# Practice scraping



## vettebob (Aug 9, 2013)

I have an old vise I've been beating on for 30 years it has a small flat area I thought I would try scraping for practice. Here are a couple of pics aside from the dents etc. I'd like some advice /tips this is my second attempt at scraping something. It is about 3 x4 inches.


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## Richard King (Aug 9, 2013)

I was hoping some of the other guys would answer first....The short scrapes look good...it looks like your scraping 90 LLL  deg to each other try 45 deg xxx.  Blue it up and lets see what it looks like.   The pic is 40 PPI done with a Biax Scraper.  The chart is one I hand out to my students.  That is a handy reference when looking at scraping sq inch.

Rich


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## Erik Brewster (Aug 10, 2013)

Some other comments:


It looks like you are scraping too shallow, but it's hard to tell from a pic. Try sweeping an indicator over it and see how deep the individual scrapes are. You want at least a few tenths deep on an individual scrape mark.
How flat is it? We need a picture of bluing marks to get an idea. I find it tempting to put pretty finish scraping marks down before getting it flat. It's just wasted effort if I isn't flat. Getting it flat calls for bigger, possibly uglier scraping to get it flat. In fact, ugly scraping can be flat an pretty scraping can be no flat. It doesn't have to be that way, though.


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## vettebob (Aug 10, 2013)

I removed about 15 thou with deep scraping to get a lot of the depressions out then tried to use really small strokes to put a nice finish to it. Tomorrow I'll make a couple more passes  rebluing it . (I tore out my rotator cuff and can only do a little at a time). I'll have to get a 0-4-0 dti mine only reads 5 tenths. From reading Rich's comments in another thread I think I over stoned it. 

 Thanks For the advice Guys I appreciate it.     Bob


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## vettebob (Aug 10, 2013)

I scraped a little more and left the blueing on for the pic.


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## Richard King (Aug 11, 2013)

vettebob said:


> I scraped a little more and left the blueing on for the pic.
> 
> 
> 
> ...



Open the PDF at the bottom of my picture on my last post, for some reason it was added under the picture and looks like its part of the picture.  It is a chart of % of points and points per inch.  We want on average machines or "conventional" which are lathes, mills, surface and centerless grinders  we want 40 to 60%  (POP) with 20 points per inch (PPI) with an accuracy of .0002" per 12" .    On straight edges, surface plates, jig bores, "super precision" machines we want 40 to 60% POP with 40 PPI with an accuracy of .00005" per 12".

You have over stoned it and have the sort of contact we want when we are looking for a static contact bearing on a steam fit 90% to 100% contact.  In way bearing we want 50% contact.  Think of the word "bearing"  a ball bearing has balls or high spots.  You have a "bearing" it has high contact points.  50% is a low spot that holds grease or oil as does a ball bearing.  The high spots carry the weight and as it moved the thin layer of oil flows over it or lubricates the high spot from the oil low pocket*. If you have ever used gage blocks and "stacked" them.  

You rub the flat surfaces of the gage block to "wringing" them together.  Friction makes them stick together (wringing; From Henry Ford trade school book "scientists have offered "atmospheric pressure", "molecular attraction" and a "minute film of oil on the lapped surface" is an explanation of this phenomena. Or maybe it's a combination of all three."). The same thing happens on a way when you get a "bearing" like this with so much contact.  In machines we call it "stick slip" when you move the way and it has a stutter motion until it either gets enough oil under it or moves smoothly of it, or it rings so perfect together no oil can reach it and the metal erodes and you get scores. 

You need to scrape deeper and make a checker board look one low spot, one high spot, etc.  the scraped spot should average .0002" deep and we do a final pass called flaking on the unexposed way of the 2 "way system" .  The most common is 1/2 mooning flaking, but other builders use a square cut for their "signature" last pass.

*  The oil is distributed to the way via an oil pump or reservoir, a oil grove, oil roller, etc.

I hope you understand and this makes sense.  Rich


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## awander (Aug 11, 2013)

Twisting gauge blocks together is called "wringing", not ringing.

Like clothes, not like a bell.


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## Richard King (Aug 11, 2013)

The old saying..You learn something everyday   Thanks, I have always thought it was spelled without the w.  But know I learned something.
I fixed it plus added something extra.   Thanks, Rich


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## Erik Brewster (Aug 11, 2013)

There are at least two ways to remedy the high bearing percentage you have:


Rescrape the area
scrape small, precise scrape to break up the big spots into more small spots.

I think it's best to rescrape, but it's good to have lots of tricks in your bag. Stoning is mostly used to remove burrs. You only need a few swipes for that.


