Surface plates & hand scraping - should I or shouldn't I?

[Highpower]

Heres the thing....
I want to start doing some hand scraping. Lets just say that funds are not real plentiful right now.
You need a good flat reference for laying out a film of spotting dye to mark the surface of the part that you want to scrape.
OK, fine. I have a nice Starrett "Crystal Pink" surface plate that I use for measuring and layout work that I can spread the dye onto. So nice that I am having a hard time thinking about covering it with permanent blue stains all over it.

So the question is: Do I just suck it up and use what I have, or do I try to scrounge up enough cash for an additional cheap, cheap import surface plate to use for spotting? Keep in mind that shipping costs on these things are almost double the cost of the surface plate itself.

What would YOU do?

 

[Highpower]

My concern is that I've read about other people spreading the blue ink/dye on their surface plate (pink granite) and having ugly permanent stains on the plate even after the ink/dye is cleaned off. If I had a piece of black granite I wouldn't really care because it would not stand out. Knowing that there is a foreign body (a stain) on my purty pink rock would just bug me. Probably much ado about nothing, but that's the way I roll. lol.

Just wanted to know what other folks might think about it.

Edit to add:

Sorry Jerry. I went back and re-read my original post and saw where it wasn't really clear as to what I was wanting to do what with what.
I have re-worded the original so hopefully it makes more sense now.

 

[Highpower]

Willie,

If the surface is being used to try to wear down the high points - then that is a different story. I've seen it done!

DaveH

No Dave, that is a different tool not a different story.

"Alex..... What is a lapping plate?" I'll take world geography for $500.....

 

[Tony Wells]

A good exercise, with beneficial products at the end, that will give you good tools for checking flatness is to make your own straightedges. Here's a good writeup of how to do it.

http://home.comcast.net/~jaswensen/machines/straight_edge/straight_edge.html

 

[Joe in Oz]

After just having finished a rwo day scraping course, may I briefly say that ther is a bit of misinformation in this thread already.
The spotting blue or bearing blue is indeed applied to the granite or other surface plate. the object to be scraped is then very lightly rubbed a shrt distance on the blued stone. The high spots on the workpiece are then scraped down - a process which removes a few 10ths of thous with effort and fractions of tenths done gently.
The process is repeated until the entire workpiece surface is covered with lots of densely spaced small bearing spots - higher spots that the valleys in between. Accuracies better than 1/10000" are possible.
That's the VERY short version.
The blue which is applied to the reference surface plate is earily removed completely. It is NOT permanent. There are both water and white spirits or methanol soluable dies. This stuff is NOT engineers' or layout blue!
A search on "metal scraping" will give a lot more detail. That's the process your granite surface plate was made for, incidentally.
Cheers,
Joe

 

[Highpower]

Yes, this video shows the general idea of the operation. And I understand that the dye used (in my case) is not permanent (indelible ink) in and of itself.
However - I have seen where other people who also own the Starrett pink surface plates have stated that the hi-spot blues get into the micro-cracks or pores in those plates, and aren't removed after cleaning and remain visible. Much like getting a water stain in a granite kitchen counter top that hasn't been sealed. The stained area stays dark and looks like Fido's butt IMO.

Apparently from what I have read in the past, it is not a problem with the Starrett black surface plates. Something to do with the "crystal" content in the pink plates I think?

I sure wish there was a class available around here.

 

[Tony Wells]

The "crystal" in granite plates is quartz. There is more of it in the pink plates, with the Starrett "Crystal Pink" plates having the highest concentration of it. That's what gives the plates their long life and hence high cost.

I use a black plate, and although they need lapping more often than the pinks, I'm not too hard on it, so don't worry so much about that. Just keep it clean and avoid sliding stuff around on it and it will last years and years. I've had several plates in an inspection area, both pink and black. Everyone wanted to use the pink, naturally, so it had to be lapped yearly. The blacks, although not used as much, wore even more. Some had to be lapped by 0.002-0.003 to restore flatness to just grade b. We kept the pinks at grade A.

I'd not use my plate for a scraping project. If I had to, I'd buy a small one for the project, then give it away, since they aren't expensive.

 

[brucer]

anytime i've seen someone scraping a machine they used hardened precision ground bars for bluing, pretty much like large gauge blocks.. seen one guy use a large starrett level one time.

only bluing i've ever done myself was bluing seal offs on cores and cavities.


any hi-spot blue i've used will stain pretty much anything, except for the water soluble hi-spot, it takes some getting use too but its cleaner to work with..

 

[Highpower]

Well I'm not looking to do scraping on machine ways, just some smaller sized individual parts.
Since I don't own a surface grinder it would be nice to be able to flatten some surfaces on things like small engine parts, warped manifolds etc., and other general use.
I may have a line on a cheap black surface plate, but it's looking like it's in the too good to be true category right now. I'll make some phone calls tomorrow and see.

Update:
As I expected, Enco (once again) prints the wrong information in their sale catalog. (November "HOTdeals".) No black surface plate for me. I guess that answers my own poll question for me. Meh.

A cast iron plate is definitely out of the picture for me though.
Demasiado dinero!

 

[Highpower]

Dave,
For what it cost me originally, not especially.

And the thought of dragging parts around on it and having to get it lapped again later, also not too appealing.
An additional "inexpensive" plate would suit me fine, but the money tree growing in my back yard died a few years ago I'm sad to say.
<wink,wink - nudge, nudge>