|Michael Gilligan||28/07/2021 08:47:20|
20108 forum posts
To quote from a post I made in 2013:
This may be the most important Engineering book you ever read.
It discusses the very foundation of Precision Engineering.
... It's short, but very sweet.
Text commencing on page 5 describes the process:
Edited By Michael Gilligan on 28/07/2021 08:50:14
|Martin Kyte||28/07/2021 08:50:01|
2728 forum posts
I know there is a desire to see nice shiny surfaces but I wonder how unserviceable your surface plates actually are. Have a go at removing the corrosion chemically (Arc Euro do stuff for this) and then check one plate against the other. Once they are cleaned up I would be surprised if they are in any way unfit for service.
Incidentally does anyone use a wax on their surface plates to reduce friction and protect from corrosion?
|Phill Spowart||02/08/2021 16:40:39|
|28 forum posts|
Been away for a few days, thankyou for the replies.
Ultimately, I'm hoping to learn scraping so I can renovate machine tools, hence the desire for high accuracy. The plates I have are just what has fallen into my lap over the years. The surface rust and finish on both is very varied, which makes getting an even coverage of blue dye much harder-and I don't have the greatest eye for it to start with. Not trusting them fully is a massive hindrance. I plan getting a proper granite table eventually, but I need to build a home for it first, currently said home is a muddy hole in my garden and piles of bricks looted out of skips.
This was very much an "on the off-chance post"-I'd feel pretty daft if it turned out a master machine rebuilder lived 5 minutes away AFTER I'd bludgeoned my way through learning it on my own.
8512 forum posts
Don't let me put you off Phil, but it takes a long time to remove metal by scraping as needed to restore a badly worn machine. For example, lathe beds tend to wear badly close to the chuck where the saddle spends most of its time make it necessary to remove a lot of unworn metal to restore flatness. Unlikely to pay off unless scraping is to be your main hobby! There's also an alternative technique for putting worn surfaces back with goo,
Scraping as a way of producing an original flat surface is rarely done today. Instead laboratory flat surfaces are produced by grinding, or perhaps a plane. The machines are laser guided and capable of producing highly accurate surfaces with minimal labour. Surface plates, starting at about £60 are cheaper than the tables needed to support them, and I feel there's not much point in a home workshop going the full Monty on a plate unless the same effort is put into supporting it correctly! Home workshops are full of dinged, out of tolerance, bent surface plates, well out of tolerance by professional standards but good enough for ordinary use. Float glass plate was once recommended as a cheap substitute.
Scraping has two main purposes today, one of them dishonest! Scraping being associated with quality, scrape marks are often added to create the illusion a piece of equipment is better than it actually is. (Same was done in the past,) More usefully, scraping is often added to provide a key to hold oil and improve lubrication. Neither of these two forms of scraping improve flatness.
Where scraping is useful for repair work is on worn plain bearings, especially if they've suffered a lube failure. Plenty of machines have roller bearings, which are just replaced.
There's always a balance between getting on with the job by flashing cash and saving money by DIY. Though I see the attraction I've decided scraping isn't worth my time. Would a renovator comment please; how much scraping is done during a typical rebuild? I get the impression time-consuming bulk flattening is usually outsourced to a professional grinding company, so the renovator can concentrate on the the machine's other needs. I may be wrong!
|Pete Rimmer||02/08/2021 21:37:00|
|1219 forum posts|
For a small lathe like a myford you could readily scrape 8-10 thou off a bed to bring the rest down to the level of the most worn section. It's a lot of work but doable especially on a flat ways bed which is quite simple to control the progress. My first scraping project was a ML7 bed with 7 thou wear in the front way which I scraped out by hand.
A commercial rebuilder would not consider it though unless it was such a size or shape and of significant value/usefulness that there was no option but to scrape out any wear. They would grind or plane the bed and then scrape the last thou or less.
Bear in mind that whatever wear you have in the bedway, it'll be much more on the underside of the saddle, probably x2. It will also be mostly at the leading and trailing edges and least in the middle causing the saddle to rock on the high spot. Sometimes you can do more for a distressed machine by scraping the saddle rather than the bed.
