kind of. Routers have very limited speed control, so this is still somewhat problematic. Also, small diameter bits tend to have shorter cutting lengths and cannot cut as deep. They are also fragile. Finally, costs do not scale well with small bits because they last much less due to poorer heat dissipation and early failure.

VLM 10y ago

"Relying on gravity" I have never built one of these, I wonder why they do that. I would think 3 strong steppers would be capable of some pretty amazing forces and would be quite well constrained. Or perhaps 4 steppers or more. I've spec'd out NEMA 42 frame steppers that could quite easily start my car (under the theory that a pony engine need be a tenth size to start a larger engine and my commuter car only has 100 ft-lb torque, so 20 or so ft-lb of torque should easily be adequate to start the engine) Lets see a KollMorgan KM11 with 3750 in-oz of torque applied to a six inch pulley is 40 pounds of force. That should accelerate a ten pound router with some authority, 4 G or so. I know from experience I can push a traditional router against a jig or fence or table much longer and more comfortably than I can curl 40 lb barbells so 40 peak should be more than adequate. A stepper of that output retails qty one to end users for like $150 delivered maybe? So figure maybe $300 for three in bulk order shipped by pallet-full? Over the course of my life the prices of steppers and control electronics doesn't seem to change but the torque seems to go up an order of magnitude per decade for several decades now, so it might be a matter of waiting until 2026 to unleash something like the above.

abakker 10y ago
Steppers are definitely strong enough. The NEMA 42s on my machine are geared down 10:1 and work very well moving a 100ish pound gantry. The issue with gravity is not really motor strength so much as it is rigidity. There is no z axis rigidity in the setup because it only has a chain. So it can't exert pressure against the material from the axis. The lack of rigidity is the real problem. As mentioned in other parts of this thread, .01" accuracy is not going to give you great tolerance for pieces where that error can be cumulatively compounded.