Speed problem when routing a lot of small lines.

[Witsenburg]

Hi,

since yesterday, my machine is up and running. I've fitted a pen instead of a router, and I'm drawing now. But there is a speed problem. Full speed is OK. Machining speed in straight lines and around circle parts is OK. But the splines I machine, which are cut up in parts slightly under 1 mm, go really slow. About 1/5th of the normal speed. Why is this? Is the speed reset for every piece of line? I could imagine the machine would think it cannot speed up because it is close to the end of the line-piece it is working on. But that would be a big problem. Can anyone explain what's happening, and how to fix the problem?

Thanks,

Hugo

[Greolt]

Hugo

Are you using Mach software?

If so you may be in "Exact Stop" mode. If so try "Constant Velocity" and see if that makes a difference.

It can be changed on the "General Config" page.

Greg

[Witsenburg]

Yep, running Mach3. I'll look into your suggestion tonight, it sounds logical!

Cheers,

Hugo

[Witsenburg]

[EDIT] Found it! [/EDIT]

Unfortunately, it doesn't solve the problem; it was already in constant velocity mode and changing it to exact stop only makes things worse.

I can set the accelleration / decelleration speed per axle higher, that reduces the problem. This makes me think Mach3 indeed only looks 1 line of G-code ahead, and with all these small steps it only speeds up to the speed it can decellerate from within the distance of the next step. So setting decelleration speed to 'as high as possible' should solve the problem, but I don't think that would work. Any other suggestions?

Cheers,

Hugo

[ger21]

There's a lookahead setting under General Config, and also a CV feedrate and distance setting on the Settings screen, although I don't know how to adjust them correctly.

[Greolt]

I don't think there is a decent source for info on the CV feature and settings. If anyone knows of one please let me know.

What I have gathered from reading a lot of posts here and on the Artsoft forum is that the acceleration affects it a lot.

Try to increase your acceleration even if it means you must drop the rapid speed down to do so.

Greg

[Witsenburg]

Originally Posted by Greolt ...Try to increase your acceleration even if it means you must drop the rapid speed down to do so. Greg

OK, I don't mind doing that, but how tdo I know when I went too far in increasing accelleration? I machine at 1500 mm/min (59"/min), rapid is 2000 mm/min (78.7"/min) and accelleration is now at 25 mm/s2 (1"/s2). So it slows down from full speed to zero in 1.2 seconds. What kind of figures do you guys run?

Cheers,

Hugo

[Witsenburg]

I've doubled the accelleration again, to 50 mm/s. Here's a little movie of the machine in action.

YouTube movie

The speed should be at 1500 mm/min constant, it is that on the straights and around circle parts, but on the contour lines it slows down at points to about 320.

Cheers,

Hugo

[Greolt]

Hugo

If you can, try it higher.

Depends on your machine of course but try to get it higher. Even if you need to sacrifice some rapid speed.

I run mine at about 2000mm/sec/sec acceleration but that may be like comparing apples and oranges.

Just get it as high as your machine will allow without loosing steps or jerking itself to bits.

Greg

[Witsenburg]

Wow, you do 2000 mm/s2, I do 75, now. There's a bit of a difference there! I've been fiddling with the speeds and steps/unit on the axle settings a bit, and it seems they do not influence the accelleration / decelleration settings. Now I have the (stupid?) idea that the software was first developed in inches, not in mm, and the 12,5 mm/s2 I started with was a default setting. Maybe it was intended as 12.5 units/s2, and I should start at 25.4 * 12.5 = 320-isch mm/s2.

By the way, what decelleration does it use when you run a program and press the red button (not e-stop, but on-screen)? It seems to do a dead stop then, without any problems. This would lead me to believe the decelleration setting could be set really high without any problems. Agree?

Cheers,

Hugo

[Greolt]

The on screen "Reset" or "Estop" is a software Estop. You will most likely loose steps. It is for Emergency.

The only way to stop mid cut without loosing steps is "Feedhold"

That's the only way I stop mid cut if I want to restart from that position.

Regarding acceleration. Crank it up. See what happens.

You will most likely be surprised. It is only a setting in software. Easy to change down if it is too high. Be brave.

Greg

[Witsenburg]

I used the red button underneath the yellow (feedhold) and green (go). The fact that I might have lost steps is that is of no great concern, yet, but it does prove to me the machine can handle a pretty short stop without mechanical difficulties.

And I just got braver; I just realized, talking it over with a colleague, that your 2000 mm/s2 is about 0.2 G. That's not a terrible lot. My 75 mm/s2 is 0.0076 G. That's nothing. I think I'll go up in steps of 250, and check whether I loose steps allong the way. And I've posted a q in the woodrouter forum, to see what figures other people use. As you said it won't be an exact comparrisson, but it would give me some reference.

Cheers,

Hugo