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Scraping v- block

lucky7

Titanium
Joined
Sep 6, 2008
Location
Canada
Am scraping a cast iron 7" x 5" v-block that was a rusty mess I found outside. Have had no problem getting the faces flat to 40 ppi and 90deg angles to within 2 tenths per 12". Don't know how to get accurate 45 deg without a master angle or a sine plate. Suggestions?

Lucky7
 
Put an indicator on a holder, register the holder against the end of the v-block and set it up to indicate the V vertically. Clamp a second indicator mount to the side of the V block, and indicate the end of the holder. As you slide the first holder against the end of the block perpendicular to the V, the indicators will change by identical amounts if the block is exactly 45 degrees.

No idea how accurate or practical this might be.

Another thought is to scrape a triangular block with a 90 degree peak to match the V. The surface of the V facing up won't necessarily be level, but if you flip the test triangle around, the same spot on the triangle will only be at the same height if the V is at 45 degrees. More work, but probably a lot more accurate.
 
You can clamp a parallel to your plate and then strike the angle..flip V block and strike again on the other side.. to know V is centered.. do again at a few other place along one side then the other to again find center is dead on...
*But yest that won't check the quality or the 90* of the V..

I had a master v block to test me B&S V block and have it near dead on..
Top quality 1-2-3 block..tested for square and marked for best sided (90*) makes a good 90 gauge for .000050 or so.
Yes you need a best surface plate to test the gauge.
 
Thanks Otter, I did read Moore's book (and am humbled) and understand how a box square with a dowelled 45deg square on end is self checking and proving a true 45deg in a v. Also understand how a mini 45 deg gauge works. Don't have either and was hoping there was some method I didn't know of that wouldn't involve either. If I was scraping a pair of v-blocks, I'd make a small square to go between the pair, which would then self prove, but have only one v-block to scrape. If push comes to shove and no other method exists short of making a mini 45deg gauge, I'll borrow a sine plate amd it'll be simple dti work. Only looking for low tenths accuracy here.

Thanks for replies.

L7
 
You said you can verify 90 degrees. Do you have a square corner you can depend on other than the V-block itself?

If so, I think there is a procedure for verification. You'v got the two sides of the V and you you know they're flat. You don't know yet that it's square, that if square it's not tilted, or that it's centered with the sides. If you have an external square, verify the 90 degrees. Using a single dowel or roll pin you can flip the V-block and verify that AT THAT POINT the dowel is centered or not. If so, do the same exercise with a larger cylinder that touches the V at a different spot and repeat the centered test. If it's not also centered, the V is tipped relative to the sides and bottom.

That should give you what you need for correction of angularity or centrality.
 








 
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