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Author Topic: BT30 spindle from scratch - with power drawbar and ATC of course  (Read 401734 times)

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Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #90 on: September 05, 2012, 05:34:30 AM »
You were talking about the finish on the disc springs, have you had them plated or is that the way you got them? The only ones I have ever seen have no plating at all and are black (maybe some sort of  passivation?)

Black Oxide, most likely. By 'finish' I was referring to the smoothness. These springs came from McMaster-Carr. Some are very nice and cleanly punched and some have ragged edges or raised ridges at the OD from the punch die. On a brand name American made part, these imperfections would have been cleaned off, but with No-Name suppliers like McMaster, you don't know where most items are coming from . .  although you can easily guess.

Raised ridges from the punch operation were left on the edges of the springs. These uneven raised edges, when facing each other in the stack, refused to stay aligned. The ridges would slip off each other driving the spring sideways with a very great force. The only solution was to remove this ridge and radius the ID slightly  - by hand - on each of 60 springs. Now they are behaving, but that is WAY too much time to put into that component. For anyone contemplating a build like this, I would recommend buying the springs from the manuf, or at least know the brand name of the springs. However, reality check; I found springs that were nearly $4 EACH. That makes a US$240 stack. The stack I used was a little over $40 and the coil spring was a bit over $50. Functionally, the springs are fine and in any un-stacked application, the ridge would be insignificant, but for stacking, the quality of the finish must be very good or the springs will splay out.
 
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The way the cylinder and springs are designed on the Beaver mill is quite nice I think, spindle, drawbar and cylinder are all in one unit thus no pressure on bearings at all as far as I can see.
Hood

My R8 power drawbar did not put pressure on the bearings. But those are much smaller bearings. I just went thru the exercise of calculating the leadscrew force and the 400 watt motor faults at about 650lbs and the 750watt motor would push the head with about 1,250lbs. The drawbar is supposed to be run at about 600lbs, but even running it at 1,000 lbs, the release force is not much more than the spindle would see from the axis drive, albeit a lot more frequently. This is all academic really, because the bottom line is that the release is about 1,400 lbs and the bearing is rated over 10,000 lbs, so there is no concern over hurting the bearing.

The R8 drawbar was a different story with a much higher release force and a much smaller bearing. Actually, one can only imagine the actual force on a typical R8 spindle bearing that is generated by the shock force of hammering on the drawbar to release the collet.

Still, There is a large steel collar on the drive end of the spindle and it would be easy enough to just fork on that to eliminate release pressure on the bearings. Perhaps I will do that. This is a first prototype so it is 'legal' for me to change my mind 50 times as I go thru the build . .  ;)

Offline Hood

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #91 on: September 05, 2012, 06:07:19 AM »
Ah Ok i see what you are saying now. The ones I got for my mill were direct from Mubea and were very nice and smooth. I have just looked back to see how much they were and for the size I need, 23mm OD x 10.2mm ID  x 0.9 mm Thickness it cost £7.84 per 100 (min quantity) , think I needed about 112 but ordered 350 as a friend also wanted some for two of his machines.
Have looked at Mubea and its phosphated and oiled finish.


Yes I often thought that about a manual (or impact power drawbar) on the Bridgeports and the torture the bearings got  but it didnt seem to harm them.


Hood

Offline Hood

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #92 on: September 05, 2012, 06:26:02 AM »
Heres a pic of the ones I had extra, bit dirty with sitting in the drawer but you can see they are decnt finish.
Hood

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #93 on: September 05, 2012, 07:54:40 AM »
The ones I got for my mill were direct from Mubea and were very nice and smooth. I have just looked back to see how much they were and for the size I need, 23mm OD x 10.2mm ID  x 0.9 mm Thickness it cost £7.84 per 100 (min quantity) , think I needed about 112 but ordered 350 as a friend also wanted some for two of his machines.
Have looked at Mubea and its phosphated and oiled finish.

