Assisted drawbar tool release from Morse taper spindle?

J

Joe in Oz

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Hi. I have a horizontal milling machine with a No.4 Morse taper spindle. The draw bar is obviously on the back of the machine.
Tightening it and undoing it (with a BIG bronze hammer) is a right pain.... To make mattes worse, the machine is located in front of a wall - the only sensible location in my shed....
Occasionally, it is so hard to loosen and push the tooling out, I had to pull the machine forward on rollers to get a good swing at the end of the drawbar with the hammer. I've now cut a small hole in the wall for such occasions and hit it using a round bar and hammer from the other side of the wall! ::)

I've been reading about various pneumatic tool changers here and on other forums, but none mention Morse taper tooling.
Does anyone have any good ideas how I could adapt or make something to suit? I can't even visualise how to "hammer" or press the drawbar forward from the back of the machine with anything than a hammer of sorts..... The force required seems awfully big.
Anyone come across this or has some good ideas?
Cheers,
Joe
 
I used to use M/T collets in my lathe. I found that they dont need to be tightend near a tight as say R-8 tooling. I never liked the hard hit to get them to release either. As others has allready said, get a ER collet chuck, install it, and never have to go at it with a hammer again.
I believe your using this on a mill, in that case the collet chuck will eat up a bit of available day lite from table to spindle.
Loosing a bit of day lite is still better than hammering the collet out. The down side, On my mill when using the collet chuck, I have to use a big wrench to hold the chuck, while using the spanner wrench to loosin the nut. With both hands full, its best to have a towel below incase the tooling drops out unexpectedly.

Paul
 
Joe

You could biuld your own powered draw bar set up. I did this on my Induma mill, same thing as a Bridge Port. I used a butter fly air gun thats commonly used for power draw bars.
I would think the airtool would have the power to easly undo the draw bar, but the second part of the system is a air clyinder to drive the air tool down to push the M/T out.

The Power draw bar kits , or home made, that I have seen use a tapped in line to the air cyl, and this doesnt give full pressure to the air cly. These work fine on a R-8 spinle tooling, but I doubt it would release a #4 M/T. How ever, there is nothing stopping you from plumbing the air cyl in separate. This wayyou could have more, and or full pressure to drive the air tool down to release your tooling. When you choose your components to build a power draw bar, you need a air tool capable of undoing the draw bar, then the air cyl to drive the tooling out. Very simple to build really.

Now as far as it goes for collets, as mentioned, they are fine on a Lathe, but suck on a mill. Ok, I dont quite get that. I see my lathe taking some pretty heavy cuts compared to my mill. My mill is 3 hp and I dont think I run my my any where near full hp. Even in a production setting, Its not like you would run a mill that hard. The Lathe, well thats a different story.lol.

For most milling jobs the collets would work fine, for heavy hogging, then fine, slide the EM holder in place, they wont slip.But for most jobs, the collets are fine. To have the end mill slip in the collets, you either have a cheapo set of collets, and should be using a EM holder. I have a few collet chucks, and have never had to hammer anything , in,or out. They self release just fine. If the right tool is chosen for the job at hand, slippage should not be a problem.
But back on topic, Your interested in a assisted draw bar release,I believe if you have a place to mount it up on your machine you can put the hammers away.
 
Thank you all for your input.
however, I don't believe I mentioned collets....
The tooling I refer to is firstly the milling spidnle that goes with horizontal mills (and ends in an overarm bearing). I don;t believe any ER collet would drive that.
Other tooling I have could perhaps be adapted to plain spindles to fit into ER collets, but not sure about the scale of things here: They comprise od an 8" faceplate that holds my fly-cutters, a 4" boring head, a 4" fly cutter, several 1-1/2" to 3" end mills, and holders for several face milling cutters up to 7" diameter and slitting saws on purpose built arbors around 5-7" diameter.... The collet set I have is of unknown origin but started as BT60 (I believe), was annealed and then tuirned and ground to 4MT. Its head is arouind 4" diameter. The collets are tapered both ends and I have collets to suit form 1/4" to 1-1/2". It can also hold the threaded (end) shank end mill and slotting cutters I have, as each collet has a thread in the bottom ot it's clamping bore.

@8ntsane: the forces to remove the 4MT taper won't be achieved with an air cylinder - sorry. Loosening the drawbar bolt is the easy part and I don't mind having to do that by hand. It's at a convenient height - even when it's not really at convenient reach... It would more likely take a 5-ton hydraulic cylinder.
However, you have just given me an idea!
I'll give some thought to a hydaulic setup braced against the end of the drive spindle with some sort of thrust collars - rather than the mill casting, so as not to transfer the forces via the spindle bearings. A butterfly or some other sort of impact spanner to loosen and toghten the drawbar would be nice and I'll see how that could be incorporated....

