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Bridgeport Ballscrew Dilemma?

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beeser

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#1
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?
 

4ssss

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#2
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.
 

brino

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#3
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
 

dlane

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#4
Wasn’t there an issue using ballscrews on a manual machine
 

MikeInOr

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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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cg285

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#6
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.
 

Wreck™Wreck

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#7
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
 

frijoli

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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.
 
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cg285

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#9
What is the lead on the screws? (1 turn = travel distance?)
DO NOT attempt to do ANY climb milling with manual ball screws.
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
 

frijoli

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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.
 

beeser

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#11
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.
Both X and Y ball screws travel 0.200"/ turn. These have double nuts that pre-load the screws, which as I understand it provide some resistance to movement when milling. The preload can be adjusted by changing the width of the spacer between the nuts. I'm just a hobbyist so I may be incorrect about the latter statement.
 
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JimDawson

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#12
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
Me too :)
 

Cadillac STS

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#13
I think Wreck's idea of using any hand wheel that can fit with comfort and spending your time/money on a DRO is best by far.

No need to do what it takes to get back to stock wheels and graduated dials, will cost significant time/money. You could just file in a flat spot on the shaft and get a hand wheel with a set screw and be good to go with a DRO setup.

If you end up using it much you likely will want to go with the DRO anyway.

Also would leave the screw ends as they are in case you or a future owner wanted to return to CNC. Try to avoid cutting off length.

Up and cutting chips in a day. Could always return to 1) 2) or 3) later if you wanted to.
 

beeser

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#14
I'm beginning to warm up to the suggestion of leaving the screw lengths as they are. The Y screw sticks out a lot but I can probably learn to live with it. The mill came with a practically new Lyman power feed, which sits on the left side of the X axis. The gears don't quite match the screw length but I'm sure something can figured out.

The mill originally had an Acu-Rite DRO. Would it be advisable to use the same manufacturer for a replacement? The mounting holes would probably be the same for the X axis scale. The mounting bracket for the Y axis is still on the mill. I also have the original bracket and mounting for the monitor.
 

JimDawson

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#15
If you are replacing the DRO, then any manufacturer of your choice will do.
 

beeser

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#16
If you are replacing the DRO, then any manufacturer of your choice will do.
Would the mounting hole locations be the same for all manufacturers? If not, wouldn't it be easier to just use the one that originally was used?
 

JimDawson

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#17
I'm going to guess that the mountings would be different. There is a good chance that even from the same manufacturer the mounting would not be the same unless you got the exact model that was installed, even then there may be some differences.

I'm a real fan of magnetic scales. I have them on all of my machines.
 

beeser

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#18
I'm going to guess that the mountings would be different. There is a good chance that even from the same manufacturer the mounting would not be the same unless you got the exact model that was installed, even then there may be some differences.

I'm a real fan of magnetic scales. I have them on all of my machines.
Why magnetic scales?
 

JimDawson

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#19
They are very compact, bullet proof, and accurate.

Here is a picture of my X axis scale read head (just above the date stamp), you can just see the magnetic tape attached to the table.

1519143915788.png
 
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