Bringing the Art of Scraping into the 21st Century?

[Oldmanandhistoy]

I’m not going to mention the techniques of bluing up a part as imho these will never change. Or even mention that bluing is an art in its self. This thread will only cover the uses of a hand scraper or not as the case maybe. My method will probably make my old grandfather turn in his grave (he was a scraping hand up until he retired) and the purists cringe into their boots.

A brief explanation about how my alternative method came about.

Trying to keep this as brief as possible; I recently bought a Chinese bench top mill. All in this tread and includes some brief posts on my scraping method (start at page 4 about scraping). XJ20 what do you think please?
As only to be expected with a Chinese mill it was in need of some serious scraping. So off I set scraping the ways of my machine with my old hand scraper (old file modified) and the usual other tools. It wasn’t until I got to scraping the ways of my column that I stopped to think “there has to be an easier way”. Added to the fact that I had a lot of bearing area to scrape was the fact that there is a 0.09mm (0.00354”) of bow in the column. So I sat and pondered “do I take this somewhere and have it skimmed on a surface grinder or just dig in and do it by hand”. Well the thought of taking it and the price got to me (tight Yorkshire man that I am) so how was I going to remove all that metal without loosing a week of my life. I then thought about the fact I had been using a Dremel type tool to remove some burrs on the castings so I put on a round belt sander type thing (see picture) and proceeded thrashing off metal off either end of my column after a quick blue so I could see where I was removing it. I realised very quickly I was removing metal far quicker and easier than I would have been with my scraper. So I stopped and wondered could this make my scraper obsolete? I went to the bench and picked up my X-Y saddle (already hand scraped) and blued it up on my surface plate. Very nervously to start I removed some of the blue (did a re scrape of the surface) and to cut this story short it worked a treat. Where before I had my surfaces within +/-0.005mm (0.0001968”) of each other I now cannot measure the error as my DTI pointer barely moves while all set up on my surface plate.

The hand scraper is not quite obsolete yet as the sanding bobbin is to large to get right under the dovetails but I have a plan. I remembered seeing some one with a narrow file sander (see here http://www.axminster.co.uk/product.a...file=1&jump=60 ) and know this will work as a scraper if the front drum is small enough to fit right under the dovetail. If I were doing a lot of this scraping (absolutely no plans to) I would look into modifying (if needed) the nose of the file sander but for a one off job I will probably just stick to my hand scraper to get where the sanding bobbin can not get.

This may all sound like crazy talk to the purists and all I will say is that with the right technique and a little practise IMHO I can do an equivalent job as the above average hand scraper as fast (if not faster), as accurate (if not more accurate) and far easier on the back so don’t knock it until you have tried it.

Before anybody decides to take a sander to their ways I would highly recommend a practice on an unimportant part of their casting as it is not as easy as it sounds. It requires a light touch (which varies as the job gets close to finished) and the tool at just the right angle or you will very quickly remove to much metal and spoil your bearing.

Ok guys get the out I got my asbestos suit on and what can’t speak can’t lie (that would be my X-Y axes saddle).

I’ll post some pictures of my saddle blued up if anyone is interested when I get a minuet?

John

EDIT: Please see post #41 Page 4 before reading the rest of this thread. :END EDIT

[mxtras]

I had to scrape a set of set precise ballnuts into a set of mounts here at work a few years ago and I used a sanding disc instead of a scraper - primarily due to convenience and time.

In my opinion it is the same priniciple - manually removing small amounts of material to achieve the desired results.

No flames from me....

Scott

[Oldmanandhistoy]

If anyone is interested in knowing more about scraping see this thread Way lapping, Scraping, Gib adjustment and Lock screws

John

[S_J_H]

John,
it sounds good to me. Infact I'll use that procedure when I do my rail risers.

Steve

[zephyr9900]

John, thank you for this post and your description of scraping your mill's ways. Having never done scraping, it has always seemed an almost mystical endeavor. You make it sound much more down-to-earth.

By the way, what's that wooden thing attached to your scraper? Is it something you add during the conversion from a file?

