An Electronic Lead Screw controller using a Teensy 4.1

[WobblyHand]

Steppers can't achieve their rated step rate from a cold start. They need to ramp up to that rate. If we stay in lockstep all the time, the max RPM will be limited. The encoder does have a home position so it should be possible to get the correct relationship between the lead screw and the spindle even if there was an initial slip, at least in my initial thoughts. As long as the sync is complete before cutting metal (threads) it should be ok. Haven't thought much more on this.

 

[AlanB]

I've thought about this quite a bit, and my plan is to avoid the complexity of acceleration for a lead screw controller. I suspect the spindle cannot out-accelerate the steppers, so it inherently limits the system acceleration. So unless you change thread gearing ratios while already running there's no need for it. I don't plan to allow changes in gearing or direction while in motion so that solves most situations. The one case I would like to allow changes while in motion is feed speeds. However those are low speeds for the stepper, and the speed changes should be small steps so that should not be a problem. I'm also planning to use a closed loop stepper which doesn't really have the acceleration problem in the first place.

If you plan to do more CNC type operations then it may well be needed. EG - starting the carriage when the chuck is already up to speed, etc. That's getting beyond an electronic gearbox, but certainly some high end ELS systems go into some CNC modes. It's a departure from a simple ELS.

One could certainly come up with a way to do it, but it adds complexity that may not have any value. I plan to wait until the need occurs before solving it. At least that's my present thinking. If your lathe accelerates instantly it might be a problem you need to solve. Then it would depend on power, weight of chuck, gearing, and stepper motor characteristics, drive voltage, and stepper drivers as well.

 

[WobblyHand]

I plan to wait until the need occurs before solving it.

Fair enough. I suspect that the world may not behave as I imagined it will... I am expecting things like that.

For one thing, I will need a means to reverse, and I do expect I will be cutting left hand threads. Just plain forgot to implement them.

I do plan to integrate my DRO's into the application. How that will pan out, I don't know. I have an ancient LED 7 segment DRO display, and I am suspicious of the circuitry in that unit. It handles metric strangely. I may - if I feel like it - put in the ability to feed to a stop, but that will require some additional safety planning. As it stands, there is no safety stuff in my code. That bothers me. I will put in something, at least a panic stop of some sort, before it goes live.

 

[WobblyHand]

Decided to attack the lathe... Literally with a die grinder and a 1/2" double cut carbide burr. Removed 10mm of the upper edge of the rectangular hole in the ways base. Filed and filed out the corners. Thought I was done. Nope, the motor was wider. Using the plate I made as the template, marked out where more material needed to be removed. Turns out I needed to remove another 5-6mm to make my piece work. I didn't think it would be that much. Lots more grunting and sweating and filing.

105 degree head on that die grinder, find it a lot more comfortable than the 90 degree heads.

You can see the initial height (sharpy mark) on the right. Thought I was done when I hit that line. Oh well, what's a little more cast iron grinding. I am glad that is over with. The sweat was running into my eyes. Had to stop and wipe my forehead with paper towels multiple times. Think it's coming out ok. I suppose I need to find a place for those gears soon. Might make a gear stand of some sort to organize them and stash them away safely. Think it will be nice to be able to clear out that part of the pan.

 

[WobblyHand]

Just because I can take this picture I did.

Now have to locate the holes for the motor mount. I figured out the belt to the last mm. It does fit - just barely makes it over the lip of the pulleys in the closest position. A couple of mm shift to the left and the belt seems to be snug. And yes the pulleys line up!

I think I need to machine both the 60T gear and the 60T pulley. I have some offset that I have to make up. Bought a spare plastic gear and gear shaft, just in case. Won't really be able to know for sure until I can mount up the 60T pulley on the shaft. Need the pulley broached to do that correctly. Suppose I could leave off the keyed bushing, or pull the key if it is separate. I do know the pulley is 11mm wide, and I only budgeted for 8mm. So I think I have to come up with about 1.5mm on the gear size and 1.5mm on the E-clip side, so the clip retainer will fit. Might just machine the gear shaft a little and be done with it. But before I do that, I need to mount up the encoder correctly and measure everything in situ. Perhaps reality is not what I think. Murphy will ensure it is worse... Got to remember, measure first, then again, and finally cut!

 

[WobblyHand]

Got some metric HW in, so I can install the 2M-40T timing pulley on the encoder. Received some M3x10 flat head screws, and some M4x8 set screws. (Some M5x10 set screw for the bigger pulleys.) Here is the rotary encoder mounted on it's bracket and the pulley mounted on the encoder.

