Axis stay short of where they should go

[alenz]

Oh man, if I had a buck for every time I did that! But again, I used a digital caliper for the lack of dial indicator.

I think you may have misunderstood TP’s comment (recalculate the steps per unit).  Calculating the steps per unit and using Mach’s axis calibration feature are two totally different procedures. The former will result in an exact correct value while the latter will be subject to measurement inaccuracies (and I would guess errors approaching the magnitude that you describe).

You will need to know the details of your system as TP mentioned in a later post, i.e., stepper deg/step, lead screw pitch, etc.

There is a spreadsheet at:
 http://www.machsupport.com/forum/index.php/topic,16315.0.html
That will do the calcs for you.

If you don’t know some of your system parameters, then give us as much info as possible and I’m sure we can work it out with you.

Al

[JustinTime]

Thanks guys for the answers. I'll go through the procedures again and will come back if I don't get it solved.

[Tweakie.CNC]

Hi Yoram,

I expect you have already seen this post http://www.phlatforum.com/viewtopic.php?f=264&t=2984 but that type of backlash would perhaps be difficult to spot and may not occur at every move. Curious because I have never seen it before.

Tweakie.

[JustinTime]

Yes, I've seen it, Tweakie, and it peeked my interest. I'll have to look into it since the x axis has a belt and it is very high tensioned. I may try to loosen it up a bit and see what will happen.

BTW, did you happen to see my post here? http://www.machsupport.com/forum/index.php/topic,19205.0.html

[RICH]

has a belt and it is very high tensioned

Is it a timing belt or a v belt?

I would recomend that when you check the backlash you base it on one complete revolution of the belt.
You can set the steps per based on a distance of one rev of the belt and then find that it will be out if you check a distance where the belt
is say only half way thru it's complete travel. Steps can be lost or gained with timing belts depending on tension, but, but, but..... you will be hard pressed to find those steps.

Even a cheap indicator will be of value in the shop and can be found new for say $15.00 on sale. Splurge my friend.

Similar problem as yours can be found when a screw profile is not linear, yes it will return to zero, but depending on how you rationalize the
steps per based on a distance you will have varing results. Let me remark that what I am talking about here are small variances.

You problem is not Mach, as i see it, but rather you system.

Been Wrong Before,
RICH

[JustinTime]

It's a timing belt, Rich.

I never thought of making sure the belt made a full rev and I will check it out, and, BTW, I did splurge and bought a dial indicator, at Harbor Freight, on Sunday.

I found an oddity after I bought the indicator which I detailed in my thread 'coming out of jog error'. I wonder what causes that problem.