questions on Bridgeport chrome ways and how to repair them

Ok I am sure this is covered in a book or some other media but I have a couple of questions about the chrome ways on the Bridgeport knee.

One of my customers has a older BP in their shop and it has been rode hard and put up wet. They asked me to look at it and see if I thought it could be repaired. I wish I had taken some photos but I didnt have a camera handy.

The previous owners must have never oiled it or took any kind of care at all. It looks like the chrome surface is very thin and in some spots, near the front of the knee, it is damaged and barely visible. There are some deep scars that are probably from chips that were allowed to be drug under the ways. And the flaking that can be seen is barely visible.

1: Does the chroming really help or do machines with chrome ways still have to be fixed just as often as older machines or other machines that do not have the chrome ways?

2: Can they be scraped or do you have to remove the chrome if it is worn to the point where it needs to be repaired? I would assume if the chrome is still there you could grind the ways but is that always necessary? If you do repair a knee that had chrome ways has anyone ever had them re-chromed after?

3: Was the flaking done before the chrome or can it be done after? The one I looked at appears to have been flaked before but I am not really sure of that.

4: Does anyone know how they chromed them in the first place? That is to say how do you selectively chrome the surface without chroming the whole part? And is there any idea of when they started chroming them in the first place?

That is a bunch of questions at one time and this can be moved to the Bridgeport forum if it would be better to answer them there. Oh and if there is such a book that covers some of these questions I would like to know it. I have seen several books on the machines but I have never seen one in person so I dont know how useful they are. Anyone want to make a recommendation?

Charles

The guys that I have seen who rebuild these things just scrap right over the chrome, no need to redo it.

I have never seen anyone do a good job trying to scrape the chrome off. Never. I have tried with a Biax and it isn't a good way. It digs in and you get chatter like crazy. The way I have had success is to have the chrome stripped of at a chrome plating shop. Or have it milled off by cutting under it. The best way is to have it stripped. I would recommend this company Industrial Hard Chrome Plating Services | Wisconsin Chrome Plating Company as this is where all the local rebuilders have it done. It can be re chromed after you scrape it, but you have to file the sharp edges with a steep radius or the chrome will build up on sharp corners. Cal themup and ask themthe questions. But the shop has to have had experience doing it because if they don't mask the places where there are tapped holes or machines surfaces the chrome will stick. Also if they put to much on it will bubble up...and get rough like sand paper. Rich

now a days a lot of hard chrome plating is much more expensive due to hexavalent chrome fume exposure limits. the EPA rules in the USA
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my old company had wheels 18 feet diameter 5 feet wide and about 20 tons. They were plated overnight. That is the fumes were so bad that everybody went home for the day (no night shift) and when they came in in the morning they shut it off. In China i saw plating places where the walls were all garage doors and they could all be opened. Basically just a roof to keep the rain out of the plating tanks.
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hard chrome i believe was done for 2 reasons. it takes longer to wear away and it lowers the friction coefficient so items slide easier.

Just wondering.... How thick is the chrome on a BP? It can't be very much, or it would get uneven in a hurry...

I could not remember how thick they put it on, so i called Todd at Indianhead Plating and he said they flash chrome .0003" to .0005" on and he said they used a special fixture to get it down in the dovetails. He also said that many of the longtime rebuilders aren't sending them as much. I would guess that because many machines now have hardened ways, chrome plating ways is becoming obsolete. Todd did say he could still do them if you needed it done, but the do more shaft plating now. Rich

The chrome can be taken off with muriadic acid. This acid is also used to clean cement. It is a long process..
JOHN

As far as I know...chrome can not be scraped off.....I take it off with acid....then wash with water to neutralize the acid. I have never had one re chromed. I suggest to customers to let me put turcite on both sides of the saddle....and rescrape all the cast iron....

John Fahnestock
J&L Scraping Service

sidecar580 said:

As far as I know...chrome can not be scraped off.....I take it off with acid....then wash with water to neutralize the acid. I have never had one re chromed. I suggest to customers to let me put turcite on both sides of the saddle....and rescrape all the cast iron....

John Fahnestock
J&L Scraping Service

Click to expand...

Yup thats what I do also ... ive never rechromed one either.
Cheers Don

Hard chromed Bridgeports will outlast a non chromed machine by a factor of at least 3 to one if both are taken care of. I always thought it a terrible waste of money to purchase a machine without that option.
My very first CNC, a Series 1 BOSS 6 with the true CNC iron (18 x 12 travel) was flat worn out and I was broke. Ways were worn badly but not scored at all, ballscrews loose, thrustbearings loose, head in bad shape. Head was easy, after all I was working for Bridgeport. The ways I carefully examined and determined since the wear was in the middle of the ways I could lap the ends down to match. Yep, hand lapped them down with a silicone carbide stone. Yep, took over a month working on it almost every night. Reloaded the ballscrews with over sized balls, shimmed the thrust bearings and relocated the bearing brackets. Rescrapped the non chromed members in for contact and squareness. Rebuilt the entire lube system. Gutted the control, cleaned everything so it looked like new and got it running. Ran that machine for 2 years and I paid for a good used Bridgeport machining center cash to replace it.
Final accuracy when I was done was .0002 squareness per foot, less than 0.0002 backlash and it would hold 0.0005 all day. Purchased it for 500.00 and sold it 2 years later for 2500.00, still making excellent parts.
To give you an idea of how bad the chrome was worn, the center of the knee to saddle ways were mottled, half chrome and half iron. When I was done, the entire area matched the middle, including the dovetails. The top of the saddle looked the same. I was a lot younger back than, don't think I have it in me to do that today.

Bill

I made dams out of Modeling Clay and stripped mine with Muriatic Acid. The warmer the parts and Acid the faster it works. Be sure and neutralize acid with ammonia after rinsing with plenty of water . If not the acid keeps working , all though very slowly !

Dwayne