What's new
What's new

High Spot Dye going to low spots. Confused

addman16

Plastic
Joined
Oct 11, 2017
Hi guys, so I've been practicing some scraping and I've run into a few issues. Ive watched about 10 youtube videos on how to scrape so I do have a bit of understanding on what's going on.

Here's what I'm working with:

My scraper is a wood chisel, yes I know I should spring for a carbide scraper with a 60 degree radius. I was thinking I could grind the radius into my wood chisel and use that.

I'm scraping on steel since I don't have cast iron right now.

So first I did a roughing pass going in opposite ways at 45 degrees

Then I put the steel part in my surface plate and ran a dial test indicator. Appears the top half of the steel plate is about two thousandths high compared to the bottom half.

So I did another roughing pass on just the high area and brought the height from two thousandths to one thousandths.

Next I spread some prussian blue on my surface plate using a speedball roller, making sure not to use too much.

Then I slowly applied the steel plate on to my surface plate and used the hinge technique trying to see where the rotation was taking place.

But I noticed that the prussian blue would leave steaks of dye on my surface plate and the print on my part looked smugged.

Second what was more confusing the blue dye was inking the low side of my part the part that is one thousandth lower. I thought the dye went to the high spots.

So I cleaned the surface plate and my part with denatured alcohol to try again to get a good print.

This time I ran the part in a figure eight pattern with no pressure and light touch.

I noticed less streaking this time but again it was the low spots the were covered with dye and the high spots that were empty.

Only thing I can think of is either my surface plate is not flat or that some how the part is tilting and the low side is getting blued.
 
Couple of thoughts. The streaking smudging may be due to too much marking blue. Work out the thickness to a thin layer. Second issue of bluing the low places and not on the high is related to the first issue of too much bluing. By rubbing it, you are pushing the bluing up into low spots and rubbing off the high spots. Get a very thin layer of bluing and just gentle rub more to just seat the part on the surface plate I think your problems with go away.

Tom
 
Keep at it, scrape a lot, fit the parts to your plate.

Then tell up what you have learned.

"A fool, persisting in folly, gains wisdom".
 
I'm afraid you are confusing flatness with alignment, or you haven't described well what you're doing. A few pictures would also help us understanding better.

The blue will transfer to the areas of your part that are in contact with the plate (i.e. flatness). If that high point is further or closer to the opposite surface of your part (alignment) it doesn't matter, or, better, you do not control it by bluing. To make the concept clearer, you could be spotting a triangular prism and getting most of the high spots near the edges between the "upper" and "lower" sides and almost no spots near the side that is almost perpendicular to the plate.
If you extend the surfaces of your part almost at infinity, you are dealing with a triangular prism.
If you want to have the faces of your part parallel, you first blind scrape for alignment (i.e. you map your part with a dial indicator resting on a surface plate with your part) and scrape (if necessary, step-scrape) without bluing the areas that are high in reference to the other side and, when you're very close to parallelism, you start bluing and scraping "straight down" checking time to time to make sure that you're maintaining the parallelism you're looking for.
The general rule is that you first scrape for alignment (necessary only when you need to preserve/restore the geometry of the part), then you scrape for bearing/flatness.

Another possibility not clear from your original description is that you did your surveying with the base of the indicator resting on the very part and not on the surface plate: in that case you were surveying only concavity and convexity and the changes between the slopes.

I hope it's clear.

Paolo
 
Get some nice, easier to scrape cast iron. Would suggest durabar.

Steel is too difficult for a beginner and often has huge burrs left from a scraping cycle. Speaking of- how are you deburring your plate?

Whispering again: cast iron...


Lucky7
 
Hi guys, so I've been practicing some scraping and I've run into a few issues. Ive watched about 10 youtube videos on how to scrape so I do have a bit of understanding on what's going on.

Here's what I'm working with:

My scraper is a wood chisel, yes I know I should spring for a carbide scraper with a 60 degree radius. I was thinking I could grind the radius into my wood chisel and use that.

I'm scraping on steel since I don't have cast iron right now.

So first I did a roughing pass going in opposite ways at 45 degrees

Then I put the steel part in my surface plate and ran a dial test indicator. Appears the top half of the steel plate is about two thousandths high compared to the bottom half.

So I did another roughing pass on just the high area and brought the height from two thousandths to one thousandths.

Next I spread some prussian blue on my surface plate using a speedball roller, making sure not to use too much.

Then I slowly applied the steel plate on to my surface plate and used the hinge technique trying to see where the rotation was taking place.

But I noticed that the prussian blue would leave steaks of dye on my surface plate and the print on my part looked smugged.

Second what was more confusing the blue dye was inking the low side of my part the part that is one thousandth lower. I thought the dye went to the high spots.

So I cleaned the surface plate and my part with denatured alcohol to try again to get a good print.

This time I ran the part in a figure eight pattern with no pressure and light touch.

I noticed less streaking this time but again it was the low spots the were covered with dye and the high spots that were empty.

Only thing I can think of is either my surface plate is not flat or that some how the part is tilting and the low side is getting blued.

What you need is simple. Any "sample" already scraped by a more expert hand. Practice your spotting technique - AND NOT any scraping. At all. Not YET.

Just applying, spreading, testing, removing - all whilst observing how the spotting medium "needs to be" as to its consistency, method of application, the "rub", and such .....until you get a feel as to what it shows, and how it is actually used to point you to what is and is not "there now" so as to show you the way to what needs to be done, next step.

