Swapping Bridgeport Mill Table

[Ronnie]

Hi DFWKen,

Removing the table is done easily with two men. Although I have done it by myself sliding the table off on a cart the right height.

As far as the play in the screws, most of the time the screw is worn, as well as the nut. If you look under the mill at the screw. Look at the width of the threads on the screw. More than likely the width of the thread its self will be wider at the end than in the center.

If you have a lathe that can accommodate turning this size screw. You can make one. No not from scratch. But buy Acme threaded precision stock from MSC or some other supplier. Turn and key the ends to suite your mill. I have done this where I work on our mills. It worked very well. The supplier will sell you threaded stock and nuts to match. The nuts need some modification as well. Oil groves etc. The basic size of the nut did fit the Bridgeport Housing.

It has been years since I have done this, but I am almost certain one screw is left hand thread the other right hand thread. I will not go into a lengthy explanation as why. If you tear the mill down, and look how each screw is supported, this will make since to you.

Just thought I would offer this as a cheaper alternative to buying a new set of screws and nuts from Bridgeport or just replacing the nuts on a worn screw.

Good luck
Ronnie

[LEW_BEST]

Hey Ken

Please keep me posted on how this goes (particularly the resurfacing). I'd like to get mine resurfaced; wanted to when I originally got it but couldn't find anyone nearby to do it.

Lew in Waco

[DFWKen]

Thanks, Ronnie. I certainly appreciate the information.

I ran the table left and right to the ends of the travel and the freeplay is the same all the way across. From this, I assumed that the screw itself was probably not the cause. Instead, I thought it might be the nuts. It does the same in the Y-axis, too. I've seen several threads about removing the table. I will try to do this soon. Also, if it's easily surfaced, I'll find someone here in Dallas that will do that for me. There are no deep holes drilled into it . . only some marks and gouges that look like could be ground out without too much removal of material.

[Ronnie]

Ken,
You seem pretty knowledgable about the whole thing. I'm sure you won't have any trouble removing the table. It's a straight forward job.

You probably know this but just in case you didn't, the nuts are split and adjustable. There is a screw in the side of the nut that tightens the split in the nut together. On older mills I have been told by older machinist that the nut was two piece although I have never seen this.

You look in from the left side of the Bridgeport (left side facing it) of the X axis. Back under the table you should see a screw. This tightens the nut compressing it together. Look good, it runs in my mind on some mills there was also a means of locking this screw after you make the adjustment. If the small adjusting screw won't turn, it may be out of adjustment or this locking screw may be tightened restricting the movement.

On the Y axis you have to remove the cover behind the Y handle and dial to get to the nut on this axis.

If you do try to adjust these nuts, pay attention how they are supported and what turns, what is held in place. You will understand the Right and Left hand thread.

Let us all know how every thing turns out.

Ronnie

[Matt_Isserstedt]

Ronnie, my understanding was that the original nut came solid but that it could be split to account for wear. Splitting the nut would be a temporary fix but it would wear quickly after that.

I guess the other danger of tightening a split nut is that a bind might result where the screw is not worn. Most of the leadscrews I've seen on older mills and lathes have visible wear in the "sweet spot" where the machine is used most often and then the screw looks pristine where it has rarely or never been used.

IMHO, the accumulated wear isn't an issue as long as it is uniform (easier stated...how many users crank their milling tables from end to end regularly??). The backlash is a little frustrating at times but it doesn't really hurt anything as long as you as the user keep it "going in the same direction".

Problems can result I think when jig-drilling via the dials alone to dimension over a long distance on a leadscrew which has varying wear. A DRO will negate this I believe since it measures position independently of any backlash or lost motion. I continue to machine via dials-only but someday....

FWIW
-Matt

[Ronnie]

Here is a link to a drawing to illustrate what I am talking about.
Notice the locking screw that can lock the main adjusting screw.


http://home.earthlink.net/~foxeye1/bp1j ... ewinfo.gif

[Matt_Isserstedt]

Gotcha. I had that footnote "solid nut may be split as shown to take up wear" in my head from awhile back.

Regards
-Matt

[DFWKen]

Thanks for the instructions, hints, drawings, and moral support, Ronnie. I moved the machine home (from my air conditioning business shop) today and am ready to get with it in earnest. I'm manning a booth at the SHOT show this weekend, but after than my spare time is devoted to the Bridgeport.

I printed the .gif you sent me. Thanks so much.

Ken [img]/ubb/images/graemlins/smile.gif"%20alt="[/img]