They can be recromed and GROUND. Both are expensive. Probably $500
for the chrome job, more if it is very thick. Old ways are usually
rescraped, replaned, or reground. Unless you have some special
application, re doing the existing surface without crome will last a
home shop several generations.
I just removed the chrome on a Sheldon lathe cross slide. The
chrome was put on real thick, on a long, very thin cross-section
piece. It warped .003" or more over 20 inches. Removing the chrome
allowed it to relax back to flat. Obviously, the chrome was flame-sprayed
onto the part, and the application of hot metal to one side only
caused the warp.
You can't scrape Chrome, I can tell you that. A carbide scraping blade
just bounces right over the stuff, without even leaving a scratch.
It can be ground, but it is hard stuff.
Given what I've seen with the Sheldon part, I'd be real careful with
any hard chrome application.
If you can't scrape chrome then how do the ways on machines like Bridgeports
with "chrome" ways get the scrape marks in them. Also are Bridgeport ways,
flame-sprayed or electroplated? I realize that I may be getting carried
away with perfection, but my Bridgeport ways, which appear to be chromed,
are worn in the middle so that the scrape marks are almost totally gone.
But, at the ends of the ways, the scrape marks are well defined. So I
would have to guess, without measuring, that there is a few thousandths of
sage or dip in the middle. I was wondering if one could electroplate the
chrome back in successively larger selective applications until the center
of the ways were back to the correct thickness. If it were possible to do
this, then the center would still have to be re-scraped.
Is this idea totally crazy?
What you see are "frosting" marks, not scraping. The tool is similar, but
the process is different and amount of metal removed is smaller.
Also are Bridgeport ways,
I believe they must be flame sprayed, or some similar process. Electroplating
is used on some small parts, but plating .003 to .005" of hard Chrome
would take a LONG time by a plating process.
I realize that I may be getting carried
That is a LOT of wear!
I'm afraid so. It could take days to put that much Chrome back on with
most processes. It would also be real hard to keep the plating process
selective with the whole piece dipped in a tank.
Note also that the inside of the dovetail will also be worn in a
similar way. And, the saddle will be worn with a matching convex.
The ways are cromed after they are scraped, that accounts for the
scrape marks apparently in the chrome. A rebuilder in out building
sends his knees and saddles out to be cromed. They electroplate them,
and just where they want it, so they must be able to isolate the area.
Since the crome surface is even, it does not throw off the scraping
accuracy, as it then only relates to the gib adjustment. Chrome
plating the ways is an expensive upgrade and used mostly where heavy
use is expected. It is usually accompanied by a ball screw upgrade
It just so happens that I have been checking into having the ways on one of
my lathes chromed.
The process takes two grindings, once before the chroming process and then
after the the ways are chromed. That in itself gets pretty expensive.
I was told that building up chrome can be done to some pretty heavy
thinknesses and that is without flame spraying.
The little lathe I want to have done has some pretty heavy wear right up by
the headstock which will probably take at least a .015-.020 grind to straighten
things out. Then chromed to a thickness of about .025 and then reground to
bring the bed back into exact factory specs. The estimate of cost was from
800.00 to 1000.00 depending on how much had to be ground off and the thinkness
of the chrome to bring the bedways back to factory specs.
Personally I am not going to have a lathe reground and NOT chromed. I realize
that this can be done but you also run into problems with the gearboxes and
also the gearrack under the saddle. I much prefer the "back to original" way of
doing things. Besides I would rather put some money into an old piece of
american iron than put a dime into a new piece of chinese junk.
Instead of chroming the bed to bring it back to the correct height, you can use
Moglice, a castable way liner material that had Molybdenum Disulfide (a solid
lubricant) to build up the carriage. I did this on my Sheldon 15" lathe
after hand-grinding the bed true. It works very well, and only cost me
about $150 for the materials. I used a bunch of brass-tip setscrews in
the carriage to pre-align the carriage to the bed and spindle before
applying the Moglice. It takes 24 Hrs to set, then you use the setscrews
to break the bond and it is ready to use. I did a little more scraping
on the Moglice to improve the alignment and contact area.
Moglice is available from Devitt Machinery at
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.