Learning how to scrape :D

[ttrikalin]

If this part of the forum is to strictly to give advice (as on first look it seems), take this as advice on how not to do what I'm just now learning how to do.

So indulge me mklotz and dsquire - if you will; if anything, the replies I hope to receive would contain some tips and tricks.

The objective is to try my hand at scraping (I'm already proficient at scrapping, thank you - I can scrap work in more ways than one).

Now, I have read what I could online and I am still waiting for books and a DVD I ordered last week... but I was never good at waiting and decided to give it a shot. I will make a small height transfer scriber such as the one Lautard describes in his second book.

The base started it's life as a former flywheel blank.

It'll get scraped flat.

I will show you what I have till now, and then will post a video with the sharpening of the scraper...

The diameter of the stock was 2.375", and from flat to flat is is 1.875" if I recall. This is after a few roughing cycles -- I hope this is the correct amount of blue??. Note the surface. Each stroke leaves little lines, and this is because the cutting edge is not smooth. Mental note to show the chips, they are nice and "curly"... pretty thin though...
IMAGE 1:

This is after an other cycle. Again, just a tad of blue on the surface plate, worked around with the brayer. Would this be flat enuf for a non bearing surface? 4-5 points per square inch?
IMAGE 2:

This is after a couple of more rounds. I was only cutting the areas with the blue...

 

[ttrikalin]

This is later still... I am using very little blue... Now I'm trying to divide the large areas while scraping (dunno why, seemed like a good idea...).
IMAGE 3:

And this is where I stopped. I may be messing it I think, so better stop now...
IMAGE 4:

Studying IMAGE 4, I see that the blue parts are almost colorless in the middle. This is probably the very apex of the high spot. I therefore should go on and scrape these apexes down to get a better surface. Whould this density be OK for, e.g., a sliding bearing surface? I count 15-20 apexes (white spots with a blue halo) per square inch on average)... This is a closeup...
IMAGE 5:

 

[ttrikalin]

Questions in search for answers...

1. In all the images you can see the marks left by my scraper... they are not a nice surface -- you can see lines... even after honing with a diamond plate... I take it that I have not honed enough?

2. I see a lot of colored (bearing) points in the periphery of the part (IMAGE 4, IMAGE 5). This should not happen, right?

3. I did not follow any pattern while scraping, just cut the blue parts from the same angle (45 degrees give or take many)...

4. I do have difficulties in hitting the apexes in IMAGES 3, 4 and 5... I am using a 1" rigid blade... I think I could make a smaller one, but I am afraid that I would gouge the surface with a smaller one... Are you supposed to change tools as you proceed?

more to come...

take care,
tom in MA

 

[ttrikalin]

more to come...

questions I meant... 8)

 

[ttrikalin]

and this video shows how I went about the following tasks:
_________________________________________________
1. grinding the scraper: 00:00:00
_________________________________________________
2. honing the scraper: 00:02:24
_________________________________________________
3. preparing the surface plate: 00:03:22
_________________________________________________
4. touching the part: 00:03:50
_________________________________________________
5. some scraping of the part: 00:04:07

Getting comments on things I do wrong is why I post this thread ;D.

[ame]http://www.youtube.com/watch?v=kMfYAGiI7Ns[/ame]

take care,
tom in MA

 

[pete]

Tom,
I don't have any experience with scrapeing so I sure can't answer any of your questions. However for scrapeing on machine tools I'd have to highly recommend "Machine Tool Reconditioning" if you don't already have it. Yeah it's expensive at almost $100 but it's more than worth it. IMO it would be a requirement. You could scrape things in perfectly flat yet still make the tool far worse for true alignment.

Pete

 

[tel]

I have only very limited experience with scaping, and that looks to be coming along ok, but this bit concerns me;

I was only cutting the areas with the blue..

... do you mean deliberately? You have to remember that the blue is a negative image of the job, and the high spots are those where the blue has been removed. Cutting away at the blue areas will only serve to dig holes!

 

[Florian]

Tel

That would be so if you put the color on the workpiece.
But if you put some color on the touching plate, you will have to scrap away the blue spots!

Tom:

You apply too much pressure when grinding the scraper and aswell when honing it!
-> is that a HSS or a carbide blade? I Assume its a HSS..? (-> different ways of grinding it!)

You should try to apply very few pressure then you will find out that the ground surface will have a better finish!
To hone the blade should be done with a silicium-carbide (or similar) hone. Diamond is only good when using a carbide blade!

When honing, only few pressure is required.
And you should rotate the honing file against the radius and not with it (as if you would like to grind a sphere on the opposite side of the blade -> did you understand what i mean? if not, i will look for a movie or make a drawing...)


For fine scraping (like you show on the movie) i hold the scraper with my left hand nearest possiple to the blade.
The other hand is directly behind the left hand.
With the left hand I apply pressure towards the durface and control the conctact point of the blade to the workpiece. With the right hand i move the blade.

When rough scrapping, The left hand only applies pressure on the scraper and the right hand either controls the contact point and moves the scraper.

I'll see if I can make a movie from my scraping work so you can see how I do it...

