[How do I?] Thoughts on simply scraping a part flat (efficiently)

[Bob Korves]

My best guess at the moment for the low bearing percentage is the too-flat radius on my finishing blade, possibly coupled with unintentionally dropping the back of the scraper is the source of the problem.

The thickness of the blueing also changes how fully covered the work looks, regardless of what the coverage actually is. Thin ink makes for small visible points. Thicker ink looks like more bearing percentage. Of course, it is also easy for an experienced scraper hand to see how much of the ink is on the highest points. For doing really fussy work it is probably smarter to stop using ink and use the evaporated alcohol and dry rub method to delineate the actual contact surfaces.

 

[Richard King 2]

Rex I never intended the pretender remark as you...you are doing fine....a pretender is someone who has never scraped anything and is giving advice...that is a guess. I picked Rex to be my assistant in the CA class as I think he is a fine scraper for the time he has spent doing it. Practice makes perfect....Ive been practicing for almost 60 years...and still am learning.

 

[Rex Walters]

Amen to more practice! I think I was a bit over-sensitive — apologies. I managed to spend a little time in the shop this afternoon and did indeed make some new discoveries. More soon.

 

[Rex Walters]

Rough grinding a scraper blade to the desired radius is not really a task for a Glendo. It is a task for something like a Baldor carbide grinder AND an adjustable jig where you can hold a consistent radius while simply swinging the blade back and forth. Much less expensive (shop made) versions are also in current use. With a decent setup a blade can be ground to a new radius in 5-10 minutes max from a blank like a Sandvik. I am using a HF carbide grinder and a very simple swing jig that can hold a Biax tool or a Sandvik hand scraper with blade (but I sure would like a Glendo as well!)

I finished cleaning up my 15mm wide blade today on my Glendo. I just inked up the blade with a sharpie, scribed a 60mm radius from a Biax gage, and ground to the line by hand with a 0 degree bevel and a 260 grit wheel. It took maybe 10 or 15 minutes, but I prefer the slow speed of a Glendo to the high pucker-factor of a green wheel or diamond cup on a high speed grinder — I prefer to make my mistakes slowly.

A smarter person would have thought to take a "before" picture, but here's the after, anyway:



This was the blade that was causing me grief, but despite fixing the issue I've since switched to a 20mm wide, 150 mm long blade with a 60 mm radius and honed to a -8 degree bevel on a 1200 grit wheel, with a long stroke (8 mm, one half turn from the maximum 10mm stroke of my ancient Biax). All of this is to follow Rich's guidance as precisely as I'm able as I rough/intermediate scrape a 36" straightedge. I'll post an update within a few days, but unsurprisingly, Rich's advice seems helpful: today's results were good.

 

[Richard King 2]

]

I finished cleaning up my 15mm wide blade today on my Glendo. I just inked up the blade with a sharpie, scribed a 60mm radius from a Biax gage, and ground to the line by hand with a 0 degree bevel and a 260 grit wheel. It took maybe 10 or 15 minutes, but I prefer the slow speed of a Glendo to the high pucker-factor of a green wheel or diamond cup on a high speed grinder — I prefer to make my mistakes slowly.

A smarter person would have thought to take a "before" picture, but here's the after, anyway:

View attachment 295315

This was the blade that was causing me grief, but despite fixing the issue I've since switched to a 20mm wide, 150 mm long blade with a 60 mm radius and honed to a -8 degree bevel on a 1200 grit wheel, with a long stroke (8 mm, one half turn from the maximum 10mm stroke of my ancient Biax). All of this is to follow Rich's guidance as precisely as I'm able as I rough/intermediate scrape a 36" straightedge. I'll post an update within a few days, but unsurprisingly, Rich's advice seems helpful: today's results were good.

My friends and co teacher hosts in Austria made a blade lapper that has a blade holder where the blade rests in and on the bottom has a 1/4" dowel pin sticking out of it and the table that it rests on has drilled holes spaced apart down from wheel so you can insert the pin in a hole that was spaced to grind 140 R, 90 R, 60 R, 40 R and 20 R. Stefan G has one like it too... Phil another friend posted the design on PM years ago ...they must have copied that...lol

 

[TakeDeadAim]

I actually contacted Dapra. Only $3,475 for the one I want. That's just for the scraper. The tooling is not included.
Hand scraping is in my future. Besides, that's what they did before Columbus discovered electricity.

Hand scraping was and is done long after electricity. I worked for a company that did not allow power scrapers so all work was done by hand. I think the end product is nicer and honestly after a while you get used to it and learn how to rough parts in quickly. Stuff with big holes or tapers need to be machined to be economically done vs. paying someone to scrape away a bunch of metal that a grinder can take off in one or two passes. Especailly pits, galling or deep scratches.

 

[TakeDeadAim]

]


My friends and co teacher hosts in Austria made a blade lapper that has a blade holder where the blade rests in and on the bottom has a 1/4" dowel pin sticking out of it and the table that it rests on has drilled holes spaced apart down from wheel so you can insert the pin in a hole that was spaced to grind 140 R, 90 R, 60 R, 40 R and 20 R. Stefan G has one like it too... Phil another friend posted the design on PM years ago ...they must have copied that...lol

We had one 40 years ago at PMA in Milwaukee

 

[Richard King 2]

I have been rebuilding machines for over 50 years and in my 20's and 30's we rebuilt several huge machines with flat ways 12" wide and 30' long: G&L, Mesta Lathes, Bliss punch pressed, etc. I recall sitting on boat cushions and scooting along and pushing the hand scraper with my knee. When we bought our first BIAX was in 1973 or so and we only rough scraped with it and finished by hand. BIAX sells hundreds of scrapers each year and have been making them since the late 1950's. As a s BIAX Instructor and distributor for them I have seen many times when people did not use them properly when they first used it and ruined the parts they were scraping and said they were NO Fking Good. Biax shipped them on the longest stroke 3/4" and on the highest speed. They sold the blades flat and when the new customer tried it the scratched the living hell out of what they were scraping.

Hand scraping does not create as much chatter as a BIAX, but I can power scrape a 24 x 24 cast iron surface plate faster and better using a BIAX. I am not just saying this as I can prove it and my students can attest to it.

Like life, times change and with my hand scraping by hand roughing and scraping 40 points per inch, teaching over 30,000 people around the world there is no comparison. I remember having hand cramps, back aches, sore everything for hand scraping day in and day out.