1678 forum posts
HR Lamb, will likely be able to refurbish your plate(s), but some distance from you and probably expensive if you wanted them to do the scraping as well.
This video (first one in a series) isn't me, but gave me a bit of inspiration to tackle to job during the first lockdown.
Edited By peak4 on 03/08/2021 02:19:10
|Kiwi Bloke||03/08/2021 07:36:49|
|654 forum posts|
Dave, I have to disagree.
Perhaps you're right that scraping in manufacturing is now relatively rare, but the machine tool reconditioning industry, and better metrology equipment manufacturers certainly still do a lot of scraping. Wyler are particularly proud of their scraped finishes - and it's for accuracy, not show!
The dishonest scraping for bling has become almost universal in dubious-quality oriental equipment. Oil-pocket scraping is somewhat contentious, but still practiced. The divots are deliberately much deeper than a scratch-keyed surface irregularity would be.
The great advantages of scraping is that there is but one step between master gauge and workpiece, it can be done by an enthusiastic amateur with minimal equipment, large workpieces can be accommodated, and the accuracy achievable depends only on master gauge and enthusiasm. It's really the only practicable and affordable way to go. As has been said already, a lot of metal can be scraped away, should it be necessary, but it's hard, slow work.
Perhaps it's obvious that I'm a scraping enthusiast - there's quite a lot of us about! In the future, I'll need to recondition a few machines. By then, I'll be less enthusiastic about all the hard physical work it will involve, so will probably buy a BIAX power scraper. Huge expense, but you can't take it with you...
|Dave S||03/08/2021 18:22:17|
|363 forum posts|
For a machine build recently I did a bit of scraping - It avoided a couple of rather dubious setups on a surface grinder, as my mill is large enough to rough out the areas in 1 setup.
Before I did that I did a little practice piece, on a gash 2" x7" wood plane. This is the end result:
I only had to knock a few thou off the plane, and I was only trying to get flat, not flat and in alignment to something else.
I have a new granite plate which I used as the reference.
The biggest thing that helped with consistency was buying an ink roller to spread the blue out. Before that I was using a wadded up cotton pad, which was very hard to get consistent blue spreading. I also ended up lookng like a smurf a lot...
For a scraper I used a chunk of power hacksaw blade clamped to a handle made from a wooden file handle and some scrapbinium:
Scraping is very relaxing, although physical work - it has a natural rhythm and work proceeds at a leisurely pace. I think the plane took about 4 or 5 evenings of an hour or two, but I wasnt rushing and I was learning as I went. The machine build needed a couple of weeks of evenings IIRC, bu then I did manage to mill it a bit wonky, so had to correct the geometry a bit as I went, as well as making the 2 dovetails fit together.
There are a few more photos in the planar plane album.
How bad are the surfaces of the plates you want to sort out? The odd pit wont matter to much - as long as there are not loads of them.
Editied to add: I have a mill that is large enough to face off your plates in a single setup (TOS FNK-25) Im based in Castle Donington if that helps. They wont be meterology flat, but they will be close and clean.
Edited By Dave S on 03/08/2021 18:24:11
|Phill Spowart||03/08/2021 18:34:09|
|28 forum posts|
That herbert grinder looks excellent, that's the sort of work I plan tackling. Some bits will have to be farmed out, but the more I can do the better.
I'll get a roller, getting the blue even is something I'm struggling with. I did a very, very small amount of blueing work as an apprentice, the instructor there was of the opinion that if you can see anything useful in the blue at all, it's too much :O This is not helped by the variable finish of the plate, some areas have black oxide in the pitting bottoms and it makes judging the amount of blue very difficult.
|Dave S||03/08/2021 18:59:50|
|363 forum posts|
I bought these from Amazon (hope the link isn’t against the rules)
They work fine with my Stuart’s blue.
1678 forum posts
No pictures of mine, but I made them out of rubber paper feed rollers from a scrap printer/photocopier.
|Kiwi Bloke||04/08/2021 09:50:50|
|654 forum posts|
Finally got around to looking at the Herbert surface grinder series. Excellent treatise on the art of scraping machines!
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