Until you have learned to use and "read" the spotting medium, it is akin to trying to learn to use your hands before you have opened your eyes - or to turn metal to a specific diameter before you have learned how to read a caliper or micrometer.

Be patient. Invest in doing your homework. It can be very cheap. It need not YET even make any chips.

Once you "get it", can "read" the surface, understand what it is showing, DUPLICATE that read one time after another because you have mastered consistency, THEN scraping will be less likely to go in the wrong direction.

Try to skip-over the basics? Misconceptions will lead you down irrelevant routes, waste your time, and annoy the grownups.
 
It's a little hard to understand what you are talking about exactly.

As I read it, you are not talking about the low "spots", i.e. scrape marks, dings, etc. I THINK you are talking abut areas of the work that you know are lower than the others relative to the plane you want to establish.

If so:

Adding to what Bill said........You may not be consistent in how you hold the part. ALWAYS hold the part by the same end, and do not let it "tip over" on a high area and mark the other "side" of that as well. You may have had the high area get rubbed clean, as someone was mentioning, and might also have let it "tip over" and mark both sides of the "bump". That will fool you into scraping the areas you should leave alone, so you have to avoid letting it happen.

If you press down, you risk tipping the part over high areas, or getting bad spotting. The part weight is usually enough to get good spotting. Just hold down enough to ensure the part does not "tip over" and mark both sides of a high spot.

That way, if there is a bump in the middle, you should see the area of the part nearer your hand spotted, and the spotting on the "far side of the bump" should be sparse , light, or non-existent. That lets you know you need to step scrape the bump, or maybe just scrape the area where the bump is, depending what the alignment issues are.

I like to start out with a rather light blue on the flat, so that I see the pattern with no blue "filling it in", just as a clue to what is going on.. Then, to get going, I put some more on and commence scraping. Not so much as to change the character of the spot pattern drastically, just enough to see it easier and catch all the places.

Also, "spotting" is spotting, "hinging" is done dry.
 
Bill, that's good advice. Color me shocked... ;)

Well... Hell. Spotting/transfer media is just one more "tool", same as any other under yer roof.

As with any OTHER "tool"? If yah don't even take the time to find out which end to look-at, hold, set-afire, put in your hand, smack with a hammer.. or insert into some sort of "orifice"?

You won't get the same results as he who HAS taken the time to understand how it is meant to be used.

:D

"Asking" is rightous enough. Shoe polish, even.

Basic Infantry training, early days, 1965. Just been issued uniforms and two pair of ugly boots meant to become shiney boots. One new recruit comes into our squad bay with a tin of GI black shoe polish in hand.

He politely asks if anyone can show him how to USE it.

He was serious. "RA all the way", carried his share of the load, good soldier enough he turned out to be.

He had simply been raised in a wealthy family where SERVANTS had always polished his shoes FOR him, childhood, onward.
 
My suggestions?

Get some cast iron, scraping steel is a bear.
Make a proper scrapper. All you need a is a piece of hardware store flat bar stock and a file handle to make one.
You're probably using to much blue.
 
Another point is that the blue will show high spots relative to the surface that you are bluing. It won't relate to what you measure if you put the work on a surface plate and measure with a dial gauge. When you do that you are measuring thickness from the back to the front, not flatness of the front itself.

When you get to making a piece parallel/same thickness everywhere, you start by making one face flat. Then you can put the flat face on the surface plate and use the dial gauge to see what is happening
 
All you need a is a piece of hardware store flat bar stock and a file handle to make one.

And some carbide or HSS, and solder, flux and torch, and a way to sharpen it, and a way to hone it. :)

Scraping on steel with a wood chisel, he may not have any of that.
 
Apologies if these things are already covered, but based on what you're saying:

-You've hit the beginner's worst enemy (IMHO): High in the middle. If you have a flat plate that's high in the middle just a little and you don't know how to spot it, you will chase it incessantly. That's because, despite your best efforts, the part will rock all over on that high spot while you're bluing it and make contact in the low spots too. This is why hinging is very important. If you hinge it and it shows high in the middle, you have to get the middle down until it won't hinge there anymore then fix the flatness.

-VERY high spots will show lighter with a darker "edge" around them. That's because there is enough pressure there it's harder for the blue to stay on, it gets polished and squeezed out as your moving around. LOWER high spots keep their blue darker throughout because there's less pressure. During finishing for good bearing area, I like to use the trick I learned from Richard of bluing the part, then moving it out of the blue and burnishing the highs on a clean section of granite.

-As has already been pointed out, steel isn't a great choice. I've never done it, but I can imagine it being much tougher due to better ductility. Cast iron produces almost fine dust and kind of fractures. If steel "cuts" and raises big burrs during the scraping process, it's going to take a lot of deburring between passes.

-If you see smearing you either have too much blue, burrs or chips on your part, or contamination (dust, chips, etc) in the bluing on your plate.
 
Lots of good info posted already.

A hardened steel scraper will go dull fairly quickly, so I'd touch it up after every pass just so you know it's not an issue. One of my projects had a steel gib that took some pressure to get the scraper to make a dent in. Not that it was hard, but the scraper just wanted to skip across it. With that in mind, it might take a few passes to get a surface that will spot well. Just because it has the holographic look doesn't mean there's enough 3-D texture to spot.

From my experience, you can never put too much pressure/force into your scraping, so long as you keep it from rolling and scratching. Deeper scrapes just get you done faster.

I'd also stone your part after every pass. A slight burr can throw you way off, but steel doesn't chip off as good as iron so if you get your scraper to "dig in" and making a scrape, you will likely see a good burr there too.
 








 
Back
Top