What am I doing wrong?

[Simops]

Hi,

I have a problem that I'm hoping someone can solve for me. I don't think it is the Buddy(brand new), but if it is I'll call Tech support.
Anyhow been cutting some sample practice pieces OK. Tried to cut my first more elaborate project and hit a snag. As per the picture attached the second circle is offset and not centered around the first circle cut. Yet in the drawing it is symetrical and the toolpaths appear correct. See attached sbp file. The Partworks file is too big to attach...won't let me.

BTW the MDF is positioned and screwed down correct and the Buddy homed to XY zero and Z zeroed.

Can anyone point the ways of my error here?

Thanks in advance...cheers

Mike

[adrianm]

File looks ok to me. 2 ips is a lot slower than I cut MDF at but I wouldn't have thought that would cause an issue like this.

It does look like you've lost steps somewhere. Trying doing it with a 1mm depth of cut only to take all the pressure off and see if you get the same results.

If you do then I'd say something is binding up somewhere on the machine.

[Simops]

Adrian, I slowed it down because I broke my 1/4" end mill at the default 6 ips....even with 4 steps down through 18mm MDF!

Cheers

[dana_swift]

It helps to know what kind of shopbot you have, whether it is standard, or alpha. If it is a alpha machine, this is a puzzle. If it is a standard, cutting 6 ips is very fast. Try 3 ips or less if it is a standard.

If you are breaking bits at any speed something is VERY wrong. What rpm? Spindle or router? Which model? Was the spindle/router running? Did it labor, or cut easily?


D

[dana_swift]

One other note.. your file is in metric. You are quoting move speeds in inches per second. Mixing units is a great way to get confused and use very inappropriate values.

Partworks allows mm/sec speed settings which is more appropriate for metric work. 75mm/sec is a good cut speed for a shopbot standard, while an alpha should have no difficulty with 125mm/sec. With either machine, start with a pass depth of the bit radius. If you are using a 10mm bit, make the pass depth 5mm. When you get more experience feel free to be more aggressive, but get it working first.

Eventually you will learn to cut some materials at 2 or 3 times the bit diameter in a single pass. Cutting a hard wood with a 3mm bit at a pass depth of 30mm at a speed of 100mm/sec is guaranteed to break the bit. It may make a few heroic cuts before snapping in half, but it will not live long.

Stepping up to a thicker stiffer bit can make the same cut with no problem and the bits will last a long time.

When you are learning how to make the machine work well in any given material, keep the feed rate high and the pass depth low. The feed rate is determined by the chip size you need to make and the RPM and number of flutes. The depth of cut is determined by the horsepower available to push the cutting edge of the bit through the material, the stiffness of the bit, and the density of the material.

Hope that makes sense.

You will figure this all out fairly quickly.. welcome aboard-

D

[adrianm]

For what it's worth I work in metric as far as measurements go but I always use IPS for the feed rates.

As the CNC industry seems to be mostly US driven nearly all information on feed rates is in imperial so I find it much easier to work that way rather than having to convert to metric.

There's no issue with mixing units as the Partworks Post Processor converts everything seamlessly to metric. Quite often I'll use someone else's imperial unit file and output it as metric so I don't have to switch units in SB3.

As Dana says something is definitely up if you're breaking 1/4" endmills on MDF.

[Brady Watson]

I know you said the circles are not concentric...do they appear/measure oblate more in the X than the Y?

If so, check the motor to rack engagement and make sure it is solid.

-B

[Simops]

Thanks guys for the info so far...

Dana, I have a Buddy 48 standard with 2.2hp spindle. The reason I used imperial feed rates is because all my bits I have are imperial and in fact the bit I used was from the Shopbot starter kit. The file was created in metric and saved as a MM shopbot file. In the control program I selected mm and then loaded the file. I think the bit broke, correct me if I'm wrong, because I used a downcut spiral 2 flute 1/4" end mill and as it plunged down about 5mm on first cut and moved at the default 6ips got around about 3/4 in the circle and must have fouled with chips (being downcut) and labored till it broke?? When I changed the speed to 2ips and this time using an upcut bit it went around easily.