Best regards,

Randy

[Mcgyver]

like Scotts says, same principal. The other way is file. no one seems to say much about the humble file anymore but they have a tremendous ability to remove material! for roughing, press on the back of the file where you want to remove material - this can provide a lot control

Scraping is a valuable bench skill - anything that isn't flat will be distorted when clamped. So a casting or some precision items should have a reference datum formed by filling & scraping - this is where it comes in as a valuable bench-work skill

The ultimate move into the 20th century is a power scraper. Biax is the on to get, probably come up on ebay, bloody expensive new (are they still made?)

the one thing i can see is that hand scraping tends to have a self regulated depth of cut - when you are finishing with lighter strokes you don't accidentally take out a thou and a half....that might be a weakness of the dremel that deserves some experiment at least

imo its not an art or a guild or anything to be purist about. its a technique that through efforts like yours, more and more will realize is very useful around the shop (for a lot more than machine ways) and that is is not beyond them to get good results from...so i applaud your efforts

[Oldmanandhistoy]

Thanks to all that have replied to this thread it is appreciated especially from the experienced members.

I did think that this could have slipped down and off the page never to be seen again without reply. It is only now after my first efforts on my mill that I can really appreciate what my grandfather was trying to tell me nearly 28 yrs ago now. I really wish I had pushed him for more guidance when I had the chance, but such is life. I may at times seem over enthusiastic but now I have seen what can be archived it makes my mind boggle (I can’t get over the flatness of an AA (00) grade surface plate its mind blowing to me, is that sad? lol).

I’ve added some tips I have picked up so far form using my method in case anybody wants to give it a try.

First thing I did was to put the bobbin on the rotary tool without a sanding belt fitted. I switched on the tool and carefully rubbed the bobbin on a piece of sand paper to curve the rubber at the edge (front edge that will contact the metal) so that it would not gouge the metal. Not sure if this made any difference because of the stiffness of the belts.

For roughing I use new belts at what is speed 2 (it has 9 speeds keep it slow) on my tool, as they ware down but before they are completely shot I turn them around to use the other end. Then when both ends are getting quite blunt and clogged I remove it, put it to one side and replace with a new one. If they clog while still good I use the rubber belt cleaning block seen in the picture in the first post to refresh them.

At what I’ll call the middle stage I slow the tool down to its lowest setting and lighten my pressure on the belt. This gives you more control of the amount of material you are removing and helps prevent you taking too much at a time. I’ll keep using the belt, refreshing as necessary until they barely removing any metal and change for a new one at that stage only.

For the finishing stage I reuse all the worn belts, refreshing as I go. Now a very light touch is all that is needed. Never use new belts at this stage it will ruin all your hard work.

Keep the angle of the belt quite low but not so all the width of the belt is used, just the front edge.

To do wider surfaces it will require a narrow rotary tool like pictured, other wise the body will hit the material forcing you to increase the angle of the belt and would give poor results.

Hopefully that will be enough to tell you the basics the rest will only come with practise and experience. I have quickly gained a technique that works very well imo and am happy to work on my mill with confidence. I’m sure that others could do as I did which was to take the plunge and go very carefully to start but I would strongly advise starting on a scrap piece or a part of a casting that will not be used in the final bearings.

I am going to finish my mill using this method and am also going to retouch all the surfaces I scraped with my scraper. I have been considering doing a detailed description with picture of the whole job start to finish but am unsure if there would be enough interest to go to what would be a lot of trouble. If this might interest you please post and let me know. I think it would also be good if the big brains of the zone could asses my methods and point out any problems or just give advice to improve the over all process. I have gained a lot from this site and its generous members it would be nice to give something of value back. Or maybe I should write a book titled “Bringing the Art of Scraping into the 21st Century” and make some money? Nah I don’t think so lol.


John

[Oldmanandhistoy]

Originally Posted by ProtoTrains John, thank you for this post and your description of scraping your mill's ways. Having never done scraping, it has always seemed an almost mystical endeavor. You make it sound much more down-to-earth. By the way, what's that wooden thing attached to your scraper? Is it something you add during the conversion from a file? Best regards, Randy

Hi Randy,

No problem I just hope it helps others

Not quite sure what you are asking; the only wooden thing is the handle of the file.

John

[Oldmanandhistoy]

Mcgyver,

I have read some of the posts (more than once) on the thread I linked to for more information about scraping. You generously supplied a lot of the information so I would like to say a personal thank you to you for that. It was that thread that encouraged me to have a go at the task and the fact I have the camelback straight edge my grandfather gave me.

Originally Posted by Mcgyver the one thing i can see is that hand scraping tends to have a self regulated depth of cut - when you are finishing with lighter strokes you don't accidentally take out a thou and a half....that might be a weakness of the dremel that deserves some experiment at least

With this comment in mind and the fact I appreciate your input.

