My home shop CNC mill is a Bridgeport with an Anilam Crusader II controller. Last time I switched it on, the controller didn't power up. I've been wanting to do the LinuxCNC upgrade on it anyway and this looks like a good time to do it. LinuxCNC will give me greater capabilities with the machine than the original control was capable of.
... So I'm considering automatic tool changing but I would need to convert my Erickson QC30 spindle to a pull-stud drawbar. Looking at the tapers, the CAT 30 or BT 30 should fit but be shorter than the QC 30, leaving me room to make a pull stud drawbar. Something like:
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At first I plan to just set the tooling up on the table, something like this:
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Anyone here know of anything like an Erickson QC 30 to pull stud drawbar conversion? Or a drawing of the inside of the Erickson spindle?
Not an Erickson spindle but here is a power drawbar drawing for a Denford Triac CNC mill
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. Actually the tool holder is held in by the disc spring stack and either hydraulic or air used to push the pull stud holder out. IIRC the tool holder used is BT30.
A few key things to keep in mind for such a conversion:
- Toolholder retention is via a stack of belville washers that exerts a
*lot* of force to pull the toolholder into the taper. This is why the actuator is usually hydraulic as it would take a very large dia pneumatic cylinder to get the required force to release.
- The actuator mechanism is "floating" and thus has no contact with the spindle when a toolchange is not taking place.
- The actuator mounting will lift from it's non-contact idle position when actuated so it is in contact with a flange at the top of the spindle while pushing down on the drawbar. This is so no toolchange force is applied to the spindle bearings which could damage them.
- The actuator travel is such that the drawbar will apply a push to the toolholder at the end of the stroke to pop free a sticking toolholder.
- Air is usually piped into the spindle and switched on during the tool loading to blow out any chips that may be on the toolholder taper.
Not in my experience, although a quill-type spindle cartridge does need to have a means of positively locking it in the full up position.
Hammering on the top of a conventional drawbar is the usual method, which doesn't seem to damage spindle bearings so far as I've been able to ascertain.
The machines I used to work on were this way, perhaps designs changed in recent years. The force was always applied between the spindle and the drawbar such that no force was applied to the spindle bearings.
A rap with a hammer vs. pressing hundreds of pounds with a hydraulic actuator. Perhaps they've beefed up spindle bearings in recent years as spindle speeds have increased so they can more readily handle the toolchange load. Or perhaps you haven't looked at the actuator closely enough since without looking at the prints it's not immediately obvious that the force is not applied to the bearings.
pressure that is placed onto the bearing is the same in either case.
The max compression of the belville spring washer stack is constant, yes. The pressure will vary if a washer or two has failed, and again on no machine I have worked on was any of this force applied to the $800 spindle bearings. The actuators all floated and pushed down on the drawbar while effectively pulling against the flange on the spindle as opposed to being rigid mounted to the head casting and pushing down against the drawbar. This was dozens of different brands and models of machine.
on 35 years now.
Well, I worked on them as in serviced them for about 6 years, including changing out belville washers on the drawbars and replacing a few sets of spindle bearings, so there is no question that the machines I worked on then ('90-'96 or so) did not apply toolchange forces to the spindle bearings. Take a close look at the prints for one of your machines to see where the force is really being applied.
max pressure that is placed onto the bearing is the same in either case.
Pressure ( on the spindle bearings ) (or on the flange, if one were present) is limited to the amount needed to release the tool, or to the total system pressure, whichever comes first.
Fadal for instance, makes use of this fact in order to set bearing preload; an indicator is placed on the spindle flange with a tool in place and the drawbar clamped, then the tool is released, the resultant change in indicator reading is noted and then the preload nut is adjusted accordingly...
Do you want a link to the procedure ?
My experience differs, and in fact I've never seen a system as you describe, the exception possibly being where a drawdar was actually being turned like for example the old devlieg jig bores.
Not saying such a system does not exist, but since it's your claim, you'd be more convincing if you could link me to the mechanical drawing of one ( which shouldn't be too hard since you've seen dozens ).
--out of curiousity, I'd like to see at least one.
for going on 35 years now.
including
The piston plate is about 4x6 and recieves air at ~90 psi, which means the total possible thrust pressure that's capable of being placed onto the drawbar on this 40 taper mill here sitting to the left of me works out to be about 2520 lbs which is well under the max static engineering load limit of the 7210 bearings which comes in at around 7081 lbs
It's oftentimes called an "orientation bridge"
Ball bearing elements are like any other metallic object in that to cause any permanent deformation to occur, forces in excess of yield.must be applied.
I forgot a step--first the spindle is run down against a solid object till the Z servo amp trips, then it is raised back up and an indicator is set...ThEN the drawbar is unclamped and the new reading noted.
pressure that is placed onto the bearing is the same in either case.
is limited to the amount needed to release the tool, or to the total system pressure, whichever comes first.
indicator is placed on the spindle flange with a tool in place and the drawbar clamped, then the tool is released, the resultant change in indicator reading is noted and then the preload nut is adjusted accordingly...
the exception possibly being where a drawdar was actually being turned like for example the old devlieg jig bores.
more convincing if you could link me to the mechanical drawing of one ( which shouldn't be too hard since you've seen dozens ).
I'm afraid I don't have any handy since I've been out of that business for 16+ years. Back then it was mostly Kitamura MyCenters that I was doing such repairs on, we also sold/serviced AWEA, but they were all new and not in need to those repairs yet. I did have to do spindle bearings on a big AWEA gantry once, but that machine was cutting synthetic graphite blocks and sucked the dust through the labyrinth into the bearings. We ended up porting and lightly pressurizing the spindle cartridge with shop air (few PSI) to prevent it from happening again.
Looking at the drawings of NMTB 30, CAT 30, BT30, looks like they would all work in an NMTB spindle with the appropriate drawbar. I've mostly looked at the internal taper dimensions, not sure about the drive keys fitting all.
I was thinking about getting a pull stud style CAT or BT 30 toolholder and seeing if I can make a spring loaded pull stud drawbar for it. If not, I would at least like to be able to use it with a threaded drawbar.
"RogerN" fired this volley in news:PNGdnVdhRLtwhBbMnZ2dnUVZ snipped-for-privacy@earthlink.com:
The only thing I'm sure of without looking at prints is that most NMTB-30 toolholders will fit a QC-30 spindle. (we've got a good mix of brands, mostly European, including ONE Chinese holder... guess which one doesn't fit ). When they don't, it has always been (for us) because the toolholder's flange is too thin (by about 0.050) to be gripped by the locking collar.
pressure that is placed onto the bearing is the same in either case.
is limited to the amount needed to release the tool, or to the total system pressure, whichever comes first.
an indicator is placed on the spindle flange with a tool in place and the drawbar clamped, then the tool is released, the resultant change in indicator reading is noted and then the preload nut is adjusted accordingly...
the exception possibly being where a drawdar was actually being turned like for example the old devlieg jig bores.
more convincing if you could link me to the mechanical drawing of one ( which shouldn't be too hard since you've seen dozens ).
OmniTurn did the same thing after we sold some lathes to shops cutting graphite as well.
Some nasty..nasty spindles when I pulled em down and apart. One is conditioned to think of graphite as a dry lubricant...chuckle...but tit sure cuts the living snot out of balls, races and spacers
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