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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #70 on: August 28, 2012, 04:03:53 PM »
Steve,

Fascinating approach!  Can't wait to see how it works out!

Regards,
Ray L.
Regards,
Ray L.

Offline Dan13

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #71 on: August 29, 2012, 04:22:45 AM »
Like your solution! Especially the fact it turned out relatively inexpensive. There are such heads ready available, but are very expensive.

By the way, don't see a reason for preloading the bearings if all it's going to is drilling. I think there would be much more backlash in the gears that could be a problem for rigid tapping.

Dan

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #72 on: August 29, 2012, 08:05:23 AM »
Like your solution! Especially the fact it turned out relatively inexpensive. There are such heads ready available, but are very expensive.
I think you are talking about the right angle gearbox? I don't know of any that would fit onto an X3 spindle, but you're right, the Bridgeport angle heads are a bit pricey. An interesting advantage of mine is that I still have the vertical spindle active while the horizontal is running, so given enough space, I could still have the mill spindle participating in the machining process. I have two mounting schemes and will implement both, one is horizontal mounted behind the spindle and belt driven. This has the advantage of being strong and rigid and allowing different ratios.

The second scheme mounts the gearbox on the spindle (ala Bridgeport) but actually bolts to a collar that in turn bolts to the bottom of the head. Advantage here is that the drill can now be rotated to any position in the horizontal plane. Disadvantages are that it consumes the spindle, interferes with the tooling bar and is a relatively weak mount because the stress has to run all the way thru the aluminum gearbox casting.  Still, If I need angled holes, I can make them.

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By the way, don't see a reason for preloading the bearings if all it's going to is drilling. I think there would be much more backlash in the gears that could be a problem for rigid tapping.

Dan

Can't have the shaft flopping around if I expect to hard tap or do any light milling. The gear lash is a good point. Had no occurred to me yet.  On first blush, it seems I could measure the backlash and compensate in the tapping macro. Worst case is I would get a bit more H than is built into the tap. For most applications, this would not be an issue.  We shall see. I have to get it mounted first and then work out any  . . .  um . . .  less than optimal characteristics . . . that may arise.

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #73 on: August 29, 2012, 08:19:32 AM »
My drives can be set up to roll over at any amount of encoder counts, it is in fact the way I use it for my lathes turret, it has a 20:1 gearbox on the motor so the drive is set up to roll over at 160,000 pulses. As the drive is also an indexing drive I can set up up to 64 positions and call any one of them from a combination of 6 inputs, life is easy :)
Can you explain the relationship between the gearbox ratio and the rollover point. I've noodled over this on and off for a while now and it is not coming clear. I'm sure it is one of those obvious things that somehow become invisible if you think about it too hard.  :-[

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Big problem you have is you are trying to design in safety features and  you have no control over the hardware it is going to be fitted to. I think likely the best you are going to manage is to have a setup that requires certain signals and leave it up to the user to provide them whether that be by real signals or trickery. Either way you have done your best to make things safe and it will be the end user that has failed if they dont do as needed.

Well, you hit the nail on the head, Mr. Hood. I already have some trouble with people modifying stuff in unsafe ways. I've been asked already for the design, including buying it, by some folks who are well known around here, but I have not shared anything other than what is in this thread. I  am a bit paranoid about liability because I live in the USA where people successfully sue because the coffee was too hot and burned them when they spilled it in their lap while driving . . . . absurd, but true. The more I contemplate your statement, the more I lean toward keeping this exclusively for my own use.

Offline Dan13

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #74 on: August 29, 2012, 09:19:23 AM »
Yes, Steve, I was talking about the Bridgeport right angle head attachment.

Regarding the backlash in rigid tapping, compensating it in software should work great. I do rigid tapping on a lathe that has about 0.1mm backlash on the Z and compensate it in Mach and it works very well.

