Quill fit upwards tolerance, opinions???

[rolfinator2002]

I know the factory quill fit is 0.0003-0.0005".
After stripping my head and cleaning the bore, my 0.0001" increment dialtest measurement , with dialtest located w/i 1/2" from the housing, with the quill fully retracted, and fully extended is the same, and approximately 0.0008" for both x and y axis. Tells me the bore is not measurably tapered. Lateral force on the quill in both cases was about 15 lbs.

Does Bridgeport advertise a service limit, or max recommended limit for this dimension?

The difference between a great mill and a so-so mill is tolerance.
Can I expect good cnc operation, or is this getting into "cheap" territory?
I have lots of machine experience, but this is my first mill rebuild.
Opinions highly valued.

[rolfinator2002]

Guys,
Some feedback would be greatly appreciated, please.
Getting ready to send out my spindle for rebearing and socket grind, so I need to determine if I am going to send out the head too.

[jmelson]

Originally Posted by rolfinator2002 I know the factory quill fit is 0.0003-0.0005". After stripping my head and cleaning the bore, my 0.0001" increment dialtest measurement , with dialtest located w/i 1/2" from the housing, with the quill fully retracted, and fully extended is the same, and approximately 0.0008" for both x and y axis. Tells me the bore is not measurably tapered. Lateral force on the quill in both cases was about 15 lbs. Does Bridgeport advertise a service limit, or max recommended limit for this dimension? The difference between a great mill and a so-so mill is tolerance. Can I expect good cnc operation, or is this getting into "cheap" territory? I have lots of machine experience, but this is my first mill rebuild. Opinions highly valued.

I'm not sure what you actually measured, here. If you can apply 15 Lbs radial force at the spindle in both directions and the indicator doesn't change, then the quill is a good fit in the bore. Is that what your .0008" reading is? Taper is not the issue, looseness is. Your .0008" could be deflection of the parts, not looseness in the fit. Depending on where you mounted the DTI from, this could easily be deflection of the head, ram, etc. Did you mount the DTI on the table? You should know that the head of a Bridgeport can be deflected .001" or so with relatively modest force applied to the spindle (I think maybe it takes 50 Lbs to do that). If you can mount the DTI onto the HEAD, you might get a smaller movement.

Jon

[rolfinator2002]

Originally Posted by jmelson I'm not sure what you actually measured, here. If you can apply 15 Lbs radial force at the spindle in both directions and the indicator doesn't change, then the quill is a good fit in the bore. Is that what your .0008" reading is? Taper is not the issue, looseness is. Your .0008" could be deflection of the parts, not looseness in the fit. Depending on where you mounted the DTI from, this could easily be deflection of the head, ram, etc. Did you mount the DTI on the table? You should know that the head of a Bridgeport can be deflected .001" or so with relatively modest force applied to the spindle (I think maybe it takes 50 Lbs to do that). If you can mount the DTI onto the HEAD, you might get a smaller movement. Jon

It's clear taper is not issue. Dialtest was mounted to the head with the needle resting w/i 1/2" of the head bore on the quill, checked both with the table x and y axes. The dialtest was mounted directly to the bore housing in other words and as close as possible to the bore on the quill to avoid multiplication of lateral reading. This provides a total diametral clearance of 0.0008" between the quill (not spindle) and its bore. If I was using the mill for strictly manual usage, I wouldn't hesitate to leave it. I'm sure that the Chinese and cheaper Taiwan mills originally built with moglice are no better, BUT this unit is being rebuilt strictly for CNC usage, producing as many small parts as large ones. Since this is my first quill fit, I don't have a reference point for this effort.

[Davo J]

Hi,
I am not much help never owning one, but 0.0008 doesn't sound much to worry about. I think I have read in the Bridgeport manual that tightening the swivel head bolts can affect the quill by distorting it if done up to tight.

My Chinese mill which is like the Grizzly 3617 has 0.006 after 1 1/2 years use so I am going to sleeve it, I would love to have your 0.0008.

Dave

[rolfinator2002]

Originally Posted by Davo J Hi, I am not much help never owning one, but 0.0008 doesn't sound much to worry about. I think I have read in the Bridgeport manual that tightening the swivel head bolts can affect the quill by distorting it if done up to tight. My Chinese mill which is like the Grizzly 3617 has 0.006 after 1 1/2 years use so I am going to sleeve it, I would love to have your 0.0008. Dave

Thanks for all the feedback. I'll consider the topic closed then. I think I'll let it fly, and if I get errant finish or dimensions, then I'll rechrome the quill and bore the head to fit.