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  1. #1

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    Jun 2021
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    770MX Spindle Keeps Stalling

    Hi all!

    I have a new 770MX, and I keep stalling the spindle. I'm not sure if this is an issue with my speeds and feeds (I'm using GWizard, but I'm very new to it), or an issue with the machine itself. I've had the spindle stall 6 times now, with different operations, and both 3/8" and 1/4" diameter tools. After the first couple of stalls, I thought the drive belt might have been too loose, so I tightened it a bit, but I'm still having the same issue (the belt is in high and it is also set to high in pathpilot!). Just before the spindle stalls, I get a readout saying that the spindle encoder RPM feedback is abnormally low, and to run an admin encoder test, which it passes easily every time. Here are the details for the most recent operation it was doing when it stalled while working in 6061 Alu:

    3/8" YG-1 end mill (36584)
    0.2145 DOC
    0.12 WOC (GWizard told me to set this to 0.3363, but I was trying to be conservative since I kept stalling the spindle)
    7197 RPM
    71.504 IPM
    Flood Coolant
    Stalled on 3rd Pass

    I got the above data after entering the SFC (785) and IPT (0.0041) that I calculated from the recommended speeds and feeds on YG-1's website (8000 RPM @ 99 IPM). Since I was worried I had calculated this wrong, I cleared these fields and let GWizard calculate these values for me, as I read this was a safe way of doing things, but the below data from GWizard also stalled the spindle.


    3/8" YG-1 end mill (36584)
    0.2145 DOC
    0.1775 WOC
    10000 RPM
    67.922 IPM
    Flood Coolant
    Stalled 1" into the first pass

    What am I doing wrong? Thanks in advance!

  2. #2

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    Re: 770MX Spindle Keeps Stalling

    Also, the 3/8" YG-1 end mill (36584) is a 3 flute with a stick out of 2.0556".

  3. #3
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    Re: 770MX Spindle Keeps Stalling

    I would try:
    WOC at 10% of the tool diameter and see what happens after a bit. That's what I've read in the past.
    For a 3/8" that's prob more like 0.037"!. Yes I know it sounds painful but if it runs fine you can build on it.
    Leave the rest as is for now.

    Looking at the specs.... Considering it's rpm max is 10k. I reckon it sounds underpowered at 1.5hp myself for that sized tool that quick.

  4. #4

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    Jun 2021
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    18

    Re: 770MX Spindle Keeps Stalling

    Thanks for the input! That does sound pretty slow but I'll try that now. GWizard says the cut at 10000RPM should be using .3679 HP, but honestly, at this point, I don't really trust GWizard...

    PS - I just checked and this operation is now going to take an hour and eight min... That's just to remove 0.2145" off the top of a 4.5"x12" block. There's gotta be a better way....?

  5. #5
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    474

    Re: 770MX Spindle Keeps Stalling

    It may be your spindle has little torque at 10000 rpm. May be better off at lower rpm and higher chip load. Save the 10k for smaller tools.

  6. #6
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    Re: 770MX Spindle Keeps Stalling

    Quote Originally Posted by Joz234 View Post
    Thanks for the input! That does sound pretty slow but I'll try that now. GWizard says the cut at 10000RPM should be using .3679 HP, but honestly, at this point, I don't really trust GWizard...

    PS - I just checked and this operation is now going to take an hour and eight min... That's just to remove 0.2145" off the top of a 4.5"x12" block. There's gotta be a better way....?
    Try cutting your DOC in half and see what that does with the original parameters. HSM evangelists always want you using all the tool flute you can, but when you're stalling out the spindle it won't help you any. The encoder feedback error is your tool can't turn the commanded speed. Also happens if your coolant cuts off for a second and chips weld into the flutes of your cutter.

  7. #7

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    Jun 2021
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    18

    Re: 770MX Spindle Keeps Stalling

    I'll have to try that tomorrow! Using a 10% WOC worked, but my god it was slow. Is there a better program than GWizard for me to use? Or is there an issue with this machine? I get that backing off the parameters will eventually stop it from stalling, but why is it stalling in the first place? I don't think these cuts should be overloading the spindle, and while I was considering that the torque is too low at 10000 rpm (although I can't find a torque curve to confirm), the first cut was at 7197 and still stalled the spindle... Am I miscalculating how aggressive these cuts are, or is something else at play?

