Spinning a Bridgeport Spindle to 5-6K??

[Jadaan27]

You are right, Hood. That is exactly what I am looking for. Anyone have one they'd like to sell? I found one for a BT 30 but not a NMTB 30. Even if I found one for a CAT 30, could I use a longer drawbar on my mill and go with that?? Maybe I would have to modify my spindle dog.
I thought about attaching a router head to the machine but I'm not sure where/how to mount to make rigid and keep my machine travel?

[wizard]

Lots of good responses here. The spindle speeds you seem to be reaching for are likely doable, but instead of geussing why not get some up to date bearing data from your local supplier. Look into alternative lubes that the bearings can be loaded with. A favorite is Krytox, but there are other options just as there are options for the bearings themselves.

If you expect to do this sort of work on the spindle you could also consider modifications to allow regular lubrication. In any event even a simple spindle is a complex mechanical device, thought before actions is key.


Dave

[NC Cams]

Krytox is an exotic grease that may or may NOT be suitable for a high speed spinde. It depends on which Krytox you use - there are MANY types and they are perfect or perfectly WRONG for any application.

Kluber is another supplier of premium greases for high speed spindles. However, they too have different greases for different applications. Use the wrong one and you might as well use lard to grease the bearings.

NOTE: grease is NOT necessarily the appropriate grease to used for high speed spindle bearings - too viscous. Moreover, grease will NOT fix the issue of centrifcal overloading that can occur if you use the wrong bearing at the wrong speed.

As a former bearing engineer, I cringe when well intended information is offered that does not take into consideration the effects of speed, bearing design and fluid/lube dynamics when folks start talking high speed bearings.

Too picky??? Maybe so but I''ve solved many more ill conceived bearing selections made by others than I've created with my bearing recommendations.

Wish I had a dollar for each time somebody mis-applied bearings and/or grease in a bearing application. Would be drinking funny drinks with umbrellas on a south sea island instead of grinding cams......

[wizard]

Originally Posted by NC Cams Krytox is an exotic grease that may or may NOT be suitable for a high speed spinde. It depends on which Krytox you use - there are MANY types and they are perfect or perfectly WRONG for any application.

This is one of the reasons I reccomended contacting the local bearing supplier. This is really key when doing an improvement like this. They have access to the latest information and know who to contact as far as bearing manufactures reps go.

Kluber is another supplier of premium greases for high speed spindles. However, they too have different greases for different applications. Use the wrong one and you might as well use lard to grease the bearings.

in a nut shell this is true of all suppliers from Mobil to Nye and everyone in between. There is a bit of research need of course, to figure out what you applications requires.

NOTE: grease is NOT necessarily the appropriate grease to used for high speed spindle bearings - too viscous. Moreover, grease will NOT fix the issue of centrifcal overloading that can occur if you use the wrong bearing at the wrong speed.

I'm wondering if you consider 5K RPM a high speed spindle? Different machine tool suppliers have different definitions, but I was under the impression that one needs to get above 7K or so before a spindle is considered high speed.

As a former bearing engineer, I cringe when well intended information is offered that does not take into consideration the effects of speed, bearing design and fluid/lube dynamics when folks start talking high speed bearings. Too picky??? Maybe so but I''ve solved many more ill conceived bearing selections made by others than I've created with my bearing recommendations. Wish I had a dollar for each time somebody mis-applied bearings and/or grease in a bearing application. Would be drinking funny drinks with umbrellas on a south sea island instead of grinding cams......

I think the thing that is differrent here is that we have somebody asking about experiences bumping up the spindle speed on a Bridgeport, not exactly an engineering effort. While it is fantastic that your experience is presented here, and very helpful I might add, there are still many of us that get by on far less in the way of engineering support.

In this case, as I understnd it, the original goal was to work with what was originally supplied in the Bridgeport. I could certainly be wrong there, but if not the only parameter you really have to play with is lubrication.

thanks
Dave

[NC Cams]

My prior posts on the first page of this thread went into excruciating and probably boring detail about speeds versus lubes and preload for BPT spindle bearings.