Brady the oblong cut is indeed in the X axis. I checked the power stick and it is engaged correctly and when I use the keyboard control moves smoothly from one end to the other. The interesting side to this is that the first inner circles cut perfectly round and in the correct place. But when it came to cutting the outer circle is when it went oblong. You would assume that if there was an issue with the machine it would have done it for the inner circle cuts as well?? Is this a correct assumption?

For your info before I loaded the file to cut I zeroed the X & Y position using the proximity switches and fixed the 18mm MDF material in place so that it was orientated correctly to the part works drawing.

This is indeed perplexing, as far as I can tell, as I seem, on the surface, to have followed things correctly but obviously something is not right and just can't put my finger on it just yet??? As always it will be something simple and stupid....just can't work it out yet!

Cheers
Mike

[robtown]

I may have missed something in the thread, but I'm wondering if the your 0,0 is the same after the cut. If you're losing steps, it won't return to the same 0,0 spot.

[dana_swift]

Michael, what is your pass depth set to on your current bit definition? If you are using a 1/4" up spiral.. I will suggest you start using 0.125 for a pass depth, 3ips for a cut speed and 12000 rpm.

Your explanation of the bit break makes sense, you probably figured that one out correctly. When you are new to the machine breaking bits is more common than later when you have used it a lot. Keep spares around..

If it isn't just losing steps, I dont see where the error is. Standard shopbots can lose their position if they are asked to cut at too many ips.

Also dont jog faster than 5 ips, the machine can lose the steps at jog time as well as cut time. Becuase the circles dont appear to be correct as individual circles, the jog speed being too high is a good suspect.

Hope that helps-

D

[Mayo]

You mentioned some sample pieces cut correctly.
Did you happen to change the unit values or other settings after the sample pieces were cut ?

[Simops]

Thanks Guys for your input...

I left the material in place and decided to re-zero the XY and Z. Then re-ran the cut over this partly cut piece. This time it cut in such a way that it did not follow the oblong cut but cut correctly. Of course some of the cuts are damaged but others OK.....so got half the cuts right out of it.

So standing at the Buddy in a cloud of thought with my iPad in hand I re-read the comments above and came up with a theory of what may have gone wrong.

Please correct me if you think my theory is half baked!

What I think happened is that during the initial cut with the bit hurtling at 6ips and a quarter inch down into the material and being a downcut it jammed with MDF and broke. Now this must have produced a certain amount of mechanical leverage which may have thrown out the XY Zero position or jumped steps. Now when I saw the breakage occur I hit the red emergency stop button that was in my hand and the whole thing paused. I then replaced the bit with a new downcut 1/4 inch end mill and then altered the ips, re-calculated and re-loaded the file. Now i did not re-zero the XY but of course re-zeroed the Z and when it started cutting again things where / may have been out of position.

Therefore what I'm saying is that could the breakage cause enough leverage to alter positional accuracy????

Cheers

Mike

[bleeth]

It probably wasn't the bit breaking that caused the lost steps. 6 ips is definitely more than your machine can take when cutting. It likely lost steps before the bit broke.
After an issue like this you should always re-zero all three axis' before restarting.
Next time you are cutting ply with a 1/4" bit try 3 ips and 12k on the spindle.
You should easily go .375 deep with no issue.
The default speeds in the library may not be appropriate for your mill.

[Simops]

The one thing I've learnt from this is that the message is clear.....tool feeds and speeds are just as important as any other aspect of CNC machining. Clearly the default settings given are just ball park figures. I am definitely going to remain on the 'conservative' side of the tool settings given!!

Without experience to guide you or a supervisor to show you tool breakages and ruined parts are an unfortunate by-product of the learning curve.

cheers

Mike

[bleeth]

Here is 1 place that may help you make less errors:

http://www.talkshopbot.com/forum/showthread.php?t=15176&page=2



Also the feed speed calculator in the SB software.
If you are getting ready to cut something new you may find the info to guide you in this section by going through previous posts.

Also see the attached pdf.

