Learning how to scrape :D

[purpleknif]

I plan to expirement with it unless an experienced voice shows up and says "it just plain won't work because _____________".

I was also toying with the idea of using one of those vibrating multi-master type tools with a brazed on HSS or carbide scraper tip on a blade.... I bet it would scrape and its a little more approachable than a Biax.

http://www.harborfreight.com/variable-speed-multifunction-power-tool-67537.html

I think you'd be wasting your money as far as using it for scraping goes. Awfully fast and a really short stroke. Just my .02. Yes, bi-ax scrapers are nice ( especially the flaker) but unless you're doing a machine Bridgeport size or larger I'd say spend the money on something like tooling or a couple cases of beer.

 

[steamer]

Im with Purpleknife...I think that will just turn into something that isn't very controlable.

JMHO

Dave

 

[Florian]

Hi Troy

If you want to use an available tool, you may use a tiger saw. I have seen a conversion with a tiger saw some time ago but i cant remeber where it was.
Fact is it seemd to work pretty well. And if I remember right, that guy modified the drive gear so the stroke was reduced to something around 5mm.

But it still will have some disadvantages compared to a biax which has adjustable cutting stroke, adjustable speed (though some tigersaws will have this feature as well) and finally its the shape of the machine which is best suitable for scraping. (unlike the one of a tigersaw)

I don't know where you have been looking for scrapers but you may search for "Hand scraper".
I found this:
www.dapra.com/
http://www.machinerepair.com/
http://www.machinerepair.com/size.html (good to know when starting)


Oh and by the Way:
You can make your reference from steel but it will be horrible to scrap because the blade will kind of stick to the material. If I remember correctly it is better to use HSS for scraping steel and carbide when scraping cast iron.
Also the angle of the blade has a great influence on how well you can scrap the workpiece.
I have just looked up in a document from a BIAX, and they say for steel scraping you need 32° scraping angle.
This means if you have a blade with a front face which is rectangular to the top and bottom face, the front face will have to be tilted for 32°. And if the Angle is positive, you have to use the side of the blade with the smaller "wedge angle" (when comparing with lathe tools).
If the Angle is negative (and that is usual when scraping cast iron, mostly somehting around 3 to 7° though you start with 3° negative and for finishing you increase the angle) you will have to use the edge with the greater "wedge angle".


Cheers Florian

 

[vedoula]

If you want to use an available tool, you may use a tiger saw.

do you mean a reciprocating saw?

 

[Florian]

Yes, ecactly
I only know it as a "Tiger Saw" 8)

Cheers Florian

 

[steamer]

I have a variable speed "Tiger Saw" which IIRC is a Porter Cable product.

Though I've used it to rip through all kinds of things with a wrecking blade, but IMHO, it is far too unwieldly to be used for scraping....at least finish scraping.

I suppose If I had to take off .020" by hand...well I might give it a look though. Then again a disk sander may work even better in that application....or just machine it.

Dave

 

[Florian]

Well, I found a movie about it:

[ame]http://www.youtube.com/watch?v=bJPS9SWn6Ys[/ame]

(Tiger saw with shortened stroke)

And also a conversion Thread: http://www.machinistweb.com/forum/showthread.php?t=501

Cheers Florian

 

[steamer]

Well, can't argue with that. :bow: If your shorten the stroke, it does seem controllable.....but it's a heavy saw.

Dave

 

[ttrikalin]

i have a horrible fright "tiger saw" that broke the second day I used it... Never returned it though... So this may be a good salvage use for it.

take care,
tom in MA

 

[lee9966]

I can't picture holding my big powerful tiger saw that steady, are there different sizes of the saw?

Lee

 

[steamer]

My reservation is based on the fact that my 120V, 15 amp saw would have no problem cutting my pickup truck In half with a rescue blade. Its not exactly subtle.....even with the stroke shortened its got to be the better part of 20 pounds

Dave

 

[vedoula]

My reservation is based on the fact that my 120V, 15 amp saw would have no problem cutting my pickup truck In half with a rescue blade. Its not exactly subtle.....even with the stroke shortened its got to be the better part of 20 pounds

Dave

probably not an HF unit then... Makita?

[tom from anastasia'a account]

 

[TroyO]

Santa didn't leave me enough for a set of the long handle scrapers AND a chunk of cast, so I am comprimising somewhat.

Current plan.... make my own long scrapers and buy a set of the cheap scrapers with short handles.