My point about the Krytox post was simply that a prior poster said (in effect) "use Krytox". I was trying to show that one needed to ask the critical "WHICH ONE????" follow up question.

Some Krytox will work great in low speed high temp pizza ovens and quite poorly in a moderate speed, room temp mill spindle. Ditto that for Kluber, Mobil or whatever. Thus, simply calling out a grease maker's name is INADEQUATE for specing a grease...

"High speed" is not purely a function of bearing geometry and/or rpm (see my post dated 12-28-05). The reason why a 6000 series bearing can run at a speed limit of ~6K with one lube and 13K with another is NOT bearing geometery, but rather lube type (grease @6K and oil at !2-13K (again explained why in prior post).

A 5K spindle, per se is NOT exceptionally high speed, but at 5k with the wrong grease (IE: high temp, low speed pizza oven grease) in a preloaded bearing like that used in a machine tool spindle would not live long due to a grease induced failure.

IN short, 5-6k would be TOO high a speed for the "pizza oven grease" but fine for "high speed spindle grease" from Kluber, Mobil, or some other grease supplier. Go from grease lube to oil drip or oil/air mist and the exact same bearing will run at 10K or even 14K. Yes, you don't need rocket science engineered bearings for a lowly BPT and many folks will get by without my or any other bearing engineer's input.

However, I have spent many an afternoon trying to help a guy fix a machine wherein they took sage wisdom and an improperly spec'd bearing and created themselves a nightmare. They didn't have time or need to call a bearing supplier for a proper recomendation but they did find and have the time and $$$ to tear it down and redo it properly once they fried the bearing and/or torched a spindle after using the wrong bearings.

Wish I had $5 for each time I heard the "wish we'd have called you before we did things our way...." line. I was merely trying to show/explain what one would do to properly size, apply and lube bearings for machine tool applications.

This is just this sort of work is what BPT did when they took pretty much generic ABEC1/3 electric mot0r bearings and obtained almost ABEC 7 performance out of them in their mills. However, they also did a lot of sorting and hand fitting special spec'd bearings at oem builds. Something BPT NEVER mentioned in their owner's manual but any factory trained service tech will admit was done at the factoy with the oem bearing builds.

Spent an evening explaining it all to Brian at BPT Machine in Carol Stream IL over dinner after he came by to tune the servos on my BPT EZTRAK. Ask him what he thought of the "seminar"....

Many a guy has taken generic bearings ("...see the numbers are stamped right on them, we don't need no special OEM high $$ ones...") and replaced the OEM's. Never could figure out why they never quite worked the same or as well afterward. Why? because the servicer may have thought he duplicated the OEM effort but probably didn't.

I have copies of most of the oem bearing specs (and was explained the reasons for said wierd specs) for a BPT mill. I can assure you that an un-engineered aftermarket replacment might not be equivalent to what BPT supplied originally. Hence, it won't necessarily perform as well. It will work but it may not PERFORM.

Yes, the prior question essentiall asked for the time and I told them how to build the watch. Like any advice, it is offered for consideration and can be followed or ignored....

I"m merrely trying to show that there simply is more to replacing bearings than matching the size and stuffing some grease in it and R&R'ing them thereafter.... The devil is in the details.

By the way, you may want to lube/relube more often if you run at high speed for long periods (not add more grease but remove and replace the old, fried lube). The grease tends to have a lessened life expentancy at high speed due to increased thermal oxidation. Oh and don't use pizza oven grease 8-))

This is not something that is widely published but it is considered in the "contact the factory for specific recommendations" qualifier that is in most bearing catalogs when you start to talk about high speed applications.

Sorry for the watch building but it is just my nature.... I hate to see people misapply/misuse things, especially simple, elegant and complex things like ball/roller bearings.....