PDA

View Full Version : What does Chrome Ways do for a Mill's Durability?



debequem
12-10-2003, 06:33 PM
I noticed that some Bridgeports have chrome ways versus simply hardened and ground ways.

How much better or resistant to wear will chrome ways be?

Is there a way to judge the wear on a chrome way visually?

Marv

Doc Nickel
12-10-2003, 07:05 PM
It is my impression that chrome is quite hard. While even "hardened and ground" cast iron is still just cast iron.

In other words, chrome is an easy way to make the wear surfaces considerably harder, without having to fiddle with the casting alloy or spot-heat-treatments of the finished casting.

Doc.

Evan
12-10-2003, 09:25 PM
There are two kinds of chrome plating, for appearance called cosmetic chrome and hard chrome, for durability. Cosmetic chrome is usually a very thin coat of chrome over nickel plate which is usually over copper. It adds essentially nothing to wear resistance. Hard chrome is much thicker, up to .004 and is more gray than shiny. It is harder than even carburized or case hardened steel. It does have disadvantages, especially applied over cast iron. It tends to microcrack and may chip or flake off the surface. Also, the plating process for hard chrome takes a long time and can result in significant hydrogen embrittlement of the metal. It would be unlikely for hard chrome ways to be worn through before the rest is toast. Chrome has extremely low friction against other metals.

LWJ33
12-10-2003, 11:06 PM
My J-head B'port serial#37xxx has Tibon hard chrome ways. Don't know much about its former life but, the frosting is still clearly visible on the ways. I've had it since 1987.

JIM

------------------

GM69camaro
12-10-2003, 11:48 PM
Isn't that the same chrome plating that Kawasaki uses on their two stroke dirt bike cylinders? Electoplating? That is why they always said not to bore the cylinder. The plating must keep the cylinder from wearing, especially around the ports.

Thrud
12-11-2003, 02:02 AM
Marv
If it has chromed ways and it looks badly worn - run away - fast. BP's Chromed ways hold up very well even when abused, so if they look like ****...

Peter S
12-11-2003, 06:27 AM
Bridgeports hard chrome is 70 Rockwell C, which is extremely hard, so very wear resistant. It is a .002" deposit and becomes an intergral part of the casting. It is porous (holds lubricant) and has an extremely low coefficient of friction. Also good corrosion resistance.
If that sounds like an advertisement, those points come from a Bridgeport catalogue!

You won't be able to see some of the chrome surfaces without dismantling, eg, the top of the crosslide and the back of the knee, plus the gibs could be chromed too.

Each hardchromed face slides against a un-chromed cast iron surface, so you can still find wear, especially if the machine has suffered from air gun assault driving swarf up under the wipers (and no doubt if the machine hasn't been lubricated as required).

Hard chrome was a particularly recommended on Bridgeports fitted with tracer control, I know why, because a place where I worked would leave the Bridgeport running all day and night unattended while doing a big contour tracing job.

debequem
12-11-2003, 08:57 AM
If I read that right, it sounds like having chrome ways is a bit of an insurance policy with respect to gauging wear on the ways.

It sounds like the chrome ways have much less wear and your chances of getting a worn clunker are reduced.

Correct?

On the other hand, the reciprical parts that slide on the ways may still wea, but you can't see it?

Marv

Thrud
12-12-2003, 06:11 AM
Marv
A quick look at the chrome will tell much, if is is buggered - run. You can look the machine over and operate the controls - a machine with little wear will be smooth through the complete range of travel, some spots might have less resistance - hence more wear.

Check the bed - if it looks in good shape it was probably well taken care of. If it has cuts and gouges in it, pock marks and drill holes, worry a little. use a straight edge to see if any of the t-slots have been pulled up (a sign of over tightening) look for signs of strees in the slots from t-bolts and bolt heads. I would not consider a machine with a severly abused bed. Check the spindle for obvious damage (signs of shanks spinning or frittering).

Ragarsed Raglan
12-12-2003, 09:08 AM
Marv,

I'd second that post of Thrud's. Get a feel for how the machine has been treated, a tidy table, drive peg still in place in the R8 socket, and the general 'feel for the machine' of the previous operators needs to be gauged.

I once bought a milling machine for a very simple reason, it was in a close down auction and the table and exposed ways were greased up. I figured that the operator ~ despite walking down the road ~ loved his machine that much he wanted to protect it. I respected that, I knew it would be a damn good machine.

It was, and still is a fantastic mill!

RR

spope14
12-13-2003, 12:47 AM
Six Bridgies in my shop. Two bought Dec 1992, the rest rebuilt summer 1993. The two new ones have the chrone ways, the rebuilts were re-scraped, new screws and such, heads done.

Oil each one regular with th one shot, and also clean the ways with rags and oil the ways with way lube and run the table.

The two chrome machines, just now starting to show a bit of wear. the other four, starting to consider a re-scrape, one worn quite a bit.

Many old timers - I have two in my night class - swear against the chrome ways - until I showed them the difference in feel and wear. They know my re-scraper who dod the original job, he IS the best in New England, so this is not his work at question.

Agreed finally, the chrome ways are the way to go.

docsteve66
12-13-2003, 03:37 PM
This sound very hokey, but we used to chrome plate aircraft parts for wear resistance. Right out of electroplate, the test was put DUCT TAPE in the parts a few seconds. rub it down well and peel by lifting straight up. If the chrome adhered, the plate jab was ok and sent on for further work and final acceptance test.

The above is observed fact. The following is theory that I have not tried.Seems that chrome DOES NOT adhere well over certain materials, though it wears well if not subjected to point loads. If I were looking at chromed ways, I would try the Duct tape thing, if chrome peeled, I'd think hard before purchase or using.

Evan
12-13-2003, 03:42 PM
Steve,

Not hokey at all. Hard chrome develops millions of tiny micro cracks from the top to the bottom of the layer. This is part of what make it work as these cracks hold oil. Hard chrome is actually porous. However, it does not adhere well to some materials, especially cast iron.