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[Noteworthy] Scraping In A Precision Straight Edge

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Ulma Doctor

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#31
Thank You Pete!
i'm not sure when the class is going to happen, but i'm looking forward to it.
i'm considering having my own party again and inviting guests....:grin:
 

tertiaryjim

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#33
Ulma Doctor Hinging?
I have noticed differing ways parts move when swinging ( rotating ) them to check that the centers aren't high.
Never thought to do this on the blue. Will give it a try when possible.
That may have sped things up a lot when scraping the gibbs flat before fitting them.
 

Ulma Doctor

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#35
Ulma Doctor Hinging?
I have noticed differing ways parts move when swinging ( rotating ) them to check that the centers aren't high.
Never thought to do this on the blue. Will give it a try when possible.
That may have sped things up a lot when scraping the gibbs flat before fitting them.
Hi Tertiayjim,
hinging is a way of testing the bearing of the scraped piece on a surface plate.
a properly hinged part will hinge at about a 1/3 from the end, on both ends.
you won't really need to have blue on the plate to do it though, it can be hinged on a bare surface plate.
another method i use, i learned form youtube video's is the-Tap,
or Thump as i like to call it-
you'll simply lay the intended scraping victim on the surface plate, and give a nice solid thump with your forefinger on the piece in the corners of the piece.
if the part is flat all you will hear is the thump of your finger.
if the part is not flat, in reference to your surface plate, there will be a slight ring that will be heard.

i hope the info is helpful to someone :)
 

tertiaryjim

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#37
Thanks Dr.
Am learning from books, U-tube, the posts of others, and experience.
I learn more from my mistakes than anything else. LOL
Working on my china lathe has been easy in that even a poor job is far superior to the factory work.
Components no longer rattle when tapped and rigidity is greatly increased.
Machining gibbs has been a pain in the tookus. So much to learn...
 

vettebob

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#38
Now that you have the first side roughed go ahead and rough in the dovetail side before finishing it as the first side will likely move after roughing in the second side. Also what is your scraping depth remember Rich's 2-4 tenths deep and percent contact rules Bob
 

Ulma Doctor

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#39
Thanks for reading Bob!
it's funny that you said to go to the dovetail next...
i already started the dovetail but did not post any updates yet.
my hand roughing scrapes may be a little deeper than 4 tenths, but thanks for the reminder!
i haven't really started scraping for points yet, i'm just trying to achieve proper bearing and hinging first.
all the pointers are greatly appreciated :)
 

The Liberal Arts Garage

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#40
Hinging? Never really thought about it, but in a lifetime of fitting things with
files and grinders, I've been doing it for years. BLJHB.
 

ericc

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#41
Hi Ulma Doctor. I'd love to look on if you have this workshop. I am in the bay area.
 

Ulma Doctor

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#42
Hi ericc,
you would be welcome to the scrape off too!
i'll make announcement nearer the date for all that would like to attend.
 

Ulma Doctor

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#43
Hello again,
i got back on the scraping horse again
i have some updated pictures.
the thread lives on!!!!

here's the top side, the bevel is facing the viewer

2016-06-05.jpg
here is the spine below
2016-06-05.jpg
the bevel is pictured next, it's still slightly high in the middle minimal distal edge contact
2016-06-05.jpg

here's the back of the straightedge, it's coming along very nicely
2016-06-05.jpg
it's time for me to get serious again about the straightedge , it's holding up other work.
the only way to get there is to keep working at it, slowly and surely and maybe even a little surly :grin big:.
as always thanks for reading!
 
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4gsr

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#44
Mike,

Looking good!!!
Might scrape it a little hard in the middle a couple times on the bevel to get more spread on the markings. Be sure to go back and recheck the top and bottom to make sure they didn't move when finished working the bevel.
 

Ulma Doctor

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#45
Thanks Ken, :grin:
the bevel is high in the middle, i'll do as you suggested and hit it hard in the middle!
i have been trying real hard to scrape opposing faces to minimize warp.
I've also been wringing the reference occasionally throughout the process too!
i appreciate the pointers very much, Thank you,
feel free to point away! :grin:
 

Flightmap

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#48
I too am trying my hand at scraping! For my project, I have an acquaintance who likes to re-build lathes, and he had an old craftsman lathe bed that he was going to scrap. It has two flat ways and should make a great scraping project for a straight edge. The bed is "good iron," old iron, stable, and reasonably flat and straight. I just couldn't see scrapping this quality iron. Resource met need so now I have a project and the material.
 

Ulma Doctor

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#49
I too am trying my hand at scraping! For my project, I have an acquaintance who likes to re-build lathes, and he had an old craftsman lathe bed that he was going to scrap. It has two flat ways and should make a great scraping project for a straight edge. The bed is "good iron," old iron, stable, and reasonably flat and straight. I just couldn't see scrapping this quality iron. Resource met need so now I have a project and the material.
An Atlas/Craftsman lathe would be a great starting point, have fun with it!!!:grin:
thanks for looking!
 

4gsr

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#52
Mike,

Looking good and getting better at it.

When you get finished there, I'll send you a compound and cross slide to my 15" lathe that needs some "touch up" scraping done to it.:D

Ken
 

Ulma Doctor

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#53
Hi Ken,
thank you very much!!
I'd be proud to touch up your compound and cross slide! :grin:
 

4gsr

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#55
Those little helpers, always show up when you are doing something in the shop. My little helper is my 3 year old grand daughter. She gets into my mill tooling and starts putting the drills/endmills into all of the open holes she can find. Any loos screws, carbide inserts laying around go into those holes, too. She loves playing with the step blocks, at least the smaller ones, can't quite pick up the bigger one's. When that happens, it's time to put her to work! Ken
 

Ulma Doctor

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#56
Those little helpers, always show up when you are doing something in the shop. My little helper is my 3 year old grand daughter. She gets into my mill tooling and starts putting the drills/endmills into all of the open holes she can find. Any loos screws, carbide inserts laying around go into those holes, too. She loves playing with the step blocks, at least the smaller ones, can't quite pick up the bigger one's. When that happens, it's time to put her to work! Ken
Hi Ken,
my son is interested in all the shop tools and in the movie making process too!
i hope some of it sticks, he could be really good starting as young as he is!
thanks for watching!
 

Dresden

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#58
well, back at the salt mines...
were getting a lot better contact, the straightedge is starting to hinge correctly on the surface plate.
Hinging, for the uninitiated, is the act of handling one end of the piece being scraped on the inked up surface plate in an arcing fashion, to see the point of greatest contact for the opposing end, which is about 1/3 the distance from the end of the work when a properly scraped piece is hinged.

View attachment 181647


and after a few more heavy scraping cycles....

View attachment 181650

as indicated by the light blue, the surface contact has broadened greatly.
another score of cycles will be necessary to call it flat!
You are holding your scraper at to high an angle and not putting enough pressure on the stroke, grind your blade to a flatter radius, 12cm and use shorter strokes, you should actually make cast iron dust when scraping.
 

Ulma Doctor

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#59
you can tell all that from a couple still pictures, wow you must be a master!


for the record, the scraping in those first pictures was done with antique carbon steel scrapers.
the old style scrapers are ground to a 0* end relief
the radius on the scraper was already pre-formed by a much more experienced scraper than you or i. i just sharpened the tool and put it back to use.
 
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