Author Topic: First attempting on scraping, advice needed  (Read 11518 times)

Offline FLG

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First attempting on scraping, advice needed
« on: July 26, 2013, 11:32:32 PM »
Hi to all

This is my first attempting on scrapping a surface, the item is an old scriber that I'm planning to refurbish, aslo it makes a perfect oportunity to practice scrapping.

I have been working on it for a couple of days, trying different approach on the technique.

Most of the time I feel that I´m just scratching the metal, and I got dents and holes all arround the surface  :thinking:

The scraper Im using is a Hss cut of blade bolt to a handle, its has a radius on the tip (see the pothos) (and I resharpen it in every pass)

Slowly I have been used to it, but I have the next problem: the spots are very small and they are very close together, its not like the pictures I have seen when the blue spots are visible and with reasonably size, mine are too small and I have to scrap almost the entire surface.

Im using Dykem blue.

This is the best photos I could take of the blue marks.







Anyway, scrapping is a lot harder that I was realizing...

Any advise will be of great help!

Saludos
« Last Edit: July 30, 2013, 11:42:06 PM by steamer »

Offline steamer

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Re: First attempting on scraping, advice needed
« Reply #1 on: July 27, 2013, 12:18:05 AM »
FLG....From what I can see, it looks like its coming along nicely!....but tough to really tell with those photo's.

What are you using for a reference?....and can you show me the reference immediately after you did a mark up?....that might shed some more light....see if you can work out a better picture...though I know it's very difficult to photograph.

Dave
« Last Edit: July 30, 2013, 11:42:25 PM by steamer »
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Offline steamer

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Re: First attempting on scraping, advice needed
« Reply #2 on: July 27, 2013, 12:27:04 AM »
FLG....try putting some tape on the shinny parts of the block, perhaps the camera will deal with this better....

Some times low angle light with a shadow plate helps too...but you will need to experiment.....

Dave
« Last Edit: July 30, 2013, 11:42:43 PM by steamer »
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Offline FLG

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Re: First attempting on scraping, advice needed
« Reply #3 on: July 27, 2013, 01:04:59 AM »
Thanks for the quick responce Dave!

Here are another shot:













As you can see, there are scratches and dents all over the place  :ROFL:

Im scrapping at 90° respect of the previos iteration.

maybe Im using too little blue on the surface plate??

Saludos

« Last Edit: July 30, 2013, 11:42:55 PM by steamer »

Offline Dave Sohlstrom

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Re: First attempting on scraping, advice needed
« Reply #4 on: July 27, 2013, 01:11:32 AM »
You will want to change from HSS to carbide for your scraper. Y will want to grind that scraper to a 60mm radius or a little over 2". You can get carbide from MSC. Silver solder to a piece of CRS tapered to the same thickness as the carbide.

Will look like this



Next you will get better finish on you scraper if you have a diamond grinder like this with a fairly fine wheel on it.



Next you will want to make yourself a diamond lap  so you can hone the cutting edge to a very sharp fine edge. Get a piece of 6" by 1" thick cast iron from McMaster Carr or Enco.



When you grind you scraper you want to grind to about 93 degrees so you get a cutting edge on both sides of the carbide. Then hone at about 95 degrees so you just hone the very cutting edge not the whole thing.

AS you scrape only remove the blue. You should see scrapings that look like coffee grounds not just dust. You want to shoot for about 40 spots per square inch and about 40% coverage.




Dave
« Last Edit: July 30, 2013, 11:43:23 PM by steamer »

Offline steamer

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Re: First attempting on scraping, advice needed
« Reply #5 on: July 27, 2013, 01:42:45 AM »
Thanks for the photo's FLG and Dave!.   Dave, nice work! and good advise!

FLG, it appears that you haven't quite carried the bearing to the back on the left side of the photo....scrape a bit more aggressively until it "carries"...and then you can back off,  and THEN shorten your strokes.

Crossing your cuts is fine....perhaps at 60 degrees.....but what I can see your doing fine......its very hard to advise from a photo though.

Dave
« Last Edit: July 30, 2013, 11:43:47 PM by steamer »
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Offline steamer

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Re: First attempting on scraping, advice needed
« Reply #6 on: July 27, 2013, 02:26:44 AM »
FLG

If you look at Dave's photograph, you see the "bullseye".   It's the shinny dot in the middle of the blue.

Now That's great!....when your bearing carries over the part, you start to scrape JUST the shinny dots.....

