[SCzEngrgGroup]

Last night, thanks to some prodding from a friend, I finally got off my lazy a$$ and designed up the stepper-driven power drawbar I've been wanting to build for the last several years. Today, between interruptions to help a neighbor build a dog run, I got most of the parts machined. All that's left is the coupling between the gearbox and the drawbar, a trivial lathe-turned part, and the spindle brake mechanism, which is also very simple. Then comes all the electronics (Gecko G201 and optical encoder I/F) and software to make it all work.

For anyone who hasn't kept up with the plan here, I've been wanting a power drawbar that would give me full drawbar tension required for TTS tooling under the worst case conditions (about 2500-3000# drawbar tension, which equates to about 25-30 ft-lbs drawbar torque), and would make it possible to "quick-change" both TTS tools (unscrew drawbar one turn), or full R8 tools (unscrew drawbar compeltely). Belleville washers were out, due to space constraints, and they would not allow R8 tools to benefit from the power drawbar functionality. So, my solution was a stepper motor, driving a planetary gearbox with a high reduction ratio (55:1 in my case). With the 400 oz-in NEMA34 stepper I have, this gives me up to 75 ft-lbs of torque to play with.

The air cylinders will provide ~200# of down-force, to pop the taper free, while springs will return the assembly to the up and disengaged position. The existing mechanical spindle brake will be mechanically activated by the PDB assembly coming down into engagement. The stepper will then unscrew the drawbar the required amount, as confirmed by feedback from the shaft encoder on the stepper. Stepper driver current limit will be controlled to provide maximum torque when loosening the drawbar, and limited torque, equating to 25 ft-lbs, then tightening the drawbar. The stepper will be driven by a spare axis of the CNC controller, under control of a macro.

With luck, I'll get the drawbar coupling done tomorrow, and be ready to give it a try as soon as I can get the electronics updated.

Regards,
Ray L.

[TOTALLYRC]

Another interesting project from the mind of Ray L.

Mike

[SCzEngrgGroup]

Making great progress here! Today I got the drawbar coupling done, made the mounting brackets, and fastened it to the machine. All that's left now is the software to make it all work. To make the coupling, I turned a piece of 1.5" 6061 round for a very snug fit over the gearbox shaft, then slit it longitudinally, and put in four cross-bolts spanning the slit to clamp the coupling to the shaft. The drawbar end I bored out to 0.005" smaller than the OD of a 19mm socket, heated it, then pressed the socket in (which took every one of the 12 tons my press has!). The whole thing came out beautiful, and seems to work perfectly, as evidenced by this brief video:

Stepper Motor Power Drawbar - YouTube

No shop time tomorrow, but Monday I'll drag out my old controller, which has four G201s in it. I'll bring up the basic functionality under Mach3, just for proof of concept, then move one of the G201s into my new controller, and do the "production" KFlop software to fully operate the drawbar. Can't wait to get this going!

Regards,
Ray L.

[SCzEngrgGroup]

I had a crazy idea for a completely different kind of power drawbar a couple of years back, and yesterday I finally had the time to build one. I specifically wanted to be able to use both TTS tooling, as well as R8. This meant Belleville spring designs were out, as it is very difficult to provide enough drawbar tension to properly retain TTS tooling under worst-case conditions (about 2500+ pounds drawbar tension, or 25+ ft-lbs drawbar torque is required). To change out a TTS tool, the drawbar only needs to be backed off about one turn, while for R8 tooling it needs to be backed out 8-10 turns.

So, here's my crazy idea - use a stepper or servo motor, driving through a high-ratio planetary gearbox. This provides very high torque capability, and makes it easy to control how much the drawbar is turned, by driving the stepper as another axis from the CNC controller. A little E-Baying got me a 55:1 NEMA34 gearbox capable of 75 ft-lbs. I picked up a 400 oz-in NEMA34 stepper, which lets me use the whole 75 ft-lbs if necessary. Mechanically, the thing is dead simple - The stepper and gearbox are mounted to a floating plate which is moved up and down by air cylinders. A 3/4" socket is attached to the gearbox output shaft by by a simple home-made coupling, and either a mechanical or pneumatic mechanism is used to actuate the spindle brake. I got a dual-shaft stepper so I can put a rotary encoder on the shaft, to monitor actual movement, if needed. Everything can be controlled by a simple macro (or, in my case, a simple KFlop C program).