Cheers Florian

 

[steamer]

Hi Tom,

The bench grinder is OK for roughing out the blade, but it should be honed after. The proper way to hone it would be to stand the scraper on end on an arkansas stone and draw it toward you across the blade while pivoting it to follow the curve of the blade ( in a direction across the end of the blade)

7 degrees is a good angle for me...it depends somewhat on what your work piece is.

Then lay the end of the blade flat on the stone and rock the blade back and forth along the flat side of the blade. The goal is to get a polished surface on both edges....it will cut noticably better if you do this.

Your first cuts or roughing out, from what I am seeing looks OK. It will take many passes. After each pass, cross your cuts. That means approach the next cut of the surface at an angle to the first cut. If you do two cuts per pass , cut at 90 angles. If three cuts, cut at 60 degree angles...approximately. If you don't, you will get chatter, which seems evident in the photo you took.

The gray area in the middle with marking compound surrounding is called a "bullseye" and is exactly what you think it is.


Dave

 

[tel]

Fair enough! I've only ever done with the blue directly applied.

 

[steamer]

The first photo looks like the surface has "carried". As I understand it, that means you have spots evenly distributed over the whole surface....no bare areas which would be low in this case.

Notice I said evenly. If you had a very high concentration of spots in the middle of that disk, I would say you have false spotting and the center is high. In that case I would make a couple of passes only on the center and get the part to bear on the periphery. Otherwise it is just a see saw and will give you false spots when you marking and will never progress to full bearing or be "unstable".

Keep going which what your have and remember to cross your cuts...and hone that blade! ;D

I eagerly await more information from our membership...I hope to learn what I'm doing wrong also!

Dave

 

[steamer]

the honing stuff is in the book your getting by the way.

Dave

 

[rake60]

I crashed a big machine at work one time.
We're talking major damage!

The company decided to have the machine totally refurbished
while the damage I had caused was being repaired.

One of the repair companies technicians did nothing but scrape ways.
He used a a reciprocating pneumatic tool with a replaceable carbide
on it to quickly work over the surfaces of the ways.

I asked him if I could try it and he handed me the scraper.
After just a few seconds he took the scraper away from me and said,
"don't worry I can fix that".

I thought I was doing OK. :

Rick

 

[steamer]

That would be a "Biax" power scraper made by the Dapra Corporation.

Great tool if you do this alot.....Rebuilding a big machine would be one of those cases..

Dave

 

[steamer]

"Dividing up the large area's " is called breaking up the surface....and it is a good idea... ;D

Dave

 

[steamer]

Florian just sent me this.

Hey Dave

I have just a moment ago discovered a Movie where a guy uses pulling-scrapers...:

[youtube=425,350][/youtube]http://www.youtube.com/watch?v=TFCVO0fXW1k&feature=player_embedded

Was also very interesting for me!

Cheers Florian

Its called "pull scraping...and is just another way to do it.

Apparently very Swiss!

Dave

 

[ttrikalin]

You apply too much pressure when grinding the scraper and aswell when honing it!
-> is that a HSS or a carbide blade? I Assume its a HSS..? (-> different ways of grinding it!)

You should try to apply very few pressure then you will find out that the ground surface will have a better finish!
To hone the blade should be done with a silicium-carbide (or similar) hone. Diamond is only good when using a carbide blade!

When honing, only few pressure is required.
And you should rotate the honing file against the radius and not with it (as if you would like to grind a sphere on the opposite side of the blade -> did you understand what i mean? if not, i will look for a movie or make a drawing...)

Florian, thank you -- such are exactly the pointers I was hoping to get.

Based what you say and what Dave wrote, I reground the scraper and honed it carefully and softly on a stone (not an arkansas stone, but not a diamond lap this time). I think I understand how to hold it to hone it, but I'll shoot a video and upload on wednesday or thursday (have a business trip coming...).

And yes, any video instructions welcome... ;D

Nevertheless, I'll be posting what I do...

So gents and ladies (if any),
"I'm listening..."

t

 

[ttrikalin]

"I'm listening..."

Yes, I'm watching Frasier on Netflix...

take care,
tom in MA


PS. Sounds pretty pathetic my friends say, but I do like Frasier...

 

[chuck foster]

great..................just great.............thanks tom now another thing i just gotta try and learn........... :big: :bow:

i have been readin and watchin you and dave and it looks very interesting............please keep us posted with what you have learned.

thanks guy's

chuck

 

[ttrikalin]

I have only very limited experience with scaping, and that looks to be coming along ok, but this bit concerns me;
... do you mean deliberately? You have to remember that the blue is a negative image of the job, and the high spots are those where the blue has been removed. Cutting away at the blue areas will only serve to dig holes!

Tel,
what Florian said, I put the blue on the surface plate...

Pete

However for scrapeing on machine tools I'd have to highly recommend "Machine Tool Reconditioning" if you don't already have it.

Yep, I got meself a copy of Conelly's book... Pretty nice read I may say... Dave commented it's a tad thin on instruction, but good on procedure... So I ordered a more instructional book... Will post a review 1 day after I get it (I'll surely read it in one swoop).

take care,

tom in MA