Cutting speed

[tucker-52@charter.net]

Hello all. I need some input from you BotHeads. I cut a lot of signfoam (HDU). Those of you familiar with it know that it cuts like butter. I cut at 2.5 inches per second. I tried to cut at 4 ips, but my machine wigged out at that speed. It acted crazy, and when I stopped it and moved it home, it didn't go quite back to home. So I spent $800 on the PR to PRT upgrade, thinking that would solve the problem, but it did not. Same problem.

Could it be I need a new or better computer? I bought my machine used and it came with on older Packard Bell 486, which is what I still use to run files. Or am I day dreaming to think I should be able to cut at 4 ips? Any comments or advice will be much appreciatted.

Mark

[gerald_d]

The PRT specs are at the bottom of this page (http://www.shopbottools.com/prts.htm). Max of 2 ips move (full cutter force) speed and 4 ips jog (no cutter force) speed. You are wanting to operate in a grey area where the amount of cutter force is relevant.

My experience was that a 486 PC could not push our PRT at full speed - a Pentium2 is working just fine now. Some people will tell you that they are okay on a 486, but I think it has a lot to do with what software is on your 486 and if it is performing any other invisible tasks in the background.

Remember that the speed shown on the monitor is the "dialled-in" speed that you request. The only way to measure the real speed is to time the SB over a known distance. (Drag race?) Our actual speeds were way short of the displayed speeds with the 486. I think that some of the satisfied 486 users are basing their satisfaction on seeing the "correct" speeds on the monitor.

[artisan]

I agree with Gerald....I had an old Zeos 486 computer lying around. I had been told that it would do the job and since the 486 had no cooling fan, the dust problem would be minimized further. Sounds good, so I tried it......it did not work well in practice. I often had "hiccups" in the programs and even lost data once. I now run the Bot on a P4 and the difference is remarkable. The 486 will run the Bot as a dedicated CPU....but if you "distract" it with any other programs or commands, the performance suffers. With used P3 workstations available for 2-300 bucks (2 sheets of HDU costs this much) I can't imagine using less than that for any reason. I cut a LOT of HDU....at 2.5 ips and slower when finer detail is necessary or when using longer bits. Hope this helps....Much Luck....D

[bjwat@comcast.net]

Mark,
As Gerald and Darrell pointed out, speed is somewhat improved with a faster processor...and I definately agree with the fact that if you have things running in the background, it will slow it down. I'm not sure what processor speed is the cutoff for diminishing return on speed.

The other issue with speed is the stepper motors and the control box. The SB moves at 3IPS loaded on my machine if going through soft foam. The issue is the fact that the control box cannot supply enough amperage to the steppers to *reliably* run them and maintain steps over 3IPS. You can put larger steppers on the Bot, but you would need another control box with a more powerful power supply. It's my prediction (or should I say wish) that SB will offer a beefier power supply and steppers in the future to be able to run faster without losing steps. I believe that is what happened when you cranked up the speed to 4IPS under cutter load. Normal acceleration and braking cannot be achieved with the stock box and steppers at that rate.

I would love to have a faster moving machine for my plasma cutting SB. The faster I can move the machine, the thinner the metal I can cut. I should theoretically be able to run 3.5+IPS since the plasma cutter never touches the surface of the material...there is no cutting load.

-Brady

[gerald_d]

Brady, thanks for reminding us about the load caused by acceleration and braking which is dependent on the weight of the carriages (plus routers etc.) and the ramp settings. Heavy spindles, dual z-axes, and short ramp settings will reduce the "speed" performance. It takes more power to "jerk" a heavy load around.

[tucker-52@charter.net]

Thanks, Guys.

Mark