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



## strantor (Dec 23, 2020)

All the tooling I see when I google these things is the pull-stud variety or TTS. I can't find any examples of a machine with a regular threaded drawbar (and power drawbar) being used with a ATC. Must be a good reason. What's the reason? ("You suck at googling" is an acceptable answer - I know I do - please help)


----------



## Boswell (Dec 23, 2020)

While it may be hard to find a tool changer that supports a threaded drawbar, you can use a threaded draw bar adapter. I believe that you can get an adapter that lets you mount to an R8 and that will accept TTS. There might be other types of adapters or ways to adapt.  It seems very mechanically more complex to build an automatic tool changer that has to manage a threaded drawbar.


----------



## sdelivery (Dec 23, 2020)

There was one threaded draw bar tool changer that I can remember....
G&L horizontal Boring Mill with the 8000A control.
We had one and it was a SOB, even with the factory documentation.
Any changes to the hydraulic system through the thing off. There was more valves and flow controls plus the hydraulic motor to turn the draw bar.
There were several more limit switches buried inside the headstock.
A complex clutch /driver assembly that could only be serviced after removing various components inside the tailstock,
Which could only be accessed by removing the quill ballscrew servo drive motor, belt and pulley.
There are many steps and potential faults with ATC's.
Micro-Swink and many of the early controls didn't time out the tool changer operations..
If you touched the right thing it would take off through the rest of the tool change!
I could tell you some stories about the hazards and close calls.....


----------



## strantor (Dec 23, 2020)

Boswell said:


> While it may be hard to find a tool changer that supports a threaded drawbar, you can use a threaded draw bar adapter. I believe that you can get an adapter that lets you mount to an R8 and that will accept TTS.


I don't have a R8. My spindle is an Erickson QC30. If you're not familiar, it's a 30 taper that uses a quarter-turn locking ring/nut on the spindle nose to draw the tool up into the spindle. It has a hollow spline, so if I removed the locking nut on the nose and added a drawbar, I _think_ (not 100% sure) I could run ISO30, CAT30, and/or NMTB30. I could probably get an adapter to R8 but the thought of running with an end mill to TTS adapter inside a TTS to R8 adapter inside an R8 to 30 taper adapter makes me a little nervous.



Boswell said:


> It seems very mechanically more complex to build an automatic tool changer that has to manage a threaded drawbar.


Can you expound on that thought? I want to understand where you're coming from because I had the opposite thought. I'm looking at all these pull stud setups that I can find documented on the internet and thinking they seem way more complicated than a good 'ol "impact wrench on top of the headstock" power drawbar. 

I'm in the early stages of planning. Maybe I shouldn't even call it planning. Tossing ideas around, that's better. Thinking about a ATC for this mill and how I could automatically torque/untorque that QC30 locknut, or add a power drawbar. My ideas for the threaded power drawbar are a lot simpler than my ideas for the QC30 nut torquer, and simpler still, than my ideas for implementing a pullstud setup. So I'm wondering why people who build ATCs into their machines almost exclusively go for pullstud or TTS, even going as far as to replace their drawbar spindle for one that can accommodate one of the two, when they could have just mounted an impact on top and used the drawbar they already had. 

I can find examples of ultra-simple power drawbar setups on manual machines that seem to me like they would be 100% compatible with an ATC, and I can find examples of people who have designed nice ATC solutions, some of whom have gotten rid of their drawbar setup in the process (they never explain why). But I can't find any examples of the two together on the same machine. You say it would be very complicated, so that's probably the reason why, but I don't see it. What would be so complicated about it?


----------



## Superburban (Dec 23, 2020)

The pull studd just needs the changer to push down on the draw bar, similar to the air tool connectors. A threaded changer would need a way to lock the spindle, and then turn the drawbar.


----------



## JimDawson (Dec 23, 2020)

I actually have such a machine in my shop.


----------



## strantor (Dec 23, 2020)

Superburban said:


> The pull studd just needs the changer to push down on the draw bar, similar to the air tool connectors. A threaded changer would need a way to lock the spindle, and then turn the drawbar.


The impact wrench setups that I've seen and used, never required any positive "locking" of the spindle other than grabbing the tool and holding it by hand. Or maybe there was a brake I didn't see. In my case, the spindle is powered by a 2.2kW servo drive which exerts a pretty stout holding torque at zero speed (and I suspect a VFD/induction motor could manage adequate resistance as well).


----------



## strantor (Dec 23, 2020)

JimDawson said:


> I actually have such a machine in my shop.


I watched that 5 times in a row and was more inappropriately aroused each time. Do you have anything locking the spindle against the torque of the impact? Is that a factory setup or something you designed? Is there more information on this machine I can look at?


----------



## JimDawson (Dec 23, 2020)

strantor said:


> I watched that 5 times in a row and was more inappropriately aroused each time. Do you have anything locking the spindle against the torque of the impact? Is that a factory setup or something you designed? Is there more information on this machine I can look at?



I think this was dealer installed option available on some machines.  This system has been highly modified from the original, the controls have been replaced and I replaced the Geneva Drive with a stepper and gear box that I designed.  

The spindle brake is air actuated.  The impact wrench is an old Black & Decker electric.  The spindle is not indexed for tool changes.

I'll be happy to provide pictures and try to answer any questions.


----------



## strantor (Dec 23, 2020)

JimDawson said:


> I think this was dealer installed option available on some machines.  This system has been highly modified from the original, the controls have been replaced and I replaced the Geneva Drive with a stepper and gear box that I designed.
> 
> The spindle brake is air actuated.  The impact wrench is an old Black & Decker electric.  The spindle is not indexed for tool changes.
> 
> I'll be happy to provide pictures and try to answer any questions.



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?
2. If the spindle is not indexed then how do the drive dogs get aligned?
3. What kind of tooling is that?
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.
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?
6. Details (pictures, video, explanation, or some combo thereof) of how the impact interfaces with the drawbar would be appreciated.
7. What's the diameter of the drawbar? The bore of my spline is 1/2", think that's sufficient?
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?


----------



## JimDawson (Dec 23, 2020)

strantor said:


> 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 (Dec 23, 2020)

Thanks for all the info!


JimDawson said:


> 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 (Dec 23, 2020)

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 (Dec 23, 2020)

strantor said:


> 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.



strantor said:


> 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 (Dec 23, 2020)

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 (Dec 23, 2020)

spumco said:


> 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 (Dec 23, 2020)

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


----------