Dan

Offline Hood

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #75 on: August 29, 2012, 01:43:25 PM »
Steve, what I was talking about is the capability of my drives to use the incremental encoders as, I suppose, you would an absolute encoder.
I have a gearbox on my turrets motor that is actually 25:1 reduction (not 20:1 previously mentioned) and my encoder on the motor  is 2000 (8000ppr) so I tell the drive that it should roll-over at 200.000 pulses (25 x 8000).
 The motor turns 25 times but the turret turns once and the count in the drive goes from 0 to 200,000 then starts again. That means as far as the drive is concerned 360 degrees is 200,000 pulses. Because I can set things up this way then  I can index to any position on the turret and the drive knows exactly where to go, doesn’t matter if the turret has rotated 30 full turns or not as the count would roll-over at one rev (200,000 pulses). In reality  that never happens   as there is another nice feature, the drive can be set to take the shortest route between index positions and thus it can go both forward and backwards depending on the index you call, this makes it ideal for a turret or an ATC.
 The tricky part was the ladder, it took me a while to get my head round how to accomplish it but it worked out well in the end.
  I keep the logic side of the drive alive so I never have to home it unless switch off at the mains or there is a power cut. Even if the drive faults for some reason, say for example some stupid person pushes a boring bar too far into the holder such that it sticks out the back and then when indexing it jams against the saddle and faults the drive (Don’t know who would ever be so stupid to do such a thing ;) ) Anyway  even if the drive faults it just needs a reset and it still knows exactly where it is as it has been keeping track of the encoder counts.
 If I lose power then all I need to do is home the turret, I have it homing to a low current value so I have it clamped when homing and thus it doesn’t move. To home after a power failure I just unclamp, manually rotate to tool 1 and then clamp then home and that’s it set.

Hood

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #76 on: August 30, 2012, 11:40:19 AM »
NEW VIDEO!!

Hood: Thanks!  Now it makes sense. Very clever use of available features -  as usual.

Dan: the amount of play in the gears did not make a noticeable difference in the tapped threads. The tap went in and out smoothly, no binding, no aftercutting, and the screw feels (I know this is subjective) the same as threads tapped in the mill spindle. Check it out.

http://www.youtube.com/watch?v=Dd_M6Li_OrA&feature=youtu.be

Offline Dan13

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #77 on: August 30, 2012, 12:08:17 PM »
Looks very good, Steve!

Dan

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #78 on: September 01, 2012, 05:38:51 AM »
Just finished another (unrelated) project and I am back on the BT30 spindle. Carving has begun on the turkey. The part is currently flipped over and I am working on the nose, which includes the nose beargin pad, the BT30 taper and threads on the nose for a bearing retainer.  Next is another flip and a steady rest for boring the 8.5" deep hole to final size. Then grinding the bearing pads to complete. The BT30 taper will be final ground in-place on the completed spindle.


Progress photos:

Initial OD turn including body,  top bearing pad and drive end.



And now drilling hard material 1" diameter 8.5" deep. The operation stalled the previous 'Super Duty' 4th axis and it had to be done in three steps. That was one of the motivations to create the new 'Mega Duty' 4th axis. The previous 4th axis could do the job with a bigger motor, but 750watt is the largest motor Mitsu makes that runs on single phase power. The new 4th axis munched thru this operation with no problem. Coolant fed drill. No pilot hole.




Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #79 on: September 01, 2012, 05:49:15 AM »
. . . .  another nice feature, the drive can be set to take the shortest route between index positions and thus it can go both forward and backwards depending on the index you call, this makes it ideal for a turret or an ATC.
Hood

It does sound ideal. I was directed (by BR, I think) to a video where a fellow (founder of Fanuc or something like that) had made a very nice ATC and apparently went on to make an entire mill. He used a Geneva mechanism in his as I recall. That was the only thing I did not like about it. I will check to see if Mitsu has a similar feature to what you describe as I have a spare 400 watt Mitsu motor and drive on a shelf. The Mitsu has the real time auto tuning which is particularly good for the 4th axis, but that feature has little advantage for a tool turret and what you describe does seem like the hot setup! Especially since it is independent of MACH!

The drive you are talking about is Allan Bradley, is that correct? (in case the Mitsu does not have such a feature). How do you talk to the drive?

« Last Edit: September 01, 2012, 05:56:32 AM by simpson36 »