Wow, dirt cheap. Is that a price recently or 10 years ago?  Your springs are not that far from mine, except less than half as thick, which would explain twice as many, perhaps. I would speculate that you have the springs stacked a couple in each direction and not alternating each spring? I went with the thicker spring to eliminate the spring to spring friction inherent in 'nesting' springs in the same direction. I have gotten numerous sizes if Bellevilles that were nicely finished, but always thinner springs like yours. These are the thickest springs I have ever worked with (compared to the small diameter), and also the roughest.  Live and learn, as they say.

Offline Hood

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #94 on: September 05, 2012, 08:06:17 AM »
It was the 29th March last year I ordered them.
Mine are stacked in 4's with the first and last set facing their respective seats.
Attached is a pic of the drawbar with the original springs, probably 25 or so years old, they were still fairly good but had lost some of their tension.

Hood

Offline derek

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #95 on: September 05, 2012, 08:14:31 AM »
The springs I got from mcmaster were very smooth. Almost like they were run through a vibratory finisher. They weren't shiny like yours but a dull grey. My springs are .090" thick so maybe you crossed a threshold thickness wise of what could be punched smoothly. Or their dies were worn out.  I'm still thinking that your idea of using a valve spring is the way to go. My rig is working really well but I still plan to give the valve spring idea a whack.

The spindle looks amazing by the way.

Derek

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #96 on: September 05, 2012, 08:34:34 AM »
The springs I got from mcmaster were very smooth. Almost like they were run through a vibratory finisher. They weren't shiny like yours but a dull grey. My springs are .090" thick so maybe you crossed a threshold thickness wise of what could be punched smoothly. Or their dies were worn out.  I'm still thinking that your idea of using a valve spring is the way to go. My rig is working really well but I still plan to give the valve spring idea a whack.

Mine are also .090 thick. Worn out dies is probably the cause, as you said. In hindsight, I should have just returned them and purchased elsewhere, but having no experience with spring stacks, I did not anticipate the problems . Incidentally, the springs were black, the shiny surface is from me polishing the stupid things. They should work fine now, but it was just a lot of unnecessary work to get there. I hate having my time wasted . . . probably more than anything else.

What part number did you purchase, if you don't mind sharing that info.

Next round I will go with the coil spring, but I only need one spindle, so unless somebody buys this one, I will be using it and not making any more.

Offline derek

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #97 on: September 05, 2012, 08:42:47 AM »
I used 9712K84
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Next round I will go with the coil spring, but I only need one spindle, so unless somebody buys this one, I will be using it and not making any more.

That's how I feel about what I have as well. When the carousel is done and it's time to change out the Bellevilles I'll probably revisit the valve spring idea.

Derek

Offline BR549

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #98 on: September 05, 2012, 05:56:38 PM »
The reason I asked about retaining the lower bearing is that you will be pushing down on the spindle each tool change and over time and heat the housing may expand enought to loosen up the press fit and cause the spindle to drop. Most spindles I have seen had a screw in retainer ring to preload and lock the bearing into the housing. Preload in this case is taken care of . Locking it into the housing under preload may be something to think about.

Just a thought, (;-) TP

Offline simpson36

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Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #99 on: September 05, 2012, 07:37:13 PM »
The reason I asked about retaining the lower bearing is that you will be pushing down on the spindle each tool change and over time and heat the housing may expand enought to loosen up the press fit and cause the spindle to drop. Most spindles I have seen had a screw in retainer ring to preload and lock the bearing into the housing. Preload in this case is taken care of . Locking it into the housing under preload may be something to think about.

Just a thought, (;-) TP

A very good thought. In case you think I don't listen to peoples ideas, your comment earlier on this topic got me thinking and I realized that while the design will work OK with the current bearing, it would not be ideal for an ABEC 7 set, which the design is supposed to accommodate, so have modified the design by splitting the labyrinth plate into two pieces. The outer one (the original one that is in the photos ) is now bolted to the housing to . . <drum roll>  . . retain the bearing.

A new inner ring will overlap the outer ring to create the labyrinth seal. So, preload or no preload on the upper bearing, the lower bearing is retained independently.

The original plate (now the retainer) is completed except for hogging out the middle. I am making the new inner ring now. Off to the gym now, so no more pictures until tomorrow.