The new scraping thread

[Greg Q]

Also, I should point out that MTR and everything listed above is solely about the geometric alignments of the machine. You'll need other references for things like electrical control modernisation and spindle repair. I find the bearing company catalogues often have great information about mounting/demounting bearings, fits and lubrication.

Machinery's Handbook has information on drive belt sizes and pulleys/sheaves. (Although it is by no means an exhaustive resource, and ignores a lot of the European standards)

A quick visit to welcome - library.nu will reveal other books when you search for machine or industrial repair. I think I saw a copy of Moore Tool's Foundations of Mechanical Accuracy there too recently. Interesting reading, that.

Greg

[.RC.]

oooh a class count me in on that for sure Greg
might stay away from the coffee though
had the nice post man turn up today with a present now all I need to do is find something to wreck i mean scrape

cheers
Harty

The Sandvik scrapers are quite good, but what I would do is regrind the radius on the carbide bit to a 90mm and 60mm radius.. They come with a 300mm radius which is hard for a beginner to use and useless for anything but roughing...

I would also remove the file type handle and make something with a big flat end that you can push with your body... I will get pics of mine later today as I am scraping today due to wet weather..

[Greg Q]

RC I'm surprised to read that. I have lessened the radius somewhat on one side of the insert, but had good results with the factory radius too.

I lengthened my scraper by adding a longer wood handle in place of the (regrettably cheap) plastic handle. Still, I use mine by cradling it with my right hand half way up the tool and my left cupped over the end very close to the blade. The tool is tucked close to the body and a swaying motion provides the bulk of the power.

One thing I did find myself doing was rushing...I had an otherwise useless metronome here that I employed to keep myself on speed...less fatigue and better strokes were the result.

GQ

[mic-d]

RC I'm surprised to read that. I have lessened the radius somewhat on one side of the insert, but had good results with the factory radius too.

I lengthened my scraper by adding a longer wood handle in place of the (regrettably cheap) plastic handle. Still, I use mine by cradling it with my right hand half way up the tool and my left cupped over the end very close to the blade. The tool is tucked close to the body and a swaying motion provides the bulk of the power.

One thing I did find myself doing was rushing...I had an otherwise useless metronome here that I employed to keep myself on speed...less fatigue and better strokes were the result.

GQ

I hone mine at a bit less than the original I reckon. Maybe I'll do a smaller radius and see how it goes. I use mine with original handle, left hand under the handle, fingers pointing forward, end of handle resting in the palm, not gripped. Left hand tucked in tight to my hip and the body provides a lot of the power. Right hand lightly grips the other end, palm on top and pressure downwards. I am a leftie. I consciously monitor my posture to make sure I'm not too hunched, shoulders are relaxed, rock my head around to make sure my shoulders and neck are loose. I tried the grip you use Greg, but I found myself hunching over too much and getting sore, so the other suits me better.

[.RC.]

O would add to Gregs list a set or two of feeler gauges.. They are very cheap ($3 from memory) from CTC tools..

[RayG]

This is possibly a dumb question, but, to what extent would a largish granite straight edge obviate the need for one of the larger surface plates, if the main use is to verify accuracy of the straight edge (sorry, spotting master)?

I'm thinking an appropriately mounted ( say 36") granite straight edge might suffice instead the larger and heavier option of a (say) 36" x 24" surface plate?

Regards
Ray

[Greg Q]

I reckon it would do away with the need for a large plate for that purpose as the granite spotting masters are like slices of surface plate anyway. By my reckoning a 600mm granite would weigh approx 8kg; I don't know that I have seen longer than that. If there were 900mm granite models they'd probably be 15-20 kg. But they'd be stable and insensitive to body heat distortion.

I am planning out the scraping of my Deckel parts. A large plate is very useful for being able to set a part on along with dial indicators and other tools for determining parallel and dimension.

(trying to talk myself into a very large plate)
Greg

[.RC.]