BUT

Until you carry the bearing, you scrape AREA's ....you have metal to take off...I think Nick described a method for roughing, though his words I can't remember at the moment...in the state it is commonly called "double cuts".    Take a roughing cut over the surface, then cross that with another cut...you know the bearing isn't close yet. your still trying to get the metal off...if you go to finish scraping before the part carries, you end up "stalled"...which is what your dealing with right now.

Here is a roughing cut on my cross slide....and I mean I was ripping at it with the scraper!....lots of stock to remove!
Long strokes...though for such a small part as yours I'd say a 10 mm long cut is just fine.


Once the part carries....and your geometry is good...I suspect you want Vee to be parallel to the base?....THEN you start finish scraping.

Here's a sine plate I made and scraped....


And a small master I made for the SB project

« Last Edit: July 30, 2013, 11:44:02 PM by steamer »
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Offline steamer

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Re: First attempting on scraping, advice needed
« Reply #7 on: July 27, 2013, 02:36:07 AM »
Here's another picture to look at.



In this photo, the bearing is developing...but if you look at the bottom right, you see the low parts that are not marked yet?....that means the bearing hasn't carried yet.

KEEP ROUGHING AREA"S....In this case draw a magic marker around this area and scrape everything else!

Here you can see it was still high in the middle of the part...but getting there...it came in eventually 8)


Dave
« Last Edit: July 30, 2013, 11:44:20 PM by steamer »
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Offline steamer

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Re: First attempting on scraping, advice needed
« Reply #8 on: July 27, 2013, 02:41:04 AM »
See attached...

See the milling marks in the low area....you still have a ways to go....

Persistence!....it will get you there!

Saludos!
« Last Edit: July 30, 2013, 11:44:35 PM by steamer »
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Offline steamer

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Re: First attempting on scraping, advice needed
« Reply #9 on: July 27, 2013, 02:44:17 AM »
I don't know how many points...but I couldn't do any better....





dave
« Last Edit: July 30, 2013, 11:44:48 PM by steamer »
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Offline FLG

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Re: First attempting on scraping, advice needed
« Reply #10 on: July 29, 2013, 04:08:56 AM »
Thanks a lot Dave steamer and Dave Sohlstrom!

The reason that I started with Hss istead of carbide is because I can grind and sharpen Hss with no problem, but I dont have any tooling besides a small cheap diamond stone to work with carbide...

Yor pictures about your scrapers aer very instructive, I will start looking to get some tooling to make a carbide scrapper like yours.

I follow your advice and take several rough cuts until I got blue in all the surface, then started to do some more fine passes, now Im only scrapping the high spots (the bull eyes), but still these are very small (I mean small!) and pass after pass they are still small (but well spreaded).

Here are some pictures of my progress:







In order to see the small spots In applying a little pressure at the moment of transfering the blue from the surface plate to the piece, because they are small doing this the "bulls eye" come very clear and shiny in the center... I know that I supouse not appliying pressure down when bluing the piece.... is this a bad practice?

 And.. is normal for a scrapped surface to show the marks, holes and scratches of the rough scrapping? because in the pictures my surface looks very nice but in person is full of these  :ROFL:

Any way thanks alot for the input I really appreciate!

Saludos
« Last Edit: July 30, 2013, 11:45:08 PM by steamer »

Offline steamer

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Re: First attempting on scraping, advice needed
« Reply #11 on: July 29, 2013, 08:31:31 AM »
Looks pretty good from here!....What do you think Nick?

I'm not quite following you comment about applying pressure during the mark up...you shouldn't apply any pressure....

Looks like you got a small blob of blue on the part but the rest looks great

Dave
« Last Edit: July 30, 2013, 11:45:27 PM by steamer »
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Offline MuellerNick

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Re: First attempting on scraping, advice needed
« Reply #12 on: July 29, 2013, 08:35:36 AM »
Hi!


First, you should hone your photographic skills. ;)


My bet is, that the base is chilled cast iron. For CI that size, regrinding HSS shouldn't be necessary. Go with carbide.
Next, I think that you do stone way too much. If you do that, the work doesn't pick up blue too well.


Let's see what you got to report …


Nick
« Last Edit: July 30, 2013, 11:45:43 PM by steamer »

Offline steamer

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Re: First attempting on scrapping, advice needed
« Reply #13 on: July 29, 2013, 08:40:18 AM »
Fair enough Nick...We'll wait for a response. 8)

Dave
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Offline MuellerNick

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Re: First attempting on scraping, advice needed
« Reply #14 on: July 29, 2013, 08:59:33 AM »
Quote
For CI that size, regrinding HSS shouldn't be necessary.


I should have said: Regrinding every pass shouldn't be necessary.


Nick
« Last Edit: July 30, 2013, 11:45:56 PM by steamer »

 

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