  8. #8
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    Re: 770MX Spindle Keeps Stalling

    Quote Originally Posted by Joz234 View Post
    I'll have to try that tomorrow! Using a 10% WOC worked, but my god it was slow. Is there a better program than GWizard for me to use? Or is there an issue with this machine? I get that backing off the parameters will eventually stop it from stalling, but why is it stalling in the first place? I don't think these cuts should be overloading the spindle, and while I was considering that the torque is too low at 10000 rpm (although I can't find a torque curve to confirm), the first cut was at 7197 and still stalled the spindle... Am I miscalculating how aggressive these cuts are, or is something else at play?
    Personally I reckon it's just the lack of hp for the rpm ratio.
    If you look at the specs of say a Haas mini mill for example, that will go pretty aggressive cutting.
    That has a 7.5hp spindle with max 6krpm or option of 15k with a 15hp!..

    You have 1.5hp at 10k... Big difference. It needs some baby-ing. I'd say the hp to rpm ratio should be at least half that (5k @ 1.5hp).
    I mean look at the hobby type mills... Many have 1.5kw (around 1hp) motors for just 2500rpm.

    Start small and build on it until you know the limit.
    Tbf Gwizard is designed for machines like the Haas.

  9. #9
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    Re: 770MX Spindle Keeps Stalling

    Quote Originally Posted by Joz234 View Post
    I'll have to try that tomorrow! Using a 10% WOC worked, but my god it was slow. Is there a better program than GWizard for me to use? Or is there an issue with this machine? I get that backing off the parameters will eventually stop it from stalling, but why is it stalling in the first place? I don't think these cuts should be overloading the spindle, and while I was considering that the torque is too low at 10000 rpm (although I can't find a torque curve to confirm), the first cut was at 7197 and still stalled the spindle... Am I miscalculating how aggressive these cuts are, or is something else at play?
    Feels to me like that's could be an aggressive cut for that tool and a 770, but I've not run either. If you are bogging down the spindle you are trying to bite off more than it can chew for sure. Possible there's a mechanical issue in the drivetrain but seems less likely. When doing new things things like this, I'll dial the feed slider way down to start and bump it up until it gets to a happy place (which is usually below what the F&S calculators say)

    You may be able to rig up a load meter as well. I did a homebrew one for my old 1100 that was just a meter that plugged into a couple VFD outputs. .

  10. #10

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    Jun 2021
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    18

    Re: 770MX Spindle Keeps Stalling

    Thanks for all of the input! I was trying to find a torque curve for my machine, but after speaking with Tormach they let me know that they don't release them, so that's kind of infuriating... I think I'm going to cut my feed rates in half and then slowly bump them up until it sounds unhappy, then back them off a bit. Maybe over time, I can collect enough data to construct a torque curve, but that sounds like more of a long-term project. Also, I think a load meter would be really helpful here, but I can't find anyone that's built one for an MX series and Tormach doesn't sell a compatible one, so I'm going to have to do some tinkering here. I've also been surprised that GWizard's feeds and speeds have been so far off out of the box, since it was sold in a bundle to me with my 770MX by Tormach, and it has a machine profile specifically for the 770MX. Lastly, if anyone has a 770MX and would be willing to compare feeds and speeds with me on similar endmills I'd really appreciate it, just to see if we're even in the same ballpark!

  11. #11

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    18

    Re: 770MX Spindle Keeps Stalling

    After a day of experimenting, I'm still confused... I was able to talk to Bob, who makes GWizard, and he looked over my speeds and feeds for me and was able to confirm that they should be within my machine's capabilities. After trying to make a bunch of cuts today I've found that at 7000rpm (which according to Tormach is about peak HP on the torque curve they don't have released) if I exceed about 0.20 HP (according to GWizard) I stall my spindle.

