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Author Topic: BT30 spindle from scratch - with power drawbar and ATC of course  (Read 401851 times)

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Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #30 on: August 08, 2012, 09:47:44 AM »
Short update; with my new 'Mega' 4th axis project completed, I am turning my attention not to completing this BT30 spindle for my new mill.

Two things became apparent while building the new D1-4 Cam loc spindle for the 'Mega Duty' 4th axis; 1) more power was needed to drive the 1" drill bit thru hard material and 2) the mill column would need to be reinforced and welded up to resist twisting during the drilling operation.

The previous 4th axis prototype had only slightly less torque than needed for the 1" drill thru. The previous 'Super Duty' had just under 6:1 reduction and the new 'Mega Duty' has 12:1, so I am not anticipating any problems at all with the drilling. I have taken down the mill column and boxed it in with 1/2" 1018 CR plate and welded it up. The column should no longer get twisted by the drilling force. The mods should allow the pre-hardened material to be drilled thru the entire 9" length from one side at 1" diameter. The material will be here tomorrow.

I had hoped top avoid the big hole by using a coil spring. This would require only a hole large enough for the rod, but when I went back to complete the spindle design, I found that this was not going to be possible for BT30 because of the small size of the adapters. I think it may be doable in the larger sizes, but I have not looked at that. I considered briefly moving to a larger size, but decided against that solution. Therefor I will be using the dreaded belleville spring stack for this first spindle due to the small adapter size. That is the situation, even though it does not sound particularly logical.

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #31 on: August 17, 2012, 06:04:15 PM »
The entire Gripper assembly is now completed and tested. Here are some photos of the complete assembly and the test rig.  I will be doing a full YouTube video on this project, and I have a small fragment showing the testing of this completed gripper. I'll post a link when I have it on my site.


Offline derek

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #32 on: August 17, 2012, 08:44:16 PM »
Looks great!
It seems you were able to fit a goodly amount of Bellevilles in there so your ejection force won't have to be as large as mine.

Just a FYI I'm running the same setup as you except all my parts are heat treated and tempered A2 ( I seem to recall your using A2 and S7). I just finished a run on a bunch of castings with over 400 tool changes and it never missed a beat. I have another set to run and after that I'm going to do a tear down and see how everything is looking.

Switching to the BT30 was one of the best things I've done to this mill in a while. I'm loving it!

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #33 on: August 18, 2012, 05:37:41 AM »
The Bellevilles are working and there are ways around the spring-to-spring friction issue, but I still do not like the whole concept. The BT30 is so small that the gripper sleeve has to be installed from the opposite end of the spindle, which leaves a much larger hole in the spindle leaving the need for a 'platform' to be created for the base of a coil spring. Plus I would have to reanalyse the stresses for a thinner spindle wall (larger hole). There was a spring washer available which met all of the requirements and has a path to a heavier 'sister' as an upgrade path, so that was the easy way out for this first iteration. As you can see from the video fragment, the assembly releases at .20" with the stack set to 1,000lbs and there is an additional; .135" of travel after that. The spring pack binds at about 1,940lbs. It should take about 1,400lbs to release. I have not calculated the max available pull, but I know it is way above what is needed, so the heavier sister will not be needed and I will design the pneumatics for  a 1,800lb release @ 90psi.

The gripper will normally run at about 600lbs. I have tested the gripper mechanism to 3,000lbs and there was zero dimensional change, so I'm calling it a done-deal. I will be making a much larger spindle immediately following this one and I will use the coil spring in that design. Interest seems to be waning in this project, so I may not post beyond this, but I will be making a video of the entire development process. After I have presented it to the folks who are behind this whole effort, I will post it up on YouTube.


www.thecubestudio.com/BT30SpindleProject/BT30GripTestFragment.wmv

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #34 on: August 18, 2012, 06:06:12 AM »
Quote
Just a FYI I'm running the same setup as you except all my parts are heat treated and tempered A2 ( I seem to recall your using A2 and S7). I just finished a run on a bunch of castings with over 400 tool changes and it never missed a beat. I have another set to run and after that I'm going to do a tear down and see how everything is looking.