(These guys .. http://www.grizzly.com/products/3-Pc-Machinist-s-Scraper-Set/T10086 )

I've got some 1/2x1/2x3/16 carbide blanks and misc HSS to play with, I think I can knock up some effective scrapers with what I have on hand.

So, the extra can go towards getting a decent chunk of cast to work with(1.5x3.25x12")

 

[steamer]

Hi Tom,

My saw is a Porter Cable "Tiger Saw".

Dave

 

[Florian]

... buy a set of the cheap scrapers with short handles.

These short scrapers are not good for scraping, it is very tiring to work with such small scrapers.
Well, the three corner and curved scraper can be used for some work like deburring holes and scraping in bearings (bronze-bearings) but the flat scraper is only suitable for removing color (and other dirt) from straight surfaces...

So you better get yourself a diamond grinding wheel to sharpen your scraper properly.
(-> RDG Tools has cheap ones...)

Cheers Florian

 

[TroyO]

I've got one of these to grind with...
http://www.harborfreight.com/1-2-half-hp-6-inch-tool-grinder-46727.html

I like it so far but have been grinding HSS on white wheels. I'll have to put the green ones back on and final lap on diamond hones by hand. I'm going to try with what I have and see how it goes. A diamond cup to fit the grinder probably wouldn't be a bad idea anyway, but money is short at the moment.

I was thinking of the short scrapers more as "Nook and cranny" tools and the long ones as the grunt work/heavy guns.

I dunno... worst case I waste some material that I already had and learn something or best case I end up with a good tool and learn something.

I'll post up pics of what I end up with... for better or worse. ;-)

 

[steamer]

Hi Tom,

My saw is a Porter Cable "Tiger Saw".

Dave

OK went out and inspected my saw. Its a Porter Cable model 737. It draws 10A....not 15...

Its more like 10 pounds....and I still think it'll rip your arm off if given half a chance..... :

Dave

 

[Florian]

I'll have to put the green ones back on and final lap on diamond hones by hand. I'm going to try with what I have and see how it goes. A diamond cup to fit the grinder probably wouldn't be a bad idea anyway, but money is short at the moment.

Hi Troy

Well, the green wheels are ok for bringing the blade into shape but not for sharpening. I had to find this out aswell when I started with scraping.

The Wheels provided by RDG are very cheap but really worth their money! I have the small 50mm one and it did only cost me around 20$!

The greatest discs cost about 25 to 30 $ and so are still very cheap and though they are cheap, they last quite long (I cant see any loss of diamond on my disc actually tough I am using it alot!)

Cheers Florian

 

[TroyO]

Ohh, I'm not saying I won't try and get a diamond wheel soon (ish). Right now, no money... maybe next month LOL.

But, I may be out of the woods on that one... I read about someone using a lapping plate with a diamond buffing compound on it to put the final sharpen on carbide bits. The idea that the wheel made of something softer than diamond (easy, LOL) and carbide (Still easy) gets the diamond particles embedded in it.

In his case he was using a wheel made of iron, but aluminium is supposed to work just as well. Dope it up with diamond compound and you can get a razor sharp edge. (In theory).

I happen to have diamond compound already from my knife making days.. old but hopefully still good.

Maybe this weekend I can get started on some of this.

I did realize that I *may* have a source for some cast iron hunks... old window sash weights.

I may try to salvage some of it... if only for practice surfaces as I realize it's pretty much the crudest cast iron you can get.

 

[TroyO]

I have seen a few examples of folks using squashed conduit and shoving a carbide insert into it and silver soldering it in place as scrapers. After sharpening it seems like it would work just fine.

I plan to do similar, brazing on to 1/8" flat stock instead because it's what I have on hand.

It just occured to me that I have MILES of material for practice scraping.... there's the drill press table, the back stop part on my jointer, the small drill press that wants to become a tapping stand's table, the jointer bed, heck my table saw top for that matter, etc etc. All kinds of of "Sure you want it kinda flat" cast iron that I can turn in to precision scraped practice pieces while being fairly confident that I'm not going to make it any worse, anyway.

So, yet again the window sash weights I was SURE I would use for something will lie there slowly turning back in to dust... LOL

(Almost forgot to add.... great scraping vid on Youtube... NOT MINE)
[ame]http://www.youtube.com/watch?v=D1eOQa1gYiU[/ame]