[luv2ride]

I have the same symptoms of jerky microsteps and have talked to others about it. They didn't seem to think it too odd but they are not very familiar with Tormach's either.

[jake hoback]

I have the weird half step thing with the motors as well. I think its just the steppers, since a lot of people seem to have the same problem? The ways arnt the most smooth thing in the world. Honestly I don't know why Tormach didn't go with Linear ways

I had a few min to adjust the ball screw bearings yesterday but didn't get it finished, so Ill try again today to finish it. I made 3 adjustments and honestly didn't see any take up of the slack in the table ill keep ya'll up to date.

[philbur]

I have the same symptoms of jerky microsteps and have talked to others about it. They didn't seem to think it too odd but they are not very familiar with Tormach's either.

What are jerky microsteps? I believe a microstep, due to the nature of the beast, is only an approximation.

Phil

[philbur]

The ways arnt the most smooth thing in the world. Honestly I don't know why Tormach didn't go with Linear ways:.

????? One surface should be ground and the other have a Teflon coating. A photo of your rough ways would be interesting.

The reason why Tormach didn't go with linear ways is dynamic rigidity.

Phil

[philbur]

With a DTI, a bit of ingenuity and a bit of common sense a person should be able to measure the lost motion between all adjacent components in the train instead of all this guessing.

Path 1a
The table is attached to the end housing.
The end housing is attached to the motor
the motor is attached to the coupling
the coupling is attached to the ball screw

Path 1b
The table is attached to the end housing.
The end housing is attached to the ball screw thrust bearings.
the ball screw thrust bearings are attach to the ball screw.

Path 2
The ball screw is attached to the balls in the ball nut.
The ball nut is attached to the nut housing
The nut housing is attached to the table.

Full circle

Phil

[TurboStep]

What are jerky microsteps? I believe a microstep, due to the nature of the beast, is only an approximation.

In my opinion there's a difference between a microstep approximation and what I attempted to describe earlier: "Although we should not expect all stepper motor microsteps to be the exactly same size I was seeing 2 or 3 very small step increments (measured statically using a dial indicator) followed by a MUCH larger step increment."
This short video shows how my mill behaves now. Prior to stripping it down there was a much greater deviation in the step size. You might like to compare this with your own results.

https://youtu.be/H8fM3os648c

Step

[luv2ride]

Mine are similar to Turbosteps I would say. The good thing is mine seem to work themselves out. Each 2 steps at .0005 show .001 on a .0005 indicator. The first step varies from no movement of the needle to close to .001. The good thing is we don't expect these machines to hold tenths so it works itself out mostly.

[pickled]

Just a question for you folks that are out there examining the micro-steps phenomena. Do you see deviations in your finished parts that are unexplained? For a while I ran a "Who's the boss" troubleshooting part program once a week because I didn't know if my machine was being abused/maintained by the operator who was running it while I was away on another project. Basically I would cut a 1/2" high helical boss of 2" OD with a final finish pass into a piece of scrap precision Aluminum plate. I would then measure it from top to bottom at 90 degree angles and record the clocked results. I started trending the deviations from X to X and Y to Y from my target on an individual moving range chart. After 2 months I didn't even bother to calculate the control limits because the normal noise was so minimal that even the naked eye could see that the machine was in perfect working order for my needs and my worries were ill founded. The only time I saw something in the data was when the end mill that I was using had a small piece of chip-weld on it that I missed seeing(pure operator error component). I would advise if you are really interested in understanding if things are getting better or worse to start logging the results of a periodic dynamic cut test to get real world baseline data. Sometimes simple measurement error can send you on an erroneous goose chase...this is especially true if the machine is robust to such minor influences in a dynamic state. I try not to react and go into tear down mode unless I see something that is a real trend or an obvious abherrant deviation that could effect my finished product. Just 2 cents thrown out there from someone who went crazy a few times before...hell I may still be crazy I don't know :-).

[philbur]

In my opinion there's a difference between a microstep approximation and what I attempted to describe earlier: "Although we should not expect all stepper motor microsteps to be the exactly same size I was seeing 2 or 3 very small step increments (measured statically using a dial indicator) followed by a MUCH larger step increment."
This short video shows how my mill behaves now. Prior to stripping it down there was a much greater deviation in the step size. You might like to compare this with your own results.
Step

What did you do/change during the strip down?

Best not to use a 2 muM DTI if you want to avoid disappointment. When you make such small steps the actual table movement is very much dominated by stick/slip. which by its very nature will be variable, the variation in microstep size will accentuate this stick/slip effect. Even a couple of shots of oil and/or a bit of adjustment will change the behavior. Large variation in microstep size (by their nature they always average out correctly, unless you actually lose steps) does not translate into greater day to day inaccuracy in your parts. Just live with yet another fact of life and carry on machining. If you need/want/expect accurate control of the table movement down at the micron level then you would need to consider a different class of machine.

