PDA

View Full Version : quill drive key



motorcyclemac
09-07-2007, 02:08 AM
Hey All...

I was setting up all my new tooling for my Bridgeport that I just bought. I picked up a full set of Nuline collets and slid one in the spindle to see how they fit. That is when I noticed that the spindle on my Bridgeport seems to be missing it's drive key. Now I did tighten the collet in the spindle with an end mill inserted in the collet. It cinched up just fine. When I removed the collet it required the "loosen it a tad and nudge the drawbar with a mallet" routine. It seemed well stuck to the taper as normal. I never have encountered a Bridgeport without a drive key. Does this pose a problem with regard to torque load on the collet without a positive drive interface to the inside of the spindle? If I drill a one inch hole with a twist drill do I risk spinning the collet and scoring the inside of the spindle? Anyone have any feed back on this one? IF it turns out that I need to replace the key in the spindle...how big of a job is that? Am I talking about fully removing the spindle to replace a key that is pinned and staked in place?

I remember a discussion a week or more ago about power drawbars and some fellow talking about removing the key. I understand about tapers engineered to "stick" but I wonder if the key removal is a recommended practice or at least a practice with no side effects. I am thinking it must be ok in that I suspect that it has been missing for a while and the spindle seems to be in fine shape.

Cheers
Mac

Joel
09-07-2007, 02:22 AM
The short answer is that you don't need the pin, it is not meant to transmit torque.
Do a search for many opinions:

http://bbs.homeshopmachinist.net/showthread.php?t=25365

http://bbs.homeshopmachinist.net/showthread.php?t=25404

motorcyclemac
09-07-2007, 02:47 AM
The short answer is that you don't need the pin, it is not meant to transmit torque.
Do a search for many opinions:

http://bbs.homeshopmachinist.net/showthread.php?t=25365

http://bbs.homeshopmachinist.net/showthread.php?t=25404


Thanks Joel.

I was reading elsewhere on the list and found other references to having lost the key. I had thought it thru earlier today and was pretty darn sure that it didn't function to transmit torque. That key or pin or grub screw or what ever you wish to call it is too small to take much torque. So it doesn't make sense to even install the darned thing. In the past I developed the habit of inserting a collet or adapter in the spindle, finding the key, then sharply seating the taper. After the taper was mated then I would lower the draw bar and begin to thread it while holding the collet and cutter. Because of this habit I never really appreciated the presence of the key. It was simply more annoying to have to align it every time. I am happy knowing that it doesn't matter because it is far easier to install collets with out that thing.

Thanks
mac.

A.K. Boomer
09-07-2007, 09:30 AM
My mill has one and it functions and thats just fine so I wont remove it because its really no hinderence, if it ever falls out then I will probably just leave it out as long as its not broke and half hangin up on collets keeping them from seating properly,

This kinda mirrors connecting rod bearings in a typical engine, The little stamped out flanges on a con. bearing are not there to keep the bearing from spinning in the rods bore, they are only there for alignment purposes, it is the crush of the rod halfs getting torqued together on the bearing halves that keeps a con. bearing from spinning,
Since there is no real purpose for the alignment of a collet to a spindle (i.e. oil ports or side to side centering ) then its even less critical...

This being said I have to add; Iv torn apart hundreds of engines and pay almost as much attention to detail in the disassembly as in the re-assembly --- I have seen connecting rod bearings that were so borderline in "crush" that they were starting to rely on the bearings little stamped out flanges to keep them from rotating, this is a bearing just before failure, and yes the flanges let them live a little longer, so for what its worth, If you dont get your drawbar tightened properly you DO have a slight extra advantage torque wise and an actual gaurentee that your tool holder does not slip --- and positive peace of mind proof when you go to unload the tool and it slides out with the collet key intact... Keep in mind that its the tool that will spin in the collet first, but if the collet ever does start to spin in the spindle it most likely means that all it will end up doing is self-tighen, Which brings this into question -------- would you find a little more comfort with a spindle key if you were doing a heavy flycut --- IN reverse? Why would you do this in the first place? I dont know but strange things happen on a mill from time to time, just give it time and they will...

A.K. Boomer
09-07-2007, 09:43 AM
That key or pin or grub screw or what ever you wish to call it is too small to take much torque. So it doesn't make sense to even install the darned thing. .


No they dont take much torque --- but coupled with the spindle taper it is a positive limiter and will increase the torque factor more than what it could do alone, while the spindle taper is the major factor the key puts a direct limit to torsional movement, this can drastically improve the resistance far beyond its own limits by removing the posibilities of slip due to frequencies/vibrations/harmonics, keep in mind that all that is needed would be to be in reverse and have a collet give just a little...

