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

[strantor]

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]

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]

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]

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.

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]

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]

I actually have such a machine in my shop.

 

[strantor]

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]

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]

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]

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?