Richards
Fri 19 October 2012, 12:15
I've spent most of my working life finding more ways to use computer technology to make things more efficient. One of the biggest problems that my customers have discussed with me is the cost of labor. Here, in the United States, minimum wage is over $15,000 a year for a full-time employee, more if benefits are offered. That's a bargain when you really need that worker, but it is an unending cost if you can find a way to using machinery to do the job, especially if the machinery costs less than a year's salary for one worker.
When I had my CNC router, I was a one-man shop. I learned how to do everything without a helper. What I soon learned is that a single CNC machine could do the job, but that multiple machines would be more efficient. Case in point. Most of my work was cutting cabinets based on the 32mm system. It only took fractions of a minute to cut each panel, but it took much longer to drill the holes, particularly because I had to change the cutter between operations. Changing the cutter usually took longer than doing the job. Of course I could have added auto-tool changing to my machine or added a secondary drilling head, but even that would not have been as efficient as having a second machine.
So, I played around with design possibilities in my mind and decided that if the main CNC router only had to cut the profiles, and if two other CNC machines were used; one to drill holes and the other to act as a horizontal boring machine; that the entire process would be significantly more efficient; i.e., I would make more money in less time without needing to hire anyone.
Let's assume that a MechMate is used as the primary machine and that it is equipt with a spindle that can make a one-pass cut in melamine coated particle board. Let's also assume that to get a near perfect edge, that the MechMate cuts each part using climb-cut and conventional. The final assumption is that the MechMate can do that while cutting at 300 ips or faster. That means that each panel will be fully cut in a minute or less. Not too bad.
Now for the drilling.
Let's assume that we build a 2nd machine designed specifically for drilling. Because there will be no horizontal load, it can be much lighter than the MechMate. Because it is much lighter, each axis can be expected to move much more quickly than 300 ips. Because it will only be used for drilling, it can be a simple point-to-point machine.
That's were the fun began for me early this morning.
I created a simple spreadsheet comparing three different motors, the Oriental Motor PK296-F4.5A, the PK299-F4.5A and the PK296-03AA, with and without gearboxes/beltdrives. I wanted to see if any of those common motors could be used with little or no ramping in a point-to-point machine with adequate speed and with adequate resolution. Adequate speed meant something running at 600 ips or higher and adequate resolution meant 0.003" (0.076 mm) or less. The PK299-F4.5A motor met all the requirements. At its FS speed (no ramping required), it could run at 300 RPM. With no gearing and with a 1.25" spur gear, that gave it a per-step resolution of 0.002" or 0.05 mm. At 1,100 ipm (18.33 ips), it more than met my speed requirement. With about 35 lb*in or torque at that speed, it would have more than enough torque to move a drill head. Best of all, it took 107.10 usecs per step, meaning that I could have a pulse of 7 usecs on and 100 usecs off for each pulse. That would allow a simple $5 microcontroller to interface with a Geckodrive stepper controller.
The whole plan consists of a bunch of drill templates, one for each panel. A simple computer reads a database and then sends the coordinates for each drill point to the point-to-point CNC machine. An Arduino using a network interface accepts that data and then sends it on to dedicated microcontrollers that run each axis of the machine. It may seem complex, but it is so very simple in the world of computerized process control.
The whole point is that tools and parts are easily available to solve almost any problem if you just dig deep enough to go beyond what others have done.
When I had my CNC router, I was a one-man shop. I learned how to do everything without a helper. What I soon learned is that a single CNC machine could do the job, but that multiple machines would be more efficient. Case in point. Most of my work was cutting cabinets based on the 32mm system. It only took fractions of a minute to cut each panel, but it took much longer to drill the holes, particularly because I had to change the cutter between operations. Changing the cutter usually took longer than doing the job. Of course I could have added auto-tool changing to my machine or added a secondary drilling head, but even that would not have been as efficient as having a second machine.
So, I played around with design possibilities in my mind and decided that if the main CNC router only had to cut the profiles, and if two other CNC machines were used; one to drill holes and the other to act as a horizontal boring machine; that the entire process would be significantly more efficient; i.e., I would make more money in less time without needing to hire anyone.
Let's assume that a MechMate is used as the primary machine and that it is equipt with a spindle that can make a one-pass cut in melamine coated particle board. Let's also assume that to get a near perfect edge, that the MechMate cuts each part using climb-cut and conventional. The final assumption is that the MechMate can do that while cutting at 300 ips or faster. That means that each panel will be fully cut in a minute or less. Not too bad.
Now for the drilling.
Let's assume that we build a 2nd machine designed specifically for drilling. Because there will be no horizontal load, it can be much lighter than the MechMate. Because it is much lighter, each axis can be expected to move much more quickly than 300 ips. Because it will only be used for drilling, it can be a simple point-to-point machine.
That's were the fun began for me early this morning.
I created a simple spreadsheet comparing three different motors, the Oriental Motor PK296-F4.5A, the PK299-F4.5A and the PK296-03AA, with and without gearboxes/beltdrives. I wanted to see if any of those common motors could be used with little or no ramping in a point-to-point machine with adequate speed and with adequate resolution. Adequate speed meant something running at 600 ips or higher and adequate resolution meant 0.003" (0.076 mm) or less. The PK299-F4.5A motor met all the requirements. At its FS speed (no ramping required), it could run at 300 RPM. With no gearing and with a 1.25" spur gear, that gave it a per-step resolution of 0.002" or 0.05 mm. At 1,100 ipm (18.33 ips), it more than met my speed requirement. With about 35 lb*in or torque at that speed, it would have more than enough torque to move a drill head. Best of all, it took 107.10 usecs per step, meaning that I could have a pulse of 7 usecs on and 100 usecs off for each pulse. That would allow a simple $5 microcontroller to interface with a Geckodrive stepper controller.
The whole plan consists of a bunch of drill templates, one for each panel. A simple computer reads a database and then sends the coordinates for each drill point to the point-to-point CNC machine. An Arduino using a network interface accepts that data and then sends it on to dedicated microcontrollers that run each axis of the machine. It may seem complex, but it is so very simple in the world of computerized process control.
The whole point is that tools and parts are easily available to solve almost any problem if you just dig deep enough to go beyond what others have done.