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View Full Version : What's a Center Scraper?



mayfieldtm
02-08-2005, 05:41 PM
I've never seen one.

I've been reading the Book "The Quorn Universal Tool and Cutter Grinder" by D.H. Chaddock.

He is explaining how to correct a mis-centered Center Hole.

Quote... "If there is an error, a square center or a center scraper will very quickly pull the hole a few thous in the right direction."

Sounds like something I could have used many-a-times.

I did a web search with zero hits.

Tom M.

ben78
02-08-2005, 06:27 PM
Not sure if this it what they are talking about but...

If you are drilling a hole, and it is off centre, you can score the hole to the opposite side it is wandering too and this will realign the bit a few thou... maybe...

Norman Atkinson
02-08-2005, 06:30 PM
Tom,

Professor Chaddock was refering to a lathe centre- centre which instead of being ground into a pointed cone had four pyramidical flats on it. Instead of acting as a bearing, it cut on one of its flutes like a sort of reamer until the new center position was created. At that point, the whole gubbins would be back in correct alignment.

If you are making a Quorn, might I add a warning- published earlier that one casting is bored with two one inch bores and is subsequently split, can nip up so much that it is impossible to insert the ground 1" precision ground bedbar.

I hope that this makes sense and explains what is a rather unusual description.

Norman

mayfieldtm
02-08-2005, 07:09 PM
Norman:
That sound interesting.
Hard to really visualize though.
Wish I could see one.
I was thinking to just apply lateral pressure with my thumb while using the center cutter.

That hole thing with the Quorn...
One guy heated the casting with a torch (after it was split) and it relaxed back to the proper fit.
I'm thinking he was just lucky.
Have not heard of any proper techniques to prevent or correct this.

Tom M.

Forrest Addy
02-08-2005, 07:19 PM
Back when I was a grinder hand I made my onw center scrapers from small triangle (three-square) files. You scraped away at the excess metal in a center hole to correct the problem, then lapped the center in an Excello center lap to restore the true conical bearing.

This was a common operation when dealing with armatures and shafts subject to the tender mercies of a dolt with a gear puller who seemd to do his best to obliterate them. The original references have to be restored before preps for plating and other repairs can commence. So the centera have to be re-rooled, scraped, corrected somehow.

One attribute of a good bench machinist is his collection of center protecters and center scrapers. If you ask an employment prospect about them and he gives you a blank stare you might want to delve a little deeper in his experience.

madman
02-09-2005, 02:03 AM
Excello centre lap DUH I never heard of one. I set up the steady and have been known to recut centres. Actually you can really easilly recentre drill them. Interesting though. I have done some lapping years ago flat surfaces and have built custom laps many years ago for harley engines crankase bores to clean and align those horribly machined things. Then deck the top cylinder faces in the bridgeport and eventually have a antique design machined perpendicular due to them having been built on a bunch of worn out drill presses at the factory. Did they really melt down bud cans to cast the early shovelhead cases...

Paul Alciatore
02-09-2005, 12:36 PM
<font face="Verdana, Arial" size="2">Originally posted by NORMAN ATKINSON:
Tom,

Professor Chaddock .....

If you are making a Quorn, might I add a warning- published earlier that one casting is bored with two one inch bores and is subsequently split, can nip up so much that it is impossible to insert the ground 1" precision ground bedbar.

I hope that this makes sense and explains what is a rather unusual description.

Norman</font>

Norman, I'm on the other side of the puddle and we have lost some of the Queen's terminology over the years. Can you explain what you mean by "nip".

Paul A.

Evan
02-09-2005, 12:46 PM
We still speak much of it here. Think nip and tuck, as in tighten or close up.

kap pullen
02-09-2005, 02:54 PM
Tool and grinder builders,

You can eliminate the nip if you split the bore, before you bore it.

Never seen a square center, except in books, but you can make a weany boring bar (or use a weany end mill), set your compound on 30 deg. and skim your center out that way.

That's assuming you can run the steady from a good surface.

kap

[This message has been edited by kap pullen (edited 02-09-2005).]

Allan Waterfall
02-09-2005, 03:14 PM
We also have....

"I'm just going to nip out for a bit",meaning I'm just going out but don't expect it to be long before I'm back.

A nip of whisky which is a small amount.

A nipper, which is a youngster.

Nippy.......anywhere near freezing point. As in,"It's a bit nippy out"

Allan

madman
02-10-2005, 02:08 AM
I think ill nip out for another case of moosehead beer.

Norman Atkinson
02-10-2005, 04:18 AM
Or another bottom????

Memories, Memories.

Norman Atkinson
02-10-2005, 06:15 AM
Comment to Mayfieldtm.

Offending Quorn Casting was replaced by Quorn casting number 2( To differentiate between the two Quorn variants) was not split. I fitted a number of cotters which Chaddock described as " Bicycle"ones or drawing B in the original write up in ME.

I wanted to avoid confusion with would be builders- and felt that a number of variations had been suggested in the text. Having issued a warning, I simply left the choice up to the individual.

I am sorry if any misunderstanding has arisen from perhaps oversimplifying things!

Norman