I am just started using a program that will only put out G-CODE in MM. I set up a profile in Machloader and configed in MM. Do I need to change the motor steps pre to MM or will Mach change In to MM .

If you told Mach that you are using mm, then it will use mm.

milimeters
 

Hello.

Wat is the pinions recomended for a 7.2

This ar the dimensions.
Manufactured in mild steel S45C Induction Finishing with chemical black
Tensile strength (min) 569 N/mm2
Pressure angle of 20 °

I think 30 or 36, the 24 A=8mm

each One 7,49 €

Those are metric module 1 gears. The 36 tooth is the popular choice for metric gears.

But, the E dimension of 10mm looks too narrow. We work with 15mm. Our rack is 15mm wide.

Ok, recommend module 1.5 The 36 tooth?

1 unit 15,10 € !!

For module 1.5 you can go for the 24 tooth. (keep the C dimension at about 36mm)

See http://www.mechmate.com/forums/showt...3&postcount=14

Okay, I'm curious.

Why is it more appropriate for 7.2 geared motor to use 30 teeth, and 3.6 use 20?

Is it because of the torque? Or will it be too slow?

begging for enlightenment....

30 teeth rolls smoother than 20 teeth
30 teeth has less wear than 20 teeth
30 teeth on a 3.6 gearbox has low torque.
20 teeth on a 7.2 gearbox needs very high step pulse frequency.

But, that is only general experience, you can use anything you want. Just remember, in a metric country the numbers 20 and 30 mean nothing.

so i guess the deterrent factor was speed...
is there any noticeable increase cut quality if a machine geared at 7.2 ratio, using 20 teeth pinion?

Sean Reish is using 7.2 ratio and 20 teeth. Doc Tanner & Greg J are using 3.6 ratio and 30 teeth. Lots of people use 7.2 and 30 teeth. Nobody has cut quality problems. Greg J would like a bit more torque at high speed.

Gerald,
I also remember Sean stating he was going to try the 30T to get a little faster rapids and cut speed as the 20T needed too high a step frequency.

Heath,
You are correct. I need a little faster rapids and at 20Khz, my machine could perform better with 30T pinions. Torque is not a problem, so I might even go to 35T if I can get the motors to swing down far enough!

Sean,
I think Doug Ford was running the 35 Tooth pinions at least for a while. His thread indicates he milled a little extra in the slot to allow extra room to disengage the pinions if he had to.

Heath,
Due to my machine being a very early "classic" machine and the fact that I mistakenly made my rails about a 1/4" taller than required, I just had new motor mount plates laser cut last week with longer slots for just this reason.
I noted that Doug did a little "metal removal" :) during his build! Thanks for the reminder.

Sean

The guys in my shop are mounting the new motor plates today and bigger pinions. Longer slide goes on next monday. Wish me luck!

I made this Excel spreadshet for a non Mechmate related project, it may help ppl understand gear values.


Pablo

Sean sounds great, will be interesting to hear about your comparison to the new pinions and the longer Z height. :)

My MechMate does not travel 100mm if I enter G0 X100 but the travel distance is more. the pinion that I used has 24 teeth and DP 20 and pitch diameter of 32.76mm, When I use the formula Gerald posted the steps per value is 26.526 steps per.... if I do calculation : 3.1416x32.76= 102.91881 then 2000/102.91881=19.432793 steps per...... for the Mach motor tuning can someone please tell me where did I go wrong
Regards

If you have direct drive motors, 24 tooth pinions and DP20 (non-metric) pitch, then your setting should be 20.886 steps per mm.

(I don't know where you got the pitch diameter of 32.76? That might be the outside diameter. The pitch diameter is about in the middle of the tooth height. =24/20*25.4=30.48 for 24tooth, dp20(inch), converted to mm.

