Great Scraping Videos

[lazlo]

Here are 3 short hand-scraping videos from a gentleman named Nick Mueller on German YouTube:

"Don't use a Chinese Tombstone."

Handscraping: Preparing the Surface Plate

Handscraping: Sharpening

Scraping in a lathe's bed

[Your Old Dog]

Thanks lazlo, first time I've seen the process.

[GrahamC]

Lazlo, thanks for posting. Learned somethine new today.

cheers, Graham in Ottawa Canada

[laddy]

Man, That does not look like fun! Wouldn't it be great to use a random orbital sander and have the job done in minutes!!!!!

[rantbot]

Scraping in a lathe's bed

Note that, despite what it says at the end, the goal is not to "scrap" the part.

[Charles Ping]

Nick's written english is usually very good - odd to make a mistake like "scrap"

[2ManyHobbies]

Man, That does not look like fun! Wouldn't it be great to use a random orbital sander and have the job done in minutes!!!!!

Heh, new this year, lathes that produce "organic" looking work.
Little bulge here, little taper there, and between 16" and 22" you can even turn Morse using only the lead screw. *TWITCH*

[J Tiers]

Interesting, but I am not so sure about all of that...... at least for the first part.

I am certainly no expert, but I understand the geometry, and the process..... and have spent many hours scraping....

The marking was quite heavy, maybe mostly for the video...... a lighter marking shows up the spots better, visually, and does not make them seem big.

The general bearing was reasonably good, spots per sq inch (!) although somewhat uneven. That surface really may not have needed scraped for bearing, which appeared to be the first part.... But then, that particular scraping would have merely moved-around the spots, since he didn't 'split" any, and scraped pretty much all over.

Then also, no de-burring shown after scraping and cleaning the part..... He should have rubbed over a fine stone or burr-file to knock down the fins and burrs, or it won't mark-up right.

The adjustment of tilt..... He could have just started off by "shoveling" off the high side, without marking, because it appeared there was a considerable 'step", unless that was in very small increments on the dial. It takes a LOT of effort to take down a surface even 1 thou (.04mm).

Then also, he absolutely left one end alone, instead of scraping heavy then lighter and finally leaving the edge. So there should be a "knuckle" where he k=left off scraping. Maybe he wanted to correct the tilt and then scrape it flat, but I am not so sure that works quite.

But, certainly shows the process.....

[Bruce Griffing]

J Tiers - I agree with your comments. He also did not demonstrate the fact that each pass of scraping should be done at 90 degrees to the last pass. The method that Forrest demonstrated for sharpening the scraper is easier and does not depend so much on a steady hand. We just used a wooden block cut to the required angle and held the scraper flat against the block and against the wheel. Pretty easy to set up and do.

[lazlo]

The marking was quite heavy, maybe mostly for the video...... a lighter marking shows up the spots better, visually, and does not make them seem big.

Nick's mark-up is about as heavy as Mike Morgan does in his video, and less than Rich King does in his video.

The adjustment of tilt....

Then also, he absolutely left one end alone, instead of scraping heavy then lighter and finally leaving the edge. So there should be a "knuckle" where he k=left off scraping. Maybe he wanted to correct the tilt and then scrape it flat, but I am not so sure that works quite.

That's actually the textbook method of correcting for tilt: you scrape the high side flat in several overlapping passes, and then re-scrape the whole surface, and re-check for flatness.

The Los Alamos scraping book that someone posted on PracticalMachinist goes even further: he makes "zones": several successive plateaus that he scrapes flat, and then when he thinks he has the geometry correct, he scrapes the whole area flat.

[lazlo]

Several folks have asked by private message for the Lawrence Livermore scraping book. I'm not sure if this is proper Netiquette, but here is Jarno Seven's post from PracticalMachnist which contains the links with the Lawrence Livermore Laboratory scraping guide. I've edited out the .PDF's which are hosted on his private web page. If you want to download the document, click over to PracticalMachinist.

