This is not the usual 'which is better - box or linear' question.
Its simple really.
I've heard several people say that box ways are 'hand scraped' ????
Whats the meaning here ? To me they look to be surface ground and then simply receive turcite coating.
It just seems that any operation where actual manual work other than assembly is concerned, will surely result in inaccuracies ?
Am I way off the mark ? (like the pun ?)
Look forward to any info.
When they use box ways, the scraping takes place on the gibs and the turcite on the saddle side of the way. This is a tediose and long prossess that alot of manufatuers have gone away from. On a C frame VMC, the link between the collum and the bed are usualy hand scraped, and on a linier way machine, under the linier ways are sometimes scraped in.
The SOP in most machines anymore is toward " cheats". Case in point, a Cincinnati Milacron Sabre 1500 VMC, 60 x 30 x 30, large and formidable looking. The column is sitting on a Moglice pad instead of being machined and hand scraped for alignment. I have had to break columns loose, clean out the moglice, and reshim the column for alignment on this machine. I rebuilt Toyoda HMC. Linear ways, big devils, THK HS55R's and lots of them on a small travel machine. Where the bearing trucks mounted were hand scraped for fit, no shims on that machine. Box ways to be deadly accurate need to be scraped on at least one side. The ways on a bridgeport are scraped, as they are on a Devleig. A lot of " box way" machines merely have ground ways, and as long as accuracy is maintained, think of it like a linear rail, they are ground too. Unfortunately Linear rails unbolt and most box ways don't, so if you have to rework a hardened box way, its a s**** job in the belly of the machine for weeks.
It just seems that any operation where actual manual work other than assembly is concerned, will surely result in inaccuracies
that's a flawed statement which assumes there are no craftsmen, that people are all idiot sheep. and robots are superior and deserve to rule the world as our rightfull masters.
I'd prefer to think that there WILL be innacuracies of all sorts, and that GOOD PEOPLE will find and fix them. wheras a robot will just keep doing it's thing, whatever that is. They cant be programmed to find or fix everything.
here try this angle:
#1 you desigh a machine such that monkeys can just assemble it. and your dumb monkey labor force is to dumb and underpaid to recognixe any problems, fix, or even CARE. but hey it's cheap, right!
#2 you design a machine that requires craftsmen to "fit" it. and your highly skilled and long experienced workforc knows where to look and how to fix and actually cares. but hey you might actually have to pay them!
there is money im both markets.
"It just seems that any operation where actual manual work other than assembly is concerned, will surely result in inaccuracies ?"
Ya this is not a true statement. Look at a Yasda or Dixi. Both are hand assembled and hand scraped, and are considered to be very accurate machines. On the Yasda, even the pallets hand scraped.
I'm not disputing the fact that there are lots of skilled workforces out there but I'd really not even considered a precision peice of machining equipment requiring manual work other than assembly. If your aiming for positional accuracy of around 3 / 5 microns then it wont take much to throw that out.
So what does the term 'scrape' refer to ?
Please pardon my lack of knowledge on this but I am learning......
Is this a proceedure using a type of oil stone ?
In relation to that Willie said.... - so your in the belly of a machine for weeks scraping the ways... how do you know your finished scraping ?
Does this mean that ways that have a plastic plug in the centre every 3 inches where not hand scraped ?
Thanks for the replies so far, very informative.
Hand scraping is an accurizing process. I can't say who pioneered it but Pratt and Whitney is a likely source. Scraping uses a tool looking somewhat like a hardened steel putty knife to " scrape away " a small amount of metal to acheive a precision surface. The amount scraped and where from is determined by spotting with precision straight edges and prussian blue. Alignment is checked via several methods, but I assure you the Moore Jig grinder that held microns in WW2 was all scraped box way. Do a search in general new on scraping seminars.... contact Mr. Forest Addy for a master's explanation.
yep and i think you might well find that whilst a grinder may make a part a few mm long very accurate, thats only because its ridding along a lot larger length of hand leveled - straightened surfaces, scraping like a lot of good ideas is a simple process, find the high spots and remove them, then do it again and again. eventualy you end up with a very flat surface, well into the micron range of accuracys but hell oil films start to come into play there too!
There's a little video on the bottom right of the Kitamura website that shows some clips of a guy performing some hand scraping.
Round 'bout 10 years ago, I witnessed 2 Romanian men hand scrape a linear 'V' way on a large Waldrich way grinder. 2 heads-1 180º adjustable, 40'+ bed travel. Prior to re-scrape, there was about -.0015 diff from front to back. After re-scrape, a laser transom measured -.0004 diff after a clean-up grind on a 40' lathe bed. Scraping IS an ART. The scrapes also aid in lubrication.
my cousin Bill Large hand scraped everything in his shop.
in 1973 he got a brand new Bridgeport and immediately dissassembled it and scraped it in to suit himself.
he was certified by the Navy and could hold .0002" flatness over 48" and he had several masters and yes there was a 50" master on hand to gage against among others.
the key, according to Bill, was to get comfortable and when you were done with a line move your feet only the amount you wanted to space the divots.
yes indeed scraping is an art if not black magic...jim