Here's how it will operate:

1) Spindle stops, spindle brake is applied
2) The PDB is dropped down, with low air pressure, and the stepper is rotated slowly, until the socket and drawbar hexes align and engage. A micro-switch will signal that the socket is fully engaged.
3) The stepper is turned at high current/torque to loosen the drawbar by the required amount - one turn for TTS tools, 8-10 turns for R8 tools.
4) Once the new tool is mounted, the stepper is turned at reduced current/torque (corresponding to 25 ft-lbs drawbar torque), until motion stops.
5) The PDB is raise up, and the spindle brake is released.

The photos below show the complete mechanical assembly, missing only the engagement microswitch and spindle brake actuator. Here's a short video showing the PDB moving up and down while mounted to the mill:

Stepper Motor Power Drawbar - YouTube

I just spun up the stepper for the first time. On Monday, I hope to get the software going, and be able to "use it in anger" for the first time.

Regards,
Ray L.

[asuratman]

himmykabibi,
Good innovation from crazy idea, just cont on. I like to see it till the end.

[SCzEngrgGroup]

himmykabibi,
Good innovation from crazy idea, just cont on. I like to see it till the end.

You'll see that within a few days. It's mounted to the machine, and I spun the motor for the first time last night. What's left to finish is all simple stuff, so I should have it completed in short order.

Regards,
Ray L.

[SCzEngrgGroup]

Sucks that this thread got moved to Siberia....

Anyway, today I got the PDB mounted, plumbed, and wired, and wrote the 20 or so lines of VB code needed to verify operation. I'm happy to report it appears to work *perfectly*! Out of 25-30 tool grabs and releases, it worked perfectly every single time. The current limiting to control tightening torque appears to work perfectly as well, and with full current for releases, there was not a single problem with getting the tool out again. I am VERY pleased with the results.

I have a few very minor updates to make to clean up a few details(raising it up a bit, so I can still get a wrench on the drawbar, to aid in "calibrating" tightening torque, adding a microswitch to signal when the PDB is fully seated on the drawbar, and adding "bumpers" to "cushion" the "landings" at the two ends of air cylinder travel.

Regards,
Ray L.

[bozidar22]

Neat idea, why not just use an air impact wrench or electric impact wrench?
It seems a little over complicated. But it looks like it would really well with an automatic tool changer as a way to index the tools.

[SCzEngrgGroup]

Neat idea, why not just use an air impact wrench or electric impact wrench?
It seems a little over complicated. But it looks like it would really well with an automatic tool changer as a way to index the tools.

I had an impact wrench drawbar, and HATED it! It was rude, and crude, and very brute-force, and LOUD. You have no control over how far it loosens, and often have to adjust the air pressure to get it to loosen a tight drawbar. And, it's totally unsuited to tool change application, which is my next step.

Regards,
Ray L.

[punisher454]

I just finished reading the whole 2009 thread about using the TTS on a bridgeport and all the problems associated with it. This looks like most of the problems are solved with your stepper solution. This is also so much cleaner than the Belleville washer mod. This looks like a true bolt on that will require no mods to the drawbar or spindle.
One of the things I was concerned with regarding the TTS is switching to non TTS tooling quickly, this looks like a great solution for that.

I really like how you apply light downward pressure while slowly turning the socket to engage the drawbar, much better than the brute force method used by the air-impact type.
I am curoius about your planetary gearbox as well as the macro and electronics configuration.

Marvin

[SCzEngrgGroup]

I just finished reading the whole 2009 thread about using the TTS on a bridgeport and all the problems associated with it. This looks like most of the problems are solved with your stepper solution. This is also so much cleaner than the Belleville washer mod. This looks like a true bolt on that will require no mods to the drawbar or spindle.
One of the things I was concerned with regarding the TTS is switching to non TTS tooling quickly, this looks like a great solution for that.

