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I am planning on replacing the variable speed pulley pulley system with a fixed ratio toothed belt drive. Primarily to raise the spindle speed and quieten the drive. Speed control will be with a VFD.
I am sure that others must have done this but my question is really "Does anyone here have any idea what is a sensible maximum spindle speed to run at with these machines"? As they came they should be able to do 4200 RPM so I guess that 5000RPM would be fine but what about 6000RPM?
tonyfoale
6,000 RPM is fine,I have done lots of them, some up to 12,000 RPM, the whole Head has to be modified to do these speeds, the noise from using a timing belt is very high,at those speeds, it's best to use a poly-V Belt, Everything has to be balanced, including the Drive motor, good quality Bearing fitted to the Drive motor, unless you are able to do rigid tapping then the Poly-v Belt is the best
many thanks. That looks like a nice conversion. A poly-V belt is what it will be then. A couple more questions.
Do you retain the backgears to increase low speed torque?
What RPM motor do you use?
I doubt that rigid tapping will be of importance to me but if it became so then I'd fit a sensor to the spindle, so the poly-V should still be OK.
tonyfoale
The Head in this photo did not have the Back-Gear, so does not have much torque below 1000-RPM, as for motors this one had the 3450 RPM motor so had a 1:1 drive & 120Hz setting in the VFD, if you need slow speeds, then you need to keep the Back-Gear, Baldor have some motors which are very good, 3Hp to 5Hp wash down motors run up to 6,000RPM & are Inverter Duty, other manufacturers may have the same type of motor, this Photo shows the same Head complete, with 5" removed out of the top
Thanks again. Very useful info.
I guess that you have got rid of the R8 collets?
This was a Boss5 CNC so it had a Erickson Quick Change Chuck 30 Taper as standardQuote:
Originally Posted by tonyfoale
Mactec54,
I am sure that you can answer this from your experience.
The stock machine has a lot of inertia on the spindle. A steel back gear and the vari-pulleys add up to quite a bit.
I can see that there are 2 sides to spindle inertia.
1. It smooths out speed variation as adjacent cutter teeth attack the work piece.
2. It takes longer to stop the spindle in an emergency.
What balance have you found works the best? In your previous pic. it looks like you have some form of flywheel on the spindle underneath the pulley.
What is below the pulley in the photo, is a Cast Iron Disc for the spindle Brake, The only backlash, you should see with your spindle is with the splines, that go up through the mating drive splines, the Back gear is a belt drive, so you should not have any backlash with that part, If the Vari-drive pulleys are worn they can have a lot of backlash, there are some plastic bushings & keys that can be replaced in the Vari-drive pulleys, the spindle can stop very fast, this depends how & what VFD Drive you are using, & the settings usedQuote:
Originally Posted by tonyfoale
mactec54,
Many thanks, that new photo makes it very clear. The brake is very neatly done. I was planning on something similar using a motor cycle brake caliper. I'll be losing the original drum brake because I'll be removing the vari-pulleys and its shaft as well as the back gears. I have a 6000rpm motor and will connect that to the spindle drive with 1:1 ratio poly V belt drive.
You should not use a spindle brake to stop the spindle when using a VFD, I found it unnecessary when retro-fitting a Similar XLO, I just used the brake for the quick change tooling when stationary.
Al.
Al,
I agree completely, but I am fitting a brake for those times when I want to hold the spindle still and for real emergencies.
I triggered mine with the output from the VFD when it was at-zero-speed (set by parameter), I also had a manual overide button if I wanted to rotate the spindle.
the automatic brake at zero is used due to the Quick change 300 tooling.
In CNC applications, I also use the wait for the VFD up-to-speed signal when a M3/M4 is issued.
Al.
I have been using a VFD with 3ph motor up to now, but I am changing to a fixed belt ratio at the same time as increasing the spindle speed to 6000rpm, and I will be trying a DC motor. I have a suitable motor and controller doing nothing so it is a no cost test. If I don't like it then I'll go back to the usual VFD and larger 3ph motor which I don't currently have.
What you are doing is the norm for a setup like this, a spindle brake is just that, used for doing tool changes, it should never play any part of stopping the spindle that is driven by a VFDQuote:
Originally Posted by Al_The_Man
The Brake used on this machine can be activated Manual Auto or Off, in Auto it is controlled through the ladder logic in the control software, & is never used to stop the spindle as the VFD can do this better than a Brake could, When a Brake is fitted to a Spindle, it's main use is for doing a tool change, or can be used also for holding the spindle, when cutting keyways
So is it a BAD idea to use a mechanical break to stop the spindle or is it just unnecessary? I can stop the spindle VERY quickly with Bridgeport's mechanical break. I have a hard time believing that a VFD would stop it as quickly....Quote:
Originally Posted by mactec54
With a breaking resistor in the vfd you can stop in less then 1 sec.
Ben
HawkJET
With a manual Bridgeport that is NOT powered by a VFD, yes you can use the brake to stop the spindle, as bhurts has posted if you have a VFD with a external Braking Resistor then the VFD can stop your spindle in less than a second, much more effective than trying to use a brake, which will Damage a VFD when used
If you have your Bridgeport powered by a VFD, then don't use the Brake to Stop the Spindle, set the VFD to do it, a good quality VFD, without an External Braking Resistor,can stop your spindle in 4 to 5 seconds
It's just not a good idea to use a spindle brake when using a VFD, only when the spindle has stopped
Thanks! That's good to know. I have not yet installed a VFD so I am in the process of learning all I can about them.Quote:
Originally Posted by mactec54
The most important thing to do with a VFD is to read the manual carefully. There are warning, like the above, but they have many programming options such as acceleration time, max frequency and many others that you'll want to set to optimize it for your own hardware.Quote:
Originally Posted by HawkJET