How does a tablesaw with motorized tilt, tilt so accurately ?

[Milacron]

2006 Martin T60 Basic, in this case. Just got machine in last week, today I checked 0 degrees (blade 90 degrees to table) and it was way off..like 5 degrees. So figured there would be a calibration procedure in the saw's control to manually bring blade to a hand square and then reset it to zero in the control. But instead there was only a "calibrate to zero" function where I did nothing but press the "calibrate" button on the touch screen and it brought itself to dead nuts zero all by itself !

So the question is, how the heck did it do that ? It has two Berger Lahr linear actuators...one for blade rise/lower and one for tilt. If there are prox sensors or electronic scales in there somewhere they are hidden well as I can't find any.

[ratbldr427]

The linear actuators may have potentiometers in them.Some of the actuators on our printing presses use them instead of encoders,probably because of cost.
Randy

[wippin' boy]

Motorized Linear Actuators Servo & Stepper, Ballscrew & Leadscrew, Electro-Mechanical Actuators by PI

[Milacron]

The linear actuators may have potentiometers in them.Some of the actuators on our printing presses use them instead of encoders,probably because of cost.

I get that part but seems like if there was some predetermined "0 degree" point on the encoder (or internal limit switch, home switch or whatever) it would never have got "off" in the first place. It's almost like the control got "drunk" but pressing "calibrate" was like injecting two cups of coffee so then the control sobers up and thinks "oh right, zero is really over here"

[wippin' boy]

i agree
my totally cynical opinion would be lazy code.
a modern device should be able to keep track of itself but if its not written into the code for the thing to keep track of each move and then reference itself it don't.
easier to just write in a reset line and upcharge for the button.
could be some to do with how much ram and processor they would need also
if you only need to keep track of a couple moves accurately you could do it with a good digital egg timer class processor

[PeteM]

Just a wild guess -- digital level sensors are now pretty cheap and widely available. Perhaps the unit checks level and also knows where 90 degrees to level is in reference to the table and blade. Once calibrated, the digital level might then be used to quickly find every angle the blade might be set to??

[bryan_machine]

It could be that it does know where it is relative to some hidden stop, so long as the tilt of the blade isn't changed by something other than the tilt motor. So if the blade gets moved relative to the "scales" in shipping, or any time the power is off, it's confused.

What was the sequence before it was 5d off? Meaning, did you turn on it and move it back and forth under computer control, and then say "go to 0" and it was off? OR - you unboxed it and turned it on, it said "0" and you measured and got "5d"?

[Milacron]

It could be that it does know where it is relative to some hidden stop, so long as the tilt of the blade isn't changed by something other than the tilt motor. So if the blade gets moved relative to the "scales" in shipping, or any time the power is off, it's confused.

What was the sequence before it was 5d off? Meaning, did you turn on it and move it back and forth under computer control, and then say "go to 0" and it was off? OR - you unboxed it and turned it on, it said "0" and you measured and got "5d"?

I bought it from a dealer who wasn't the sharpest tack in the drawer, but for that matter neither were the folks he got it from apparently (long story, but the Tiger Fence was mounted such that there was no way it could have worked properly...maybe that's why they sold it with practically no hours on it...damn thing is pristine) so tilt screw probably shifted somehow in two rounds of shipping (to dealer and then 1,000 miles to me)

I had been playing with the tilt a few times over days but only yesterday did it occur to me to check just how accurate the angle was against known references, and only then did I see it was pretty far off. Tilted it to various angles since I recalibrated and it's dead nuts now...just hope it stays that way. As I said, I just assumed calibration would be a process of manually getting it to a known reference via hand guages and hitting zero....so was surprised it could find zero on it's own so accurately when it seemed to be confused about the matter prior to my touching "calibrate" on the LCD screen.

[bryan_machine]

Think about the references on a milling machine. The ones I own, you boot them up, and they have no clue[1] where they are. So they move slowly until they hit an indicator or stop or switch, and then they know exactly where they are. For something like a saw, where metal machine accuracies aren't required, it wouldn't be frontier to just remember where it was.

Of course, you know all that, and are really wondering "where is the micro-switch or reference light or ????'. Good question, I don't know.