The "Step Cut" process of correcting geometry like Nick Mueller is doing, by scraping one or more plateaus on the high side, is described on page 23 (the second .PDF download):

http://www.practicalmachinist.com/vb/showpost.php?p=681916&postcount=38

08-03-2007, 12:53 AM
Jarno Seven

Regarding books on scraping, earlier in this thread both "Machine Tool Reconditioning & Applications of Hand Scraping" and "Foundations of Mechanical Accuracy" were mentioned and, of course are both outstanding books.

The booklet that is linked to below in PDF format is titled simply "The Art of Hand Scraping", by Robert Wade. It was prepared in 1981 for training purposes at Lawrence Livermore Laboratory, and I do not believe that it is a copyrighted work.

It is concise and I felt very descriptive of the methods you would have seen in use if you were to see high accuracy machine tools being built during that era.

I had to scan the booklet in three sections to get it to feed through my scanner. Total is 46 pages.

There is no substitute for having an accomplished scraper show you their technique, however if this is not an option, the guidance provided may help get you started on the correct path.

[aboard_epsilon]

how about you guys find all links to scraping hints

put them here and i will combine them all the webpages into readable pdf...
which someone can host

here's number 1

http://www.bugattirevue.com/revue23/scrape.htm

all the best......markj

[alsinaj]

Carbide for scraping

Does anyone know what grade carbide is needed for scraping? Carbide blades from Dapra work great, but they are expensive. I tried several kinds of generic rectangular carbide inserts, but none would hold an edge. Under magnification I could see that the edge was chipped, even after just a few strokes.

[J Tiers]

Laslo,

Maybe so about the tilt, but I do it the other way, and find that it works well.

As far as the marking, whatever..... for the video was one choice, and may be the reason..... For very precise work the marking is with a medium that is lighter than condensed breath........ I tried it, but don't need that sort of precision.

The heavy marking I have tried was just not helpful....... Then again, that may be a different medium, hi-spot that heavy smears out marks for me.

[Forrest Addy]

alsinaj

The grade I've always used is C2 which is a straight unalloyed tungsten carbide. The generic C2 carbide is available in a wide rangse fo sizes from MSC's "unground carbide blanks". I use 3/32 x 1/4 x 1 blanks for my home made scrapers. I think I've made over a hundred of them. I silver braze the egde of the carbide on the end of the scraper shank and grind and lap from there. It pays to flatten and stone the carbide faces to a near mirror finish before brazing.

MSC #: 04120754

or look at MSC catalog page 723 or this PDF:

http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=723&PARTPG=GSDRVSM&PMT4NO=43233058&PMITEM=04157061&PMCTLG=00&PMT4TP=*LTIP

Correcting an alignment by selecticve scraping involves a few minor tricks. One is to determine the low corner(s). The other is to step scrape a slope to make the correction. If you know the true angle of the correction you can establish a slope by calculation. I prefer to scrape out small hollows at the very corners to provide stopping points. I calculate the depth for the correction at each corner and use a depth mike to deternine their depths. I scrape across the slope in a series of parallel cuts leaving a "shingle." Then I scrape the surface down until the hollows clean up. Follow the scraping with a surface plate or other accurate reference so you don't get undulations in the surface.

I've said it before: correcting the alignments of a machine tool's elements is a problem of the simultaneous solution of several unknowns and knowing where to start. Many start with the milling machine's table or the compound slide of a lathe. Wrong. Wrong. Wrong. You start with the immovable reference - the spindle axis - and bring the next fixed way system into alignment with it: the column ways on the mill or the bed ways on the lathe respectively. Then scrape and stack axis element on axis element until you run out and every element is in alignment, the way bearings are linear, mutually square, properly fitted, and the gibs fitted and assembled.

The thickness of the transfer medium (marking medium) is also a variable. Before you start you cross scrape the worn surface to 80% clean up leaving a checker board of witness marks. Only then do you apply the scraped surface to the reference. Put it on thick enough to cover but thin enough to see the teexture of the plate through it. Use a ink roller (burin).

Well, I'm gonna rewrite Connelly's RMC if I'm not careful. Scraping takes hours and days. Target fixation is an inevitable hazard. If the scraping work not gone about right a neophyte scraper hand can go a long ways down the wrong path before he discovers he's lost. What I'm trying to say is: plan your work then work your plan. And do it in writing.