measuring play in quill+spindle of milling machines & drills

rec.crafts.metalworking measuring play in quill+spindle of milling machines & drills I'm hoping that some here have measured the play in the quill+spindle of bridgeport & equivilent millers, which will be a deciding factor when I buy one in the future. The measurements that I have made were by chucking a 10 inch piece of bar stock and pulling 10 lbs left then 10 lbs right at the end with a spring scale with the quill lock, when present, loose. A dial indicater set on the spindle indicates the play. A small bench size drill press, a $60 version, showed 13 thousandths of an inch play, 8 for a full size and heavier drill press, and 5 for a spanking new mill/drill from Harbor Freight. The last omitted the scale which leaves it a bit questionable. If anyone has made equivilent measurements, posting the results here would be greatly appreciated.

Hul

I cobbled a massively abused Bridgeport 1-J head onto my ancient round-ram Bridgeport mill some years ago. I did some checks on it when I was done. I got about .001" total back and forth movement when pushing about 50 Lbs one way, then the other way on the spindle. I was measuring with a magnetic mount indicator stand clamped onto the main head casting, so I was only measuring quill+spindle radial play, not any flexing of the head to base component stack. This amount of play is the displacement of oil from the bearing balls, and will be zero when the bearing is spinning. I can't find any movement at all in the quill. Unless horribly worn, the Bridgeport quill is a very fine fit, and rarely gets loose. The spindle bearings can get worn out, and they can be pretty expensive ($300 - 700 a set.) But, it is much easier to check them by listening when they are run. If they sound rough, diesngage the direct-drive clutch and try again. The motor and backgear bearings are cheap and easy to replace, so don't reject it is only the small bearings are noisy. You can spind the spindle by hand when the direct-drive clutch is open, and then ONLY the spindle bearings will be turning, so if it sounds OK then, it should be fine.

Jon

There should be very close to zero play. Not more than a few tenths between the quill and its housing, and none between the spindle and the quill. What you've been measuring is play plus deflection. If you were to plot your indicator reading vs. force applied, the play would appear as a steep line starting at the origin; the elastic deflection would be a relatively gentle and more or less straight slope. The knee where the two parts of the curve join represents total free play. In other words, play is the parts rattling around when small forces are applied; after the free play is taken up, and you apply more force, you're elastically deforming the machine.

Measure the quill play with the indicator base on the quill housing and the point applied to the quill close to the housing. Try it with the quill both locked and unlocked. Stick the indicator base to the quill to detect spindle looseness. As much as possible, you want to isolate what you're trying to measure.

The spindle runout, measured on the inside taper or with a known good collet and pin, should be less than about 5 tenths. Perhaps a bit more or less depending on what sort of work you expect to do. A good BP spindle will be less than about .0002, though more may not be a problem for non-critical work.

Any play in the spindle bearings in a mill is likely to cause trouble.

Drill presses inherently have more quill+spindle play than milling machines. Compared to milling machines, drill presses are not precision tools. While troubling if you measure it, a small amount of play in a drill spindle is not a bid deal. Even a well-worn drill press will deliver reasonably straight holes if good drill bits are used in it. Drill bit geometry determines where the hole goes more than slop in the way it is held. (Think hand drilling here) Tapping in a drill press might be another matter entirely. Excessive slop could be a real factor in starting taps straight in the hole. Runout in the tapping spindle can be bad enough to break taps, exp. small ones.

Bob (doesn't mill with a drill)Swinney

I'm hoping that some here have measured the play in the quill+spindle of bridgeport & equivilent millers, which will be a deciding factor when I buy one in the future. The measurements that I have made were by chucking a 10 inch piece of bar stock and pulling 10 lbs left then 10 lbs right at the end with a spring scale with the quill lock, when present, loose. A dial indicater set on the spindle indicates the play. A small bench size drill press, a $60 version, showed 13 thousandths of an inch play, 8 for a full size and heavier drill press, and 5 for a spanking new mill/drill from Harbor Freight. The last omitted the scale which leaves it a bit questionable. If anyone has made equivilent measurements, posting the results here would be greatly appreciated.

Hul

rec.crafts.metalworking measuring play in quill+spindle of milling machines & drills

Ned & Jon - thanks for the data and the insight regarding the flexure of the head & stand or body of the tool. The numbers both of you mention are reasuring. A gap is left, however. Have either of you made measurements along the lines I described? Possibly more significant would be mounting an indicator on the table touching the spindle and then applying a measured force between the spindle & the table. Both left & right and then again in & out would be best and indicate what could be expected tolerence wise.

Hul

I've never done that with a measured force and don't see that it would be useful unless you wanted to compare the stiffness of two machines. It would tell you very little about the accuracy you could expect from a mill, or the condition of the quill and spindle, except perhaps in the case where one or the other was really trashed. In any case, the methods that Jon and I described will yield much more information.

I do disagree with Jon about the amount of play that tolerable in a mill spindle, anything more than zero is too much, but other than that I think we're on the same page.

Hul, Zero is good. If you see anything else, you would hear it as well. Steve

Well, the measurement on my Bridgeport is not much different, if you include the turret - ram - head knuckle - head stackup. Maybe .0015 - .002" with a 50 Lb load applied both ways. I have a home-made hack-job of a jury-rig to mount a J-head on a machine originally made for an M-head. It is totally inadequate for the weight and tool extension possible with the J-head, but I am using it anyway.

I applied force manually pushing against the floor, not touching the machine table, as that is yet another stack-up of movable parts, and probably a lot looser that the spindle/quill, if you include the leadscrew backlash.

Jon

rec.crafts.metalworking measuring play in quill+spindle of milling machines & drills

Ned & Jon - The level of tightness in the quill/spindle of these machines that you both are stating is impressive. Jon's finding of 1.5 - 2 thou for 50 lbs both ways measured from the table but moved from the floor looks significant. As a guage, a C made from a 4 foot steel 2x4 would show a deflection of 4 thou with 10 lbs in & out. Surely a miller, with such masive castings, would make a better show. But, with the number of joints between the cutting tool and the table, there is room for Murphy. Especially, as Jon mentions, when the lead screws are considered. Actually, locking the various movements and then measuring might be an effective approach. Provide a measure of the foundation, so to speak, then consider the leadscrew, which would probably lead to inertial & harmonic calculations fairly quickly. Ned, if the tool is tight as it should be, then you are most likely correct about the use of such a measure as an indicator of expected tolerences; but if the ways are worn or the gibs are gimped or something similar then maybe not. Jon's last mentioned measure provides an indication of what could be expected, which is useful. Perhaps mostly to avoid buying a marginal tool.

Hul