If you look carefully at the first picture, you can see a prototype Z axis DRO reading on the screen. For now, I am using the rotary encoder as the stimulus. The DRO read head outputs A & B at 5V levels, like the rotary encoder. So I can use the identical hardware to capture the data from my lathe's DRO. The encoder software has no idea if the encoder is linear or rotary and is the same. For the DRO's I will have to determine the scaling factor. Will use a 123 block for that determination. Whether I can decode 3 inputs at full speed, I don't know that yet. I did test a single input to 200 KHz rate without failure. Fortunately the Z axis isn't going that fast, and the X axis hardly moves. Worth a try. I will test the two axis DRO stuff separately, probably using a separate Teensy.

 

[RJSakowski]

I suppose I need to find a place for those gears soon. Might make a gear stand of some sort to organize them and stash them away safely. Think it will be nice to be able to clear out that part of the pan.

A 5" long 1/2" bolt and nut works out nicely for storing the gear set.

 

[WobblyHand]

A 5" long 1/2" bolt and nut works out nicely for storing the gear set.

Had a 7/16" bolt that was barely long enough, caught 2-1/2 threads. I will get a 1/2" bolt that's long enough, so I can eventually put the gears away.

Unfortunately, that won't be right away. Somebody, not saying who, didn't account for the chip pan being in the way! So I can't drill the bottom holes to retain the motor plate. Need to jack up the lathe relative to the pan so I can get a drill in there. Maybe I can make a simple screw jack (machinist jack) to lift the lathe some. I need a lift of about 1/2 - 3/4" to get above the lip of the pan, and to have clearance for the drill chuck and drill. Thought I would use a piece of 1/4" plate to span the ways underneath and a screw jack. Wished I had such a device, but I don't. So I will make one. The lathe has to be reconfigured so I can make the screw jack. Designing a simple screw jack now. Have some weird 1-11/16" stock I could use. I will make a 1"-12 TPI screw.

 

[RJSakowski]

Had a 7/16" bolt that was barely long enough, caught 2-1/2 threads. I will get a 1/2" bolt that's long enough, so I can eventually put the gears away.

Unfortunately, that won't be right away. Somebody, not saying who, didn't account for the chip pan being in the way! So I can't drill the bottom holes to retain the motor plate. Need to jack up the lathe relative to the pan so I can get a drill in there. Maybe I can make a simple screw jack (machinist jack) to lift the lathe some. I need a lift of about 1/2 - 3/4" to get above the lip of the pan, and to have clearance for the drill chuck and drill. Thought I would use a piece of 1/4" plate to span the ways underneath and a screw jack. Wished I had such a device, but I don't. So I will make one. The lathe has to be reconfigured so I can make the screw jack. Designing a simple screw jack now. Have some weird 1-11/16" stock I could use. I will make a 1"-12 TPI screw.

Ah yes, my 602 sits on 7/8" risers so no problem when I did mine.

Getting a Rise

I have a Grizzly G0602 lathe. One of my issues has been the clearance beneath the bed. It makes it difficult to clean chips from the chip tray. Another concern was the inability to access the two lower mounting nuts on the motor. I decided to put two 1" risers under the lathe. My lathe...

www.hobby-machinist.com

I made a simple screw jack using a 3/4" bolt and nut, a 1`-1/2" long piece of 1" pipe, and a2"d. by 1/4" disk. It has served me well over the years.

But you needn't go to that bother. The lathe isn't that heavy. With some 2x4 cribbing, you can easily lever it up once you remove the two mounting bolts. Once raise sufficiently place some blocking under the ways to support it while you are drilling and tapping your holes.

 

[WobblyHand]

Ah yes, my 602 sits on 7/8" risers so no problem when I did mine.

Getting a Rise

I have a Grizzly G0602 lathe. One of my issues has been the clearance beneath the bed. It makes it difficult to clean chips from the chip tray. Another concern was the inability to access the two lower mounting nuts on the motor. I decided to put two 1" risers under the lathe. My lathe...

www.hobby-machinist.com

I made a simple screw jack using a 3/4" bolt and nut, a 1`-1/2" long piece of 1" pipe, and a2"d. by 1/4" disk. It has served me well over the years.
View attachment 417493
But you needn't go to that bother. The lathe isn't that heavy. With some 2x4 cribbing, you can easily lever it up once you remove the two mounting bolts. Once raise sufficiently place some blocking under the ways to support it while you are drilling and tapping your holes.

If the lathe is being lifted, might as well install a riser. Have some 1"x4" plate that would work. Would definitely help get better access to clean out the chip pan. A little leery about levering the lathe up, just because of the high center of gravity, and the fact I would be alone. It was my first thought on how to lift it. Suppose that if I take it slow and avoid any tilt it should be ok.

Nice simple screw jack. Standard hardware and a couple of welds. I could make something like that. I will scrounge around to see if I can find some larger hardware. Bigger stuff isn't that common around here.