[RCaffin]

Hi Azalin

I was suggesting ADDING a speed reducer to the spindle: say a 20: 1 reduction. You might need two toothed belts for that. I like GT2.
But a proper mill would certainly be better.

Cheers
Roger

[Azalin]

Most of the good ones do, or they have a thrust bearing right at the top, and this takes the loading instead of the main spindle Bearings, there are other ways to do it also, but this is the easiest way to do it

Mac,
The very last part in this project is to do something to take handle load coming from the pneumatic cylinder. Regarding to the subject, can you please explain more?

This is almost the where I am. Except the shank of the pulely you see in the pic. It's is gone now.

[Azalin]

This might be the easiest solution but can a clamp like this hancle 5kN force? Besides, The guy only used 6 washers in series. Not much I guess.

[engnerdan]

This might be the easiest solution but can a clamp like this hancle 5kN force? Besides, The guy only used 6 washers in series. Not much I guess.

You should look at the static load capacity of your spindle bearings with a force applied from the top of the spindle. While most small hobby machines that are converted, use the floating pneumatic cylinder setup like you pictured here. Industrial machines have large enough bearings that they don't bother with a floating cylinder setup. Even my BT30 spindle form AliExpress has more than enough load capacity to handle the full 3000 lbs of force it takes to compress my drawbar.

I am using a small hydraulic cylinder with a remote air/hydraulic booster.

http://www.cnczone.com/forums/novako...ml#post1497324

http://www.cnczone.com/forums/novako...ml#post1529230

http://www.cnczone.com/forums/novako...ml#post1573000

-Dan

[G59]

Industrial machines have large enough bearings that they don't bother with a floating cylinder setup. Even my BT30 spindle form AliExpress has more than enough load capacity to handle the full 3000 lbs of force it takes to compress my drawbar.

I tried to make that point to them already, but was shotdown by handlewanker and Mactec54 as being a dumb engineer. They obviously know more than I do.

The floating setup was introduced as a solution to high speed spindles using relatively small bearings, that wouldn't be able to take anywhere near the 1500 lbs being applied, during the tool release.

Azalin's bearings can handle twice that and as I stated previously(laughed at), brinelling can only happen if you exceed the bearing material's compressive strength or through lack of lubrication.

In any case I gave up a while back. It's just nice to see I'm not the only dummy.

[RCaffin]

I know that you can brinell a bearing by hammering it, or putting many tons of force on the outer ring while loading the inner onto an oversize shaft, but a 3000 lb force is not that high. I can't remember what size bearing is being proposed here, but I suspect that it would be able to handle that sort of STATIC NON-IMPACT load without too much trouble. Hammering can make far bigger impact loads.

I would not expect any significant amount of mushrooming of the drawbar from the cylinder as shown, and if the drawbar can take that the bearings should be fine. I would suggest a throttle on the cylinder so it does not slam down on the drawbar: that would be a very wise precaution of course. And don't spin the bearing under that sort of load either.

Just my 2c
Cheers
Roger

[handlewanker]

Hi....if anyone wants to imagine....envisage ....or just plain see how much a 1 1/2 ton or 3,000 lb load is.....imagine trying to support a Bridgeport milling machine on the top of your spindle drawbar.....that's how much pressure is being talked about......probably only half this amount on average.

You could go overboard and design for extreme pressure loading, but mainly it's the fear of damaging a bearing in a most inaccessible place, and precision bearings are that much more expensive again, so who wants to take a chance when a solution is commonplace.

I would say, if you can do it in a way that prevents damage without having some complicated design to make, you'd be daft to not consider it as an option.....the choice is in the making.

Making the power applicator a floating design is no more complicated than just fixing it to the top of the spindle housing.......when you pump up a bicycle tire you hold the barrel of the pump while pushing the piston in to produce the inflating pressure, otherwise the force would push the inflating valve out of the wheel rim.....same principle.....pull while pushing etc.

The question is, do you really need it that bad.
Ian.

[RCaffin]

'Damaging' would depends on the size of the bearing, wouldn't it?
But I certainly agree that a floating cylinder would be (much) better.

On the other hand, where did this force of 3000 lb come from? It seems wildly excessive for a stack of 2 Belleville washers of that size in parallel. Even 3000 Newtons would be pretty high, and that is ~300 kgf or ~670 lbf.
And, you know, I reckon a Bridgeport would absolutely flatten those springs!

I may be wrong of course.
Cheers
Roger

[G59]

Making the power applicator a floating design is no more complicated than just fixing it to the top of the spindle housing.......when you pump up a bicycle tire you hold the barrel of the pump while pushing the piston in to produce the inflating pressure, otherwise the force would push the inflating valve out of the wheel rim.....same principle.....pull while pushing etc.

