View Full Version : Problem with calibration

06-04-2010, 02:06 PM
Okay here's the rub;

Recently installed a new bearing on a trapezoidal screw after which was able to true everything up just nicely and reassemble went wonderful. Recalibrating is turning in to a nightmare. at 1/8 step I can get it to move wonderfully but to calibrate it to steps per distance it goes nuts and drops steps and over rev's. I am using a Motion King 23HS8603 NEMA23 motor, a DIYCNC PCPPS-3 BOB and DRV25PS drivers with a 24V 14.6A PSU on a 500mm by 250mm by 50mm Gantry router. It wants to set at 514 steps per unit on the Mach3 control I am using via a pure serial (no USB involved).

If I set it at 250 for step up testing it will run out from the motor fine and back. When I start trying to run it at the setting that comes up from testing which is slightly above 514. It will start dropping steps and over reving. This is setting the acceleration as low as it will for the steps per unit. the speed is at either 1000mm/min or 1500mm/min and same results.

So the question is do I need to upgrade the motor or slow down the speed? As this is slowing a few important projects down. Thanks for any and all useful responses.


06-04-2010, 07:43 PM
Well further checking the lead screw seems to have developed a bit of a bend to it. Will check the bearing screw to be sure that is secure and not causing a problem on the free end. If it is the lead screw, any suggestions on a Marchant Dice 3 axis router for fixing the problem as this is really a bummer as need to get some cutting done yesterday for a client.


07-04-2010, 02:57 PM
Well the cap screw was loose and decided to re-true the whole system. Which now has me able to run at 550mm/min on the long axis with an acceleration of 2.5 which at 1/8 stepping gives me pretty good accuracy. As it is going to have to grind a bit off the end of the x axis or double check it's cap screw as it is now binding against the stepper post. Man am I looking forward to the oldham clamps getting here.

Still would like in put as to why not able to hit anything above 550 without dropping steps and locking up with over rev's. Z is doing fine at 450mm/min which gives a really nice smooth movement up and down and more than enough control in steps. So figured a good bit of it out myself. Still would like to get it up to 850 or 1000mm/min movement only to allow a bit faster cutting speed and quicker movement between cutting points.


08-04-2010, 11:48 PM

What screw dia/pitch on X?

22-04-2010, 02:20 PM

Let me be sure I understand. You want the thread pitch (angle of the face of the thread) for the short axis on my machine? I have gotten the calibration under control though and down to .05mm repeatable tolerances. Which is good enough for now. I cut off a bit of the X axis as it was butting against the axle of the nema motor when mounted in properly. So that is fixed and is now running very well.


22-04-2010, 05:19 PM
no, I was interested in the size of the leadscrew dia, length, pitch (e.g. 16mm, 800mm long, 5mm pitch) so to see if you were getting any effects from the screw inertia exceeding you motor capability at the acceleration you had programmed. Sounds like you were hitting some issues due to excessive endloading due to the screw being too long and this translated to a binding effect which may have been limiting your top speed by preventing your rig accelerating without loosing steps.