And remember that asking in advance on the forum will usually get you a pretty quick response to feed/speed questions. ALWAYS include what your machine and router is in the question as answers vary depending on that info.

[Simops]

Thanks for that Dave......will do!
Cheers

PS: that PDF is very handy reference?...ta muchly!

[dana_swift]

Michael- are you getting reliably good results now?

Once you get it running the way it should, you will learn what the limits are and stay away from them.

What do your current test cuts look like?

The good news is, it appears your problem is identified- cutting more aggressively than a standard can handle. Future cuts will be very reliable and accurate. I am looking forward to a post in a few months talking about the results you get after a little experience.

Keep us posted-

D

[Simops]

Sure will Dana.....I'm out of town at the moment and soon as I get back I'll try another clean re-cut with the speeds recommended.

Cheers

[Brady Watson]

Clearly the default settings given are just ball park figures. I am definitely going to remain on the 'conservative' side of the tool settings given!!

Mike,
This is true in ANY CAD/CAM software - sorry you had to go through that! While you are getting your 'CNC Legs' - try running your 2D toolpaths at 2,1 - depending on the size of the part. Try to keep your step downs in the .125 to .25" range. Run 13-15,000 RPM on your spindle or router and cut away.

After you get comfortable with the machine & understand how to hold different materials down, then you can get all scientific with the chipload calculations et al. It is important that you are comfortable running the tool before you worry about running it under ideal conditions.

-B

[Simops]

Thanks Brady for the tips.....but what do you mean by "2,1"?

Anyhow I think I just got a bit cocky with the machine. Having learnt how to use Partworks to draw and toolpath and then relate that to the machine may have made me a little over confident without due respect to the tooling requirements.

Cheers......

[Simops]

Michael- are you getting reliably good results now?

Once you get it running the way it should, you will learn what the limits are and stay away from them.

What do your current test cuts look like?

The good news is, it appears your problem is identified- cutting more aggressively than a standard can handle. Future cuts will be very reliable and accurate. I am looking forward to a post in a few months talking about the results you get after a little experience.

Keep us posted-

D

All good now Dana.....slowing the bit and more passes solved the problem. Bit selecion and speeds are important and easily overlooked in early stages when somewhat overwhelmed by all the setting up considerations.
Cheers

[dana_swift]

Michael- glad to get this report! Bots are amazing machines, but the limits are not clear to a person starting out.

Experience improves results vastly.

I have a lot of suggestions for a future SB design.. such as feedback on how much cutting force is being used at any given moment. Then the operator can know that they are over the capacity of the steppers.

That is only one of my suggestions. But think how it would have helped you, or anybody using a new material/bit combination.

Keep us posted on your progress. We all love to see each others work, so when you get wonderful new things built, post some photos!

D

[Simops]

Hey Guys,

I think I found what the problem with my cutting was! And it isn't just the feed rate and passes. Houston I have a problem!

The spindle RPM is stuck on 6000 even though the cutting file has the tool set at 12000. I assumed that the spindle speed was correct and as calculated but got suspicious when TJ at Shopbot mentioned in his last Webinar that the spindle noise increases sharply with high spindle RPMs. So I ran the warm up routine and noticed that the spindle noise did not change with the higher stepped RPMs called for in the routine. Checked the VFD readout and it is stuck at 6000.

So hence the original feed rates may have been OK and I ended up fixing the cutting issues by reducing the feed rates due to a highly reduced spindle RPM.

I have sent Shopbot Tech Support an email to see what is wrong with my setup ( it would of been like this out of the box). The time zone is such that I would need to get up in the middle of the night to talk to them so hopefully they can solve via email ??

Cheers
Mike

[jerry_stanek]

What spindle and vfd do you have I just ran into the same thing when I had to reload my Shopbot control software. It showed I had the wrong VFD listed in the fill in page. Changed that to the one I have and all is fine

[adrianm]

Do you have the RPM speed control window open?

If it's not there then typing TR should bring it up. You can double click on the left of the RPM display to set it to start automatically. The TR commands in the SBP files won't work without that window open.

Assuming of course that your 'bot has the speed control board installed.