Each tool steel, or any material for that matter, has characteristics that are good in some applications and not-so-good in others. A2 when hardness is the primary requirement. S7 is tougher and shock resistant. A2 would outlive the S7 (used for the ball holder), but would be more likely to fracture. These are not super stressed parts, and should not break nor wear out in our lifetimes, so either is acceptable. The pull stud is the only scary part of the mechanism as a whole. 

I watched your video. Very clever indeed. The opening lid was really a surprise!  You should spice that up just for fun. Paint it green and put some big teeth and some crocodile eyes on it. I have to build the spindle and the pneumatics, which are fairly straightforward tasks, and then attack the ATC. I have looked at a lot of arrangements. Mohammad comes to the mountain and vice-versa. Somewhere between ideal, realistic and practical is where It will probably end up. 
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #35 on: August 18, 2012, 06:21:26 AM »
have you seen this, it's a denford triac bt30 head.
http://www.denfordata.com/bb/viewtopic.php?t=1953

Offline derek

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #36 on: August 18, 2012, 07:22:09 AM »
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The pull stud is the only scary part of the mechanism as a whole.
You know I've thought about this a lot. If we only have 1000 lbs of up force then 1001 pounds of downforce is going to start to move the tool into the work. But more than that it's going to let the tool holder wobble which in most cases will be catastrophic to the tool. I can understand the concern about pull studs in regular VMCs that are running 2-5K pounds of force but I just can't see it being a problem at the levels we're working at. Feel free to punch holes in this theory as I'm wondering about all this as well!

Quote
I watched your video. Very clever indeed. The opening lid was really a surprise!  You should spice that up just for fun. Paint it green and put some big teeth and some crocodile eyes on it. I have to build the spindle and the pneumatics, which are fairly straightforward tasks, and then attack the ATC. I have looked at a lot of arrangements. Mohammad comes to the mountain and vice-versa. Somewhere between ideal, realistic and practical is where It will probably end up.

I was thinking of running a MIDI that went "Bwa Ha Ha Ha" every time it opens and closes! It reminded me of the toy bank coffin that lifted and the hand popped out to grab the coin.

Before I started this maching job I was convinced that mounting my carousel on the end of the table was the best way to go. Keep it simple. Well after watching all of the unnecessary  X axis motion with my tool tray I saw the value in flying in the carousel. I think I've settled into the best choice for me which is  the ATC is positioned to the left of the spindle and up high enough so my longest tool will be above the spindle nose. This is 8.5". The motion is down 8.5" to bring the fork level with the BT30 groove. Over 8" to engage the fork. Down again 3.5" to clear the pull stud to the spindle. Rotate carousel. Up to engage and then reverse out. Bimba makes a nice 3 position round body cylinder. I used their online configuration tool and it was only $75.00 for a 3/4" cylinder.

Now I just need to find the time to make it!


Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #37 on: August 18, 2012, 07:49:32 AM »
You may want to consider that you'll need to move the x axis to one end when you're changing tools to avoid the tools striking the job. Unless you have sufficient z movement to allow this.

Offline derek

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #38 on: August 18, 2012, 08:04:14 AM »
Quote
You may want to consider that you'll need to move the x axis to one end when you're changing tools to avoid the tools striking the job. Unless you have sufficient z movement to allow this.
Hi
I'm driving the knee so I have a fair amount of travel. I also noticed that efficient tool changing depends entirely on the job your running. Tool length, Height of work etc. So that being said I figured using a macro for the tool change that picks up the tool change position DROs. I would then specify where I needed the table to be in order for the tools to clear. Why move the Z 12" if only moving it 6 will get the job done. At least that's todays theory Check back with me in a couple of hours and I may have a different take  :D

Derek
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #39 on: August 18, 2012, 08:23:27 AM »
sounds like the best way to go.