Best practice for mill VFD control wiring

O.K. I thought that you had perhaps done that well on a single fast approach, which would have been *very* impressive.

It is only a 5" swing -- and perhaps 10" between centers. There is a steel splash backplate which also includes the electronics, with the keypad and readout at the upper right-hand corner, and most other things high enough to be above the splashes.

To zero it (for each tool) there ia a bed-mounted microscope, so you zero the Y and Z Axes for the first tool move to the intersection of the cross hairs, then swap in the other tools and write down the offsets as you move the tool to the same intersection. But there is no provision for storing the offsets in a single place in the program -- you have to enter the offsets *every* time you call up that tool. A royal pain.

I've been collecting servos of various sizes, and have some which are not that much larger than the steppers, which stick out from the end of the bed and where the cross-feed crank would otherwise be, so there is room for *them* at least. No provisions for linear encoders, so I'll have to put a rotary encoder with each servo motor.

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Well ... that tells you which trace is likely open. Perhaps it is an open via, and simply filling it with fresh solder might make it work.

O.K. When driving the knee -- is there automatic gibb locking between motions?

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Hmm ... what if you need to cut a 13-1/2 TPI thread? That might be difficult with the 2:1 coupling.

Of course, an encoder directly on my Clausing's spindle would be difficult with clearance for a 5C lever-acting drawbar. So -- the trick there is to add another gear engaging the spindle's own gear -- and ideally a spring-loaded zero-backlash gear for that. Another use for the set of gear cutters and the index head on my (very manual) horizontal mill. :-)

O.K. I could probably do that as fast on the Clausing, using the bed turret and a Geometric die head. 3/4-16 is within the range of the sizes which I have.

I really don't want steppers at all. It was bad enough trying to cut a Morse 2 taper with the Compact-5. Not only was the resolution limited ot 0.001" or 0.01mm -- but it was measuring radial dimensions, so the diameter goes in steps of 0.002" - *that* I could see with my bare eyes. Servos, told to move at speed N for one axis and speed J for the other will cut a very straight taper.

The Bridgeport BOSS-3 has two tapered roller bearings ground to fit together to mount the ball nut (which is rotated for the 'X' axis, with a fixed ball screw simply clamped at one end, so there is less whip with rapid moves). There is very little measurable backlash there.

The 'Y' axis leadscrew does rotate -- but that is only for a 12" motion, not the 18" for the Y axis.

The 'Z' zxis is a ground hollow ball screw around the quill, and another rotating ball nut to move it up and down, so the force is concentric with the spindle axis.

Perhaps -- but I really want servos on those when I EMC them.

Enjoy, DoN.

Reply to
DoN. Nichols
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I don't have a servo on my knee, I was just giving an example of how EMC would see 2 servos acting on the same axis as a single axis to help explain how EMC can use 8 servos for the six axis. But just like a brake on a motor you could configure EMC to unlock gibs while moving the knee.

When starting a spindle syncronized move, EMC zeros the spindle counter on an index and synchronizes from there. The difference with a 2 spindle revs vs. 1 encoder rev is that the index only comes around once every other revolution. I bought a 500 line encoder for my spindle giving 2000 counts per encoder rev or 1000 counts per spindle revolution. So, in 1000 counts my axis can position can be 1/13" or 1/13-1/2" or any other standard, metric, or non-standard pitch is no problem.

In general I think a manual machine can be set up to out run a CNC machine but the advantage I see in a CNC machine is to use a few tools to produce many different shapes. For example on the lathe pawn program, there are various tapers and radius cuts. A turret lathe with form tools, etc could probably outrun a CNC on a setup but the CNC lathe could probably be hours ahead if you have to make 2 of this part and 3 of that part.

I was kind of thinking as a step between, using EMC to replace your control now and swapping out the steppers for servo's later. But, it doesn't seem reasonable to replace your existing drives with micro-stepping drives or anything like that for a temporary transistion.

I know what you mean, I prefer servos too. One thing I like about servos is that their torque is generally rated as continuous and goes up from the rating whereas stepper torque is rated as holding and goes down. I didn't know that the Emco lathe had ball screws, is sounds like it will be a very nice project for an EMC conversion. The hardware sounds great, just sounds like the control need updated a bit.

RogerN

Reply to
RogerN

O.K. So this is a hypothetical, instead of an actual bit of hardware. Yes -- I can see benefits to this -- when you need a lot longer Z travel -- perhaps to accommodate varying length tools in the quick-change spindle.

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O.K. Just a potentially longer wait to start the next thread pass. I kept thinking in times of gear synchronized leadscrews for whatever reason.

Agreed. And another type of lathe which might be good for the pawn production is a tracer lathe.

Remember -- I've got a fully working stepper driven Compact-5/CNC, and a totally spare machine with dead electronics for using to built the EMC-driven package. And I'm actually missing one of the steppers -- sold to someone else who was restoring another machine. So -- I can make this as a servo based lathe without losing the existing stepper based machine -- until I have everything working, then I swap over and look into making a second servo-based lathe so I can do things like second-operation CNC without having to reconfigure the first machine.

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Just as the hardware on the Bridgeport BOSS-3 mill is great for CNC (as it started life as a stepper CNC machine). The only problem is that the servo motors are longer than the steppers, so they won't fit where the steppers did for the Y-axis. Bridgeport made a recess in the knee to clear the stepper which pointed towards the knee's jackscrew from the Y-axis timing belt pulley below the Y-axis ballscrew. I need to make a new belt housing and motor mount, with the belt going diagonally to the right and down at about a 45 degree angle so the motor will stick back beside the knee, instead of into the cast-in recess. I've seen photos of newer Bridgeport CNC machines, with servos instead of steppers and with the diagonal belt to the servo mount. I just wish that one of those had been part of what I got with the machine.

The original CPU on that machine is a LSI-11 -- the same 64K address space as the Compact-5/CNC -- but arranged as 32K 16-bit words, instead of 64K 8-bit bytes. (Later LSI-11 CPUs had memory management hardware, allowing splitting into 128 KBytes of address space, half for "text" (machine code) and half for "data" (the G-code and variables). But this one is too early a version for that.

Enjoy, DoN.

Reply to
DoN. Nichols

I always thought it would be interesting to have a small lathe I could put on my Bridgeport table and use a Servo and brake on the lathe spindle. Having a lathe combined with a 4th mill axis... I guess it isn't any better than a lathe with live tooling but probably a lot cheaper for a home shop.

RogerN

Reply to
RogerN

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