So Ian, what do you reckon for Z Axis speed.
Theoretically on the build I will do I could have
X and Y rapid 60m/min, whether the build will stand that at decent accel,  time will tell.
So anyway if I have these kind of X and Y rapids would it be best to get the Z as high as possible or would it not matter too much seeing as the travel on Z will be very small.

With the Z I see no problems in setting an extremely high accel with the setup I propose as there will be little mass to it and the servo should  be more than capable of handling it even direct drive.

Hood

I've been here before

My answers were no and no

I think i calculated I can follow a warp of about 5-10mm across a distance of 1000mm on a good day.
Sounds bad but i don't cut corrugated and a 10mm warp is pretty bad i think, i gave up chasing some time back;)

Hi Hood - Hopefully I've worded this carefully enough to avoid a good kicking from Terry   - but here goes...

I kinda left it vague because it depends on what you want to do and what your THC can do. We can wax lyrical about speeds but ultimately you'll probably end up slowing Z down to match the capabilities of any (including mine) "budget" THC. Spend a few grand on one and the game changes entirely (so I'm told).

To give some perspective though, here's what the tables I've built in the past did (with my THC). I'm sure there are better (and worse) tables out there so I'm not saying this is good or bad - just what they were.

My THC samples at 1KHz. If it's set to do 1 step pulse per sample (which it is) then it can obviously drive the Z at 1000 pps. The Z was rack n pinion with a steps per of 42.44131816 steps/mm.

so Z moved at 1000 / 42.44131816 * 60 / 1000 m/min i.e. 1.4m/min.

Lets say then that it's cutting at 6m/min. It can therefore handle a slope of 6/1.4 = approx 13 degrees. I've yet to find this to be inadequate. Of course it means it couldn't cut corrugated - but it wasn't designed to - it was simply designed to cope with "typical" warpage.

With the Z I see no problems in setting an extremely high accel with the setup I propose as there will be little mass to it and the servo should  be more than capable of handling it even direct drive.

Remember with THC the Z accel is not used so it's irrelevant.

Ian, and all, thanks for taking the time to explain and cover this aspect a little more than I've read anywhere else.

...If you never get a chance to discuss your viewpoint... you never get a chance to question, consider or change it...

Like the discussion about z axis speeds, THC and plasma, I've never seen much posted on it as to what people use and although it may be viewed as boasting or something, at least it gives us an idea of how others may have done it and what they got.

I am not keen on the use of a 2mm acme thread (actually trapezoidal, but similar), but a change would require a redesign hence a pointer to speed what others use / expect is really something that someone like myself can use to value the redesign benefit from thread + delrin nut (or threaded rod + nut), to ballscrew (overkill on accuracy maybe?), rack & pinion or even belt?

Thanks for giving the insight into the 1kHz sample rate / step rate its a bit more of the chunk of infomation to consider.

Rob

so Z moved at 1000 / 42.44131816 * 60 / 1000 m/min i.e. 1.4m/min.

Lets say then that it's cutting at 6m/min. It can therefore handle a slope of 6/1.4 = approx 13 degrees.

Any chance you can show the full workings of that sum please?
How you arrive at 13deg;)

the 13º is from the arctan (tan-1) of (1.4 / 6)  (opposide / adjacent)

sorry... post corrected... muppet!

What he said. Sorry, was it the slope of 6/1.4 that confused? I should of course have said 1.4/6

HI Ian, Sounds good to me (;-).  As to teh Z design the best solution I have seen was a very light very low inertia setup. It used linear rails and a small diam ballscrew 2TPI. The motor was as very low inertia servo drive.  IT was wickedly quick but if you turned off the machine the head would fall to the table. The frame was thin 4130 chromoly plate. It was built by one of the aircraft guys.

What always interested me was IF direct pulsing of the stepper to gain max accel and minimum time HOW is it they can do it WITH accel curve and go MUCH faster and quicker with an outside controller driving teh Z ?  

IF direct pulsing is the fastest possible way to move the motor HOW can it be done faster

(;-) TP

What always interested me was IF direct pulsing of the stepper to gain max accel and minimum time HOW is it they can do it WITH accel curve and go MUCH faster and quicker with an outside controller driving teh Z ? 

IF direct pulsing is the fastest possible way to move the motor HOW can it be done faster

This sounds interesting Terry but I'm not with you. Can you run this one by me again?

Robert you commented on teh lost steps. The probem with lost steps in Z is that Mach3 does not know it happened and THAT alters where it thinks Z actually is. Normall it makes it think the teh Z is HIGHER than it actually is so when the Torch head goes to cycle and the next cut it drives the torch into the metal.

NOW if teh Z motor had an encoder for position you could fix that via software and correct teh position before it caused a problem.

As to adjusting teh Torch parameters long ago I used small steppers attatached to teh Amp knob and to teh pressure regulator to adjust teh machine settings on the fly. The problem was EACH curve in teh toolpath required a different setting based on the dynamics of the curve. High end machines can calculate that on teh fly Mach3 would not stand a chance there, and did not (;-). It may be possible for Scam to do it in CaM BUT with all teh changes the Gcode would be horrible. AND you still would not get much improvent if any in cut quality.

You idea on speed changes is interesting BUT I don't think you will never get it to work at teh macropump level it s FAR to slow. You MAY be able to do it at teh Plugin level where you have access to a higher sampling rate and process speed.

But in reality what have you gained IF you never cut at Very HIGH SPEED or cut highly warped sheets .  Mosst of teh DIY tables I have seen are not rigid enough for high speed cutting. The high accel rates jerks the table around to much causing poor cut edges.

I emailed JIM as to the NEED for a different rs485 board and the first round of the conversation was all Standard HT sales GibberJab and totally talked around the need. (;-) I rephrased the question and tried again .

Worse case senario we hack into teh Motherboard and use a port sniffer to get the protocal then talk directly to it OR yous guys can develope a RTU modual to talk to it.

(;-) TP