I really like how you apply light downward pressure while slowly turning the socket to engage the drawbar, much better than the brute force method used by the air-impact type.
I am curoius about your planetary gearbox as well as the macro and electronics configuration.

Marvin

The gearbox is a standard NEMA34 gearbox, found on E-Bay for $140. The electronics is nothing more than a stepper driver (Gecko G201), a couple of pneumatic solenoids, and a relay to select the current limit resistor for the Gecko. The macros are a total of about 20 lines of Mach3 VB code - activate air solenoid to drop the PDB down, and engage the spindle brake, activate the relay to select the correct current limit resistor, then activate the stepper to spin the drawbar. To tighten the drawbar, I just turn it 1.5 turns at high speed, stop, then do another 1/4 turn at low speed, to ensure the torque is correct (the stepper should stall at the end of both moves). To loosen, I just turn it 1.25 turns. I still have to install the encoder, which will provide useful feedback to make the operation more fool-proof.

So far, it seems to work perfectly.

Regards,
Ray L.

[tc429]

excellent idea/work there

wonder why they moved this from the bridgeport section?


if I ever get to tinkering around with my garage bridgeport again(Fanuc 0M-A control) Ive got to add the drive for a 4th axis, and maybe then a ATC of sorts...I had thought about just bellevilles and using the last 1/4" of quill travel to knockout, but the thought of making tiny retention knobs and a drawbar/spindle mod didnt sound like fun...and my spindle dont have feedback for orientation- had a hair-brained idea of just balancing 2 analog prox switches to edges of 180 degree target on the spindle, just stop spindle/switch drive reference to the prox switch outputs with a few resistors for balancing, and maybe a r/c tuner to soften the response a bit...yeah in my spare time. adding a encoder would be easiest, but on my control if i go closed loop spindle, cant add 4th axis, so still contemplating a external orientation method.

[CNC-Joe]

Nice work, Ray !

[Uguessedit]

Found it, that ooks great however not what I need for a bt40 spindle. I had pictured a motor with a cam in my mind that rotated to apply pressure for quick change. Guess I will go back to the pneumatic cylinder idea and roll with it. Glad I found this post anyways it’s a great build for what you have it offers up more options for guys in similar scenarios as yours. Great job Ray,

Making great progress here! Today I got the drawbar coupling done, made the mounting brackets, and fastened it to the machine. All that's left now is the software to make it all work. To make the coupling, I turned a piece of 1.5" 6061 round for a very snug fit over the gearbox shaft, then slit it longitudinally, and put in four cross-bolts spanning the slit to clamp the coupling to the shaft. The drawbar end I bored out to 0.005" smaller than the OD of a 19mm socket, heated it, then pressed the socket in (which took every one of the 12 tons my press has!). The whole thing came out beautiful, and seems to work perfectly, as evidenced by this brief video:

Stepper Motor Power Drawbar - YouTube

No shop time tomorrow, but Monday I'll drag out my old controller, which has four G201s in it. I'll bring up the basic functionality under Mach3, just for proof of concept, then move one of the G201s into my new controller, and do the "production" KFlop software to fully operate the drawbar. Can't wait to get this going!

Regards,
Ray L.

[jcdammeyer]

Nicely done. I was just given the link to this thread. I've been working on the same thing for my combination R8 and TT holders. The Butterfly Wrench approach sucks! I've got a hall sensor to see a magnet on the socket and another to know when it's all the way down.

My system is designed to run manually or with LinuxCNC which sends my controller board CANopen messages. Manually I tap the release button and the system tries to do only two turns. Most of the time that works. If I hold the release button it runs the butterfly wrench for a longer time to release the R8 tool.

I've ordered a 25:1 planetary drive. I have a small DC servo that I will run with an HP_UHU drive.