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## astjp2 (Aug 25, 2013)

What about starting with a surface that has been ground on a surface grinder?  I have several machines that really need cleaned up and was thinking that a surface grinder would straighten and flatten out to create a good surface to start with.  Tim


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## Erik Brewster (Aug 25, 2013)

astjp2 said:


> What about starting with a surface that has been ground on a surface grinder?  I have several machines that really need cleaned up and was thinking that a surface grinder would straighten and flatten out to create a good surface to start with.  Tim



You could certainly scrape from a surface ground surface. It's a litter harder to get a "bite" on the first pass with the scraper. 

But why would you scrape after surface grinding? The grinder should leave everything nice and true. You could flake it after to get the oil pockets and be done really quickly.


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## Richard King (Aug 25, 2013)

I read this before and didn't have time to comment.   You need to tell us a couple of things first.  How accurate are you planning on scraping the machines to will be scraping?  You would first need to know how accurate the is the surface grinder you are using. 
As you will not be able to get the plate any better then the machine it ground on.  That is why we scrape so we can get parts better then can be machined or ground.  I have a wonderful little booklet called "Why are they Scraped" and will share it with anyone who wants a copy.  Just email me for a copy.  Rich    Richard@Handscraping.com     For those who worry about Copyright I have a permission letter from the writer so I can make copies.


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## astjp2 (Aug 27, 2013)

We use the Thompson grinder to sharpen the BT's (dies for punching out aluminum parts) and it is well used but seems to make a straight surface.  I was thinking that I could take a piece of 4340 and grind it smooth and flat to use as a precision surface.  I dont have a surface plate at my home shop so this would be used to make a straight edge.  Would I need to get it heat treated to harder than annealed?  Tim


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## 4GSR (Aug 27, 2013)

astjp2 said:


> I was thinking that I could take a piece of 4340 and grind it smooth and flat to use as a precision surface.  I dont have a surface plate at my home shop so this would be used to make a straight edge. .....  Tim



Tim,

My first "surface plate" was a piece of 1-1/2" A-36 plate about 9" x 12" surfaced ground flat.  Still have it here somewhere.  Not much good for scraping and fitting, but for other needs worked good.

A ground surface does not "mark" good when taking impressions for scraping.  You could scrape the ground surface to accept marking compound, but you still need a master to check it against.


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## Richard King (Aug 27, 2013)

If you ever look at a cast iron plate or cast iron straight edge they are ribbed so they won't bend.  A flat bar will follow the contour of a concave or convex part.  You might make your machines better using your ground bar, but more then likely with out a solid re-enforced  scraping plate or straight edge with ribbing you could possibly make your machines  worse.  But nothing ventured nothing gained. I have found over the years if a man gets an  idea in his head he should give it a try. Tell us  long will you make it, how thick and how close do you want to make your machines when your done?  Lets talk more about it and attach some pictures as you make your scraping gage.  Rich
 Below:
Cast Iron Plate.....................Straight Edge top left ....  small plate to show ribs ......24" straight edges...  triangle cast iron and ribbed camel backs


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## astjp2 (Aug 28, 2013)

I have some a2 and some 4340 that is 1.5 square and 16-20 inches long, I can put either on the grinder.  I was thinking that I would like to hold .001 from end to end, I don't think it is unreasonable if I am patient.  Our machines at work have to hold .0002 with box ways.  Tim


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## Richard King (Aug 28, 2013)

You will have to be careful how you push down on it and not bend it into a depression   After you grind it lay it on a surface plate and hinge it to see where the Airy or swivel points are.  When it is flat the should be about 30% from each end.  One more thing as Erick mentioned.  a super flat finish will not hold the blue and rub of easy  You should 1/2 moon or scrape square cuts in a checker board patern so the blue can have some cavities to hold the blue.  When you apply the blue I recommend a soft foam roller like you can buy from a hardware store.  1" x 4".  Apply it so you can still see the steel under it.   If it's so thick you can't see through it, it will smear and you will get a false reading.  A test you can make is blue up your surface plate  lay 2 pieces of .0015" or .002" feeler gage on the extreme ends and set your gage on the feeler gages, hold down on it and slide it back and forth a couple of inches and then turn it over and see if any blue has transferred to the bar.  Rich


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## astjp2 (Aug 29, 2013)

[SUP]This is what I am trying to fix, mill was free to me but I need to get it into a workable condition...
	

		
			
		

		
	






[/SUP]


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## Richard King (Aug 29, 2013)

That's Nasty.  