[dana_swift]

During the warmup period if the spindle is not changing speeds that is a strong clue something is not communicating.

The RPM changes are very audible.

D

[Simops]

Frank at Shopbot was quick to reply to my email......excellent technical support I must say!

Anyhow this was his reply:

Click on the RMP in the window and a yellow fill-in sheet will open. Make sure the port number is correct, the VFD is set to V1000 and the Hertz scale is set to 60.

I'm not the smartest so I'm going to ask him for clarification because have no idea what RMP is. Looked all over SB3 but could not find it to open it and amend the fill-in sheet???

Cheers
MT

[jerry_stanek]

When you do a TR comand the window that pops up for your spindle. Click on the left side on RPM.

[adrianm]

Frank at Shopbot was quick to reply to my email......excellent technical support I must say!

Anyhow this was his reply:

Click on the RMP in the window and a yellow fill-in sheet will open. Make sure the port number is correct, the VFD is set to V1000 and the Hertz scale is set to 60.

I'm not the smartest so I'm going to ask him for clarification because have no idea what RMP is. Looked all over SB3 but could not find it to open it and amend the fill-in sheet???

Cheers
MT

See reply #25 above

[Simops]

Thanks Dana, Adrainm and Jerry,

Actually I did do as mentioned and also as advised by Frank at Shopbot.....the fill in sheet is as suggested but still the spindle defaults to 6000 and stays there unless I manually change the RPM figure in the TR window then hit enter and then the spindle will spool up to this new (manually) entered RPM.

Anyhow Frank suggests that I change the 'start when SB3 starts' parameter from 0 to 1 and see if that fixes the problem with automatic spindle RPM control??

At this stage the spindle RPM has to be manually entered prior to running a cut file otherwise it will just run at 6000 RPM by default.

Cheers

[Simops]

Ok now I know what you mean Adrianm in your post 25 above!

The spindle control window now appears as soon as SB3 starts (by changing the parameter to 1 for 'start when SB3starts') and now when I run the warmup routine or cut file the spindle goes to the programmed RPM.

So the spindle RPM window needs to be running in the background every time SB3 is running for the spindle to work automatically. I was not aware of this and no matter how hard I try could not find this documented (probably is but it alludes me)!

All good now and at last I can run feed rates higher without breaking the bit:p

Thanks for your input...

Cheers

[Bob Eustace]

Ok now I know what you mean Adrianm in your post 25 above!

So the spindle RPM window needs to be running in the background every time SB3 is running for the spindle to work automatically. I was not aware of this and no matter how hard I try could not find this documented (probably is but it alludes me)!


Cheers

Mike it isnt in any literature in Buddies sent ot Oz as both Russel and myself had exactly the same no rpm change problem in our machines which are only a few months older than yours. Neither of us have ever broken a cutter (specialise in hitting screws instead!) as we are both metal machinists and 6 inches a sec are unheard of in metal. I prefer downcuts as they put less load on the hold down method. In case you have "strayed" from using Onsrud bits we tried Carbatec and that other one in the yellow packet (seniors moment). They are nowhere near as good and you get the dreaded screaming. Garry Becker on this forum sells Onsrud and you get them in a week. Amazing guy - no matter what time you email you get a reply in an hour! Also great for 3D graphics. Suggest you get a spare 1/4" collet as these only last a year and you can get cutters walking out in hard wood on heavy loads particularly Spotted Gum.

Still waiting for your helicopter to land in the back yard. Should I mark out a big X?

Bob

[Simops]

Hi Bob,

Yep already bought Becker's 3D cutter set. You are right got it no time.

I also have a spare 1/4" collet....so good there. Plus I purchased a 1/8" collet as well as I have some 1/8 bits for some ally work....but haven't tried it yet.

Onsrud bits seem the way to go.....what about Carbi-tool.....their manufacturing plant is 30 min from me and they have a compression bit I've been eyeing!

Hey I flew over your place a couple months ago but you must have been to engrossed in your shopbot to hear me:p

Cheers

[bleeth]

Would that be Gary Beckwith?:)

[Simops]

Yes, that's correct.....BDP cutters....