Why can't I find any example of automatic tool changers used with threaded draw bars?

[JimDawson]

Thanks! Yeah any more pictures or videos would be great. Here are some questions:

1. Is it possible for the draw bar to get cross threaded?

Possible? Yes, but not likely. The biggest problem is thread wear over time.

2. If the spindle is not indexed then how do the drive dogs get aligned?

They don't, there are no dogs on the spindle on this machine. Just friction on the taper holds the tool holder, not really a great system for a 5HP machine.

3. What kind of tooling is that?

It is BT40, 5/8-11 thread. BT30 is a 1/2-13 thread.

4. Is the drawbar captive? This ties in with question #1 a bit. I've been thinking a captive drawbar would be best, so it would positively "eject" the tool. However when inserting a new tool, it would be best if the drawbar were "floating" so the ATC inserts the tool fully in the taper, ensuring alignment before the drawbar starts spinning, to prevent cross threading.

It is sort of captative, the free travel is limited by the impact wrench assembly. There is an impact socket on the impact wrench that engages the hex on the draw bar as I recall. The impact assembly is moved up/down by a pancake air cylinder attached to the belt housing. I think the travel of that cylinder is limited by the top of the drawbar and the socket depth. I know the drawbar is pushed down by the pancake cylinder. I can't exactly remember how it all goes together. I'll have to look, and get some pictures of it.

5. You mention an air brake but I saw the spindle turn a bit at the end of the video. Is it a weak airbrake? How much resistance is needed for the impact to do its job?

It doesn't require a lot of brake, and in fact maybe doesn't even need the brake to make it work. I'm pretty sure you could hold it with your hand, but not recommended. I think the timing is a bit off in the program, releasing the brake before the end of the impact cycle. That video was the first testing of the system.

6. Details (pictures, video, explanation, or some combo thereof) of how the impact interfaces with the drawbar would be appreciated.

This is the only picture I have of it right now, I'll get a few more with some detail.

7. What's the diameter of the drawbar? The bore of my spline is 1/2", think that's sufficient?

5/8'' in this case, in your case you would use a 1/2''

8. Have you ever had any issues with it? What kind? Do you like it? Think it's as good as a pullstud setup or TTS? Why/why not? Do you have any insight on why this isn't more common?

This thing has only been operated a few dozen times in my shop, just for testing, it has never done a tool change when doing actual work. This machine is not in use, it's only made chips a couple of times.

IMHO a tool changer on a knee mill is useless, at least unless you have a servo knee to drop the table out of the way to do the tool change. You only have 5 inches of quill travel, so not a heck of a lot of room. There is a reason that VMCs have 18 or more inches of Z travel.

 

[strantor]

Thanks for all the info!

This thing has only been operated a few dozen times in my shop, just for testing, it has never done a tool change when doing actual work. This machine is not in use, it's only made chips a couple of times.

IMHO a tool changer on a knee mill is useless, at least unless you have a servo knee to drop the table out of the way to do the tool change. You only have 5 inches of quill travel, so not a heck of a lot of room. There is a reason that VMCs have 18 or more inches of Z travel.

Sounds like this useless thing might be taking up valuable real estate in your shop. I would be happy to remove it for you at no charge!

 

[strantor]

Ok I've watched that tool change video at least another 20 times throughout the day. Initially I was thinking "that's cool, too complicated, but very cool. I'll do something dumber." But the more I watch it, the more I think it (the robot-esque arm movement) is probably not as complicated as it looks. If you're going to do a photo shoot for that machine, a little detail on the tool changer carousel and arm would satisfy a few new curiosities that I have.

 

[JimDawson]

Sounds like this useless thing might be taking up valuable real estate in your shop. I would be happy to remove it for you at no charge!

That's for sure. This machine is actually owned by HM member Alloy (Dan). It came in for a retrofit, about 4 years ago and Dan's plans changed so it's been sitting here. It is for sale. ($6500?) Actually a really nice tight machine.

Ok I've watched that tool change video at least another 20 times throughout the day. Initially I was thinking "that's cool, too complicated, but very cool. I'll do something dumber." But the more I watch it, the more I think it (the robot-esque arm movement) is probably not as complicated as it looks. If you're going to do a photo shoot for that machine, a little detail on the tool changer carousel and arm would satisfy a few new curiosities that I have.

The tool changer arm is operated by the oil damped air cylinder at the top of the pic. The air cylinder rod is attached to the drive chain. The arm shaft has a cam groove cut in it, so as it turns it is driven down. It also has a bevel gear set that causes the claw to rotate as the arm swings around. The claw is operated by a small air cylinder in the end of the arm. The position limit switches and actuating cam are above the air cylinder.

The relays in the right center are tied back to the computer, they operate all of the pneumatic valves in the system. The original control for the tool changer was a nightmare.

I built the carousel drive gear case to be more compatible with my system, and smooth out the motion. The Geneva drive tended to be very jerky.

This is the best pic I have handy.

 

[spumco]

The Novakon Torus has a PDB available which uses a threaded drawbar with R8 collets. No bellevilles, no air. I believe it was designed by one of the CNCZone forum members and licensed to Novakon.

Looks like it could be adapted to (or at least inspire) a different threaded spindle taper system.

A slotted wheel on the top of the spindle is engaged by a shot pin to keep the spindle from turning. I believe the original design mentioned in forum posts used a stepper motor, but it appears it now uses a simple brushed DC motor with some current (torque) sensing electronics to ensure it can always loosen the drawbar.

https://www.novakon.net/collections/torus-pro-vmc/products/power-draw-bar-for-torus-pro

There are some youtube videos of it in action if you search for Novakon.

I still don't understand how any of the threaded systems avoid cross-threading, but I also don't understand how the NASCAR guys get away with gluing wheel nuts to the wheels and then blast them on. I could cross-thread a spline.

 

[Superburban]

I still don't understand how any of the threaded systems avoid cross-threading, but I also don't understand how the NASCAR guys get away with gluing wheel nuts to the wheels and then blast them on. I could cross-thread a spline.

The lugs have a long unthreaded section, that is a slide fit for the lug nuts, so they are already aligned straight to the threads when they are hit by the impact.

 

[spumco]

Them NASCAR boys seem to be pretty clever. Thanks for the back-story on those.