I started the conversion from original set up to Mach 3 with Gecko drives in October 2009.  Fast run down of changes: break out board from Bob Campbell, Windows XP Pro, stripped out old and replaced with new power supply and rewired everything, and a new computer.
Problem: X and Y axis has intermittent bumping and losing steps randomly. I have read a lot of the posts concerning lost steps and have tried many of the solutions offered with no luck. Motor tuning will run without any problems as high as 102 IPM but I can not get the mill to perform without losing steps as far down as 2 IPM which is unacceptable for a rapid rate or a G0 function. I have spent hours reading posts of other Bridgeport posts that only get 50-60 IPM on rapids which would be fine with me if I could get that without missing steps.
Any and all suggestions would be most welcome as I am at my wits end. Trying to keep post short but rebuilt  ball screws, replaced steppers (NEMA 42) and drive. There is a lot more I have tried, if you need more information on what else was done in order to help me please let me know.  Basically just about everything has been replaced with new.

Thanks in advance
Coke 

Start with the basics.Power supply size and voltage, drives model ampsettings, stepper make model. What are the tuning parameters, Vel, accel.

Are the drives direct drive to the screws or reduction.

WHen you say the drives tune ok up to 100 ipm, how are you testing them?

(;-) TP

Power supply size and voltage: 60 volt DC; Drives: Gecko 201; AMP settings 6 amps; Stepper make and model: Z and Y axis are original NEMA 42, X axis has a new Kelling NEMA 40 tooth; Tuning: Currently 55 VEL acceleration is set a 1.75; Drives are belt 1 to 1 5 tpi lead; Drive test: with the tune feature in Mach and the settings for X and Z is 105 acceleration of 5 and the Y will only do 102 ipm with the same settings. I realize that is Mach running flat out but the motors all run smooth and quiet, the problem comes in when I slow down to run a program at slower speeds.
Thanks for your rapid response and willingness to help.

POwer supply size in amps??  IF the capacity is too low when all drives run at the same time the drives may not prove enough power to the motors and may loose steps.

How do you have the drives setup do you use micro stepping?? Large steppers suffer from mid range resonance microstepping helps with that.

(;-) TP

My Bridgeport is a UK version of the Boss 6, in other words a Boss 6.1. It has metric ballscrews (5mm pitch) and gearing of 2.5:1 as standard and  I use G201/G202 and have Nema 34 916 ozin steppers. I can get 2500mm/min (100IPM) with Accel of 40mm/s/s but I have chosen to reduce the Vel to 2200mm/min and can now get the Accel to 120mm/s/s.

There may be several issues with your mill, first is the bigger frame motors may be holding things back a bit, however you should still get better performance than you are. Velocity may be helped slightly by getting a slightly higher DC voltage, I am using 77 VDC
As Terry has mentioned your power supply may not have enough wattage for running more than one motor at a time.
 If you have not done so already run the driver test to see what  it looks like and if you have the kernel set in Mach to higher than you need try reducing it.
Hood

Terry, Hood    What I have is 1970 Bridgeport Series 1 Cnc updated to BOSS 5
                     I installed a AN TEK 800VA Toroidal Transformer 10 Amp and built the rest of the power supply from parts
                     The original steppers are Superior steppers (90 VDC 8Amps)
                     I replaced one with a Kelling KL42H2150-42-8B 
                     All 3 drives are Gecko 201 they are set microstepping the way I read the set up sheet
                     Sound Logic BOB Rev 1.9 (Bob Campbell has been a grate help)
                     Added a Sumitomo VFD and a sound Logic inter face board
                     Current motor setup
                     Steps Per            Velocity                Acceleration           Step Pulse               Dir Pulse
                        10000                70.0                       2                         5                          5


I run a progran to make a 6" square with a 1.5 pause at each corner as to read indicator before next axis move, it misses steps at all speeds worst at 31 IPM.                 

Coke

As I said previously your Nema 42 motors may be the problem and looking at the specs of them it could well be that. The G201 says "Motor winding inductance should be 500uH or greater, but generally no more than 7mH." and from the motor specs on Keling site it says your motors range between 16mH and 64mH. Might be worth emailing or calling Gecko to see what they say.
Hood

Well if you have the drives set to max6 amps and you have 3 drives running that would be 18amps total.

So you may have a problem in a worse case senario EVEN with only 2 drives active at a time as that exceeds your power supply.

IF you only run 1 axis back and forth as fast as they go does it loose steps?

Just a thought, (;-) TP

Terry,
I don't think it loses any steps at high speed. It runs very smooth in motor tuning. I will set the speed up on the program and try that later tonight.
Thanks Coke

Terry, Hood    What I have is 1970 Bridgeport Series 1 Cnc updated to BOSS 5
                     I installed a AN TEK 800VA Toroidal Transformer 10 Amp and built the rest of the power supply from parts
                     The original steppers are Superior steppers (90 VDC 8Amps)
                     I replaced one with a Kelling KL42H2150-42-8B 
                     All 3 drives are Gecko 201 they are set microstepping the way I read the set up sheet
                     Sound Logic BOB Rev 1.9 (Bob Campbell has been a grate help)
                     Added a Sumitomo VFD and a sound Logic inter face board
                     Current motor setup
                     Steps Per            Velocity                Acceleration           Step Pulse               Dir Pulse
                        10000                70.0                       2                         5                          5


I run a progran to make a 6" square with a 1.5 pause at each corner as to read indicator before next axis move, it misses steps at all speeds worst at 31 IPM.                 

Coke

The power supply for stepper motors should be sized at roughly 70% of the total rated current of the motors.  So, if you're using Geckos set for 6A, and you have three motors, the supply should be rated for at least 18 * 0.7 = 12.6A continuous.  AND, you must have sufficient capacitance in the filter as well.  For 3 6A motors, you should have probably on the order of 20,000-30,000uF of filtering.

Regards,
Ray L.