Anyone else got any suggestions? Anyone ever seen a hydraulic tool changer of some sort?

Keep the ideas coming, please!

Cheers,
Joe

PS: An edit:
More thought are flooding my brain now! I should consider doing away with the drawbar nut altogether! Use a two-way hydraulic cylinder to pull the drawbar in AND push it out! I could perhaps ensure that the driven pulley is located securely enough (against axial forces) to mount the cylinder to it (so it spins with it - or on some bearings located against thrust collars so it doesn't).
I can probably measure the torque I need to pull the drawbar tight - calculate from that the force achieved on the 1/2"x12tpi drawbar and have some sort of gauge or control which limits the hydraulic pressure to that force for pulling, and no limit for pushing out again....

Any ideas or photos of commercial equipment very welcome!
Joe
 
Of course, many of the new, modern milling machines use a means other than a threaded drawbar. You will find what is called a "retention knob" screwed into a tool holder. It is shaped roughly like a doorknob, and inside the spindle there are "fingers" arranged somewhat like a wide range collet that close around the knob and pull it into the spindle taper. On top of the spindle, there is a pneumatic or hydraulic cylinder arranged to pull and push against the drawbar. It probably be practical to duplicate this from scratch, but it might be possible to salvage a power drawbar from a scrap machine and modify it to suit.

Another idea I have seen work is to simply make a slide hammer that drives the drawbar put from the opposite end from the nut. It seems hard on the arbor threads to me, but some people swear by it. I suppose if care were taken to make a full length sleeve that actually tightened up on the arbor that had a shoulder to beat against, the stress on the arbor threads would be minimized.

Otherwise, if I had to come up with an alternative, I think I would fabricate a sleeve that was large enough on the spindle housing end to bear against the spindle bearing retainer and use a nut to pull the arbor out of the spindle taper. The sleeve would need to be long enough to get back to the arbor threads to use them to jack the arbor out.
 
That's why MT isn't seen on newer milling equipment. They are considered "self holding" tapers. Really aren't supposed to need a drawbar. But then, I wouldn't want to mill with one that didn't have a drawbar. Good point about the tightness though. Doesn't take much to hold a MT in place.
 
Hi Joe
Maybe Im getting confused with all this. It is a MT #4 your knocking out of your spindle? I do understand that a MT4 or any MT takes a bit of force to get them to release. Like you have said, pulling the draw bar up tight should be the easy part.
Now the problem seems to be the release.

You had mentioned a hydraulic with x-amount of tons pressure!
I cant see why in the world you would need that. Are you sure your not over doing it when tightening the draw bar? I realize the MT has a good amount of surface area to grip. The MT may need a fair hit to release, but I dont think it needs, or should have as much force as yours does. Being your MT is using a 1/2 threaded draw bar, I would think the draw bar would be stout enough to use it to push your taper out of the spindle.

I thought I have. I used to have a lathe that used a MT5 spindle socket, and that thing was a bear to drive out, not sure why, but it was. I had concern with damage to the headstock bearings hitting it that hard. What was suggested to me was to turn the centre part of the socket down, much like a R-8 taper has. This worked great on my machine. Instead of a heavy hit to release it, one sharp rap, and she was out. Now Im not sure if this would be ok for your deal, but worked fine on mine. Of coarse myspindle socket was installed, and did not need to be removedseveral times per work session..

If you have a spare MT, you might want to try this, I found it held just as good, and released without near as much force.

Paul
 
Thanks for all the input.
Keep it coming.
Maybe I'm misjudging the forces in volved, but I've had the Morse taper (No 4) drive slip a few times in the past, when I tightened it gently - so I learnt to tighten it by feel. It's not a lot of force on the draw bar pulling the tools in, really. Some of my tooling, if not all, have a relief section in the middle of the taper.
However, I have a pretty good feel for what forces are required to release it again - and its huge. I have used some larger MT shank drills (1" and 1"1/4") without drawbar, just "thrown" into the socket, and they took more or less the same amount of force pushing out again as my drawbar tooling.
The size hammer and the swing and force needed to push the taper out again in the order of tons - I judge this from trying to take bearings off shafts with a hammer and drift and then doing the job on the hydraulic press (Mine has a pressure gauge on it).
I do have a 10-ton porta-power and a few small hydraulic rams. So I might jury-rig something up to find out what the forces really are without impact and then go form there with a design of some sort.
I also thought about using a finer thread drawbar and some end-stop outrigger on the drive spindle do jack the taper out with the drawbar. That may be possible and could be done with a remote drive or electric drive.Will have to think about that some more.
I've looked at lots of drawings of more modern tool holders (on Google) with fingers, collets and powerdrawbars in the last day or so - nothing jumps out as a doable solution for my spindle yet.
Cheers,
Joe
 
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