Attachment 483984

And here's the controller.
Attachment 483986

There's more in this thread.
https://www.cnczone.com/forums/uhu-s...ovement-3.html

[bill south]

Take a look at the old thread for the Novakon Power drawbar. I think the title is something like Novakon Torus Pro as a production machine. The PDB design that Ray created for Novakon was (at least in my opinion) one of the best designs on the market. It seems a bit over complex but is quite simple when broken down into its key parts. I built one which is close to the Novakon (my own interpretation of the design) and have never looked back. It took about six months working only with the information provided in the thread but was a fun and rewarding. Ray is very talented with his designs.

[jcdammeyer]

Thanks. The only threads I can find with that subject use the belville washers compressed which then release the tool.

Ray's version in this thread is very similar to what I designed other than I used a butterfly wrench. I need to be able to automatically release/capture R8 and TT holders.

I have a planetary reduction on order. When it arrives I can continue. Currently working on modifying the HP_UHU so I can dynamically change torque much like Ray used a relay on the Gecko to do this.

Ah.... Hang on. Didn't find it in this forum but did with google for $1495.
https://www.novakon.net/products/pow...-for-torus-pro

And yes essentially that's what I'm building. Hopefully today I'll have the spindle lock made. I do like how moving the drawbar down locks the spindle with a pin. I wonder if they park the spindle to do that?

Here's the thread on the HP_UHU.
https://www.cnczone.com/forums/uhu-s...ovement-3.html

[bill south]

The Novakon design features a spindle lock works with a simple hall effect sensor to sense a magnet located in the locking collar when it is aligned with the pin/collar slot. The VFD roates the spindle in slow motiion until the magnetic is sensed which then fires the air solenoid to lower the PDB into position for the 100:1 Planetary to Lock/Unlock the drawbar. Quite a nifty little circuit and not very expensive!!! Just one of the circuits designed by Ray!!! Again, this is my guess at how the PDB was designed. I've never had access to a production unit so I man be wrong but I built the thing and it works flawlessly.

[jcdammeyer]

Mine has two hall effect sensors. One for the socket to detect number of turns before it is told to stop. In hindsight more than one PPR will be more useful. The second sensor tests if the socket has made it all the way down. I've had issues with it jamming on top of the draw bar half way between flanks. So if it doesn't make it down I send it up and then down to try again.

Mine is designed to function without the LinuxCNC system running. So no access to spindle which is driven by AC Servo rather than VFD. That means if I did insist that LinuxCNC was running, I could step it around to an index position since the spindle is run with step/dir signals. I may find I have to be able to do this. I'm trying to avoid it.

Here's a photo of my controller. Uses a dsPIC30F5011 which talks to the LinuxCNC system via CAN bus. Not the final wiring or mounting position by any means.
Attachment 484084

[jcdammeyer]

The Novakon design features a spindle lock works with a simple hall effect sensor to sense a magnet located in the locking collar when it is aligned with the pin/collar slot. The VFD roates the spindle in slow motiion until the magnetic is sensed which then fires the air solenoid to lower the PDB into position for the 100:1 Planetary to Lock/Unlock the drawbar. Quite a nifty little circuit and not very expensive!!! Just one of the circuits designed by Ray!!! Again, this is my guess at how the PDB was designed. I've never had access to a production unit so I man be wrong but I built the thing and it works flawlessly.

Bill,
I do have a question about how yours operates. I can see how the spindle is locked with the toothed wheel which is bolted to the nut which captures and probably even sets the bearing preload on the spindle. But of course the draw bar rotates independently inside that and therefore the nut position isn't predictable.

I've had problems with the socket jamming onto the nut. Especially when I was using the original equipment really really soft draw bar. Here's a photo of the 12 point socket jamming (and sticking tight) onto draw bar.

So I have a few questions:
1. Is the air pressure on the cylinder that pushes down the motor assembly quite low so that the force down is minimal?
2. Is it a 12 point or 6 point socket?
3. Does the stepper motor that turns the socket through the 100:1 drive turn until it lines up to the draw bar? If so how does it know. If the draw bar is loose with no R8 installed yet then there's nothing to prevent it from turning with the socket sitting on top of it.

Attachment 484088

4. Is it a custom socket? How is it connected to the planetary gear assembly? Pinned or set screws?

Thanks
John