Scraping in a straight edge

[ddickey]

This video shows the angle of attack pretty well.

 

[Richard King 2]

Looks good... the is roughing in the beginning where his scrapes are touching ends. To the left there is no bluing, Then in the 2nd part he is a "sniper" aiming and hitting the high spotys. Both show the same pressure down but narrower and shorter scrape marks. Also see the angle of the handle to the work.

 

[rabler]

Progress. Still have a few low areas before I try going for more PPI.

I would have to say, this reminds me of my private pilot exam flight, simulated engine failure. The examiners pulls the throttle, says "engine failure", and you pick out a landing field, set up and make the approach. The examiners starts yammering on about not flying over the chicken sheds, the farmers get really ****** as it kills chickens, etc. I get a little rattled, then tune him out. If he doesn't like it he can give me power back. I ignore him and set up. He eventually says "good", set the throttle back to climb power and I climb out (probably about 200 ft up). I ask, "The chickens were a distraction?" He replies "more or less". I later learned there is a famous airspace lawsuit settled in favor of a chicken farmer. Anyway, sometimes you need to ignore the copious internet comments and focus on getting it done. I've seen it before WRT scraping discussions, and like other manual skills, you need to find the kernel of truth and ignore the distractions, and work on the muscle memory.

 

[Richard King 2]

Looks better. Your flying story and your photo reminds me of a trick. My Dad shared this story with me when he was alive. 60 years ago or so, My Dad had crew of men work alone scraping in a JIG Bore at 3M in Saint Paul, MN back then they only hand scraped. They called him and said they were done scraping the top of the 30 x 48" table top. You scrape the table top to 40 points per inch (PPI) and measures from the spindle .0001". He first looked at it and he said it looked odd, so he said "clean it off and blue it off again." The protested and said " NO it's Good, let leave it" He insisted and they did and after they blued it up again, there were several areas that weren't touching or holes. He then said he looked at them and said "Where is the pencil?" and he said it again "Where is the pencil, I was in your shoes before and know how you can use a pencil eraser to dab in the low spots," LOL... They never admitted doing that, but he knew. I see you have a blue Sharpie laying next to your part.....lol...

 

[Richard King 2]

So what did you do to improve? Scraping 40 PPI and 40 to 50 % percentage of points (POP) is difficult and as I say in Taiwan "soenen sun chow" (Practice makes perfect") Yeah once you practice eye hand coordination it as anything it gets better. One thing I can say it your trying to get it to good to fast. That's an issue many rookies have. So next time scrape or semi rough a bit longer. I mailed the HSB stick yesterday 2 day mail and inside the envelope I put in a couple copies of pages of my work booklet I give out to students show the PPI chart I attached here. Plus a couple others. One thing is to scrape xoxoxoxo X being a scrape and O being an open area as in the one spot in the last video I linked to when John was talking to Lance you don't have to scrape every blue spot or you will leave a long not touching hole. I see that on your part xxxxx all touching creating a long hole. Also wipe off a clean spot on your plate and rub the blued SE on the clean area to shine or polis the high spots. That is also in the video. Keith Rucker and John both take a black sharpie and dot the shinny high spots. You still need to press down harder as your depth is still around .0001" or on the low side. You have discovered that many people on the internet forums guess because they do not have the skill to teach. I don't guess and have taught several people to scrape 40 PPI on the net. You Tube has sure helped. You noticed all the good shows on You Tube are done by my students I hope. Your having fun now...

 

[rabler]

So what did you do to improve? Scraping 40 PPI and 40 to 50 % percentage of points (POP) is difficult and as I say in Taiwan "soenen sun chow" (Practice makes perfect") Yeah once you practice eye hand coordination it as anything it gets better. One thing I can say it your trying to get it to good to fast. That's an issue many rookies have. So next time scrape or semi rough a bit longer.

This is where it gets into building experience. To "improve" I went from a long roughing stroke to shorter "finishing" strokes, and more attention toward "checkerboarding" as Gotteswinter calls it in his video, or X's as you refer to it. But, as you noted, it was a bit early for that. I'm building experience by making mistakes.

I prefer a green sharpie for marking boundaries between areas to scrape and areas to skip, but I couldn't find my green this morning. I'm not yet to the point of playing sniper.

 

[Richard King 2]

To help teach the others reading this, did you measure the depth of the scrape marks?

I was not accusing you of adding blue sharpie high spots...LOL just telling the story.

 

[rabler]

To help teach the others reading this, did you measure the depth of the scrape marks?

I was not accusing you of adding blue sharpie high spots...LOL just telling the story.

I measured between .0004 - 0007 when roughing. I have used a scale and am getting around 8 lbs. I haven't measured depth for these shorter strokes but am using similar pressure. I am thinking that thinning/slotting my scraper body to give it some flex would make it a bit easier, but haven't yet made the leap to doing that.

 

[Richard King 2]

Depth sounds good. Remember to always press down the same when scraping 40 PPI - don't lighten up the depth when you get more points. Did you experiment raising the back of the scraper handle to get a narrower cut and lower to get a wider cut? Curious so the others can learn too. I like what I see, your a fast learner. Plus you have a plane? You have to tell us about that sometime too.

 

[rabler]

Depth sounds good. Remember to always press down the same when scraping 40 PPI - don't lighten up the depth when you get more points. Did you experiment raising the back of the scraper handle to get a narrower cut and lower to get a wider cut? Curious so the others can learn too. I like what I see, your a fast learner. Plus you have a plane? You have to tell us about that sometime too.

Thanks
I have worked with changing angle to change cut width. I have not yet built a hand-eye coordination that I can adjust as I go, so I understand the idea, but need more practice. I'm working on spacing and stroke length too. Making those mechanical is just practice, practice, practice. But I'm only good for a few hours a day before I'm worn out.

I was a flight instructor and had a plane for a while, but age and medical issues (resection of part of the illeum and ileocecal valve due to Crohn's fissure) have made that story of the distant past. Flight instructing is one area where you absolutely learn to teach, when to talk, when to let them process and try it out, and when to grab the controls and say "my plane". You get to see your instruction in a very real "the ground is coming up at us" kind of way