Iv seen this effect on the connecting rod bearings, all they needed was a little vibration limiter, the reciprication and occilation trying to work the bearing around but the little tabs held their ground, Con. bearing dont have the disadvatage (or advantage depending which direction your using your mill ) of being "threaded" in one holding direction either...

Forrest Addy
09-07-2007, 11:46 AM
Boomer, the little collet alignment screw won't just fall out. Some day you'll use a fly cutter sweep or a 4" carbide mill just a bit enthusiastically and stall the cutter - while the spindle keeps on turning. This will break the screw dog off and roll it between the collet and spindle, or try to. The tooling will be jammed because of the busted set screw dog and be difficult to extract. Also it's certain there will be minor damage inside the spindle that may affect the concentricity of the spindle tooling for evermore.

Better take it out for the safety of your spindle. It will survive a couple of revolutions of tool slippage better and with less damage than an anti-rotation key casualty.

IOWOLF
09-07-2007, 06:39 PM
Forrest, that is just an opinion, I have known Bridgeports that are 50 years old with the same pin in them,Honest.

But the same Mill has never had a drill bigger than 3/8" used in power downfeed mode. ;)

A.K. Boomer
09-07-2007, 09:09 PM
Good point Forest but if mine is in then its in and stays in, the paranoia of the event you just described does not warrant me tearing into my spindle to remove it, No more than the paranoia of the event I desribed earlier would make me disassemble my spindle to replace the key if it were not there...

But If anybody would want every last possible fail safe on their mill for a torque situation it is I --- cuz i use mine as a lathe and have to run in reverse many of the times, really dont want my R8 three jaw coming loose on my prestine little mill table catching a bite in the table groove and propelling itself into god knows where, if she has enough to rotate the collet under drawbar tension and severe the pin then I personally hope the pin welds itself to my spindle and the collet--- just trying to think ahead thats all:) Spindles are a dime a dozen, foreheads aint cheap...

dalee100
09-07-2007, 10:05 PM
Hi,

If I may add to this discussion. The key has very little to do with transmitting torque. If you're relying on that to help drive the cutter, you really need to re-think what you're doing and how you're doing it.

It has more to do with making sure the collet goes into the spindle the same way each time. Think about it. There's a little run-out in your spindle, a little run -out in the cutter, and a little run-out in to collet too. Toss in some wear and pretty soon cumulative error rears it's ugly head. And that say, 3/8" slot is suddenly .379. It happens. One way to try to limit such errors is to make sure it all goes together the same way each time you do it. Well, it doesn't eliminate the error, but makes it repeatable so you can apply some good old fashion "Kentucky Windage" every time you make that slot. Remember these machines were meant for production work. Absolute accuracy does not mean as much as repeatability of process. Fool-proofing the collet and spindle was/is a cheap, easy way to get a little more repeatability.

And Forrest is so right. Break that little nub off, you'll add a whole level of vocabulary to your speech. Though I wouldn't worry about breaking it.

dalee

A.K. Boomer
09-07-2007, 11:21 PM
Hi,

If I may add to this discussion. The key has very little to do with transmitting torque. If you're relying on that to help drive the cutter, you really need to re-think what you're doing and how you're doing it.




Its true, and also not my arguement, this is a statement from my first post ---" If you dont get your drawbar tightened properly you DO have a slight extra advantage torque wise "--- its by no means anything to rely on, it however not only does take effort to shear it will also stop vibrations/harmonic slippage dead in its tracks and as I stated could be critical for running in reverse in a borderline situation... borderline possibly meaning someone who does not consider the various different torque loads that should be aplied to a drawbar for different aplications, Generally (knock on wood) this type of accident wont happen to me because I hand torque every tool differently (see the recent power drawbar thread) and My R8 three jaw gets the most out of any tool item i have ---------- but, some people dont compensate, some people also like to run a powerdraw bar and maybe one day they dont have good judgement with what they got on it, or their air pressure is low --- or they didnt compensate with drawbar tension for the task at hand ------- I'll say it again, if your putting as much tension on your 1/8" endmill as you are your 7/8" or R/8 three jaw then your doing it wrong... there's either no reason to torque a little bit that high or your putting way to little on your larger tooling,

Basically key or no key, when I tighten the drawbar while putting on my R8 chuck its tight enough that I know about the only thing that could make it slip is a complete and utter crash --- Thats not in any way being reliant on a key for torque transmission.

tattoomike68
09-07-2007, 11:45 PM
Forrest Addy is right, you do not need it at all. We all know he knows his stuff.

Besides with that thing gone it saves on carple tunnel wrist spinning the tool around to go in the spindle.

