Let me ask you this.? What do you CUT above 10mtr/min.?? . . .Not much if anything I bet.! . . Also out of the last job (other than mass drilling, which high rapids can help) you cut how much of the overall job cycle time consisted time wise of rapid moves.? . . bet it was easily less than 10% of total cycle time.?
Thats an awfull lot of extra work and expense incorparating 2 rotating ballnuts into a DIY machine just to gain a few percent saving on cycle times, the Key word being DIY machine where cycle times are usually not an issue. . . .Yes in industry every little bit helps but in DIY it's not worth the expense and trouble just for a few percent.!! . . IF . . normal screw setup can be used.
Said this before .!!. . .It takes a substancial machine with a powerfull spindle using high quality tooling to cut at high feed rates. . . . High rapids are only usefull on very small percentage of jobs other than that they are just used for bragging.!!
Also seen as most DIY builders use modified routers usually of the cheaper quality range or spindles like Kress then high cutting feeds with any reasonable depth are simply not achievable anyway.
At last a man after my own heart. All this 10,000mm / sec is just dick slapping. Think about it your part is programmed to run at say 600mm / min the only time this high speed comes into effect is on rapid moves and unless you are belting 4 holes into the corner of an 8 x 4 board any long rapids usually means you are not cutting / programming efficiently.
Even when you ar look at the sceen and see if the actual speed ever gets close to what's' allowed for rapids given that it has to accelerate to speed then slow.
Most time it never gets close to max rapid given the short distance it has to travel.
All insane rapids do is wear a machine out, put undue stress on parts probably not capable of handling them and more chances of loosing steps.
I say dick slapping because a beginners reads all this on here, CNCZone etc and thinks that's what he has to do, most are on small machines that can never, ever reach these speeds and even if they get close how fast can someone get to an Estop ?
When we were first doing the X3 CNC conversions we tried to see what the max they would run at before loosing steps and it was nearly 5 1/2m /min.
We then dropped this back to 4 m/min but it was still scary on such a small machine so finished up at 2m /min.
As a test the machines were sent out with a Sieg Logo badge so the punter could engrave a plate to cover the defunct Z axis handwheel hole as a first job.
There was 4 seconds difference in running at 4m /min and 2m /minJohn S -
The same with over rating components because of bad advise. Following a conversion at the moment on another form of a Taiwanese 636 milling machine.
The guy is using 25mm ballscrews and 1640 oz in type 34 motors, unless he can hit that with 10,000 volts it will crawl but bigger is better - yes ?
End of the day he'll get as much 'useable' power as a 600 oz/in motor and probably twice the speed.John S -
I agree entirely that 10m/min is more than enough and that the difference in machining time between 10m/min and greater is often negligeble. My machine will do at least 15m/min on X and 60m/min on Y, but I leave it at 10-12m/min as it's less likely to go wrong and more time to react should something go wrong. I think the most I've actually cut at is 8m/min.
The reason I tested the Y-axis up to 60m/min was an experiment to verify my modifications to Irving's motor calculation spreadsheet to include pulleys. I was ascertaining how accurate the calculation was by trying different ratios and comparing the limit to the calculated value.
I meant that comment to be just pointing out it is probably possible to get round the vibration problem and the feedrate gain is a bonus.
RE 60M/min Y axis out of interest how much pulley ratio did you have to use and what sort of accelleration did you achieve.? . . . If you don't mind me asking.!
Been out the loop for a couple of days but I note some fascinating posts from you cnc guru's.. Love the one about Mach and kernal speeds, have popped mine back down to 25KHz and it seems fine..
The sort of speeds you guys are talking about seem more than fanciful to me at the moment.. Have been running my machine at 1.8mts/min max during all these other problems, now that I can achieve more, I still dont dare go above 2.5mts/min due to the bent ballscrew shaking the machine so much.. I did try 4mts/min which the motors seem to easily achieve, but shaking was so severe I thought something was going to rattle off the machine.. Am going to try straightening the ballscrew today, will let you know how I get on..
I'm guessing it's a 25mm screw, what length is it?
I can't remember what the acceleration was... think it was 2m/s^2, might have been 3. Either way it only hits 60m/min for about 200mm... except if you smash it into the side :whistling:
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