    This 2D contour cut stalled my spindle:

    3/8" YG-1 end mill (36584)
    0.283 DOC
    0.1 WOC (GWizard told me to set this to 0.3363, but I was trying to be conservative since I kept stalling the spindle)
    7196 RPM
    58.14 IPM
    Flood Coolant
    Stalled about an inch in
    Estimated HP: 0.3159

    And this cut was okay:

    3/8" YG-1 end mill (36584)
    0.14 DOC
    0.1 WOC (GWizard told me to set this to 0.3363, but I was trying to be conservative since I kept stalling the spindle)
    7196 RPM
    58.14 IPM
    Flood Coolant
    Estimated HP: 0.3159

    My first question, which I haven't gotten to ask Bob yet, is how is GWizard calculating the HP? When I calculate it, if I use 0.3 as the coefficient for 6061 T6 aluminum, I get 0.509HP, not 0.3159. Am I overestimating the unit power of aluminum, or is GWizard under? Also, this leads to a removal rate of 1.698 which sounds about right for a 770MX but it still stalls. I also checked my power delivery and checked for any loose connections but there doesn't seem to be any to speak of. I'm a bit more lost now than when I started looking into this. Am I just really bad at estimating how aggressive these cuts are? Any ideas?

    PS - I'm not just letting my machine stall over and over again. Now I just pensively hover at the estop and wait to see if my machine bogs down. I also did some testing with my 1/4" end mill and had similar results, a cut estimated to take .22HP stalled my spindle and I didn't catch it in time though, so I snapped that endmill :/

  12. #12
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    Re: 770MX Spindle Keeps Stalling

    Quote Originally Posted by Joz234 View Post
    0.283 DOC
    Estimated HP: 0.3159

    And this cut was okay:

    0.14 DOC
    Estimated HP: 0.3159
    For sure if it's telling you that taking 0.143" off the DOC doesn't change the HP, then something is wrong.

    This is basically why experienced machinists set feeds and speeds based on 'experience'. There's no plug-and-play answer that works in all cases. Use the calculators to get a ballpark starting number, then adjust from there until the machine is happy. It's all kinds of frustrating for engineers that want a magic number, but it is what it is.

    Are you contouring from the outside in or what? The shape of the toolpath can be important. Tight corners can create much more actual-feed than you programmed, since it runs off the center of the tool.

  13. #13

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    Re: 770MX Spindle Keeps Stalling

    Quote Originally Posted by dazp1976 View Post
    Personally I reckon it's just the lack of hp for the rpm ratio.
    If you look at the specs of say a Haas mini mill for example, that will go pretty aggressive cutting.
    That has a 7.5hp spindle with max 6krpm or option of 15k with a 15hp!..

    You have 1.5hp at 10k... Big difference. It needs some baby-ing. I'd say the hp to rpm ratio should be at least half that (5k @ 1.5hp).
    I mean look at the hobby type mills... Many have 1.5kw (around 1hp) motors for just 2500rpm.

    Start small and build on it until you know the limit.
    Tbf Gwizard is designed for machines like the Haas.
    Am I doing myself any good by looking at the estimated HP, or is that just a waste of time? I was thinking so long as I leave at least a 40% buffer I should be okay, but if this is a flawed way of thinking about things that's probably my problem. Also, while Tormach couldn't give me the torque curve for my machine, they said peek power is in the 6000-7500RPM range, so I should be aiming to be within that range most of the time, right?

  14. #14

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    Re: 770MX Spindle Keeps Stalling

    Quote Originally Posted by shred View Post
    For sure if it's telling you that taking 0.143" off the DOC doesn't change the HP, then something is wrong.

    This is basically why experienced machinists set feeds and speeds based on 'experience'. There's no plug-and-play answer that works in all cases. Use the calculators to get a ballpark starting number, then adjust from there until the machine is happy. It's all kinds of frustrating for engineers that want a magic number, but it is what it is.

    Are you contouring from the outside in or what? The shape of the toolpath can be important. Tight corners can create much more actual-feed than you programmed, since it runs off the center of the tool.
    That's actually just my typo... The second cut was estimated at 0.1631HP. The smallest radius on my external contour was 0.77" inches so I don't think that would have been a problem, but I only made it 1" into the cut before I needed to E-stop so I guess who knows. Sadly I don't have a ton of experience which is why I'm trying to ballpark things with GWizard, but even cutting their rates in half I'm still stalling most of the time. Am I wrong to be looking at the estimated HP of a cut? And if I use shallower DOC and WOC and find one that's working, should I start increasing my feed rate to try and take more aggressive cuts, or should I leave that alone and try more aggressive WOCs? Thanks for taking the time to help me sort this out btw! I wasn't expecting to have this many issues with my speeds and feeds since the Tormach sales rep gave me a pretty strong recommendation for GWizard, but here we are I guess.