I have horsed the hell out of R8 taper 3HP mills and stalled the spindle and never had a collet or big face mill spin in the spindle. The motor will stop or the belts will slip.

piniongear
09-08-2007, 12:50 AM
Recently I bought my first ever Bridgeport. It came with 8 collets of different size.
Six out of the eight would not go into the spindle. Period....they would stop after the first inch was shoved in. The other two will slip right in and tighten up.
Yesterday I replaced the collet set screw with another new one. When I removed the old screw the end was a long rectangle shape. I looked at the new one and the shape was a perfect square.
I installed the new one. All eight collets slip easily into the spindle now and seat fully. So I am a happy man.
Now I find this thread and I have read all of the posts fully and in great detail. I see all these opinions and theory on to have or have not the set screw, and I have to stop and think....Duh, and I always thought the reason for Bridgeport to put this collet set screw in was to simply align and hold the collet and keep it from turning until the taper took hold. Gee, I never realized there was so much science attached to the little collet pin.......pg

wierdscience
09-08-2007, 01:18 AM
Over time dirt,swarf and downright gunk will build up in the draw bar threads and collet threads,add to that a little distortion in the drawbar threads as they wear(which they do completely sometimes) and you have the reason for the little pin.

It's just there so the spindle grabs the collet enough so you can thread the drawbar into and out of the collet with out it slipping and spinning in your hand.

Forrest is right,you don't need or want it.

To keep the threads working right,clean them with a tap every so often and replace the drawbar when the tips of the threads start to roll.

IOWOLF
09-08-2007, 06:46 AM
Only the mill owner can say IF he wants it or not.
Can it be problematic? Yes in a few cases,poor upkeep etc. does it need to be there? Why the hell are they still putting them in there B/P, Wells,Chinese crap,Taiwan , and a number of others even mill drills have them.Someone thinks we need them and they have been doing this a lot longer than we have. but it is your mills do what you want.

Forrest is right, and so are the others,because it is a personal preference thing. And that's all I'm going to say about that.

A.K. Boomer
09-08-2007, 10:05 AM
Forrest Addy is right, you do not need it at all. We all know he knows his stuff.

Besides with that thing gone it saves on carple tunnel wrist spinning the tool around to go in the spindle.

I have horsed the hell out of R8 taper 3HP mills and stalled the spindle and never had a collet or big face mill spin in the spindle. The motor will stop or the belts will slip.



Im really not in disagreement until he mentions that you should go through extra effort to remove it, You may not really ever need it at all but my point is - is you may not ever need to remove it at all either, There are slight factors that are in favor in either choice but if mine were missing --- missing it would stay, and if mine were in --- in it shall remain, This does not mean that it does not matter -- there are differences that I already weighed out and excepted for my machine and what I do with it --- key words --- "for my machine and what I do with it" but to tell people to make a choice one better have covered all the basis and Im not trying to offend but his advise falls short in my camp... When something takes extra effort and has the possibility of being the wrong decision its called a lose - lose, If you believe that you can predict the outcome of either of the slight advantages or disadvantages then thats far beyond my comprehension as I dont believe I know everything about who is reading this, what kind of machine they have and how and what their using it for, what I can do is give people an in depth discription of the forces at be and maybe shed a little light in an area that they did not consider, this then in turn will help them with their personalized decision, what im incapable of doing is to tell them what to do as I realize it will be right for some but absolutly know it will be wrong for others...



Carpel tunnel can work both ways, in the example that you described it may save the hand from having to rotate under no load, but without a pin the hand will have a static load to counteract till the drawbar is fully tightened, My understanding of carpel tunnel is not just the reps but the static loads (I.E. operating a jack hammer V.S. a more healthy full range less load motion)
But im not a doctor -- just throwing a different light on it.

Forrest Addy
09-08-2007, 12:49 PM
Here's some more gratuitous opining:

The R8's reason for existance is its low cost. The original Bridgport R8 spindle config was never intend for heavy torque. The oridinal Bridgepot motor was about 1/2 HP and 3/4 endmills was about it. A #30 MMT is about the same taper but it has that keyed flange to provide the drive.

Nowadays Bridgeports have options up to 5 HP motors. You can buy honkin 3" carbide face mills with R8 shanks and shell mill adaptors that will accept 6". Unless you really horse the drawbolt the larger toolling will slip eventually. I have a 2 HP motor on my BP clone and I slip the tooling in the spindle every now and then.

For that kind of action you really need a #40 MMT in a robustly spindle designed for it like the BP series 2 milling head or the Rambudi. I wish my mill was so equipped. R8 really is weenie tooling. Real stock removal is a PITA on an R8 equipped machine.

Boomer, you really don't have to "tear in" to your BP spindle to remove the infamous set screw. It's accessed quite easily. Use a strap wrench to unscrew the retainer from the end of the quill. This exposes the setscrew which may be removed with an allen wrench. Some of these may be LokTited; some may have a double set screw. Regardless remove the set screw fully so there is clear air all the way to the spindle bore. Then replace the retainer.

