Early ascending Z travel

[esteeme1]

Hi All,

I recently had to swap my Z stepper and harness, using Mack 3, with encoders. I'm having trouble with the Z travel ascending to early. It is ramping up to the programmed height and I am losing detail in all my 3D carvings. I didn't have the problem before and am certain it is a motor tuning issue.

The questions are,

1. Is my initial assumption correct or is there another issue I need to address?

2. If correct, armed with the knowledge of the motor ascending early / ramping up to height should I tune the motor up or down?"

I should add that the motor seems to sound OK, z travel is dropping correctly and I am not losing reference.

Thanks for the help.

[esteeme1]

Ok, Maybe I'm answering my own question with another question. I just have a lot of reserve concerning motor tuning and changing those setting. I just don't recall making any other changes to my setting after I replaced the stepper.

Should I use G61 and if so where can I program / set it to automatically code in the PostP? Is there a setting Aspire or Mach 3?

[zeeway]

Hi Jim,

If you really want to change the exact mode or constant velocity mode in Mach3, you can set these under Config/General - in the second column, I think.

But are you sure you are not losing Z steps? One of my old problems was that my Z axis would gain height through complex programs - turned out I was losing steps in the feed direction. Does it still happen if you slow the acceleration for the Z axis way down (in Motor Tuning Screen)?

Angie

[zeeway]

Jim,

One more thought - if you are truly not losing your Z reference back to zero, perhaps you need to fine tune your z motor in terms of steps per inch. So, if you are asking it to make a z move of say 1 inch - are you getting 1-1/8 or something like that? If that is the case, you can correct that by clicking on the settings button on the top of the Mach 3 screen. Next click the "set steps per unit" button and follow the directions.

Good luck,
Angie

[esteeme1]

Angie,

I'm pretty sure I'm not losing Z ref. I checked the movement last night and wasn't able to measure any deflection.

I have a previous photo before I replaced the motor but will have to post later this evening. I found the location to change to exact mode (it is where you said it was) but, it slows the machining process down by at least +60%.

I did tune the motor down from 160 ipm to 155 and also changed the number of look forward lines from 100 to 300 and didn't detect a differance. My acceleration was set at 4 do you think I should set it any lower? I guess I'll give it a shot.

I'm only running at 60 ipm and would be surprised that I need to slow it down much more. I'll try 55 ipm and compare the differance.

The carvings are acceptable but the quality isn't what I'm acustomed to.

I'll get back to you after I run a few more tests and follow up on your suggestions. Thanks for the help it always helps to talk thing through with someone.

[zeeway]

Jim-
Accel of 4 is pretty dang low. I think you are okay there. Also your feed rates are low. Is everything tight mechanically - any backlash to speak of?

Angie

[esteeme1]

Angie,

Just got home and slowed the motors to 3, no help. I reran my tool path at 50 ipm and it reduced the ramping quite a bit. It just didn't have to run this slow before.

I have ball screws on all 3 axis. They are clean and freshly lubed. The pulley / drive wheels are tight as well.

What bit sizes are you usually running? Maybe it has something to do with that? I'm using a .062 BN on this one but again I just don't remember using such a slow toolpath.

I think I will stay with this for a while until I get completely annoyed.

Thanks for your help, your insight is most appreciated. I will post some photos later.

[zeeway]

Jim,

I try to avoid using the .062 diameter - as it takes forever. I am using a .125 ball nose bit right now with an 8% stepover at 100ipm (nominal) for a carving of an angel that is roughly 6 inches by 8 inches. The finish pass is taking about three hours - also slow.

Angie

[esteeme1]

Most of my carvings are 6 x 4 I use a step over of about 5% - 6%. Depending on the detail I will use a .093 or 062BN. It would be nice if there was a setting that would control the lead or ramping into an elevation change. Something that corresponds to the step over would be good. My carvings are averaging 1.5 .3 hours as well.

[esteeme1]

OK I'm back the first photo is before changing the stepper at 60 ipm, the second is at 60 ipm after and the third is at 50 ipm after. the model presentation looks great. I should add the first one is a little larger.

[esteeme1]

OK, I hate to admit but I made a rookie mistake. I never cut this plaque at the size I am cutting it at. What happened was I made the plaque some time before my machine went on the fritz. I actually reduced it fro 6.5 inches to 4.

So this is what I ended up doing.

I resized the existing model and copied it into the plaque model. After I copied the model at the size I need I baked it and auto smoothed to about 3/3 on the level bar. I'm running a test run 60 ipm and it looks much better.

Angie thanks for all the help you kept me on the right track.

[zeeway]

Jim-

Whew, glad you figured it out. Just one more thing - in general this post talks about speeding up carvings by cutting in the direction of your gantry - if you haven't seen it, I think it is worth a look: http://www.vectric.com/forum/viewtopic.php?f=28&t=4220.

Angie

[esteeme1]

That's a great post. How is it that I'm running at 4 and 5 acceleration and tuned at 160 ipm? I use encoders and seem to lock up or lose steps if I run with a faster acceleration. So I dropped it down to 4. It doesn't lock out until it is in the rapid movement. The carver still averages 60 ipm as ordered by the tool path. I generally use climb cuts and stay away from the raster but only on oval or round cuts. With the climb cut I get l cleaner lines and don't see the bit stepover as much.

Man I can't amagine increasing the acceleration to 30+. I'll have to run a few test so find out my limits.

Thanks again.

Jim