See what I mean???

In Azalin's case it's more complicated than what handle is suggesting, as on his spindle shaft, there is very little material left to which he can add provisions for installing a thrust bearing to. Applying pressure to the release bar transfers the pressure down into the bearings and then through to the spindle body.


You see,...... not that simple.

So as I've suggested a few post back before being shotdown, just forego this unnecessary floating setup, as your bearings are plenty large enough to handle the 1500 lbs required to compress the Bellevilles and release your tool, without ever being damaged.

[handlewanker]

Hi.....I think it's all a matter of personal desire to have a trouble free situation without the power of hindsight making you wish you could wind the clock back, but it has to be kept in a rational think sense.

The drawbar on my SVM-0 mill is reputed to need 400Kg approx.of direct pressure to depress it......in that case I don't think 800lb is enough to worry about.......but a lot different if the draw bar depressor was an impact type, like some designs on UTUBE that use an impact driver to unscrew a threaded drawbar nut........that is an area that definitely "could" have impact problems on the spindle bearings.

Another aspect is also a decider.......if you have a TTS spindle, then that would be a worry when you consider the forces needed to hold the tool shank in the collet and the amount to release it.

With an ISO30 taper the forces compared to the TTS are not all that massive to worry about......that's just my opinion.

There is a line in the sand that you apply when drawbar pressure raises it's ugly head.
Ian.

[Azalin]

Let's see if I can find 40mm ID 68mm OD tapered roller bearing to replace the upper single bearing or a thrust bearing to use with the upper bearing.

[G59]

Let's see if I can find 40mm ID 68mm OD tapered roller bearing to replace the upper single bearing or a thrust bearing to use with the upper bearing.

I see I didn't get my point across.

By adding a tapered roller bearing you will be messing with the AC bearing preload. I think you worry too much.

Many years ago, when I had just finished my engineering degree, my uncle once told me, "Many people think they know the strength of steel, but very few actually do."

In this thread it actually shows.

In any case, best of luck.

[Azalin]

Yes, you are right. I worry too much. And I realized that adding a tapered roller bearing or a thrust bearing requires threading on the top of the spindle and a lock nut too.

I just spent very long time to build this. This pushes me to make it right but I don't know what's right until I read your posts.

I appreciate your help.
Thanks.

[G59]

I would suggest a throttle on the cylinder so it does not slam down on the drawbar: that would be a very wise precaution of course.

RCaffin has made a great suggestion here if you are still worried.

Your tool change time would not be greatly affected either, but this would be the easiest and most practical in your case.

[Azalin]

I wanted to ask about this. What is a throttle on the cylinder?

[G59]

Think about your "IN" port on the cylinder. Without airflow restrictor, it has full air being applied to the piston. By adding a restriction or reducing the port hole size, it slows down the filling of the cylinder.

[handlewanker]

Hi..........I just went to the first post to see what bearing configuration you were using.....the one with the deep groove top...... (I would suggest 2 deep groove at the top)......and 2 AC bottom is the simplest and will suffice for all your needs.........going to a taper roller at the top is a complication as you also need to have seals both sides whilst the deep groove radial(s) is sealed and lubed for it's life.

KISS is a state of mind most people tend to overlook when design gets in the way of simple logic.

I think now the spindle is finished it's time to post the proposed design of the mill I assume you are going to build from the ground up.
Ian.

[hanermo]

A typical 50 mm inner D bearing, like 7210, has a static thrust rating of 40 kN or 4000 kg.
Ie it will support 2 bridgeports on it, no fear.

Typical drawbar forces are about 500 kgf - 1000 kgf.

[Azalin]

OK then! How about this. My spindle support 4 bearings on the low end and I luckily have two pairs of 7009C bearings. I can use 2 or 3 bearings looking upwards for the drawbar pressure. Would that help even more? And of course another 1 or 2 bearings for the opposite.

And probably my last question for this project is about lubrication. What grease do you recommend? Brand or part number would be great

[handlewanker]

Hi....do you really need more bearings?......are you contemplating hogging huge amounts of metal off?.......it's a CNC mode machining operation........the frame of the mill will dictate how the mill will perform not the spindle as much.

The weakest point is the overhang of the head on the column that cantilevers any impact force from the cutting action against the column, so the spindle is well housed in a box construction.

Even a Bridgeport with it's 1 1/2 ton frame weight is not capable of hogging metal off any material as it's relatively lightly built overhung swivel head construction is more for precision, and the R8 capacity of it's spindle will accept cutters no more than 20mm diam......slightly bigger if the flutes are bigger than the 19mm shank.

I would suggest that the bearing manufacturers' recommended lube should be followed if you want to get the best performance at whatever loading you contemplate.....the RPM range will be the deciding factor.
Ian.