Thread: Yet another Router table build.

Erick, just got around to testing the stepper and controller, all working. So next step is getting the Screw and ball nut drive connected to the test motor and a DRO connected to the ball nut mounting collar, that gives me the chance to start writing the closed-loop control code for the micro while I await the parts to build a working Router Lift and Fence movement mechanism. Those lines of code are going to grow some more, but at least I can see the light at the end of the tunnel, or is that the train coming?

Originally Posted by HypnoToad

I have this winder thingy I made from a knob and some scrap metal.

I have one as well, but this will be better.

Originally Posted by MandJ

Erick, just got around to testing the stepper and controller, all working. So next step is getting the Screw and ball nut drive connected to the test motor and a DRO connected to the ball nut mounting collar, that gives me the chance to start writing the closed-loop control code for the micro while I await the parts to build a working Router Lift and Fence movement mechanism. Those lines of code are going to grow some more, but at least I can see the light at the end of the tunnel, or is that the train coming?

Well done!!

Just received my missing Ezi-view DRO head today Interestingly there is an additional port for Data Output on the side. Looks like it takes the Mitutoyo SPC lead. You can buy a USB box that plugs into it and sends data via a USB connection to your PC. There is a switch on the box so it only sends a single data packet each time you press the button. Expensive accessory at approx. $140.

Know what you mean about lots of code - just printed mine out for a read through and it’s 13 pages!

Small FYI.

A common problem with DRO's is the interference from motors and other electrical equipment. I just tested the Stepper drive controller, stepper motor and wiring with the DRO Scale head and it's not interfering in any way, normally you see this in the scale position readings jumping all over the place.

I placed the Scale electronics on top of the controller and on top of the exposed stepper wiring, stepper running, speed changes and being suddenly reversed, not a glitch. Looks like the only things that will give us grief are the usual suspects, the Router or Spindle drive and VFD. But the good news is that even those can usually be be overcome.

One of the tests I wanted to do was to see if the speed reduction of the "screw and bearing nut drive" in combination with the auto idle holding current (set low hopefully) would have enough holding power to stop a heavy router motor / spindle motor from moving, especially with the vibration of a big routing bit. Now this is only bench testing but, I'd have to hit the motor with a sledge hammer, and it likely wouldn't move, well it would, but from the complete assembly been smashed into the bottom of the router cabinet.

So it looks like the only area of movement / flex will be in the mechanical construction that is utilised when attaching the router motor to the side bearing rails. It also means that there's no need for any locking mechanism for the Router motor or fence - BUT - What of the safety aspect? Now the drive assembly itself, even with the loss of stepper holding current, would still hold, the problem is if a glitch caused the motor or fence to move while in use. Sure, I can easily remove the drive signal between the Micro controller and the stepper drive unit when the router motor is running, but what if the stepper drive box itself suddenly goes faulty, even with it's inbuilt fault sensing circuits, it's still a possibility. I have a few ideas for safety locking, especially the fence, but just putting it out there for some input.

Thoughts?

The only sure way is to isolate the power supply to the stepper motor, no power = no motor movement.

Yes that would be one way and it will need final testing for the router motor, but the fence will work like that, IMHOP the fence can't really overcome the screw drive reduction holding force. The way the stepper drive works it's extremely unlikely to fail and start moving the motor, it's likely the opposite and will fail jamming the motor and trip it's over current or fault circuits.

BTW Chris I should be able to move the Spindle motor 140mm in around 5 seconds or less, the final speed will depend on the stepper motor design and size, quick for Home and Bit changes. That speed was measured with a big old stepper I just found in the (stuff I might want some day) bin, It's been there from 40 years ago when I used it to make a remote High power "link coupled" antenna tuner for the 160m Amateur band. Sigh!

By utilising the the Enable pin on the driver controller, you can either lock the stepper, or allow it to freewheel ie. so you can manually rotate it. While ever the controller is powered up, this feature will be enabled.
If the controller is disconnected then you may need some form of mechanical locking but I don’t think it will be a problem.

That would still leave the electronics that could move it connected to the motor and still powered, that switch is likely only a soft switch so hardware is still running and connected to the motor.

As said, the chances of a fault in the stepper controller making the motors move is pretty remote, this is really about food for thought and how people feel about safety, but even if it did move the fence it's rate of travel would be slow because of the reduction drive.

I guess when it's up and running in test mode I'll force a few conditions in software and see if really is a problem in practise.

I was referring to it staying “locked” while in use so it doesn’t move/screw itself down the thread from the selected position while routing.
As far as safety goes, that’s why I use limit switches set just before the ends and fail safe switches at max. Travel. Cheap insurance. The fail safes trigger relays which can be set to cut the supply.

OK, you may have slightly misunderstood the original question, or I'm not making sense.

Locking the shaft is not the problem, as I posted above, the idle holding current is able to 100% positively lock the shaft and lock the router and fence, especially with the drive reduction "torque multiplier" that we are using.

Fail-safe limit of travel sensors are a given when using powerful steppers and a reduction drive.

But none of that means anything if the electronics, due to a glitch, decide to move the router and especially the fence while you are actually using the router, that's a good way to loose half a hand, I've seen people doing stupid things on a router table "AND HAND HELD ROUTERS" that make my blood run cold, so I'm thinking of them.

The "out loud" thinking was about the safety of an electronically controlled and locked fence VERSES the typical manually locked fence. Once again limit switches mean nothing and holding current is meaningless if the electronics fail - But the testing I have done indicates that even with no holding current, the reduction drive and a non-powered stepper is still able to hold its position, especially with the fence.

Now if the user doesn't correctly lock a typical fence then it can move. I could give a technical reason as to why a failure in the H-Bridge in the stepper controller won't cause the stepper motor to move, and why the controllers we are using won't cause that even if it faults BEFORE the H-Bridge, the problem is that the command could come from the Micro Controller driving the stepper drive controller, for whatever make believe reason or due to some random unlikely once in a blue moon event.

Now after thinking about this some more, I'm of the opinion that the electronic control that I current have over the Fence and Router lock position is possibly safer then relying on a manual lock. The only thing I "might" add is a simple $10 circuit to disconnect the drive pulses coming from the Micro computer whenever the Spindle or Router motor is spinning. I.E. Something "independent" of the Micro controller as that is a fail safe. Again I'm taking an independent fail safe, so using the control PINS on the Stepper drive controller itself, is not really a "totally independent" fail save.

I have found from experience with micro's and mains operated equipment that "noise" could cause issues. However there are ways to solve this

Yes I've programmed micros for heavy industrial use over the years so that won't be a problem as far as coding for glitches / noise goes, or adding appropriate filtering on IO ports where required. The micro I'm using has never had an issue around the router table or any equipment in the workshop, one was used for the dust sensor and that was placed on top of equipment for hours on end. It's just this one aspect of safety that I wanted to think through and get some opinions. I know it's hard for most as this is really an unknown area for most DIY router tables, and it's not like a CNC, in an R-Table someone could be pushing a work piece against the fence and have their fingers a 100 mm away from the cutter OR WAY less as I've seen on numerous videos, anyway it's made me stop and take a realistic hard look at the problem, I'm now confident that this won't be an issue.

Cheers.