Hand scraping

[loply]

Hi folks,

For a while I've aspired to do some hand scraping and finally gave it a try last night.

I started by bluing up my granite plate and checked various objects to get the hang of it - a tailstock, a compound slide, some parallels, etc.

I then ground an old file into a scraper and did a few practice runs on unused CI lathe and mill parts.

I kinda get the idea but I struggled to get a neat finish and I also struggled with reliably bluing my parts. Sometimes I'd test the same part two or three times and get two or three different results?

Query 1 is whether anybody knows of anybody who hosts classes in the UK (preferably the northern half!) where I could get some practice and see what a proper tool should look like?

Query 2 is whether making a set of scrapers from O1 tool steel would be worthwhile, or whether I'd be better off making some form of indexable carbide job.

Query 3 is about scraping lathe ways. I wanted to use a large parallel as a master to scrape out some dinks and wobbly spots on my Viceroy, but I can't get anything resembling a logical transfer. The stuff just ends up all over the shop making it difficult to ascertain where the highs are. Any tips here?

Cheers for any help,
Rich

[Fergus OMore]

I can't help directly but I've PM'd you as I also live in Newcastle.

[andyf]

Rich, my scraping experience is very limited indeed, and only extends to relatively small parts, but I did find that a very thin layer of blue is needed, as evenly spread as you can get it. That's all I have to say, because the rest of what I did was probably all wrong (though it worked OK).

Andy

[DavidBraley]

Rich,

I'm no where near you, but I might be able to offer some suggestions.

Query 2: Don't waste your time with a tool steel tip. Use carbide. The edge stays keener longer. Also, only sharpen the edge on your scraper with a diamond wheel. If you have access to a power scraper, use it. A HUGE time saver. Some rebuild shops will rent you one. Bosch makes the best power scrapers.

Query 3: Before each rub with the straight edge, clean the way off with some kind of solvent. Rubbing alcohol works fine. Then use the side of a piece of chalk (like your math teacher used) and rub it down the way surfaces. White or yellow is fine. If you are having trouble getting the chalk to stick to the way, mix some chalk powder in some rubbing alcohol and apply a very thin layer on the way surface with a rag (you can make chalk powder by scraping the stick of chalk with a pocket knife). Let it dry before you rub for high spots with your straight edge. The thin layer of chalk will help "bring out" the transfer of blueing to the way for marking the high spots. Don't slide the straight edge very far. Only about an inch back and forth. Make sure the bluing is VERY thin on the straight edge.

I hope that helps.

David

[DavidBraley]

Sorry Rich, I made a mistake in my answer to you in Query 2. It's not Bosch that make the best power scrapers, it's Biax. It was late and I was tired.

[Joules]

Use a rubber roller (artists store) to transfer your blue onto surfaces.  You really need to roll out the blue on a surface plate so you have a thin layer on the roller then apply to the mating part you "aren't" scraping.  Is your granite surface a true surface or a chunk of worktop.  Worktop is OK, but don't assume it to be as true as a surface plate, try to get it checked against a known surface, or all your parts will have the same defect....

Nothing wrong with HSS scrapers if the job isn't huge, you need to take your time and be gentle when you start.  Short strokes, for me a 45 degree herring bone pattern worked on larger areas.  Don't be afraid to recheck the work often to begin with.  Use a digital camera to record the pattern of blue as you work to see if anything inconsistent happens.  After a few hours your eyes go GA GA and you forget what pattern the blue was when you started, clean off and re-blue.

HSS tools can have the edge resharpened with a fine diamond stone, and on a flat tool remember you have two edges, so flip it over if things seem to slow.

Biggest Tip : -   Start on a scrap part...

                   Have fun.

p.s

Should also add, don't worry about a messy looking scraped finish or aiming for total contact.  To start with you are looking to optimise contact of you parts rather than making it look pretty.  Regular contact spots across the surface is better than large gaps and remember how much material you are taking off.  If the parts rock you need more than scraping.