What's new
What's new

Help! How much axial force from the table can a Bridgeport spindle head take?

Saketh123

Plastic
Joined
Aug 10, 2023
Hello!

I am extremly new to manual milling, in fact I have never ran a bridgeport before. I have quite a bit of expierence with machining though, with cnc machines, haas and DMG MORI 5 axis machines. I am doing research and running experiments that will involve driving the spindle of a milling machine at a force of around 3000N or about 650lbf onto a workpiece. For the safety of our cnc machines I have decided to do this on an old Bridgeport with EZtrak power feeds for x and y we have lying in the back. I will be driving the Z axis table feed elevating screw with a servo motor capable of the torque I will need.

I am trying to find information of how much axial load the spindle head can handle but have had no luck? Anyone have any idea if 1 the spindle head can handle 650lbf of force and 2 if the elevating screw can handle 650lbf of force?

Thanks
 
Elevating screw, no problem. The spindle head itself, dubious. You are likely to damage/break something in the quill Z drive mechanism. You are also going to run into trouble with the 2-rotational-degrees-of-freedom head joints.
Now if you can hack up this old Bridgeport, you can probably arrange to transfer the quill thrust directly to the head casing, taking the load off the quill Z drive mechanism. You can also pin and preload the nod and tilt axes of the head mount, to eliminate backlash and possible stick-split jumps.
 
I think my Bridgeport is rated for a 1/2" drill in steel. You could back-track and look up the force from that.
 
I've seen it mentioned previously, supposedly with no pilot hole, driving a sharp 1/2" drill into the average mild steel takes approximately 150 lbf down feed pressure on the quill. On my sounds about right gut-o-meter, that number seemed reasonable. At 650 lbf your probably ok on the table as long as the head was pretty close to being inline with the knee screw and column ways. As far as the head and knuckle assembly taking it, I'd be paying attention to what Sfriedberg and 4GSR said. This seems more in line with adding what you need to something like a proper shop press than risking costly machine parts. In fact with how much the ram end, head and knuckle assembly is going to deflect even if none of it breaks, that alone would throw any even semi accurate drive force numbers out the window.
 
7207 25° contact angle bearings are rated at about 16kN of axial thrust. The quill power feed might not be up to the load, but if the quill is clamped, the ram itself will be perfectly happy with that load (you can and do lift turret mills with the ram, after all).
 
I don't think the head knuckle will stay put. Istr power feed is supposed to be set at 100# kickoff. I think rated drill size for hand feed is 3/4".
 
Hand feed a 3/4" drill in a Bridgeport? I've done it, it's not easy. Very hard if you ask me. People wonder why the handles get bent on the hand feed.
 
I'd be inclined to say the front -to-back tilt will handle it.

I'd hang two 325# girls off that joint and not think twice.

The weak link is the quill lock. I don't know what the innards look like with the quill fully retracted. IOW is there a good stop with the quill fully retracted? You can jam a block between the top of the depth stop and the head casting. Then the friction of the quill lock and the 3/8? SHCS that holds the depth stop takes the load.

Saketh123 it's not clear to me whay you want to do. If the spindle doesn't hsve to turn doin the head around and use the slotter mount.
 
Surely to goodness you can't write a story/question like this and not tell us what the end use would be for. That's just not fair!:D.

Why don't you just set a little load cell on the table with a thrust bearing on top with an empty tool holder or something in the spindle and do a quick grass roots test raising the knee with it running? Wouldn't take long to get a feel when the pucker factor kicks in looking at the gauge.
 
I want to see the milling cutter or prints. Material and feed rates.
Something is so way,way wrong here to me. Plunge cutting? High feed cutter? Low lead? Missed a decimal place?
We do not axial load this number in 20 plus inch cutters on 50-80hp machines that will deck a V6 or V8 with .050-.100 stock in under 15 seconds.
Talk to me.
I do not understand as I am missing something here. That sticks in my craw. Not knowing is bad and leads to no sleep.
Confused. (As all on the board will testify to I am sort of a brain dead tool engineer so no surprises there)
Bob
 
Last edited:
1. The OP stated "Z axis table feed elevating screw". to me this means locking the quill and driving the table, not locking the table and driving the quill.
2. I'd guess the quill will slip. You could always put the quill all the way up and throw on a larger quill lock handle. I'm not sure what the quill bottoms out on in the up position, but I doubt it's wimpy.
3. Broaching or slotting operation with a really big bite?
 
Lets say there is 620 pounds of force upwards.
Some have questioned the knuckle.
When just sitting how much down force is there on this joint from the head weight?
Lets say 300 on big motor 10x54. So now this 620 up is just about what is sitting there always downwards.
Anyone want to do the beam deflection for the ram if fully extended?
Knee screw compression?
Never put a 500 lb part on a B-port but my Tri-vise, rotary, 2nd vise must be over 250.
I think a 10x54 with the quill full up can handle this with ease but maybe a fair amount of deflection as you come on and off the part.
Milling cutters for heads and blocks are designed to minimize axial force so that you do not get waves as you go across open bores to full engagement at each cylinder.
When looking at the bearings one must know at what diameter the cut is taking place. (moment arm)
Example here is a 27 foot pole saw I just bought. The saw blade and end are very light.
Put 25 feet of extensions on and try to lift it up from the handle end with a 2 to 3 foot grab/pivot. Whoa.
Bob
 
Last edited:
Can you do this on a drill press? The knee screw can handle this without question, the table if part is centered over screw- sure. As carbidebob points out the knuckles can handle it- the innards of the quill/bearings, rolling dice.
A boring drill press can do this, they are of the press family.
 
1. The OP stated "Z axis table feed elevating screw". to me this means locking the quill and driving the table, not locking the table and driving the quill.
2. I'd guess the quill will slip. You could always put the quill all the way up and throw on a larger quill lock handle. I'm not sure what the quill bottoms out on in the up position, but I doubt it's wimpy.
3. Broaching or slotting operation with a really big bite?

Yes. He’s driving the table +ve in Z with the quill bottomed out I reckon.

Maybe a friction-weld apparatus. We had a Bridgeport that some prof wanted to use for friction stir welding experiments. Luckily for the machine I don’t think they ever figured out how to wire it.
 
Maybe a friction-weld apparatus. We had a Bridgeport that some prof wanted to use for friction stir welding experiments. Luckily for the machine I don’t think they ever figured out how to wire it.
That would be my guess as well. Saw someone doing that on youtube awhile back. Not gonna hurt the castings at all, 650lbs is nothing for them. I would be worried about the bearings if there is any intermittent loads from vibrations or whatever. They should be at 650lbs of constant load, but that could easily be plus/minus a thousand or two if its is vibrating.

Edit: Found the video here.
 








 
Back
Top