Milli a new composite mill kit

[joeavaerage]

Hi Jackjr,

Well there is simply no speed regulation. The actual spindle speed will vary with the load. And also the low torque below rated speed.

That is not really correct, or not as dramatically as you suggest.

Any asynchronous motor when fed with a constant frequency voltage will rotate not at synchronous frequency but somewhat less due to slip. The slip is what causes the rotor to be magnetized
and an induction motor would not work without it. Should the motor experience an increase in load its speed will drop and thus the slip increases, which in turn increases the rotor magnetization
which in turn increases the torque delivery to the load. A typical induction motor with have a no load speed, and a speed at rated output and they seldom differ by more than a few percent.
If I dial up 20,000 rpm on my spindle, at no load I might expect 19,750 rpm given slip, but even at full load I would expect at least 19,000rpm. Does that 1000rpm make any difference?.
Remember also this is exactly how many millions of induction motors work around the planet as the load increases the speed drops....a little. If the motor is overloaded, say by 50% of rated torque it may
well slow enough that it will stall....but clearly that is just a case of overload and you'd be silly to operate any motor that way, a spindle included.

For how many years have we operated manual lathes, mills, drills etc.....and they had a gearbox at best with a number of fixed speeds. Lets say you would ideally want a spindle speed
of 300rpm on your lathe. The nearest gearbox setting is 340rpm....so you use it. Does it wreck the job? No. Why is everyone so fixated on spindle speed on a CNC machine. I certainly like to think that
if I dial up a speed with my spindle I'll get within 10%, but mostly I get within 5% which is much better than many a manual machine I've used. Likewise manual machines slow a little as the torque of the
load increases, usually not by much, and does that wreck the job? No. Provided the demanded torque does not stall the spindle I would expect a slow down of 5% or less. Is that a problem?

As for low torque at low speed.....that's not correct either. When you first turn on an induction motor it exhibits its starting torque, and typically is 50% more the its rated torque. At that time
the slip is very high and consequently the rotor currents are high which in turn means the applied current to the stator will be high. This will cause an overheat should it continue for long periods
of time. So I argue that it is not that you get low torque at low rpm but rather you risk high rotor currents and consequent overheating of the motor.

A vector controlled induction motor is still an induction motor. The vector control does not suddenly and magically increase the torque of the motor. What vector control does is control
the applied stator current to maximize the torque with the minimum of current and reduce its propensity to overheat. Note the qualifier 'reduce' , not 'eliminate' overheating.

My spindle is air cooled and I don't like to run it below half speed, ie 12000rpm. When I use a slitting saw I do however run it down to 1/4 speed, ie 6000 rpm. When I use it in such a manner I am
very careful NOT TO DEMAND high torque from the spindle for the certainty that it would overheat. So I am in no way concerned about the lack of torque but rather that I might overheat my spindle.

Craig

[joeavaerage]

Hi peteeng,
jackjr is right, do not buy el-cheapo Chinese servos. Its not because they don't work but they typically have atrocious documentation, even worse technical support and no set up and tuning software.
A modern AC servo has many hundreds of parameters, many of which you'll never need or touch but there are many that you will need. In the case of my Delta B2's there are 270 parameters.
You do not want o program those by pushing buttons like a microwave, its just too error prone. Do not do that to yourself.

If you buy a cheap Chinese spindle you'll have a nuclear meltdown guaranteed, and you are only 3000km away.....I don't want to be caught up in the blast!

Most AC servos are very similar, if one manufacturer has a feature all manufacturers follow suit. So within the difference in terminology of each manufacturer if you can program one then its highly probable
you can program another. Your problem is that you have not set up and/or tuned ANY servo....choose a make and model that gives you the best probability of success.

I use Delta, but there are many good brands. The same company I buy my servos from sell ToAuto servos, their own brand. I have no reason to doubt they work and I have good history with
the supplier and they are approx $100USD to $150USD cheaper than the same size Delta B2. Given I've programmed Delta, Allen Bradley, Omron, Yaskawa, Mitsubishi and Schneider
servos I could in all probability handle ToAuto but I vote with my wallet and buy the Delta's.

Craig

[peteeng]

Hi all- Here's the documentation for the BST servos. Looks pretty good to me. Peter

[joeavaerage]

Hi peteeng,
yes, looks great, but looks can be deceptive. Does it have tuning software? If not walk away, in fact don't walk....run away.

Craig

[peteeng]

Hi Craig - I'll ask. Peter

[G-Spot]

Did the FEA thing on your machine. Here are the results I got.
Do your deflection results correlate with mine?

I did the analysis with the force applied between the face where your spindle shaft intersects the motor face and the test pad on the base.

[peteeng]

Hi G - Convert your results to N/um so we have common units to discuss. What load did you use? I'm sure all commercial FE systems will give the same result if given the same data and geometry. Peter

In the optimisation image the parts seem to have a double mesh. Check you don't have two bodies superimposed on each other for those parts. If they are then the part will be twice as stiff as it should be... Peter

[G-Spot]

Hi G - Convert your results to N/um so we have common units to discuss. What load did you use? I'm sure all commercial FE systems will give the same result if given the same data and geometry. Peter

In the optimisation image the parts seem to have a double mesh. Check you don't have two bodies superimposed on each other for those parts. If they are then the part will be twice as stiff as it should be... Peter

I am doing all my tests with 1000N, there is no option to display relative stiffness, I am sure your brainy brain can do the conversion without a calculator|

[peteeng]

Hi G - You can also apply 1um deflection to your part and the FE will figure out what the reaction is to achieve that deflection then no brains needed as then you know its N/um immediately... Peter

[peteeng]

Hi all you brains out there - I'm designing a 3mx1.5m rack and pinion router with helical rack and pinion drives. Any one done R&P before and have any words of wisdom? I'm nailing down the final drive details at the moment. First time through the movie is always interesting. I'm going to try and use as many "optimised" and organic designs as possible. Peter

[Momentz]

Hi all you brains out there - I'm designing a 3mx1.5m rack and pinion router with helical rack and pinion drives. Any one done R&P before and have any words of wisdom? I'm nailing down the final drive details at the moment. First time through the movie is always interesting. I'm going to try and use as many "optimised" and organic designs as possible. Peter

I've used the 5:1 reduction from AliExpress with there helical rack quite a few times, I think it's great for a router application and have no problem setting it up to step at 0.01-0.02mm no problem with minimal anti backlash and zero with software intervention.

