[rolfinator2002]

Thought I'd post my (cast iron) scraping eductation so far, some hard learned, some passed along by others with experience. Hoping to save others my frustrations and mistakes.

First, hard won lesson:
Never use prussian blue spotting fluid; if you have those little tubes from permatex or wherever, give or throw them away. I have 2 brand-new tubes if anyone wants them.
*I forgot just how hard it is to clean up anything after using it. Impossible to get stains out of anything but metal.
*Use Canode spotting ink. Non-drying, water soluble ink, works great. I clean up my straight edges and work with just a damp cloth or running water. Got a stain out of the carpet fairly easily too.
Dapra sells it, but were very expensive with all the other related items, so I bought mine from Volk.com for $10 for 1/2 pint (lifetime supply).
2nd:
You'll need a rubber roller (2" to 3" wide, your preference) to apply the ink. Not very critical, I bought one from the craft store for $2 as opposed to spending bucks online.
3rd:
Try to use a carbide scraper to reduce your downtime dressing the tip.
There is nothing wrong with using a steel scraper from Enco.com, but you'll need to grind a radius on the nose to avoid end-gouging.
4th:
Scraper dressing is all important. Dress the tip with a 140-300 mm radius to begin your work or large areas and dress it to 60mm radius for spotting those canode spots toward the end of your journey. A DVD/CD is a perfect template for 60mm radius.
5th:
Scraper dressing pt.2
You must dress the tip so that the scrapes have no streaks or scratches (not issue with steel scraper). Grind the nose of the tip between 1-4 negative degrees, and grind it so the working edge "sees" the lead side on the grinding wheel to prevent carbide breakdown, then flip the tip over and repeat. The finished tip will have a little edge-nose to it, and the carbide won't break-out, leaving nicks. Can't stress how clean and sharp tip must be; lathe sharp is not good enough. If you can see any nicks under a 20x loupe, no good.
6th:
Carbide blanks are usually dull, no good. Faces must be ground and polished; inserts for Biax scrapers come mirror bright, which is why they are expensive.
7th:
My homemade scraper will accept anywhere from 3/32 thick to 1/8 thick blanks, so I can use cheap ebay carbide or the good stuff. The standard biax insert is 3/32 thick, with 3/4" x 1" being the most popular (most people seem to use the inserts dressed with the 3/4 side as the cutting edge. They are ground with 4 work edges, so don't get too frightened if you order some inserts from Dapra; you might grind that insert once if you do this for a hobby.
8th:
I use a granite straight edge for the box ways and flats because it is a whole lot cheaper to get accuracy/foot with granite. Regardless of the straight edge, always run a sharpening stone (any kind) lightly across the surface before touching with your master, even if you haven't started scraping, otherwise you risk scratching the master (like I did). A few scratches don't hurt, but they add up. Brush off the surface also beforehand.
9th:
Apply spotting fluid to the master sparingly, everybody always starts out with too much. Use a small amount and take your time spreading it out with the rubber roller. A good spot with show light color in the center, with blue around the edges, not all blue.

When I think of more screw-ups and lessons, I'll post for anybody who wants to scrape their own machines.

[TOTALLYRC]

Do you have any before and after pics or a video or 2?


Mike

[rolfinator2002]

I learned on some scrap class 40 iron, didn't take pics, but starting to take pics on latest iron. This is pretty new for me too, by no means an expert, just an engineer whose profession puts him in touch with a lot of prototyping equipment and machinists.

Brand new lesson regarding biax scrapers:
Bought an electronic variable speed; just had to speed up the process for reasons I'll disclose in the future.
There are still single-speed power scrapers floating around. Do NOT buy one unless you can get an external speed control. Why? Tough to use for any higher point work, turcite, or smaller parts, even with stroke turned down to 2mm. The level of skill required to operate a power scraper is directly proportional to it's speed. The variable speed version is so much easier to use; my hand work to finish up will probably be the last 1 or 2 passes if at all.

[TOTALLYRC]

I will keep watching since I will probably want to scrape a machine or 2 in the future.

Mike

[jalessi]

[ame="http://www.youtube.com/watch?v=2HvEw5k09R8"]YouTube- Kitamura Machinery - Hand Scraping Techniques on a Horizontal Machining Center[/ame]

[ame="http://www.youtube.com/watch?v=R3Bc1-VZ__s"]YouTube- Kitamura Machinery - Handscraping Techniques on a Vertical Machining Center[/ame]

[skullworks]

Could you post some close up pics of the insert after grinding?

[rolfinator2002]

I have a lot of irons in the fire at the moment, so the project is going to be stretched out a bit.
Lost my job for christmas (all of us); seems my company is selling part and shutting down the remaining part of a division, so a job search is going to take a lot of focus with near 20% unemployment in this area. The US unemployment rate is very deceptive because it only counts people who have been unemployed for 6 months or less, not very accurate in this economy. I digress.

