Bridgeport Ballscrew Dilemma?

beeser

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I recently purchased a Bridgeport mill that was originally outfitted as a CNC by MillPWR. All of the CNC specific equipment, e.g. controls, servos, etc. were stripped from the machine, basically rendering it strictly manual. It does however have the original precision ground ballscrews for the X and Y axes. Although the screws have the advantage of minimal or no backlash the ends do not fit a normal handwheel setup without modification. It seems to me that I have 3 options;
1) Modifify the screws to accommodate handwheels. The Y axis screw would have to be cut down, a woodruff key added and the end threaded to accept the normal nut on the end of the handwheel. The X axis screw would have to be threaded on one end for the handwheel and possibly lengthened on the other with possibly an extension.
2) Purchase new precision ground ballscrews, optimistically without the nut to save cost. If that's not possible because of an incompatibility of existing nut to new screw, then purchase a new precision or rolled ballscrew retrofit kit.
3) Convert the screws to an ACME thread setup.

Any thoughts of suggestions?
 
I'd rework the screws. You already have them and it won't cost you a dime except the time you put into them, not to mention those screws are better than the Acme's in my opinion.
 
Although the screws have the advantage of minimal or no backlash the ends do not fit a normal handwheel setup without modification.

How about option 4) make some custom handwheels that fit the existing screw ends? (or an adapter from the screw to a handwheel)
What are they now?
Maybe you could modify some "off the shelf" handwheels.

-brino
 
Wasn’t there an issue using ballscrews on a manual machine
 
I recall reading a thread on here about a manual mill with ballscrews. I recall a lot of negative comments about the TPI of the ball screws being MUCH too course for a manual mill. Turning the handwheels a few degrees moved the table much too far for precision work. I think they also said that because the threading on ball screws are so course that a milling operation that required any amount of force would actually move the other axis and index the handwheels... so you had to lock the table axis you weren't using. I.e. taking a long cut on the X axis would actually cause the Y axis and Y handwheel to move. So every time you index the Y axis you have to lock it down after indexing. Not a terminal condition but annoying.

Have you considered reworking the mill back into a CNC mill?

If you don't have any CNC aspirations for the mill it sounds like #3 - Convert back to Acme threads might be your best choice... But I am only going by what I read and have no direct experience myself.
 
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a friend is the milling foreman at a large manufacturing co and, at one time, they were replacing some older bridgeports -in which case they always scrap old equipment. i stripped one for the ball screws for mine. i asked the same questions to him and he stated they have always had ball screws on the manual bridgeports with no issues. i can say i have not had a problem with mine after converted. the ball screws did not change the travel in mine.
 
Leave the screws be and make some hand wheels to fit them, they do not need to be graduated if you install a DRO, any comfortable handle will do.
If you have ever used a manual machine with a DRO you will stop looking at the dials in the first ten minutes and never look at a dial again as long as you live.

Make sure that the axis locks work well or you will likely spit some tools and work right out of the machine.

Good Luck
 
Any thoughts of suggestions?
What is the lead on the screws? (1 turn = travel distance?)
DO NOT attempt to do ANY climb milling with manual ball screws.
I personally would convert back to CNC using a Centroid Acorn board, if that's not an option and the screw lead is not large, make new handles or handle adapters and leave the ball screws alone.
 
i have manual ball screws and i climb mill with no issues.. i think that may be an old wife;s tail like batteries on concrete
If you say so.
It really depends on the thread pitch. If you have a large pitch you might be surprised at what happens.
 
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