You should take it to work and fly cut or mill the ways first.  Trying to scrape that would take lots of hours even if you had a Biax Power Scraper.   If the machine you using to fly cut is decent you could probably hold .001".   Then scrape off the machine marks to give it a smooth surface and some oil pockets.  I would also be sure the ways are getting lots of way lube too   with a gravity feed oil cup or a pressure pump lube like a BiJur or LubeUSA.   Rich


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## astjp2 (Aug 29, 2013)

Richard King said:


> That's Nasty.
> 
> You should take it to work and fly cut or mill the ways first.  Trying to scrape that would take lots of hours even if you had a Biax Power Scraper.   If the machine you using to fly cut is decent you could probably hold .001".   Then scrape off the machine marks to give it a smooth surface and some oil pockets.  I would also be sure the ways are getting lots of way lube too   with a gravity feed oil cup or a pressure pump lube like a BiJur or LubeUSA.   Rich



I was thinking of getting a chi com one shot, the bijur pumps are 500+ without lines, distribution blocks or nozzles.  I wish there was a chart with the size of nozzle for each way, gets confusing with 10-20 lube lines running everywhere....


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## Erik Brewster (Aug 29, 2013)

Whatever you do, make sure the oil gets there. Your oiler doesn't need to be gold plated. It just needs to get oil where it needs to go.

- - - Updated - - -



Richard King said:


> You should take it to work and fly cut or mill the ways first.  Trying to scrape that would take lots of hours even if you had a Biax Power Scraper.



The man speaks the truth. I have been scraping a drill press table for the heck of it. It was only out a few thou, but that is ~4 hours of rough scraping with a Biax to get it flat. And that is an easier shape to scrape than a mill way.


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## astjp2 (Aug 29, 2013)

Richard King said:


> That's Nasty.
> 
> You should take it to work and fly cut or mill the ways first.  Trying to scrape that would take lots of hours even if you had a Biax Power Scraper.   If the machine you using to fly cut is decent you could probably hold .001".   Then scrape off the machine marks to give it a smooth surface and some oil pockets.  I would also be sure the ways are getting lots of way lube too   with a gravity feed oil cup or a pressure pump lube like a BiJur or LubeUSA.   Rich


I had to think about this, do I just mill the flat surfaces or do I do inside the dovetails also?


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## Richard King (Aug 29, 2013)

astjp2 said:


> I had to think about this, do I just mill the flat surfaces or do I do inside the dovetails also?



Both..the easiest way to do the doves is to use a dovetail cutter.  If you can't afford one you could tilt the head on a Bridgeport type mill and carefully indicate in the angle of the dove within. 0002". If you have never used a fly cutter ànd you have some experienced machinist's in the shop ask them to help.  On the Chinese mills I've seen the base bosses are not parallel with the top and I've seen where only 3 of the 4 feet touch, so I would set it on a surface plate and test it.   The one we machined in the CA class we started by machining the bottom first off the bad ways.  The flipped over and cut the top.   Scroll down the list of thread and look for the CA class and read it.  Mel had the base and we took pictures of it on the mill and fly cutting.  Rich

PS :  check on the thread above CA class almost full started by Mel..he owns the Chinese mills mill i spoke of.


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## astjp2 (Sep 5, 2013)

I went to measure the table, it was .008 tall in the middle, so I ground the top on a surface grinderand measured the distance between the ways and the fresh ground top, it is within .0018 from middle to end and .0012 from side to side.  The gibs are within .0015 parallel with .050 ground dowels between them.  Now I just need to get it on the saddle and make sure it is spotless before lube with way oil.  Scraping will come later, this is to get nice surfaces to work with.  

I took .018 off the top of the table and it was parallel within the first .006ish but I wanted to clean up most of the drill and hammer marks, the additional .012
	

		
			
		

		
	



	

		
			
		

		
	
 cleaned it up real nice.  I used a stone to break the edges, now onto another part tomarrow if I can get to it.  Tim



Richard King said:


> Both..the easiest way to do the doves is to use a dovetail cutter. If you can't afford one you could tilt the head on a Bridgeport type mill and carefully indicate in the angle of the dove within. 0002". If you have never used a fly cutter ànd you have some experienced machinist's in the shop ask them to help. On the Chinese mills I've seen the base bosses are not parallel with the top and I've seen where only 3 of the 4 feet touch, so I would set it on a surface plate and test it. The one we machined in the CA class we started by machining the bottom first off the bad ways. The flipped over and cut the top. Scroll down the list of thread and look for the CA class and read it. Mel had the base and we took pictures of it on the mill and fly cutting. Rich
> 
> PS : check on the thread above CA class almost full started by Mel..he owns the Chinese mills mill i spoke of.


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## astjp2 (Sep 9, 2013)

This is the saddle before grinding, it looks pretty rough but cleaned up nicely with about a total of .012 from each side.  I found that the surface grinder Y axis is off by .0017 down ward slope, so I used a .0015 shim and got it within .0002 from side to side.  The center of the table is low by .0012 because the mag chuck did not support the ends.  Overall I think I have a good starting point for scraping.  Tim


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