The biax paperwork I found on an EU website suggests grinding the carbide insert to -3.5 degrees for cast iron. Here is a closeup of a standard 3/4" biax carbide insert as ground to show you what I meant in a previous post regarding the shape. Grind it so that the grinding wheel "sees" the flat sides first. Some people grind just one work edge, preferring to grind sideways (see nick Mueller), but I like this method since I can flip the blade over for another working edge.

[rolfinator2002]

Here are some pics of my homemade scraper. It cost me about $6 in material and my time as opposed to the $75-$100 for either an Anderson or Dapra. I purchased carbide blanks on ebay, with extra blanks for form tools or whatever. They are NOT the standard biax thickness(3/32), which is hard to find for cheap. These blanks are approx 1/8" thick, so I can shim to clamp biax inserts. Was not happy with the results until I got the hang of grinding the inserts, now very happy with the function.

Here is the mill saddle of the present project, after measurement to determine what needed to be scraped and after rough scraping. Scraping starts as rough scraping to remove tool marks (whether grinding or milling according to the biax folks), then plane scraping, followed by finish scraping, then oil film scraping.

Last, I'm not far enough along to determine if I really needed a straight edge to "spot" the dovetails in the saddle top and table ways, so it would be unwise to purchase a straight edge (>$2,000); I was losing my job where I had the resources to fabricate a straight edge, so I decided to at least rough-in a tool in the evenings after work before the layoff day.
It was made from G2 dura bar cast iron (similar to class 30-40) which I purchased from a local supplier. Milled it square, clamped it in a large set of v-blocks and split the bar across corners on a vertical bandsaw. Then proceeded to both side-mill and face-mill the sides to get a 90 degree, 50 and 40 degree triangle, carefully setting up the mill to ensure precise angles. Turned some handles out of 3/4" scrap, threaded to 9/16-18, drilled and tapped holes in the bar to match. The dura bar supposedly comes stress-relieved, but I didn't want to take chances so the metallurgy dept let me use an oven to stress-relieve it at 1100 deg F to be sure. It was then milled again to touch it up. It will be scraped when/if I need it for this project, but certainly in the future for another mill.

[tobyaxis]

A true Art Form to say the least.

[rolfinator2002]

This was suppose to be a straight cnc conversion for a taiwanese vertical mill, but when I started to strip it down for power washing, it became clear that the saddle had moved from 20 years of aging. The center of the box way was depressed by .010" and the top side surface had the same issue, with flaking still intact where it had sunk.

Now I own a power scraper, learning the art and certainly appreciating the craft because I won't be that good at it, but would like to avoid the $1100 or more for a total regrind and scrape by sending it out. I figure that the lathe in my future will probably need similar attention. The mill at my former employer is a mess in terms of stick-slip; they just pump it with a grease gun, now I understand why some mills are more accurate than others.

Hopefully all this effort will yield a cnc mill that will accurately mill everything without oil film "rise-up" or stick-slip issues.

[Eson]

I wonder what your thoughts are on scraping brass or aluminum just for getting started if you don't have any cast iron laying around? Also how much difference is there between scraping cast iron and say carbon steel?

What is 'oil film scraping'? Is that frosting or flaking? Im trying to learn the glossary.

[rolfinator2002]

Internet is a great place, except if everybody has a different opinion on a topic that really needs to be in one track. Check your IM. I sent you the US (english) biax scraper how-to manual, which includes different materials.
Cheers.

[rolfinator2002]

latest thing that I found.
anybody want a great, concise explanation on how to scrape, im me for one of the biax manuals. The 40point manual geared for the US seems to cover more ground, but the EU manual (in english is pretty good too.

Regarding blade prep:
The typical cup wheel for the HF baldor tool grinder copiy, is available in 150 diamond grit from places like shars.com. The grinder combined with the diamond wheel does a great job getting the prescribed -3.5 rake angle, but a tad too coarse for all work. I found that the power scraper works ok for rough and plane scraping, but not ideal for finish scraping. I am no stranger to hand lapping blades, etc but this doesn't do well for the power scraper. Lap with strict control to angle. Suggest 600 grit diamond lap; however, place it against your tool grinder to ensure that you maintain the desired rake. This ensures the velvety scrapes when you get to the finishing passes, even the 40 point work if you are a fanatic.

If I had the time, I'd make a hard steel plate to mount to the tool grinder and charge with 20 micron diamond paste; that would make the perfect edge and simulate the edge on the bits provided to me with the scraper in the first place.
cheers

[rolfinator2002]

This started life as a rectangle of G2 iron, which i stress-relieved and milled.
So far rough-in and started plane scraping. Attached are some items to help other novices like myself. Keep the blade honed after rough-in pass. As the machine speed increases, chatter risk increases tremendously.
Attached are some troubleshooting pics.
The final pic shows a good finish pass, at full machine speed, proper lap, proper machine angle, good grasp on machine.
Rolfinator

[rolfinator2002]

Edge wouldn't carry, so I had to go back to rough-in and plane a few more times until I could pick up t he entire length. Since I'm a novice, it took a while.
The center of the plane had a substantial dip,so the ends were scraped to bring up the middle, then to favor opposite sides to correct slight twist. The final pic shows the edge ready to bring in points. Stroke was 15mm until the dip was brought up, then the stroke was reduced in increments to 4 mm at this point, as points come in, I'll drop to 3mm. Planing was done with 140 radius tip. I switched to 60 mm radius when i dropped down to shorter stroke.