If that is your desire of course.

A.K. Boomer
09-09-2007, 11:49 AM
R8 really is weenie tooling. Real stock removal is a PITA on an R8 equipped machine.

.



I believe that for the average HSM R/8 is actually overkill, but overkill without bulky hinderence --- there are all kinds of reasons its still around today - low cost being just one of them, Id be hard pressed to call any design that has out excelled its original intentions by something like 800% "weenie" just because you can throw it into another league of industrial production tooling to compare with, What I would call it is actually amazing, it does surprizingly well, There are examples in the machining world that would make the #30 MMT or #40 MMT look like a complete limp wristed joke, so what --- do they do well for what their designed to handle --- yup, Same with the R/8, its all about the question of "how much do you need" yes --- but its also the question of "how much is to much" since ungodly overkill does play a factor in how much your tooling will cost and the extra unessesary bulk of just using it day to day this is an important factor.....

My mill is 1 1/2 hp, In all fairness Im already using a tool holding system that has a ton of overkill, I will never need anything bigger than R/8 tool holding capabilities, I see what my very experienced friend does on his 3 hp sharp and will never aproach that kind of material removal in that short of time, NEVER, I simply dont need to ------ EVER, and short of a crash or using inapropriate diameter cutters tool slippage is actually a non-factor on my machine WITH proper drawbar tension, but thats just for me, other people have more ponie's and other people actually have less, the limits are not only in your machine but also how and what your using it for, just because you may have double the ponie's that i got does not mean your R/8 is insufficient, all you would need to see is my friends sharp in action, believe me --- you dont want to be standing on the wrong side of the 3" insert cutter unless your wearing a nomex suite, a decade of production and I still have to take the time to align his collets in the spindle because the key is still there:D , that being said just because you have close to half the HP of what I got does not mean your "safe"...

Some kid puts an R/8 chuck on his geared head china mill and runs it backwards for a cut, Lets look at this a little closer, He's kinda inexperienced, so doesnt really compensate for drawbar tension, not hard to imagine as Iv argued with experienced machinist on this very site about the importance of this, lets throw in a couple other little things that can attribute to failure, Say he's got a heavy layer of vactra #2 all over everything including his hands that he just used to install his collet, say there wasnt barley any time delay between when the collet was installed and when he took his cut, last but not least say he misjudged his depth of cut and took off a little more then he wanted, and also say someone told him to remove his spindle key,,, a few seconds later he's wearing his 3,000 RPM 7lb chuck in his lap, to add insult to injury he wasnt holding anything real heavy with the chuck, but it was large in diameter so the "ben hurr" spikes of the chuck were sticking a good 3/4" out --- what the hell went wrong?

All of the above, and in fact if just one of the following details wasnt present this accident would not have occured, Lets start at the beginning, #1; the first thing is the R/8 chuck, there is no option of tool slippage in the collet here, its a direct collet mount to the chuck base, if the chuck rotates so does the collet - no ifs ands or buts---- so there goes that failsafe, #2; the second Fuqe is the geared head mill, thier straight cut (in china!) and have all kinds of vibratory/resonance/frequency patterns that are being transmitted into the collet while the collet is under torque load in the loosening direction, #3; His drawbar tension was marginal to start with --- this flaw speaks for itself, #4; The vactra's job is to keep parts away from each other, especially precision bored smooth parts #5; the longer the collet is under tension the more contact patch of molecular bond it will achieve with the spindle esp. if a heavy high parrafin lubricant is involved (like vactra #2) thereby increasing its holding power -- oops, forgot he took his cut almost imediatly after installing his R/8 chuck :( #5; His excessive depth of cut speaks for itself, #6; Without a collet key in a borderline situation like this the collet was allowed to vibrate/rotate, loosening to the point of complete release of the 3,000 RPM 7lb "ben hurr" R/8 chuck...

Still comfortable in telling people to pull their pins?
Im not...

Not trying to dethrone you Forest, as everybody here knows you are a master machinist, when it comes to what happens when a tool bit hits a certain material you can predict the outcome like no other,
Im only a mechanic --- I really dont even consider myself a machinist although I can "hang" a little ------- I do however know machines and all thier behaviors very well --- over the years I have proven to myself that I have an uncanny ability of predicting failure in just about anything of mechanical design, in my world milling machines and lathes are about the most simplist things iv encountered in about 30 years --- its not to say there is not any kind of a challenge there, as you see you can get into detail with just about anything, As much as I feel like I know about the subject I will also add this ----- Im not qualified to make a statement as to tell people to either keep or remove their spindle keys, and would in fact believe if you error you need to be in favor of them but thats pretending I know what everyone is up to with thier mills, and I dont,
The purpose for this post is not to tell people what to do --- but maybe get them to thinking --- or uncover an area that they may have not considered thats all;)