[Angelok]

I'm not sure if this is the right place to be posting this, (I'm new here) so if it's not any suggestion on a better location would be appreciated.

I recently purchased a used machine (Digital Tools RD-903-1) and for the most part it works well but it does give me some accuracy issues. It's have a 5' x 10' cutting area with stepper motor and a Porter Cable router, I'm using Vcarve Pro for the drawing and a older version of Mach3.

What happens is if i cut a small circle say round 1.5" diameter, it isn't perfectly round, but if i cut that same circle over and over again it is constant. If I cut a larger circle say around 8" diameter it fine. I did a test, where I put a 4' x 8' sheet on the table and cut out 11" x 11" squares and there weren't all the same. It was only a small difference but it seems that the accuracy is different at different placed on the table.

Does anyone have any ideas on what I can do or what the issue is.

Thanks,

[wmgeorge]

If you set it to do say a 12x12 inch square is it the right size? If its the right size but not repeatable or not square you have some setup issues. If its an older machine it might mean worn parts or adjustments as needed. Start by making the test squares and then look for worn out or loose parts.

[Angelok]

I've been doing a bit of research and that does sound like the best place to start. this is my plan:
Set the machine at zero and run an patters to see if it ends at the same starting point, from what I recall from the last tests I did is it was only the X axis. So that would lead me to believe that it's mechanical.
Then I'm going to do the 12 x 12 test you suggest on different areas on the table and see what that gives me.

Is it possible its a software problem?

Thanks for the info.

Angelo

[wmgeorge]

I've been doing a bit of research and that does sound like the best place to start. this is my plan:
Set the machine at zero and run an patters to see if it ends at the same starting point, from what I recall from the last tests I did is it was only the X axis. So that would lead me to believe that it's mechanical.
Then I'm going to do the 12 x 12 test you suggest on different areas on the table and see what that gives me.

Is it possible its a software problem?

Thanks for the info.

Angelo

I can be anything, but its an used machine, The easiest thing you can do right now is a good visual inspection of all the moving parts. If its got belts check them, and so on. It could be combination of things. Rule #1 start with the simplest first. Don't change a lot of adjustments until you see what the last one you did changes. KISS rule. Good Luck!!

[ger21]

Is it possible its a software problem?

Not likely.
Flex in the machine is far more likely.

[peteeng]

Hi Angelo - Are you cutting a true circle (G2 or G3?) or is the cutting via a dxf file? If its via dxf use a fixed small increment such as 1/16" or smaller on export, some dxf settings use angles and chords and these can make arcs funny shapes. Imperative you need to check all mechanical stuff is OK. I'm not familiar with Mach3 but most CAM software also has accuracy settings via the speed of cut. So accuracy can depend on feed speed. In UCCNC this is called interpolation mode. Its either exact or constant velocity mode. In constant velocity mode the path interpolation is trying to maintain a constant velocity so will try to stay between path parameters set. So if you cut a circle using a slow speed and then a fast speed and they are different then it could be your interpolation settings as well....Cheers Peter

[Angelok]

Thanks

[Angelok]

Hi Angelo - Are you cutting a true circle (G2 or G3?) or is the cutting via a dxf file? If its via dxf use a fixed small increment such as 1/16" or smaller on export, some dxf settings use angles and chords and these can make arcs funny shapes. Imperative you need to check all mechanical stuff is OK. I'm not familiar with Mach3 but most CAM software also has accuracy settings via the speed of cut. So accuracy can depend on feed speed. In UCCNC this is called interpolation mode. Its either exact or constant velocity mode. In constant velocity mode the path interpolation is trying to maintain a constant velocity so will try to stay between path parameters set. So if you cut a circle using a slow speed and then a fast speed and they are different then it could be your interpolation settings as well....Cheers Peter

Hey Peter, Thanks for the info. i think what your talking about is still a bit too advanced for me I've found some inaccuracies on my X axis. i'm not sure what it is yet but I feel much better about the machine now that I'm starting to isolate the issues. Once I have that figured out I'll look into what you were talking about.

Once again thanks for putting in the time and sending the info.

[Angelok]

Hello everyone,
I want to say thanks to everyone here, this forum is awesome!
I did some testing on my machine today to see if I could isolate some of the issues and I’m starting to think this may need more work than I anticipated.
First what I did was set the machine to zero and ran a few patterns. I wanted to make sure that it went back to zero each time. It was perfect!
The next thing I did was cut out some 10” x 10” squares. I cut out 24 pieces form a sheet 34” x 92” so 3 pieces along the Y axis and 8 along the X axis. (See attached)
On the X axis they were all the same, not perfect with a bit of a bow but not my concern at this point (baby steps). The Y axis on the other hand… the first row was 9.9375” the middle row was 10” and the last row was 10.03125”. As the machine move to the right the cut get larger.
I later did another test with 11.5” x 11.5” pieces and got similar results.
What would cause the measurement to increase?
Thanks

[wmgeorge]

Hello, did you check your machine for wear as I suggested and others did also? If not your chasing a rainbow. No amount of questions posted on here will solve your problem until you decide to to the basics.

