Hello all, My OCD is getting the best of me. I have a Shapeoko 5 Pro 4x4 with Carbides 65mm 110v VFD spindle and have noticed that the RPM’s displayed on the VFD box don’t match the expected RPM’s. I checked the grbl settings at $30 is set to 24000 and $31 is set to zero, so those appear to be correct. When I run a spindle warmup I get the following numbers:
CM=Displayed
8000=7998
12000=11460
18000=16890
24000=24000
Both the CNC controller and the VFD are plugged into directly into dedicated outlets and I have confirmed all wiring is undamaged and all connections are secure. Any ideas on how to correct this?
It appears to be cutting fine, it’s more just me wanting to make sure everything is running as expected. I did have two Genmitsu 2mm carbide bits break recently on a project, which is what made me think things might be off a bit. Other than that I haven’t had any issues.
My VFD controller is mounted on the back of the machine for now so I don’t even look at it.
I have plenty of other routers with adjustable speeds and I never worried about the actual rpm vs speed setting. The speed I selected worked with the bit I had.
In the use-to-plant, we were happy and content with a reading of 250 deg F. Then came the improved accuracy of digital displays with the ability display out to the .001’s and everybody was worried about the system being 250.9 deg F vs 250 deg F. When in reality we changed nothing on the actual system controls to be able to control to the tenths place.
I’m not too worried about it on my 5 Pro. As of now there is no real adjustment the average person can make anyway. I can’t control it, I don’t worry about it.
Multiple have reported here on the forum that the displayed speed and actual speed are not the same. However lets take one of your speeds.
18000 (Displayed) and 16890 (Actual Speed) is 9.38% lower than advertised. So the fix is 1 of 2.
Live with it because 9% is not much at 18,000 RPM.
Setup the bits with a custom tool adding 1800 RPM to 19,800 RPM and get your desired acctual speed.
The way a CNC cuts the 9% is not likely to cause any problems. But if you think it is critical that you run at 18,000 RPM then you will have to intervene.
A 3rd option is to edit your tool and add your own speed which for 18,000 would be 19,800 RPM. It would be necessary to edit the tool on every tool path every time or set up custom tools that already have your desired speed.
I can do that, no problem. For most projects with bigger bits, I do go in and modify the feeds and speeds for each path based on what I get from HSMAdvisor. I haven’t attached a tach to the spindle yet to see what the true speeds are, but if I have a path that I set the RPM to say 18000rpm, the display on the VFD says 16890, so I don’t want to change the RPM on the tool to compensate for the 110rpm difference if the spindle is in fact spinning at 18000rpm. I have noticed the variance increases between 19k-22k rpm. I can’t remember off the top of my head, but when I’m set at 19500rpm, the display is around 17750. Once I go under 10k rpm and over 22k rpm the variance is minimal.
I’m sure none of this is a big deal, but my perfectionist OCD brain is fighting me on it
