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Author Topic: BT30 spindle from scratch - with power drawbar and ATC of course  (Read 411890 times)

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Offline budman68

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #190 on: October 01, 2012, 05:13:30 AM »


PS  Mostly, joking, but a friend has a SCARA and they're remarkably simple and useful.  He uses it to move parts around on his lathe.  For example, to flip them so he can machine the part that had been chucked.

Any video, Bob? Would love to see that-

Dave
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Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #191 on: October 01, 2012, 08:03:03 AM »
So I have gotten lots of Kudos in this thread. However, sooner or later, we all take our 'turn in the barrel' and I thought I should reveal one of mine on this project. If I make a change to incorporate a good suggestion, I don't count that as a fail, but here is a clear SNAFU.

There are a lot  . . .  a LOT . . . of reads of this thread and not much participation, so I conclude there are a lot of newbees lurking around who don't speak up or ask questions. To those folks this post is dedicated. Even a well seasoned engineer does not always hit a home run each time up. Don't be discouraged if your project does not work at first. Just keep on truckin' and make it happen.  

OK, moving on to the fail. Below are photos of the claw that grabs the BT30 adapters and swings them around between the carousel and the spindle nose. The challenge in this part is to get it to snap over the adapter without excessive force (which may not be available from a small servo motor), and yet have a sufficient hold on the tool to function properly and safely (#1 priority). The current prototype meets those goals, but only up to a certain arm speed. For a typical DIY project, it would be completely adequate at a nice slow pace, but this ATC is slated for 'kick ass' performance and I do not want any impediments to that goal. Well at least not designed in.

The design shown works perfectly as expected, but the hold on the tool failed testing at the speeds I intend to run the arm. Sudden extreme decel at the end of the swing (the spindle nose) can dislodge the adapter (and whatever expensive and razor sharp tool it is holding). Finding a powerful spring that could be somehow mounted on the unusually shaped claw without interfering with other operations was a very big challenge. Ultimately as you see, I cut a channel to house the heaviest spring I could find. The swinging finger on the claw snaps smartly, but is unable to retain the tool during a sudden stop. There is no real estate on the part to allow for a larger spring and the back of the claw is off limits because it 'parks' against the mill column to clear the rotating carousel.

Result: back to the drawing board. Ashes to ashes, dust to dust and scrap to scrap. The claw started as chunks of 7075 scrap and it is now very expensive scrap.

The replacement design is completed, but not fabricated. The solution was to add a rocker in place of the swing finger. The rocker stays in either open or closed position via a high powered 'over center' spring plunger arrangement. Most important, the new claw has a positive mechanical lock. It can grip the adapter simply by moving over the groves in the same manner as the failed claw, but it is not able to release the tool until a mechanical interference is withdrawn. Similar in function to the interlock on the drawbar actuator.

Photos will be in the next post . . if I can figure out how to do the thumbnails.

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #192 on: October 01, 2012, 08:28:04 AM »
Could not get the thumbnails to work. Anybody have a quick 'thumbnails for dummies' course?





Offline budman68

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #193 on: October 01, 2012, 09:44:28 AM »
Could not get the thumbnails to work. Anybody have a quick 'thumbnails for dummies' course?


Yes, you can upload your pics right from your PC by using the following method:

When replying, click the Additional option drop down arrow (highlighted in the pic below).

To get the maximum amount of photos per post (4), click the "more attachments" option also highlighted below in the pic.

If you have more than 4 photos, you'll have to post twice as the forum only allows 4 photos per post.

Hope that helps-  ;)
Dave

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Just because I'm a Global Moderator, don't assume that I know anything !

Dave->    ;)

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #194 on: October 01, 2012, 11:06:22 AM »
Thanks Dave.

What your describe is exactly what I did, but when I clicked to post, it just hung. Maybe I did not wait long enough. Is it a long process? I have 6Mb/sec upload speed and I uploaded those and a few more to my site in only a few seconds.

Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #195 on: October 01, 2012, 11:24:59 AM »
Steve, the retention mechansims being used on most VMC's for the carousel look pretty strong to me, and most are simple umbrella changes that aren't going to move as fast as the intermediate swing arm style you're building.

Check out these two videos to get a better idea:

http://www.youtube.com/watch?v=RQ4UT3IwTUg&feature=channel&list=UL

http://www.youtube.com/watch?v=aTwcBMvcqjA&feature=relmfu

And this one for a shopmade intermediate arm:

http://www.youtube.com/watch?v=KEBNB2d-syg

Tool holders are being flung hard. 

Cheers,

BW
www.cnccookbook.com

PS Dave, I'll hunt for some similar video.  My buddy never lets me video because he doesn't want customers getting irritated that their parts are showing up on the Internet.
Try G-Wizard Machinist's Calculator for free:

http://www.cnccookbook.com/CCGWizard.html

Offline budman68

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #196 on: October 01, 2012, 11:26:09 AM »
Possibly the forum itself, as I noticed many "lag" times when I'm here. Heck, even if I'm changing threads to look at something else, it lags for a bit.

Give it another go and I can delete it if it gets messed up for you.

Dave
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Just because I'm a Global Moderator, don't assume that I know anything !

Dave->    ;)

Offline budman68

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #197 on: October 01, 2012, 11:26:40 AM »


PS Dave, I'll hunt for some similar video.  My buddy never lets me video because he doesn't want customers getting irritated that their parts are showing up on the Internet.

Completely understood, Bob!

Dave
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Just because I'm a Global Moderator, don't assume that I know anything !

Dave->    ;)
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #198 on: October 01, 2012, 11:33:47 AM »
Steve,

If it were me, I'd design the arm such that the centrifugal force during rotation *could not* allow the tool to come out.  The last link Bob provided shows one way of doing this, with the tool being inserted into the arm from the side, rather than the end.  A very simple retention device can then be used.

That same video offers an approach I'd never seen before, that could be quite attractive to many hobbyists - rather than having a full toolchanger, just a means of "queuing up" the next tool.  The mechanism in the video is very simple and elegant.  I may have to build such a device, just for grins.....

Regards,
Ray L.
Regards,
Ray L.
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #199 on: October 01, 2012, 11:45:45 AM »
Dave, here is a SCARA robot loading and unloading a lathe:

http://vimeo.com/3355086

Not my friend's setup, but similar.  The thing I like is the SCARA's have such simple geometry and construction.

Ray, yup, make the centrifugal force work for you.  Use a stronger spring in the extractor too!

I have a big collection of tool changer vids and other details I have been studying.  Eventually I will upload to CNCCookbook.  Not gonna happen until I finish a few of the giant open 55 gallon drums of worms around the shop!

Specifically, I am just putting finishing touches on installing the mill in a new Flood Enclosure and will shortly start fabricating a new head to mount my Tormach BT30 Cartridge Spindle.  Just order a Delta VFD-M and will shortly start experimenting with spindle position control.

Cheers,

BW
www.cnccookbook.com
Try G-Wizard Machinist's Calculator for free:

http://www.cnccookbook.com/CCGWizard.html