Learning how to scrape :D

[purpleknif]

Even the Bi-ax scrapes are pretty heavy.

 

[TroyO]

Some info that may be of use...

SmartFlix has the Hand Scraping DVD as a rental for $10. (You will note, I rented mine before announcing this just in case there is only one copy, LOL. ;-)

www.smartflix.com

 

[TroyO]

OK, I have the scraping vid on the way and I just looked in my back issues of "The Home Shop Machinist". Sure enough, as I "kinda rememebered" there is a 3 part article starting with the May/June issue about scraping. Unfortunatley I have May/June and Sept/Oct but not the one in between. So, I ordered it from Village press... a whopping $6.

By the way, so far:
May/June:
Basic scraping proceedure and getting stuff flat.

July/Aug:
???????? I *think* this will be about referencing surfaces to each other and scraping to refine alignment?

Sept/Oct:
All about making home made scrapers.

A very good read so far and great pics.... kudo's to Michael Ward, the author!

In further news, I made my first crack at some carbide tipped scrapers with what was on hand... the wide one is about an inch, the smaller one about .7" The carbide on the small one was .5x.5x.187 turned on it's diamond angle to get a little more width.

The wide one was a carbide paint scraper blade refill from Home Depot for like $5

(PS.. no laughing at my crap brazing, LOL... my MAPP/Oxy torch just barellllly melts it, LOL!)

(Not sure why, it keeps saying I already posted this message but it doesn't show up. So, appologies if I actually do end up double posting, but I think it never took the first one but now thinks it's a dupe anyway)

 

[steamer]

Michael Ward has published another article on scraping in HSM. I've read through it , It is very informative, and he takes you through the basics of some projects.

I wish he spent a bit of time on step scraping.. I think the person starting out would need to understand that technique.
But all in all a very informative article. Well worth the read and the cover price.

Dave

 

[TroyO]

So far, there has been a fair amount of information... and some portion of it is actually about scraping but quite a bit centers on making the scrapers. (And on making the tools to make the scrapers.)

I wish (And maybe the 6th and later articles will get there) that more of it was about things like how to make sure one surface is paralell or square or at the appropriate angle to another etc, and how to change from just scraping to "flat" to change that relation between two faces and so on.

For my part... made up some scrapers, made a "Lap" using an old step pulley attached to a spare motor and filed to run true then doped with some diamond compound. So, I'm good on basic tooling.

I have my large blank faced on one side and will start scraping it in but still have some other pressing stuff ahead of that project.

I will get the latest edition, just need to find who in my area still sells it, I still read... well, anything I can find.

It will get there... someday, LOL.

 

[steamer]

Hi TroyO

Yeah this one has a bit more "meat" to it.

Dave

 

[zeeprogrammer]

Thanks for starting this thread Tom.
I always appreciate seeing videos of basics in prepping tools...not just using them.
I have that same grinder and just seeing how you dressed it was useful.
And thanks to everyone who contributed to this.

I've known about scraping machine beds by hand when you can't use a large power tool. But a couple of questions...

Someone mentioned flycutting as a preliminary step in scraping a small part.
Why isn't that sufficient? I suspect that polishing afterwards leaves dips?

After scraping that base is there additional finishing work?

 

[Florian]

After scraping, you're done! (except if you want to make some lubrication grooves; Its far easier to first scrape and afterwards make grooves than the other way round!)

If you had a High precision machine which can mill large surfaces within 0.005 mm, then you may be happy with fly cut guide-ways.
But if your axis is slightly concave, the guide will stick on the ends while in the middle there may be too much play.

When scraping, you can easily remove all the high spots and then you get an almost perfect surface.
But a scraped surface isnt totally plain, instead it is very little dimpeled. And that is even better than a perfect surface because it reduces slip-stick and also keeps the oil better than a perfectly even surface.

Cheers Florian

 

[zeeprogrammer]

Thanks! And thanks for the point about oil and slip-stick.

 

[purpleknif]

After scraping and getting everything right comes "flaking". This is to provide space for the oil and to prevent "wringing". There is a Bi-ax scraper made for this op too. Takes quite a bit of practice to do this by hand.

 

[steamer]

Another way is to bump scrape. No quite as technical but still tricky to do consistently.

Dave