The key issue is whether you have inch based DP20 pitch, or millimeter based Module1. (obviously the tooth count of 24 is definite)

For DP20 your Mach setting should be 20.886 steps per (mm)
For Mod1 your Mach setting should be 26.526 steps per (mm)

Hi Koning, I calculated my steps more or less then used the facility in Mach3 to fine tune my machine....there is an option on the 3rd page of mach3...I think (green page) where you can do it. I cannot remember it all offhand, but what happens is you tell mach 3 to move a certain distance in the X direction....it will then move there..You then manually measure this distance and enter the ACTUAL distance your axis has moved into Mach3. It then calculates the steps for you. You can do it on X, then Y en also on Z.
But my experience is that you should do it on a LONG distance...not 100mm...rather 1000mm

When I am in front of MACH 3 I can write it up more clearly, or somebody else can explain better...I suck with explaining things to people.:o

Thank you Gerald
I have played with the settings this afternoon, used the 20.886 and it worked perfectly, Kobus i will have a look for that page and measure over long distance, learn-learn that is the only way, thank you for the input, much appreciated

Just a thought
 

Hi all,

one might consider the power supply as well in all this drive selection process. Torque problems can come from inadequate PS as well as gearing.

Yves

I am looking at every thing since I realized I had a problem with my cutting on my machine. I am looking at threads that I might have read before or skimmed over in the past.

If I understand the "Gear Speed Step Freq Calculator" correctly, for gear box of 7.2 and with 20 pitch, 30 tooth pinion gears, my motors steps should be set at 3055.775 which they are but my kernal should be set to 37 kHz which it is not. I am currently running at 25 kHz.

What I don't understand is what effect does this have on the way the machine runs? Further clarification, please.

Thanks

Nils, you may have put your finger on a problem here.

25 Khz, or 37 Khz is the number of update cycles your system can make per second.

If you are familiar with the concept of a 'carrier wave' in radio transmission, it's similar.

If you attempt a movement that requires more updates than your kernel can sustain per cycle, it will "jump" to catch up. This can cause stairstep like patterns.

Unfortunately the max kernel Khz is a function of the computer you are running on, and isn't always directly related to the clock speed; it's related to the I/O and interrupt handling capacity of the machine, which is much harder to predict.

If you push it too high you'll know, because the machine will hang, or you'll get errors reported.

Brad,

Thanks for that explination and I will at least set kernal at the speed recommended by the Geard, Speed....Calculator. That is a good place to start.

Brad, Nils,
Correct me if I am wrong here, but isn't the nubmer for kernal speed in the calculator for MIN kernal speed for the gearing/pinions/max move speed? All I mean is that number is the kernal speed you would need to do the max speed move (rapids). When cutting at slower speeds , as long as the kernal is capable of covering the speed your at you should be fine. There is also a risk of running your computer at too high a kernal speed for the hardware you have also.

Heath, you are correct. However, I don't know what the max speed of Nils' machine is, and the fact that his setting is low in combination with the other symptoms makes me suspicious. It may turn out the the problem is that it's too high for the computer to sustain, and that's what causes the issue.

What I'm looking for at this point is some evidence that changing his computer configuration affects the periodicity of the cut problem.

Brad,
Thats a good point, it might shed some more light on the computer in use. I did not mean to discredit your test.:o

Don't we have to look at what is being processed and what is being sent out.

Lets look at an extreme example. When a computer is running simulator software, it is taking in lots of data, sending out data or commands and processing lots of data so the kernal has to be set at a level that will handle all this processing or traffic.

If I understand how Mach works, G Code is processed one line at a time. A line of G Code is sent one after the other. I don't know if there is a message sent back from the PMDX that says I got the line send the next or if mach is just sending lines and assumes the PMDX is processing but I suspect there has to be some communication because if you push hold it takes a little time to process that command and send a message back that says "ok, we will hold".

This is simple communications and so the kernal is not going to be handling a lot of traffic. So the Kernel needs to be set at a very low level but it still needs to be high enough so it can handle the traffic. To low and we have a problem and to high, it might use processing that could be used some place else but we don't have any thing else going on so high doesn't matter as long as it is not too high.

Is that the way it works or is my thinking off?