Just do it Greg.... You cannot compare a large plate to a small plate is you have large workpieces..

I am happy with mine...

[Greg Q]

I know you're right RC, especially given the small difference in price once you get up into the 800 and larger plates. I am planning to put whatever I buy onto my next tool cart project, and you know what's involved in supporting 600 kg (total) in something mobile with drawers. I wasn't planning on quite that much engineering. But I don't want the horror of popping for a biggish plate that ends up being just a bit too small down the road.

I should have bought that big one in Wollongong a few years ago for $1500...

Eight feet by five feet and 16" thick. Only problem I could see was the 5 tonnes fitting on the roof racks.

[.RC.]

Some pictures as promised..

My Sandvik holder with some inserts and the pine handle I on it (woodworking is not my forte)

A pic showing me hard at it and showing how using yellow highlighter really brings out the blue

[harty69]

while i am gleaming as much info out of everyone as possible could i get some pic's and info of how and what you use to sharpen your carbide tips

cheers
Harty

[Greg Q]

I just rediscovered this site which covers the tools for scraping, and has pictures of the process of a scraping class such as I attended. The grinder shown isn't necessary if you just buy a diamond wheel on ebay for under $50 and mount it on whatever grinder you own. Make a small wooden block bevelled at around 5º for a sharpening and lapping rest. You'll need some diamond paste..also ebay.

The following is must read:

Shop Stuff: Scraping Class

[mic-d]

while i am gleaming as much info out of everyone as possible could i get some pic's and info of how and what you use to sharpen your carbide tips

cheers
Harty

Hi Harty, don't know if you saw my earlier link, but I'll post a photo of how I sharpen mine. The top hand is a pivot, move it lower for a tighter radius. Bottom hand sweeps it over the lap. I used an angle gauge to determine the 93º angle to the lap and noted the distance from the edge of the lap. From then on I just eyeball the position. I use 3000 grit diamond powder from a lapidary store and charge the lap with that in a bit of mineral oil.
I found that the finest diamond lapping plates (1200 I think) were still too coarse and didn't leave a nice finish on the work, although others just use them. Don't be tempted to use a SiC green wheel.

[Anorak Bob]

Michael,

Why do you blokes hand scrape your plane soles? What's wrong with just lapping the sole on wet and dry carborundum paper affixed to a flat surface?

Bob.

[mic-d]

Michael,

Why do you blokes hand scrape your plane soles? What's wrong with just lapping the sole on wet and dry carborundum paper affixed to a flat surface?

Bob.

Bob, some people make it a religious argument and I don't want to start a hijack in this thread
There's a seven page thread here about the why's and wherefores and blog entries here where I've outlined the mathematical reasons why a flat plane with a sharp blade has fewer errors than a convex plane which is often produced by lapping.

When I was researching scraping, I came across an old machining reference that when these processes were being developed, that in trying to speed up the process of flattening by scraping, any attempt to do lapping as an intermediate step always resulted in taking the object further away from flat than the last scraping step... or something along those lines I have never been able to find that reference again

I have both lapped and scraped planes. The lapped planes are convex, every one I have ever lapped became convex, but they work OK because I have learnt the tricks to use. A scraped flat plane requires less guile. Some planemakers swear by scraping. In the seven page thread there is a link to a thread in Practical Machinist on lapping/ scraping planes. Forrest Addy is not a fan of lapping either.


[edit] I should add that the argument is made that wood moves so why bother making a flat plane. It is a spurious argument. If you plane a panel flat with a convex plane, it will tend to make the panel Biconcave in cross-section and however the wood moves after that it will always maintain that original error. If you joint an edge with a convex plane it will tend to make the edge concave. If you plane two edges and place them back to back for a glue up, there will be a big gap in the middle of the boards (how much is in my blog). The convex plane tends towards maximum error, a flat plane tends towards minimum error although there will still be an error because a plane planes a concave even when flat because of the way it's built - I call it the natural curve - also in my blog - you will need coffee!

Cheers
Michael