Still learning balance between stiffer, more flexible holders, grinding angles, etc. -4.5 degree seems to work better to avoid gouging. Have ordered some more blades for tighter areas.

[rolfinator2002]

Doing anything w/o rigid, formal education takes a lot more time, but I finally got the first side done with about 36 points, far more than I needed. I'm mainly using this straightedge as a guinea pig.
bought a short 25mm wide 90 mm radius rougher and a long, flexible 15mm wide 40 mm radius finisher to get the 40 point work per Biax. This will give me a complete span of basic cutters, at least until I try to dig into the mill table dovetails.

Started the 2nd side.
Here are pics:
Before work, showing the flycutter marks.
first pass on left side, cross pass in other direction on right side.
Closeup of previous pic.
I'll go over it a couple of more times until I have a planar, clean base to work on, then shorten the stroke, and go to a tighter radius.
More later.

[rolfinator2002]

Tada.
2 working sides of a 50 degree prismatic scraper. why 50 degree? It is the dovetail angle in the table ways for my Supermax mill.
Finally starting to get the hang of using a power scraper; work is tremendously speeding up (for a hobbyist like me).
Iron is always straining (thus the reason that I'm scraping my mill in the first place) as the years go by, so I expect that I"ll have to touch up the spotting with a granite plate a year from now as it ages.
Now I can get back to finish scraping the mill saddle.

[rolfinator2002]

The mill project will be on the back burner for a while, but I'll post related stuff when I get it.

A while back I made a separate post on making your own carbide scraper using inserts. Repeat pics below. I think it cost me $13 as opposed to the $100 Dapra equivalent.
If you choose to make a carbide insert scraper, I can confirm that you need high-quality carbide to avoid excessive aggravation. I went to great lengths polishing my C2 carbide because the chip frost was wrong and it took excessive pressure to scrape, even more than HS steel inserts.
Ready to throw the scraper across the room, and began a temper tantrum, I switched out the carbide for a Biax insert, polished very little, and problem solved.

Biax stresses the use of "special" fine-grained carbide for their power scrapers, but won't say what grade it is; don't buy generic carbide and expect good results for either your hand or power scraper.
They work fine for BS turning operations, but not good enough for this kind of work.

[rolfinator2002]

Connelly's book is excellent and I cannot stress enough to get it and read the whole thing.
A professional scraper may not agree with my posts, but since I am not, be gentle with me.

1) Human nature is addressed; I couldn't get my prismatic straight edge to master quality, and I didn't immediately see why. Connelly made it clear. In short, both human nature and a host of other things cause long, slender work pieces to become convex, and if you are shooting for flatness of no more than 0.0002" over a length of 2 feet, this can be distressing, yes I said distressing.
There are specific operating techniques to get good results, AND some very, very simple tests, that in themselves need to be practiced in order to master the difference between convexity (slight bow less than a hair in the center) and marking compound effects.

2) If you don't have $3,000 for prismatic straight edges, inside and outside 90's, and special gaging you don't realize are needed which total a bazillion dollars (until you read Connelly's book), then you'll be making them on surface plates. If you fall into this category, I strongly suggest that you buy pink granite whenever you can get it. It is much harder than black granite and it's easier to unlock a work piece as it gets flat, and if you are using spotting compound correctly to make masters, not general spotting, you won't be using enough to protect the plate from scratches. The compound lubricates and protects the stone master, but to get accurate points on master work, only the minimum amount can be used, not enough to protect anythng. If you are really picky, you might use alcohol colored with lamp black as the compound. If you don't trust pink granite, get it certified and/or repaired so you know the true flatness, or make 3 identical pieces and use the law of divided error to make masters, which is how master plates are made in the first place if a reference is not available.

3) I mentioned it before, but it so important to avoid damaging any granite gages, that I mention it again. Don't use stones, even soft Arkansas to debur in between cast iron scraping. No matter how hard you try, there will be some stone debris that scratches your plate sooner or later. A deburring file does a much better job working the material anyway. A stone grinds down burrs while the file simply knocks them down, the more desired effect.
Use a 8-10" double cut smooth flat file and dull the teeth with a diamond honing stick. One of mine is a smooth single cut (mill) file that works well too. Do this until the teeth take on that "dull" look as you examine it under light. The file must NOT do any cutting or scratching, nor must you feel any cutting action in your hand. Keep dressing the file until it doesn't feel like a file anymore. Use only back-forth motion, not circular on the work piece. When you're happy, grind a safe edge on one short side and 40 degree on the other. This will allow you to use it in the tightest places, including all dovetail angles.

[stk2008]

Why can they just not surface grind instead of scraping like he was?.

Or am I missing some thing here?