Scraping practice

[jhovel]

I spent some of today putting in practice what I've learnt during the week.
Thought someone else might be interested....
A week or so ago, I checked my surface plate against a friend's Grade A surface plate in perfect condition. I touched up (gently scraped) a few high spots and made a mental note and photos of the areas which were low. One day I'll scrape it completely flat - maybe that will be my project at the scraping class.
1st Photo shows the blueing before I corrected the high spots and my mate's plate below it.

On Wednesday, I checked my cast iron "master right angle" against Machtool's master right angle on his master granite surface plate. It was found to be correct within 4 micron or so. It's visible in Photo 2.

I have an angle plate for my milling machine that I want to make flat and true 90deg before milling some T-slots in one face. I spent a couple of hours on it today, getting more used to my home-made "Aldi" power scraper. Turns out I really have to make an off-set and angled blade holder, because it has to be held too low to work and then gets in the way on larger surfaces. I tried a slightly higher angle to reach across the surface and promptly made a whole series of deeper gouges across the surface. Back to the drawing board....
None-the-less, I got it quite flat and to a good starting point for hand spotting and sraping to right angle - next weekend....
Photo 3 shows a close-up of a corner. What a pain those holes in the surface were! Must learn how to scrape near holes...
Cheers,
Joe

[Anorak Bob]

What a pain those holes in the surface were! Must learn how to scrape near holes...

Please refer to page 34 of Connelly's MTR for instructions... :U

Good to see you making progress Joe.

BT

[Stustoys]

Hi Joe,
I'm a little confused my your first picture. You blued the work so the bare spots are the high spots? (or am I looking at it wrong?)

I know edges are a pain, I assume holes are no easier.

Stuart

[jhovel]

I found out that reading instructions and putting them into practice are two different things altogether! I read those pages in Connelly last night in preparation. Using the power scraper is quite different and it seems to catch on corners of holes VERY easily - and hit you in the hand when it does....
Joe

[jhovel]

Stu,
I'm still confused too. The small bright shiney spots are high spots. They disappeared and took blue after I scraped them. The big areas without blue are low (didn't touch the ink) by at least the thickness of the ink film. The darker rings around a lighter spot are also high, but not bearing spots yet. When you move the surface around the blued reference, the slightly higher spots seem to rub their ink off to their outside - or collect more ink as you move. They also evened out with gentle scraping.
I intend to bring this plate to the class and get Phil to coach me take off the few microns in the central large high area and level the lot to maybe 10 - 30 bearing spots per square inch. He may advise against that and recommend surface grinding (I suspect).
Joe

[.RC.]

What are you using for a spotting medium....

It looks to be all smearing to me...

[jhovel]

.RC.
that is bearing blue applied VERY thin. Both surfaces are very flat and smooth, however. I've since learnt that I put too much pressure on - I had no idea that the work should sort of 'float' on the air and ink on the tool. My first lesson from Phil...
Cheers,
Joe

[.RC.]

It should be spotting.....

This is what spotting looks like

http://img.photobucket.com/albums/v606/OzRinger/macsongrinder022.jpg

They also say when you scrape you should be leaving your cuttings in little lines... Like this... That is a pretty light cut, maybe a ten thousand's of an inch... no more then two though... It is surprising how much swarf you create for taking off so little..

http://img.photobucket.com/albums/v606/OzRinger/macsongrinder021.jpg