[1] One of the scales on my DMU - for the B head - is absolute - it doesn't have to home, it always knows where it is.

[Milacron]

[1] One of the scales on my DMU - for the B head - is absolute - it doesn't have to home, it always knows where it is.

Maybe that's the bottom line with this thing is you need to "home" it (via "calibrate") after it's been on a truck or moved around the shop. But unlike a mill for example, once you get the saw in it's final resting place in the shop, it should stay at "home" position most of the time and be pretty accurate without having to calibrate at each bootup.

[matt_isserstedt]

After dealing with other servo machinery, many of them use a prox to find home. When I say find I mean the servo has a creep speed (very slow) where it finds the point where the prox signal changes state...sort of the "edge" of the prox signal. Apparently its very repeatable, as after homing via above, a servo pick and place machine with about 4 feet of travel in all 3 axes will repeat less than 0,5mm.

Usually the homing above needs to happen when the machine gets crashed. This can cause the zero-backlash coupling between the servo motor and its belt drive cog to slip if the overload is severe enough and the machine is running at peak velocity.

Hopefully your tablesaw did not experience this. Could be related to the point not being written into a memory that survives power being completely off or the backup battery became discharged...guessing of course.

[Milacron]

Hopefully your tablesaw did not experience this. Could be related to the point not being written into a memory that survives power being completely off or the backup battery became discharged...guessing of course.

I need to find out if this simplistic control has a backup battery and parameters as that would be a bit annoying if it does. I mean it's a friggin table saw for gawd's sake...all it does is raise/lower and tilt the blade. But because Martin made it programmable for specific figures if you want (i.e. you can input 27.5 degrees tilt and it will go to that angle and stop) and a few other programs for dados and tenons, it may sure enough have parameters and a battery...sure hope not.

I'll see them in their booth at the IWF show in Atlanta this week but won't surprise me if the folks in the booth haven't a clue. When I first got the saw and ran it I was getting a error relating to the saw brake. I speculated this was because there was no blade on there, and therefore the saw arbor was stopping "too soon" compared to what the control was expecting to see and thus the error. Martin folks did not agree and had some other speculations about the cause...but sure enough, put a blade on there and the error went away.

[S_W_Bausch]

Just a wild guess -- digital level sensors are now pretty cheap and widely available. Perhaps the unit checks level and also knows where 90 degrees to level is in reference to the table and blade. Once calibrated, the digital level might then be used to quickly find every angle the blade might be set to??

"How...cheap...are... they???"

RC aircraft use pizeo gyros.

iPhones have them.

And Pete's answer makes the most sense. Milacron hasn't related the machine going to zero (as our dot-matrix printers did), or any other sort of homing.

[Peter.]

In the Chinglish instructions for my cheapo DRO there's a page with a proceedure for finding zero if the scale had been moved with the DRO powered off. It says there is a 'base mark' (for want of a better term) on the scale that the DRO unit can use to pick up off and re-align the scale to where you last had it zeroed.

[Mr Bridgeport]

Don, If it has a reference mark on the scale like most scales do today, than it just tilt it in a + or - direction, what ever it's supposed to do and backs up a preset amount, adjustable by some parameter. Yea, I'd see about backing up the parameters.
Bill

[Milacron]

Don, If it has a reference mark on the scale like most scales do today, than it just tilt it in a + or - direction, what ever it's supposed to do and backs up a preset amount, adjustable by some parameter. Yea, I'd see about backing up the parameters.

Yes, but as I already alluded to, if that was the case why did it get off in the first place ? Seems like the operations of that saw are so comparatively simple it would be designed to go to that reference point automatically any time you program in "zero" degrees. Should be no need to "calibrate" to zero, it should just go to zero.

[Mr Bridgeport]

Don, I service a Wilton roll in saw that does the same thing. Every time it's started up it must be "zeroed in" on the angle setting. I think that uses an encoder at the pivot point and a hydraulic cylinder for movement. Always pivots off center and comes back. Actually, it's not that smart, the operator uses the control buttons to move it off center and than can look at the digital display to bring it back to zero.
Bill