Questions about scrapers

macardoso

H-M Supporter - Silver Member
H-M Supporter - Silver Member
Joined
Mar 26, 2018
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I am completely new to scraping. I have never really scraped a surface but I understand the high level concepts. I am not trying to fully invest myself into learning all the tiny details, nor do I expect to have many projects that require scraping. With that being said, I'd like to have the ability to do a small amount of scraping to improve the fit and function of the machine tools that I own. They are all imports and not worth the effort to fully scrape in the machine, but I think a few passes on the various surfaces would make a dramatic difference in how the parts fit together.

My questions are:
  1. I've seen Sandvik, Biax, and Anderson scrapers for sale but they are large and fairly expensive. Are there any smaller sub-$100 scrapers for things like gibs and touchups that you could recommend. Maybe one day I'll take the leap and get all the scraping essentials, but for now having something to do some touchup would be great. I'm using a file right now, but I think it is a far cry from working as well as a real scraper.
  2. Can anyone provide a reference for how a blade should be ground? I have been using the end of a file to do some trial scraping but I find that it wants to skim and burnish the surface much more than it wants to cut. This is especially true of a positive rake. I can seem to get the negative rake tool to bite very slightly into the cast iron.
 
Below is a design and plans for a generic scraper by Keith Rucker. The drawing below is page 1 of 6. It can hold Biax tooling or Sandvik inserts, or other tools of the same thickness. It can be modified to meet your needs. I made two of them. It works every bit as well as a store bought one, and is relatively easy to make. Add a file handle or other push device of your choice. At some point I will be milling some relief into the shank to make it a bit less stiff.
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Attachments

  • Keith Rucker hand scraper design.pdf
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Wow. Thanks! That's perfect. I'm sure I have enough material on hand to make this.

What about the inserts? Are they all a standard size and grade or do they vary as much as lathe inserts? Any special grinding requirements?
 
Many of us find that learning scraping by ourselves does not really give good results. I can vouch for that. It seems that most of us need some amount of mentoring to get the concepts and techniques down well enough to do decent work. I highly recommend that you find a mentor and/or take a Richard King class if you are interested in scraping machines, surface plates, and other tooling. If not, you may very well do more harm than good. My scraping sucked, even after I had a couple sessions of mentor support from a H-M member who understood scraping well. On about day 3 of Richard King's class, something clicked and I started getting quite acceptable results. Part of that was immersion with a group and a master instructor, and part of it was working hard at it all day for multiple days. I now consider myself barely competent to work on stuff that really matters.
 
Wow. Thanks! That's perfect. I'm sure I have enough material on hand to make this.

What about the inserts? Are they all a standard size and grade or do they vary as much as lathe inserts? Any special grinding requirements?
Sandvik inserts work perfectly with that tool. They are available from eBay, but the prices keep going up and up. They are very high quality carbide, but need reshaping for scraping before using them. The 25x25mm (1x1") ones work well for ordinary work on larger surfaces. It takes a carbide grinder of some sort to shape them, and a lapping setup to finish them for use. It takes some knowledge to purchase, shape, lap, and use generic carbide blanks.
 
I'd love the opportunity to learn formally, but I can't justify the expense of the Richard King scraping class as much as I'd love to go. Hopefully I might be able find someone willing to mentor. To start off, I am hoping that I could (for a small expense) get enough of a tool and skill set to simply clean up the substantially crappy ways of my machines. I don't expect to generate perfect alignment or bearing surfaces, but at least going from 2 or 3 points of contact up to maybe 30-40% would be a wonderful improvement. I won't venture any further than that as like you said, I don't want to do more harm than good.
 
One more thing. YouTube videos on how to scrape are often put up by people with no clue what they are doing. Well more than half of them. As a novice, you will be totally unable to discern what is good technique and advice, and what is not.
 
One more thing. YouTube videos on how to scrape are often put up by people with no clue what they are doing. Well more than half of them. As a novice, you will be totally unable to discern what is good technique and advice, and what is not.


Good advice. I've watched many of them and haven't seen a difference...
 
I made a crude scraping tool by brazing a broken carbide insert onto a piece of thin (1/8 - 3/32") 1/2" wide scrap with a file handle on the end. I roughed out the shape of the cutting edge on the grinder and honed it with diamond hone. Its not the most ergonomic, but it works.
 
My first scraping tools were made from mill files that I ground the teeth off of, then heated and forged down to a thin edge and re hardened and ground to a working edge, they worked fine, but dulled much sooner than carbide, but were easily re sharpened with an oil stone. when I apprenticed, the shop had Sandvik scrapers, and I made one of them my own, that was nearly 50 years ago --- and it still works just fine, but I was lucky to be given a Biax scraper and a flaker after their owner passed away. If you are just touching things up a hand scraper like the Sandvik is just fine, even the one made from a file is good enough, it just needs more sharpening. A tool of that sort is sharpened straight across with no rake, actually a slight negative rake, as the end of the tool is forged down on a taper, on the other hand, a carbide insert such as the Sandvik is parallel in cross section, the working end of the insert is ground/lapped to a negative rake on both sides so that there is a ridge in the center of the end. I like to round over the corners at each side of the insert to avoid scratching the work if the corner should catch, and also chamfer the corners of an insert for working into dovetails.
 
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