Thread: Accurate Strong Gantry
Let me ask something I have a doubt about.
I saw your latest general frame design and I am wonder how the steel hollow tube beams bracing react to the machining force on a router .(generally).The seems like "strings" and source of resonance but I have never seen or heard router during operation.
Actually I am wonder of the smallest applicable size ie 50x50x3 showed many times.
It was meant as more of an idea than a finished design. Yes if the bracing became long and slender then it could resonate. They are all different lengths so they would have different resonant frequencies.
It is also the base frame so the bolting down fixings will help with damping.
Like I said it was more of a basic idea, I did quite a few different options and it started getting messy. So look at the bracing for layout and size accordingly.
I plan to build a similar heavy duty fixed gantry mill, better not mention that I want it to cut steel. He he
too much of a problem. My machine (converted commercial PCB drill/router) had a steel section right across the middle of the aluminium table that was used to locate dowelled stacked boards for drilling etc. Careless use by the previous owners operatives has led to to both the alluminium and steel parts of the bed covered in holes and grooves all over the place!!! These have maily been cut with sub 1mm cutters, which probably did end up breaking, but not before inflicting serious scars everywhere. With a slower speed spindle, and the right cutter I feel sure that I could cut steel, but would not need to be greedy with regards to feed speed DOC etc. G.
My router which in the grand scheme of things is weak compared to even lightest duty milling machine as cut steel on the odd occasion and even cast iron. But it's not really practicle or advisable as it knocks the stuffing out the machine and takes an age to cut due to restrictions on feed and DOC.
The whole reason or point of my objections is that one machine can't cut every material correctly and when comes to steel a moving gantry design is not practical due to the strength needed and all that it brings with it to the build. Far cheaper and easier to build/buy to separate machines each designed for it's purpose.
Not forgetting the steel I am planning to attach an easy removable really small, geared spindle driven by the HS one with belt or directly coupled. (EDIT: i see now that the belt not good at this speed) In this method the supposed extension of the original spindle would be only about 60-80 mm and the force not bother the main spindle bearings
With 1:0,5 ratio (12000-to 6000 rpm) and quite enough torque I probably can make a typical steel milling with DIA 4-5 mm mill.
This would be making opening on a flat parts of electrical enclosures ( mainly doors) and mainly Dia 30,5 mm holes for push buttons.
The only problem is that the thickness is 2 mm but I suppose a 3kW spindle can do it with full DOC( the pre drilling- hydraulic method works but too slow and there are other shapes). This will not be bottleneck if I cannot do it just an idea.
pls adjust me if someone has experience.
One question about the steppers:
Normally they do their job and do not care of step loss and go on.
Is there any no too expensive mean, method to persuade them to stop at step loss and not multiply the mistake.
Last edited by vargai; 13-01-2015 at 07:34 PM.
I've run a stepper based machine for several years and when configured conservatively it will not loose steps under normal conditions. But if you are looking for something else maybe try EasyServo, its steppers that offer some of the features of servos but still easy to set up. Not sure about how the cost compares to the stepper motors you have in mind. They are basically steppers with build in encoders and run closed loop. They will try to correct lost steps and if they can't they would stop and give a fault signal it the error goes over a configurable amount of steps + some other cool features not really possible on other steppers without encoders. They also have a model for 110-220 volt AC so no power supplies required for those.
Nice video made by JazzCNC of how they work
Company that makes them
I got them but my machine is in the build process so I have no idea how well they will work. I have played with them and its easy to get them running and the configuration software also allows many parameters to be modified if need be.
As you said the first to "play" and know the new built machine to find its sweet points.
In this thread and (others) you can find opinion of JAZZCNC of easyservo and he says it works excellent.
Little bit expensive but you have them and you can compare the price.
Could you tell this comparing the same torque stepper pls?
Last edited by vargai; 13-01-2015 at 08:56 PM.
One thing to note is that when we say -"this is bad, can not be done, not like that, you need other type of machine" , its not that it will not work. It will work.But not consistently, not for a long time. No perfect finish. Not be able to hold consistently precision. Ruining some element with time , /bearings/, etc. I can drive a city car where 4x4 car goes, but for how long? So actually its not a discouragement, its a reality check. I will be more than happy to see it done. Cause i will do it also.
Why don't you sketch your idea for the spindle and investigate the bearings.
As for the motors you could fit cheap encoder to steppers and then feed the signal to the breakout board/you will need available inputs/ . When out of programmed way, the machine could stop so you don't damage material. I have a plugin on my PC that does exactly that. Though that's not a true closed loop. The closed loop motors will push till all is where is meant to be and stop only if they could not overcome the force. If you decide to go this way, i will send you the plugin. There are cheap normal steppers with integrated encoders. though definetely will be mistake for the sake of encoders to buy some steppers witch are not low inductance.
Just use good PSU, good board and motors and you will not need these. Though closed loop would be nice on a metal working machine.
The Following User Says Thank You to Boyan Silyavski For This Useful Post:
What spindle are you planning to use? I know there were a few mentioned but cant see which one you decided on.
The thing to remember with spindle bearings is the amount of pre-load they have which affects the rigidity and speed.
Taper bearings with a heavy preload will be super rigid and cut hard materials but will be limited to a low speed. If your milling steel this is what you need.
Angular contact (AC) bearings are similar and the heavier the preload the more rigid they become. Due to the reduced contact area they have a higher speed capability but lower load bearing capacity than a similar sized taper bearing.
So as most of the high rpm (15-20k) router spindles will be using AC bearings then the rigidity will probably be low. This will be the weak link and no matter how strong the machine is it wont be at its best.
Bottom line is you can have a machine capable of both but realistically you will need two separate spindles.
You could always get high end spindle with hydraulic adjustable preload :0)
I have 75x40 precision AC bearings for mine and should get me up to 12k for HSM with adjustable preload and with oil mist lubrication lol.
The Following User Says Thank You to Ross77 For This Useful Post:
The secondary small spindle would be a really light loaded ocassionally used one for the special purpose mentioned.
Short video is attached. The door steel sheet is 1,5 or 2 mm. At issue.That is why I do not want to pay too much attention to it but some searching is not a sin. I will show up some details in the answering to Syliavski and waiting for your comments.
By the way do you have something more then Chinese spindle do not you? from low rpm to 12000
Last edited by vargai; 16-01-2015 at 11:43 PM.
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