Phil

[bevinp]

As Ray L said previously in this thread, the hestitant jumpy steps evident when manually stepping an axis will most likely disappear during a cutting motion. The vibration and cutting load will certainly overcome any "stick - jump" behaviour in any axis (unless the gib is way too tight). And as pickled says, the only reliable test is a test cut, A circular milled outside diameter will give you excellent info on backlash of the two axes; and OD is easier to accurately measure than an ID.
Bevin

[IMT]

What TurboStep's video is showing is a characteristic of microstepping. Full torque is only available when the rotor and stator line up at a full step (every 1.2 degrees on the 3 phase Tormach series III motors). Every microstep produces an much smaller amount of torque that may or may not be able to overcome the static friction of the system. If it isn't enough torque to move the load the motor shaft doesn't move. Commanding additional microsteps incrementialy increases the torque. When it becomes enough to move the load it jumps all those steps at once. Here is an article (written by a servo motor manufacturer so it's a little biased) that explains in better detail.

Microstepping: Myths and Realities | MICROMO

Dan

[mountaindew]

After spending the better part of a another day testing different ways to measure and adjust my machine I worked out a decent system I think.
Looking for consistency I found setting small steps like 0.0001 as noted before and by others was all over the place and frustrating. I changed step to the same tick as dti indicator marks of 0.0005 and then moved the target axis 0.002 in each direction and carefully watched and estimated the difference over those steps and distance. I found I could measure and get consistent results for each axis x,y,z. Made bearing preload and gib adjustments a more straight forward effort.
Hope this helps others zero in on a method to use with their tools and machine.
md

[philbur]

What TurboStep's video is showing is a characteristic of microstepping...................... If it isn't enough torque to move the load the motor shaft doesn't move. Commanding additional microsteps incrementialy increases the torque. When it becomes enough to move the load it jumps all those steps at once.

Dan

I'm not sure this is completely correct. If you look at the video there is movement for EVERY microstep, it's just that the magnitude of the movement varies for each step. In the case of the video the variation is actually quite small.

Phil

[philbur]

Another thing to consider is that if your small movement command is not actually a whole number of microsteps, which it almost certainly will never be if you work in imperial, you will get variations in successive movements due to rounding errors. The errors however are not cumulative.

As Mach calculates in imperial units but the ball screws are metric this also introduces a very small rounding error. This is why for example if you command a move to X10.0000 mm You may see X10.0002 on the DRO. However because of the way Mach calculates this error is also not cumulative.

All of this goes to show that you need to be careful when trying to determine your real life day to day performance based on measurements down at the microstep level.

Phil

[jake hoback]

Well that was a wash and a waste of time. I got the ball screw bearings adjusted per Tormach's manual. Managed to take a woping .0003 backlash out of the system Guess Ill have to live with .003 on all axis besides the z until I can replace the ball screws. what a pain in my a$$. Should have bought a real VMC, honestly need better tolerance than what Tormach says it can do from the factory anyhow so time to save pennies.

[hayes]

Hey Jake,
I've been following this thread with interest as what you do is of interest to me and what I'm wanting to do. Since you brought up buying a VMC, have you considered selling the Tormach's and getting a fullsize VMC? Any ideas of what mfr. you'd go with?

All the best,
Josh

[TurboStep]

...but the ball screws are metric...

Are you sure about this?
Check out Small CNC Buyer's Guide -Engineering and Machine Design | Tormach Inc. providers of personal small CNC machines, CNC tooling, and many more CNC items. and search for "5 tpi"
Step

[SCzEngrgGroup]

Are you sure about this?
Check out Small CNC Buyer's Guide -Engineering and Machine Design | Tormach Inc. providers of personal small CNC machines, CNC tooling, and many more CNC items. and search for "5 tpi"
Step

You can easily tell - just look at the Steps/Unit setting in Mach3.... If it's an integer multiple of the steps/rev, then the screw is in the native units of the machine setup, be that inches or mm. If it has a factor of 25.4 or 1/25.4 then it's not.

Regards,
Ray L.

[philbur]

It looks like my memory was incorrect. I wrongly remembered the screw as being a 5mm pitch. I apologise for the error. It doesn't alter the principle though, in that if you are working in none native units you will almost never have moves that are exactly a round number of microsteps.

Phil

Are you sure about this?
Check out Small CNC Buyer's Guide -Engineering and Machine Design | Tormach Inc. providers of personal small CNC machines, CNC tooling, and many more CNC items. and search for "5 tpi"
Step

[TurboStep]

That's why I changed to inches for the video
Step