Bridgeport - best way to clean rusty table and ball screws

[supahonkey]

I received a free Bridgeport with the Prototrak conversion. The mill was in a shop that had roof catch on fire. The wires are melted but the machine works just fine. Unfortunately the roof was missing for a few weeks. What is the best way to clean both the table, the ball screws and the ways? As you can see, the ball screws are a little rusty. I hope they can be salvaged.







Poor ProtoTrak...

[Davo J]

Great score, some people have all the luck.

I would dismantle the table saddle etc and give it a good clean. To clean up the top of the table you could use a scourer pad or steel wool, hopefully the table is not warped from the heat.
With the ballscrew I would remove it and clean it up with a soft wire wheel then inspect it for pits.
If it does need replacing, linear motion bearing on ebay are about the cheapest around and would probably cost around $300 fully machined and delivered from them.

Dave

[79TigerPilot]

The table doesn't look all that bad. The ball screws are another matter. I guess I would go after the table rust with some WD-40 and some wet and dry paper just to clean things up a bit. Then I would remove the X axis bearing supports, table way gibs and oil lines. The table should slide off at this point and you can clean and inspect all the critical surfaces. The ways may not be all that bad since they are usually coated in oil. Next remove the X ball screw flange from the yoke and take out the ball screw. Remove the Y-axis bearing block and Y ball screw flange from the yoke. Then remove the y axis ball screw. Next remove the yoke, then slide off the saddle.

The table, saddle, and knee ways can all be ground and scraped if necessary.

Once the table and saddle are off I would try and remove the knee from the columb.

I would try not to rotate the ball screws with all the rust on them. See if you can remove the rust and repolish the ball screws before you rotate them in the nut. With a little care the ball nuts can be disassembled and cleaned. You would need to keep track of all the balls for each circuit. Sometimes they put different diameter balls in the same circuit and or different sizes between circuits to provide the correct preload.

Here is a link to some pictures of my BP getting refurbished.
http://picasaweb.google.com/cschaffter/CNCMillProject

Good luck
Craig

[mactec54]

supahonkey

There is another post,were they used critic acid to clean up the rust,( I think they used 3% to a gallon of water, it needs to be in a container for a while) it worked really well, your machine was not looked after very well before the fire. all the drill holes in the table

[supahonkey]

Thanks for the replies. I am going to start taking it apart today. I assume the knee is a lot of fun to take off. I am guessing you have to crank it all the way up and then use a engine hoist to bring it off the ways. Are service manuals for these old Bridgeports available online or do I have to order one? I have seen a few websites with electronic copies that are around $90.

As for the condition of the table, the mill was originally owned by Lilly drug company. The previous owner bought it, and two weeks later the roof caught on fire. I work at Rolls-Royce gas turbine. The machines in the tool room are abused too. I would never do it, but I guess these guys just don't care because it is not their equipment. You guys wouldn't believe the stuff that gets thrown away. I saw five Brown and Sharp 5" compound sine plates in the dumpster. They 5S stuff where things are thrown away if it isn't used in a specific amount of time.

[ImanCarrot]

You could try reverse electrolysis- search this site, there' splenty of stuff about how to do it

[krutch]

A free mill? I would send the ball screw assemblies to Proto or some other ball screw mfg. or reconditioner. I've read serveral places not to remove the screw from the nut. Let the people who do it for a living do it. The cost may be a little high, but the mill was free, right? I'd spend the money to have it done right. After all if the screws are screwed the mill isn't going to be accurate with them. You could always put OEM screws back in, there must be some around, and do without the Proto. The rest of the mill looks to be salvagable.
Just my .0002 cents worth.

[supahonkey]

I am weary of removing the screw from the nut. Isn't a specific preload set on the screws that I will screw up by removing the balls? The Y axis screw is just fine. Won't I have problems if I buy a new X axis screw and try to screw it into the old nut? Do the screws have to be replaced as a X/Y pair with a new nut?

Craig: I really enjoy looking through your pictures. I really like your table riser system. Are the gas shocks from an automotive application? How does the stepper perform against the heavy knee and lead screw?

[79TigerPilot]

If you have two circuit ball nut then the preload is set by the ball diameter but if you have a double nut then the preload is set by the spacing of the nuts. It’s not all that hard to remove the nut or reload the ball circuits. I had to do this on my Y-axis when I ran the nut off the end and lost some of the balls. My nut had two external return tubes with different balls sizes in each circuit, one had.1250" balls and the other had .1241" dia balls to provide the preload. Do one circuit at a time, measure and count the balls. I was told if you have to replace any balls you need to replace them all from the same lot ( a tolerance thing). Was also told to watch for spacer balls thought this is not very common. These are slightly smaller dia balls that alternate with the main balls in the ball string. I guess it is used to reduce friction. To reload a circuit just fill it to the return tube seat in the nut, load the return tube, use a dab of grease to hold the balls in the return tube then install the return tube. Do one circuit at a time. I got my new balls from Bal-tec. www.precisionballs.com

I wouldn’t think it possible to get a new screw for the old nut unless you knew the manufacturer. The X and Y ball screws don’t have to be the same if you are running CNC.

The gas springs are 200 lbs each from McMaster. The knee drive works fine I only get 25 IPM, any faster and I loose steps, its gots to move over 750 lbs of iron. A ball screw on the knee would help but for now its just fine and anyway I just use the quill drive for rapid Z milling.

Craig

[Davo J]

You will have to replace the nut with the screw if needed.
The manual that is sold on ebay that has been written buy a private guy has been getting a good rap up on other forums.
I am not sure which on but it either on this forum
http://bbs.homeshopmachinist.net/index.php
or this one
http://www.chaski.org/homemachinist/viewforum.php?f=38

If you join the second one there is a guy offering to send a PDF of a few different manuals here in post 4
http://www.chaski.org/homemachinist/...p?f=43&t=87279

Hope that helps

Dave

[krutch]

I see the original post is old.
I just moved a mill into my older shop to get it running. It had sat in the new addition for quite some time and had developed rust under the grease I had smeared on the table. It was surface rust and not pitted but I wasn't sure the table was serviceable. I took an orbital sander with scotch-brite in place of sandpaper and the rust came right off. The table looks good but has some staining from the rust. It helped to use a little oil with the scotch-brite. I used 3in1 oil but any lite oil should work.

Thats my experiance with rusty machines. Now, the ball screws on that BP are a different problem. I would send them to a place that repairs them. But that would be my choise

Krutch

[Lewertek]

I am a freelance tech in Canada, I worked at Hardinge/Bridgeport service for 10 years previously. That machine is a nightmare IMHO, but I thought I would share some experience with rust removal. I began using a product called Fluid Film over a year ago and now swear by it. In Canada you can find it at most Hardware stores and industrial supply houses. Canadian Tire carries it, approximately 15$ for a regular sized spray can. It is natural, derived from wool wax and is food grade approved. It is a penetrating lubricant, but also a rust and corrosion inhibitor. Spray it on rust and it stops it dead, dissolves it and prevents it from coming back. It is also electrically neutral. Amazing stuff that I now recommend to all my customers. Do not use WD40! WD40 is a good product for cleaning the exterior of a machine, and that is about all I would ever use it for anymore.