  15. #15
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    Re: 770MX Spindle Keeps Stalling

    Why do so many people get caught in the speed and feed trap?.
    It is subjective and depends on a host of factors and conditions.
    10 years ago that is all people discussed, argued and hyped day in and day out. Didn't matter if it was big machine or small. Those same people would also talk about how they hand write a g code programs. And how great it all works. I would read this and think what are they making.
    At that same time I spent hours modeling parts and then hours in cam software refining tool paths to generate g code. Then focused on material and machine setup to get accurate results with decent finish. The files were often thousands of lines long and require half dozen tool changes. I quickly learned that feed and speeds of tools was only a few parameters in the process and there are hundreds of other parameters that are just as important. Also there was no way your going to do this writing code by hand.

    In summary. I focused on drawing and cam tool path skills with good methods for fixturing material and combined those skills with conservative cutter speeds to get drama free results over and over. Then went on to make mountains of accurate shiny stuff and not break a tool. I also learned the faster I tried to make parts the more drama, scrap, tool breaks, and overall problems encountered. But that is the nature of production.
    If your learning and making a new widget of some form who cares how fast you do it. Slow is often fast in the cnc machine tool world. And far less expensive.
    IMHO your better off getting results first. Then if your making thousands you can refine the many steps to make them faster. Also with experience you learn ways to push your tools and about what you can get away with and not crash machine or scare the dog.

  16. #16
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    Re: 770MX Spindle Keeps Stalling

    Quote Originally Posted by mountaindew View Post
    Why do so many people get caught in the speed and feed trap?.

    If your learning and making a new widget of some form who cares how fast you do it. Slow is often fast in the cnc machine tool world. And far less expensive.
    IMHO your better off getting results first. Then if your making thousands you can refine the many steps to make them faster. Also with experience you learn ways to push your tools and about what you can get away with and not crash machine or scare the dog.
    ^^^ This.

    Find something that works. Ignore the HP numbers. Make parts. Then figure out how to make them better and faster if you need to.

    It does not sound like your spindle is defective or underpowered but maybe a 770MX user can chime in with something that works for them as a comparison.
    You could stick a cheap load meter on the incoming power line to get an approximation of load if you really wanted, but that seems like premature optimization again.

  17. #17
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    Re: 770MX Spindle Keeps Stalling

    I profile slot in aluminum 6061,
    feedrate 20 to 25 ipm
    .25 endmill
    5140 rpm
    flood coolant (oil)
    doc .130
    woc .25

    Water based coolant results will be a bit different as oil doesnt cool as well as water.


    Start at a low feedrate and increase from there

    most newer operators want to go way too fast on feed rates and RPM
    mike sr

  18. #18
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    Re: 770MX Spindle Keeps Stalling

    Quote Originally Posted by popspipes View Post
    I profile slot in aluminum 6061,
    feedrate 20 to 25 ipm
    .25 endmill
    5140 rpm
    flood coolant (oil)
    doc .130
    woc .25

    Water based coolant results will be a bit different as oil doesnt cool as well as water.


    Start at a low feedrate and increase from there

    most newer operators want to go way too fast on feed rates and RPM
    That's about the same as me on a 1.1kw PM25 hobby mill.
    I only have half the rpm (2.5k) and ended up just over half your feedrate with a straight slottiing process
    The rest is identical. Sounds about right to me.

    TBF I generally just go by my chip load per tooth for rpm & feedrates.
    Then stick to 1/2 tool diam for doc and 10% - 20% tool diam for woc. (unless it's slotting which is full woc and slower, generally half of normal).
    It's steady but results are normally great.

  19. #19
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    Re: 770MX Spindle Keeps Stalling

    Question.

    What is the max tool diameter in the specs recommended for milling?.

    Whatever the specs on machines suggest, it usually ends up being half that or smaller for decent speed & cut results.

  20. #20
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    Re: 770MX Spindle Keeps Stalling

    I don't think there is a maximum "recommended" size, but the max you can get into R-8 with typical collets is 3/4" and the max you can get into ER-20 with typical collets is 1/2".
    I find that 1/2" only works for thin profile cuts, 3/8" can work well if you take it easy, and 1/4" works very well, very similar to the numbers in the thread below.

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