losing steps

[wood400]

Hi Folks. Good morning. I am having a problem with running 3d files ,Free vase rose is the file i am running at this minute. What happens is during the rough cut there are 3/4 passes and on each pass the bit moves along the plus Y axis about 2mm so after 3 passes there are 3 steps on there right side of the model and the left side ends up vertical because the cutter ends up cutting the full depth, What results is a finishing toolpath that does not machine the whole surface and is left with roughing passes. when the tool is placed back to origin its position has moved up the Y axis by about 6 to 8 mm. I dont know if this is a machanical /electrical problem.
Can anyone please give advise.
Thanks alan

[TReischl]

It would help if you told us what feedrates you were attempting to run at.

Not familiar with your machine or how it is controlled, ie, via Mach 3?

Normally, lost steps are caused by the feedrate being too high for the machine. However, if you are using Mach 3 it can easily be a combination of feedrate and/or acceleration settings.

We like pics, btw, they help a lot in diagnosing problems.

It is definitely mechanical/electrical. In my years on this forum I have never seen one of these problems to be software related. And, just so you know, having built my own machine I am very, very familiar with exactly what you are describing.

[COWBOY1296]

Not sure I totally understand your problem. But when my machine starts missing steps it means that the brushes in router are burned out and need replacing. This has ruined more than one project.

[TReischl]

Brushes burning out could cause two things:

Lots of electrical noise or it reduces the efficiency of the motor but you should be able to hear the change unless it sneaks up on you real stealthy like.

I run a Porter Cable router and it goes for years between brushes. I believe it is the 892 with VS. The VS gave out a while back and the little spindle locking pin finally gave up the ghost so I am back to using two wrenches. :::::sigh::::: just too cheap to buy a new one for those inconveniences.

[wood400]

Hi Folks, Thank you to everyone who gave advise. Although i had checked that the coupler on the Y axis was as tight as i could secure it with the allen key before it would slip off i rechecked to see if there was movement at the coupler by placing a piece of masking tape around the leadscrew adjacent to the coupler and marked a line with a felt tip across both the tape and the alloy coupler. After running the roughing toolpath i was able to visually check the position of the line, Removed the hex head screws and oiled and replaced . i was able to obtain a bit more tightness. Although this seemed to be the proble and all is working fine now. i will try to obtain better hex head screws that dont slip when tightening.
Cnc router 7090 of chinese origin. Dsp handle , aspire software, Richnc controller.
I was feeding the cutter into white oak 2000 mm per minute and spindle speed 12000 rpm , 6 mm spiral cutter not sure if this is the most suitable speed for this project.
Thanks alan

[COWBOY1296]

Years lucky you. I am considering doing a quarterly maintenance checkup on the shopbot and replace the brushes whether they need it are not. The change is easy and cheap. I cut nothing but hardwood and almost always large 3-d files, the extra pressure may put a strain on the brushes. This is a hobby for me so the shopbot is not running all the time. But if you have any suggestions, I am all ears.

[TReischl]

For us old folks, that 2000 mm/min rounds out to about 80 IPM. That is not real fast.

You didn't state the depth of cut you were taking but I would presume it was not more than the diameter of the cutter.

[wood400]

Hi TReischi, have now moved the speed up to 3000mm per minute 6mm cutter and 5mm pass with 40% overlap everything seems to be cutting well in white oak, although a bit louder. Is there any info on speed rates for hardwoods?
Thanks for your help
Alan

[COWBOY1296]

When I do roughing in black walnut and cherry I use a 1/4 inch ball nose end mill, 40% step over, doc .07 inch, feed rate of 3.3 inches per second. Sill working on my second cup so I will let you do the math on the conversion.

[TReischl]

Hi TReischi, have now moved the speed up to 3000mm per minute 6mm cutter and 5mm pass with 40% overlap everything seems to be cutting well in white oak, although a bit louder. Is there any info on speed rates for hardwoods?
Thanks for your help
Alan

Hello Alan,

Feedrates are dependent on a lot of factors, but the one that seems the most limiting is the machine itself. Rigid smooth machines can achieve speeds of 1600 IPM. Some of the people here regularly cut at 600 IPM, others cannot go faster than 100 or less.

In an earlier post I put up a link to a video of my homebuilt machine cutting at 800 IPM.

So, when I read anyone professing that they know precisely how fast to cut in a certain wood, I find something else to read.