While reading through the thread I came across this statement.

Originally Posted by IndHobby A scraped surface is accurate to a few tenths. (0.0001”) or so.

Just to be sure of what this statement means; is it describing the maximum difference between the highest points and the lowest points on a surface?

To your knowledge is this statement correct?

If not what figure would you use in the statement?

Would that be the best possible accuracy achievable using a hand scraper period?

The best accuracy that could be expected within a reasonable amount of time?

I maybe pushing my luck but would you briefly explain the benefits of scraped bearing on a milling machine. Comparing it to a bearing finished on a surface grinder with a few scrapes using a power scraper (no bluing involved)?

What would be the recommended difference between the high and low points on a milling machines ways (thinking about the oil reservoir effect)?

It may or may not be a big deal (depending on your answers to the figure in question) but I have achieved a higher accuracy on one of the ways of my X-Y saddle using the dremel. I know I could do better but would be unable to measure my results with the DTI I have. I won’t get excited about this until you or another suitable skilled member gives their opinions/answers to my question.

One last point; I’m not looking for bragging rights I am genuinely interested in the skill of scraping and its benefits. I would also be very interested to know if my method is at least equal to if not better than using a hand scraper.

John

[Mcgyver]

I recall being told by an old hand that when finish scraping (ie light, small cuts) the depth of cut typically is in the neighborhood of a tenth, so that may be where it comes from

John thanks for the kind words - but i want to emphasize that old expression "the different between a layperson and expert is 5%". I happily share what i know but you'll get us both into trouble if you take it as being some deep expertise or authority on the matter. I'm no where near qualified to be the scraping expert....in fact by the time you finish the mill i think you're going to get to wear that hat around here .

To your surface grinder vs scraping question, don't know if there is a big advantage once the job is done. Some even push back on the value of the oil reservoir benefit. still, its one big honking surface grinder to take the main castings of a mill - if you're not talking production, grinding might be precluded just because the equipment isn't available. I guess the other aspect is the nature of scraping mating parts. A is done to a reference and B is done A. for example, to surface grind dovetails that's going to take some careful work to keep the angles perfect so they mate. when scraping, we don't care, the exact angle doesn't matter, so long as the parts are the same. sort of like making model T's requires standardization and production but for onesy machine reconditioning the hand fit nature of scraping might be more efficient.

[Oldmanandhistoy]

Originally Posted by Mcgyver I recall being told by an old hand that when finish scraping (ie light, small cuts) the depth of cut typically is in the neighborhood of a tenth, so that may be where it comes from John thanks for the kind words - but i want to emphasize that old expression "the different between a layperson and expert is 5%". I happily share what i know but you'll get us both into trouble if you take it as being some deep expertise or authority on the matter. I'm no where near qualified to be the scraping expert....in fact by the time you finish the mill i think you're going to get to wear that hat around here . To your surface grinder vs scraping question, don't know if there is a big advantage once the job is done. Some even push back on the value of the oil reservoir benefit. still, its one big honking surface grinder to take the main castings of a mill - if you're not talking production, grinding might be precluded just because the equipment isn't available. I guess the other aspect is the nature of scraping mating parts. A is done to a reference and B is done A. for example, to surface grind dovetails that's going to take some careful work to keep the angles perfect so they mate. when scraping, we don't care, the exact angle doesn't matter, so long as the parts are the same. sort of like making model T's requires standardization and production but for onesy machine reconditioning the hand fit nature of scraping might be more efficient.

I will probably have to buy the book that was mentioned in the other thread. It’s a shame to think out of 50,000 odd members none are skilled in scraping. For the sake of old mills/lathes needing re scraping and diy improvers with these Chinese mills it is a skill that should not be lost and more widely used imho. I’ve spent some time digging around on the net for information but it is thin on the ground to say the least.

Thanks any way for helping me getting started.

As for being an expert, is there any point? One thing for sure even with my very limited knowledge my cheap Chinese mill will be a far better machine for my efforts.

Regards,
John

If anyone reading this has the book (they will know which book I am talking about) it would be excellent if they can chip in here with some information.

EDIT :You threw me a bit there with your edit

One thing I would like to say about the scraped vs grinded surface. I have tested the effects of “sticktion” between the two and a scraped surface is far superior in eliminating/reducing this effect. END EDIT

[JROM]

I can't believe that guy who didn't know what a file handle was!!!
Does this mean that he has been using files without handles forever?
LOL what is the world coming too?