Look What Happened!

OK, this is one of my first attempts and after figuring out a bit of VCarvePro and GCode sender, I feel a lot more comfortable with the workflow. I am attempting an address sign that is an oval with a number in the middle with a rope model and a V Carve number 10. This is what happened when I attempted it last night. I am using a Dewalt 611 with:

.125" ball bit for the rope
.25" end mill for the profile
.25" V carve bit 60 degrees for numbers

I am fairly certain that the rope is lighter on one side due to material not being flat. The profile jumped to the right and went across the pice, probably due to the router speed or movement being too fast.

What I can’t figure out is why the number got so messed up. I zero’d the machine with each toolpath and started over so it can’t be a problem with the tool jumping from the previous profile cut SNAFU. Any ideas?

Is there a list of speeds for bits and/or materials when using the Dewalt 611? I had the thing set at 4 for everything and the speed of the router moving on the x and y were unchanged settings from VcarvePro.
Link to the picture of my disaster
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[/url]Address_Sign%20by%20Matthew%20Jamison,%20on%20Flickr

Here is a spreadsheet I put together to give you feed rates and 611 speed setting for various bit sizes and materials

The main idea to take from the calculations is that a slower setting on the 611 is almost always better than a faster one for the bit sizes and feedrates we commonly use.

CNC Speed Calculator.xlsx (14.6 KB)

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Resetting the zero cleared the slip error but it looks like it slipped multiple times. I am guessing on the Y axis?
It should not be slipping. You should start seeing quality issues (chatter, char) of your are feeding too fast not slip.

Check the usual suspects:
Belts (This things loosen up after the first carve)
V Wheels
Pulleys (set screws)
And you may need to bump your y axis current

Allen, this is a HUGE help, thanks so much. I was in the dark as to the speeds and settings for material and bits!

Aaron, I guess I just assumed everything was ok in that regard and overlooked something mid project. I’ll remember to double check everything before each cut. Thanks!

Considering I’ve never changed mine off 6 I might need to look at that.

Angus, I’ll check the screws on the toothed pulleys when I get home.

Matthew, see my comments about axis voltage settings and go to this web site (https://github.com/synthetos/grblShield/wiki/Using-grblShield#setting-motor-current) and give it a read. Just may help you out.

I used the speed setting on the spreadsheet and got a much better outcome. I also upped the current to the Y axis but am not sure if it made a difference.

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maybe I’m not seeing something on your chart, how do i translate chip speed into imp/feed rate? Or are you saying if I want a higher speed rate then i just need to increase RPM? (I am looking at your spreadsheet right now trying to figure it out). I have my 611 mount on its way per UPS, before end of day.

What I try to do is figure out the recommended chip size for the material and bit I am using.

For example if I am cutting hardwood with a .125 inch 2 flute bit then the recommended chip size is between .003 and .005

Then I look on the chart for the number of flutes my bit has (in this example 2) and see if the feedrate I want to use (in this example 90 inches per minute) has a Dewalt speed setting that works.

In this case at 90 ipm to get close to the recommended chip size the speed setting on the dewalt needs to be a little less that one (.7) So I would just set the speed to 1.

If I wanted to cut faster at 120 ipm then see on the chart that I would need a Dewalt speed setting of close to 3

Basically for most cuts, I wind up increasing the feedrate till I get a speed that is not to slow for the Dewalt to handle. The spreadsheet is designed to show “To Slow” if the recommended RPM is much below 16,000 rpm. Since the lowest speed the Dewalt can operate at is about 16,000 rpm (this is very fast for most bits and feedrates) I am almost always setting the speed between 1 and 3.

If you set the speed to high you run the risk of really heating up the bit and even burning the wood.

I hope that helps.

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I’ve downloaded the chart and it makes sense ,but how do you get the feed speed calculations?

Chip Load = feed rate ( ipm ) ÷ ( cutting rpm x number of cutting edges )

Thanks @AllenMassey

I do like your spreadsheet but depth of cut and step over also play into the feeds and speeds. What are you using for depth of cut and step over?

That is an excellent question. The calculator for chip load does not take DOC or stepover into account at all. All the chipload is doing is calculating how much material is removed by the cutter each rotation as it moves through the material. The DOC and stepover certainly are very important (probably more important than chipload) but those values are largely dependent on variables like the stiffness of the machine and the power/torque of the spindle.

The main reason I concentrated on chipload was to make it easy to see that running the Dewalt 611 at lower speeds was generally better than higher speeds for most of the work the X-Carve does. Determining the optimal DOC and stepover requires a dynamic analysis of the entire system (including bit stickout).

The G-Wizard Feed and Speed Calculator is the best full system analysis software that I have found so far.

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Not long after I got my X-Carve I downloaded a trial of the G-Wizard calculator. It is impressive to say the least but never quite figured out how to make it realistic with the X-Carve. I could never achieve decent results with the settings they recommended. I believe this was due to the lack of rigidity of the X-Carve. This was well before I upgraded to the DWP-611 and stiffened my X and Y axis. Still need to work out a good way to stiffen the Z axis.

I would love to use the G-Wizard but just don’t know what parameters to use to define my machine in their machine setup. Are you using it and if so would you be willing to share your machine setup with G-Wizard?

I never purchased it, I just used the trial for a short period.

The G-Wizard does have tons of setting that allow you to specify the stiffness of the machine and the power of the spindle so it can model the X-Carve pretty well. But I found that for carving wood it was not really necessary. I am getting nice cuts by just keeping the spindle speed low, and feedrates of about 60 ipm. I adjust my DOC and stepover based on the bit I am using and the quality of the finish I need.

If I was trying to cut new materials (especially metals) then I can see a tool like G-Wizard being necessary. But for the woods I carve finding the optimal feeds and speeds it not worth it to me. Maybe if I was doing serious production runs where I was trying to optimize the production rates and life of the tooling then it would be more important.

That is about the same thought process I had when considering it. Thanks for the input.

Charley

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Charley, I just watched your video on your three axis auto zero solution. Nicely done! Thank you for sharing your solution.