Sent from my SM-G781B using Tapatalk

[peteeng]

Hi Momentz - I was going to use 5:1 gearboxes on this one. So that's good - Did you use a spring contact for the pinion or just mechanically aligned? Peter

[Momentz]

Hi Momentz - I was going to use 5:1 gearboxes on this one. So that's good - Did you use a spring contact for the pinion or just mechanically aligned? Peter

I've done both.

First one was aligned and was quite the mission.

Second one I made a plate that the gearbox was mounted to, it to allowed it to pivot and be spring tensioned.

First one was harder to setup and took days to align the rack but ran faster and quieter.

Second one was easier to setup but does rack If run about 30m per min+ and is a little noiser because the mesh between rack and pinion is tensioned tighter.

Sent from my SM-G781B using Tapatalk

[peteeng]

Hi Momentz - I'm currently going with the alignment method vs the spring drive. I think a little patience is worth the result. Good to know it works well once done. The rack is in 1.4m lengths so I have joints in the rack how did you align them (correct teeth spacing)? small bits of rack? by counter meshing teeth? Regards Peter

[Momentz]

Yes I used a small piece of rack. But you can't use the same rack, you have to buy a small piece that's mirror opposite. The seller can send you a small piece for joining rack for a fee.

Sent from my SM-G781B using Tapatalk

[peteeng]

Hi Momentz - Yes I've read you can't use the same rack. With straight rack you can. Thanks I'll send a note to the supplier to see If they have mirrored rack. Thanks for the heads up. The forum comes through again. Peter

[peteeng]

Hi All- I think Milli will need a chip compactor as well. Peter

[joeavaerage]

Hi,
got my new spindle today....after a long battle with NZ Customs (my fault). Really nice.....and worth the wait.

First impression is that the HSK32 toolholders are small, you can fit one in the palm of your hand easily. The toolholders supplied are ER20/HSK32.
I can see why it not necessary or even desirable to put an ER32 onto an HSK32 interface. The HSK interface is small enough I would be reluctant to fit a tool bigger than 12mm
for the sake of rigidity.

Can only guess that an HSK25 or ISO20 interface which are even smaller would give you similar concerns, ie the rigidity of the tool is questionable given the size of the
tool interface.

Depending on the sort of tools you want to use and in what material I would say most would be happier with ISO30, BT30, HSK32 or HSK40 or even bigger.

Craig

[joeavaerage]

Hi,
second impression....the tool change is silky smooth.

The Vietnamese supplier threw in a 2 position 5 way pneumatic solenoid so I have set it up and it works perfectly.

Could very easily have made a mistake though. The pneumatic cylinder that operates the tool release bar is double acting but has no spring return. When the cylinder activates
it presses the release bar against the tension of the bellvue washers. When the cylinder deactivates the piston moves but only as far as the bellvue washer return, and so the face of the piston is still
bearing on the release bar. The release bar rotates at spindle speed, and thus that contact between the piston and the release bar would soon generate friction....wrecking the whole thing.
Thus the piston needs to be actively retracted so that there is clearance between the piston and the release bar when the spindle is spinning. There is another air-port for this purpose.
I have no instructions other than some .jpegs....and those in Chinese. I could identify the tool release port, the seal air port and taper cleaning air port....but not this extraneous port that did not seem to do anything.
I now know that the extra port is to retract the piston. Glad I found that out prior to powering up and running the thing!

I do have a reasonable photo of the pinout of the three plugs
.
One is the three phase power input and earth, easy enough.

The 17 pin aircraft connector is the Sin-Cos encoder, and I have the pinout for that.....not that I really need it.

The last 12 pin aircraft connector is a little more troublesome. The pic I have does a pretty good job of the pinout. Two are for the PTC temperature sender, easy enough.
The remaining pins are for the three proximity sensors built into the spindle for sensing the presence/absence of a tool but also the state of the tool release. Clearly I need to thoroughly understand these later switches
to operate this thing properly. The truth table for the switch states are in Chinese. Hoping my Vietnamese supplier can help with decoding them. Either way I will have to experiment with then until I'm 100%
on them. The last thing I want to do is have the spindle start without a tool in it.....the tool retainer claws would suffer irreparable damage because of unconstrained radial movement due to centrifugal force.

At this stage I think I will build a small electronic board that senses the PTC temp sender. Such instructions as I have give a very good characteristic of the PTC temp sender around its critical temp. I need to build
a current source to measure the resistance and then have a threshold detect to Estop the machine should the temp go out of bounds. May in fact make the temp available as a continuous analog variable
to monitor spindle temp. This electronic board will also need some circuits to detect the prox switches and logic to ensure the VFD is cut-off if a fault is detected. I could use Mach4 to do that....I do have
half a dozen or so inputs to spare, but I rather think I'll have a small dedicated microprocessor board to handle temp and prox switches autonomously.

Craig