I don't think that having the kernal too high will be a factor but too low could be.

We're definitely drifting off topic here in gear pinions (my fault).

The PMDX never sees the GCode. All it sees are the step and direction signals that are calculated in software. Generally software that handles GCode will pause after it completes a line. So if you start a long slow cut from one end of the table to the other, and press pause, the pause takes effect after that cut completes, not in the middle.

The kernel is handling a pretty substantial amount of traffic, in that to move an inch, it has to output thousands of step pulses, and each one has to come at precisely the right moment. You are correct that having it's setting too high is not a problem unless it exceeds the capacity of the computer in question.

Nils,

I'm not sure about how Mach3 does it but here is what I understand about g-code. First, this is a command language which means it as to be interpreted and transformed into signals then you have what is called a trajectory planner which basically looks ahead for the next move(s) in order to keep the path as smooth as possible (set by config) and all this while taking into account accel. and decel. and a few other things as well.

All this planning and calculations take quite a bit of time compared to just maintaining the signal (pulse) stream at a desired level. There are also real time events such as an E-stop that needs to taken into account, the response time for this also affects the overall system performance.

Basically, you need to have a signal (pulse) cycle active time long enough so that the CPU as time to do its other (required) tasks with time to spare just in case it needs to stop on a dime and this active time needs to be short enough that the cutting speed is acceptable.

One other thing to consider is the rather steep decline in torque of the stepper motors as its RPM increases. This physical limitation also limits the maximum signal frequency required for the controller. In other words, even if you could generate pulse in the hundreds of Khz there will come a frequency beyond which the motor will stall and begin to miss steps.

Hope this helps,
Yves

Brad and Yves,

Thanks for the clarification.

Hello Guys,

I did some calculations on my Gears etc. As I use Module 1, OM7.2, gears 35 teeth I get a magic Number of 130.962. Everything looks ok up to here..but when I calculate with the max rot of the OM of 250rpm I get out a speed of only 3800 mm/min. One whole minute for the spindle to go one full x direction? Can this be really correct? How long will it take to surface the table?
Please tell me I did a mistake and the working speed will be higher...:)

I don't know where you see: "the max rot of the OM of 250rpm"?

Maybe the output shaft max speed is 250rpm while the actual motor turns 7.2 times faster?

If the output shaft can turn at 250rpm, the pinion has about 100mm circumference, the x-speed is about 25000 mm per minute which is fast enough! :)

Gerald,
Oriental Motor lists the permissible speed on page C-231 of one of their older catalogs. I haven't downloaded the current catalog, so that information might be missing.

Claus,
That is the output speed of the gearbox, which, with a 7.2:1 gearbox, means that the motor would have to be spinning at 1,800 RPM. At that speed, the motor only produces only 30 oz*in of torque, so it is not practical to run that fast.

Because I'm on the inch system, I haven't paid any attention to the metric spur gears, but a spur gear with 1.25" pitch diameter (25 tooth) moves about 3.925 inches per revolution, so 250 X 3.925 = 981 inches per minute, or 16 inches per second. Getting 50% of that speed would meet most needs.

Hi
I have a Mod 1 rack, 31 tooth pinions 5:1 gearbox microstepping to give 1600 pulses per rev of the stepper.
I set Mach 3 to 82.144 steps per mm.

I am getting about a 6% error in the movement distance.
Where have I gone wrong in my Calc?
Thanks
David

What drives are you using for the motors, and what are they set to for micro-stepping? (The geckodrive is fixed at 10 micro-steps).

The 5:1 gearbox 1600 pulses has me scratching my head....

Also count the number of rack teeth over 100mm to verify that it is Mod1. (a quick mental calc says 32 teeth?)

Hi Gerald
The drives are motion King pulse per rev set for 1600 pulses per rev (8 micro steps 1.8 degree per step) followed by a gearbox mechanical gear reduction by G5
32 teeth on the rack very close to 100mm.
Cheers
David

Then 82.144 is correct. Are you sure that you didn't type in 87.144? :)