View Full Version : Ebay 3040 issue with mach3 - incorrect scale when machining?

Wayne Kinney
03-03-2012, 11:18 AM
Hi Guys, first post here :)

I recently bought an Ebay 3040 CNC mill, Mach3 and Vcarve Pro for an upcoming project (producing model railway track bases).

I've done setting up mach3 with the recommended mach3 settings of the manufacture here:

My problem is that when mach3 says the axis has moved say 20mm, it has actually moved more like 30-35mm.

Does anyone know why this might be?

The recommending settings for both x & y axis are 400 'steps per' in mach3 motor tuning, but I could only get it working correctly if I lowered this to around the 320 mark.

Also, it recommends velocity as 2000 for x & y, when I enter this and click 'save axis settings', it changes to 1999.98 or something.

I work in MM's in all cad and have mach3 set to MM's.

If anyone has any ideas, I would appreciate the help.


03-03-2012, 10:30 PM
To work this out, you'd need to know the pitch of your leadscrews...and if your stepper driver board is using microstepping - do you know?

If you don't know but have access to a dial meter (pretty essential if you've a CNC machine), then goto to the mach 3 settings 'tab' (ie one of the other screens) & click on calibrate axis (that's from memory...so might be just calibrate) - choose an axis ....instruct mach3 to move your axis say 5mm is the 'distance to move' box (again from memory)!) - then see how far it actually moves by looking at the dial meter - tell mach3 this info (it'll ask you after it has moved the axis "how far did the axis move?") & it'll auto alculate your steps per unit for you.

03-03-2012, 10:33 PM
Hi Wayne,
We are working on our Wiki at the moment and axis calibration is something we have covered. Take a look here:
Hope this helps. If you need any further assistance send us an email or give us a call and we'll talk you through it.

04-03-2012, 12:49 AM
The specified settings (400) worked for us with the same model machine. Unless they have used different leadscrews on yours, then those settings should work.

It could be an idea to double check your stepper motor couplings for tightness to confirm that their isnt any slippage.

Wayne Kinney
04-03-2012, 10:29 AM
Thanks for your replies,

I will try the calibrate process and report back on the settings mach3 gives me for steps per..

I don't beleive this is due to any slippage, as it is consistently out of scale.

04-03-2012, 11:11 AM
The SET STEPS PER in the settings tab will be your best option but you due to the fact you don't fully know the pitch of the screw and if it's cheap lead screw, which it will be, then there could be error between spec's and reality.!! The SET STEPS PER gets round this because it measures actual movement BUT YOU MUST MEASURE ACCURATELY.

Best easyist way is to get the longest vernier gauge you can find, longer the measurement the more accurate the machine will be. Clamp the end to the bed with a block of wood or something in between but still so the scale can slide then open them up wide as will go and zero them out, then bring the Z axis done so when you type movement amount in SET STEPS PER it push's them towards closed position. This will give you most accurate reading with out user error creeping in.

I recommend you do it twice, the first time with a small movement just in case your miles off with the steps per in motor tuning,(Dont forget to save each time). Do this for all Axis, this will get you very close, then do another pritty much the full length of your verniers capabilty.

Hopefully this will get you back on track.!!

Wayne Kinney
04-03-2012, 11:17 AM
Thanks for the tip!

Thats a great idea, I was thinkig about drilling holes and then measuring this but your method is much better and as you say removes user error!

My caliper has 150mm max, which is bigger than the parts I mill.

Thanks again for the advice!