[peteeng]

There are several mechanical reasons for inconsistent results eg is the gantry orthogonal to the bed axis? Is the gantry mechanically sound in regard to travel on each side. If the bearings or the rack is poor on one side then the gantry "walks" as it runs along. ie one side leads then the other side leads or lags etc. This is a sort of slip/stick mechanism. All mechanical components must be checked and found to be correctly operating. My really big question is how are you measuring objects to 1/10000" ? Peter

[GJeff]

From the picture it looks like you have vertical racks with plenty of chip debris collecting on them. That could be one source of inaccuracy.

If the two tracks that your gantry run on are not parallel, then it could be squeezing or pulling the legs of your gantry apart. This could cause the gantry to flex more when at one side of the table, and a flex in your gantry would result in the travel of the tip of your end mill increasing or decreasing during Y travel. That could be an explanation to the differing Y measurements of your squares.

[mactec54]

I'm not sure if this is the right place to be posting this, (I'm new here) so if it's not any suggestion on a better location would be appreciated.

I recently purchased a used machine (Digital Tools RD-903-1) and for the most part it works well but it does give me some accuracy issues. It's have a 5' x 10' cutting area with stepper motor and a Porter Cable router, I'm using Vcarve Pro for the drawing and a older version of Mach3.

What happens is if i cut a small circle say round 1.5" diameter, it isn't perfectly round, but if i cut that same circle over and over again it is constant. If I cut a larger circle say around 8" diameter it fine. I did a test, where I put a 4' x 8' sheet on the table and cut out 11" x 11" squares and there weren't all the same. It was only a small difference but it seems that the accuracy is different at different placed on the table.

Does anyone have any ideas on what I can do or what the issue is.

Thanks,

How is the machine build 5' x10' is a big machine to be only using a router for a spindle, post a photo of the machine

If your 11" x 11" squares where different you need need to check the calibration of each axes to get the steps/per set correct, or you may have backlash also

Try cutting the 1.5" at a slower speed, it sounds like you have flex as well, it should cut the same as the 8" just may be getting flex and backlash going to fast when cutting

[mactec54]

Hello everyone,
I want to say thanks to everyone here, this forum is awesome!
I did some testing on my machine today to see if I could isolate some of the issues and I’m starting to think this may need more work than I anticipated.
First what I did was set the machine to zero and ran a few patterns. I wanted to make sure that it went back to zero each time. It was perfect!
The next thing I did was cut out some 10” x 10” squares. I cut out 24 pieces form a sheet 34” x 92” so 3 pieces along the Y axis and 8 along the X axis. (See attached)
On the X axis they were all the same, not perfect with a bit of a bow but not my concern at this point (baby steps). The Y axis on the other hand… the first row was 9.9375” the middle row was 10” and the last row was 10.03125”. As the machine move to the right the cut get larger.
I later did another test with 11.5” x 11.5” pieces and got similar results.
What would cause the measurement to increase?
Thanks

Gantry Y Axes may not be square to the X Axes, the Y Axes may have a calibration problem or wear in the drive what ever that is, it looks like you have a light weight construction so expect to have flex as well

[mactec54]

Hey Peter, Thanks for the info. i think what your talking about is still a bit too advanced for me I've found some inaccuracies on my X axis. i'm not sure what it is yet but I feel much better about the machine now that I'm starting to isolate the issues. Once I have that figured out I'll look into what you were talking about.

Once again thanks for putting in the time and sending the info.

Don't get confused with what he has posted I believe Peter is confused himself, it is amazing what some people will post, I think what he post is over his head as well

[Angelok]

Hello all.

I've been working on my machine and I'm stuck. I'm hoping someone can give me a bit of direction. To recap, I have an older 5' x 10' CNC that uses stepper motors with a rack and pinion and a Portor Cable router. It was giving me some accuracy issues so I changed all the V groove bearing as well as a couple of others. I tightened up the rack and pinion and overall the machine is running ok, not great but ok. When I run at a very slow feed speed it works well but once I speed it up not so much. I attached a picture of two 5" x 5" squares that I cut. Both are 5" x 5" and the inside cut out are accurate and the same. The only thing is on the one run at a high speed the corners have rounded. I've run the test a few times and the same thing every time. Everything looks ok but I'm clearly missing something and just don't know what.

Does anyone have any ideas on what I should be looking for? The machine is running on an XP computer with an old version of Mach 3. Could it be software?

Any direction would help.

Thanks

[ger21]

It's caused by a combination of low acceleration and CV mode in Mach3. Mach3 is trying to maintain a constant velocity, so it has to round off the corners to do so.

[Angelok]

Can I turn off the CV mode to correct this?

[Angelok]

I just looked it up. I will do some tests with exact stop tomorrow. Thank you Ger21, I appreciate the feedback.