Small sine plate

[steamer]

Hi,

Last year at the NEMES annual exibition, I won 2 or three door prizes. ( yeah for me!)

OK....at the door prize table at the end of the show was this little partially completed sine plate,,, no rolls and it was kinda rough..

NO ONE wanted it...I walked up to the person in charge of the door prizes at the end of the show and asked about it. He said no one wanted it and he didn't know what to do with it.....I DID.

Take it ! he said....It went in a draw for a while until this afternoon when I had a hankering for some scraping work. First I got the top flat to a couple of tenths....that to 25 cycles of scraping, but its flat...I won't be quiting my day job. I'm still working on my "Hook", but I know its flat.....

Next I trammed up my mill as best as I could and milled the sockets for the yet to be made rolls. ON the button...5"

I like the result so far. I'll finish it up in time for this years show.

Dave

 

[Majorstrain]

Sweet Dave,

Cast iron or steel?
I'm too much of a nubie to tell by looking.

Cheers,
Phil

 

[steamer]

Thanks for the comments Phil.

Best I can figure, it is some form of mild steel........

It scraps OKm, but you need to keep the blade sharp or it scratches and chatters.

I'll put some rolls on it now...

Dave

 

[arnoldb]

Nice one Dave Thm: - Who wouldn't want a sine plate ???

Did you get right down and scrape it? - from the original top surface it looks like it was fly-cut in two passes.

Between you and Phil you've (hopefully) got my weekend project sorted - though I'm not going to attempt scraping... yet!

Kind regards, Arnold

 

[cl350rr]

Nice project Dave,
any chance of you showing your scraping technique? I have been wanting to try it for years but am hesitant to destroy a perfectly unflat piece of metal just to find out I don't know what I'm doing

Randel

 

[coopertje]

Hi Dave,

Nice work on the tool! No better fun that to turn a rusty piece of metal into a fine working tool.
Just for my information, what can you do with a sine table? I saw them many times for sale, looks great but no clue about usage :-[

Regards Jeroen

 

[steamer]

Hi

Thanks for the kind comments!

Well, I'm no expert by far....but I'm having fun

Yes I did scrape it flat from a rather crude flycut surface, originally about .002" flat with steps...the person who originally made this didn't tram the mill. While roughing it down, your shoveling stock off....its rude and crude, but it doesn't matter as your just getting the stock off....then, once the bearing "carrys" across the full part, you can start to refine your scraping technique from " areas" to specific spots until you get a good distribution of spots evenly spaced.....then it's just more of the same, shorter strokes and more patience.



Mr. Morgan's book can be found here complete with DVD.

http://www.machinerepair.com/

WELL worth the investment I thought

I use my new Anderson Tube scraper....( this years Christmas present) HOO HOO!

I am using the marking medium shown on Tony's site

http://www.myheap.com/projects/gingerylathe/part_99/images/TonysScrapingPage.pdf
It's water based and cleans up nice...but you have to get used to working with it...it has to go on REAL thin, or you'll get smear and false marks...but you can feel it when that happens during the marking

And I love watching Nick Mueller work his magic

[ame]http://www.youtube.com/watch?v=uHF7TtHVSWE&feature=related[/ame]

[ame]http://www.youtube.com/watch?v=D1eOQa1gYiU&feature=related[/ame]

He has others if you poke around

Connelly's book "Machine Tool Reconditioning" is a must have if your going to do anything beyond make something flat....worth the Investment...and then some...cures insomnia too! ;D

There are many checks in this book that are worth knowing even if your not scraping, like the "spin" test for flatness, and the straight edge test for flatness verification...they are independent tests for flatness...but they better agree with each other, or something is not really flat!

Additionally, as an engineer with experience in the machine tool industry, I've worked with a lot of scrapers. Many have shown me a trick or two...for which I am forever grateful. I don't even hold a candle.......

I have another medium that I am just trying out. It consists of Crayola Powder paint and Hi spot blue. It is used by the Masters where I currently work. I have some but I haven't used it yet. As I do, for those that are interested, I'll post.....it's just not Model engine related ....so I'll go easy.

As far as my style. Sure...I was going to try and sketch what I do, but it doesn't sketch well

I'll try to show it with some pictures this weekend maybe.

Bottom line, if you want to learn how to scrape...there's only one way....read and start.
It's a "finger tip technology" kinda thing.

Get a small piece of nice iron bar and have at it...worst that can happen....you throw it in the mill and mill it off! ( there by hiding the evidence ;D)...you'll learn something every time you do it.

I started this part by scraping the center somewhat hollow. That way I knew I was bearing on the edges and not see-sawing in the middle. If it see-saws, you will not get a stable marking, and you will chase your tail for a while before you figure it out.

Once I was there , and got bearing all around the edges, (picture frame if you will) I started to refine that to make the contact area's wider and wider until the center filled in.

Dave

 

[Bolster]

Dave thanks for the encouragement...I would like to learn how to scrape and you've given us a great head start here.

 

[zeeprogrammer]

That was pretty interesting. I'd always wondered what people meant by 'scraping'.

Thanks.

 

[Maryak]

complete with DVD.
Bottom line, if you want to learn how to scrape...there's only one way....read and start.
It's a "finger tip technology" kinda thing.

Dave

I know another...................junior engineer in a recip steamship. At the time, "WHY ME,"............... now I am grateful for the experience.

You can spend big money on scrapers but old worn out flat and triangular files suitably ground take a lot of beating. This only leaves you with buying a bearing scraper.

Best Regards
Bob

 

[steamer]

I know another...................junior engineer in a recip steamship. At the time, "WHY ME,"............... now I am grateful for the experience.

You can spend big money on scrapers but old worn out flat and triangular files suitably ground take a lot of beating. This only leaves you with buying a bearing scraper.

Best Regards
Bob

Cross head guides or Journals! ;D

My first scraper was a file...then I took a big parting tool blade made of HSS and ground the clearance flat. Then I ground the forward radius...then I taped it to the file with electrical tape....worked great!

I like my Anderson better......



Dave

 

[steamer]

Hi Jeroen,

A sign plate is used to hold a part at an exact angle. The distance between the rolls is 5" in this case

The Sine of an angle is the Opposite side of the triangle / Hypotenuse of the triangle.

Therefore The Side opposite = Sine angle X Hypotenuse

OK the Hypotenuse of the triangle is, in our case, fixed at 5".

If you look up the sine of the angle you want, or use your calculator,

You now have the Sine of the angle.

Doing the math, you get the dimension for the side opposite the triangle. If you stack some gage blocks to that height under the rear roll of the sine plate, the plate will be at exactly that angle.

Example

We want to position our Sine Plate at a 30 degree angle.

The Sine of 30 degrees is 0.500

Side opposite = 0.500 x 5.00" = 2.5000"

If I stack some gage blocks to that height and put them under the rear roll, the plate is at 30 degrees

Here's some further reading



http://www.auto-met.com/subtool/stcat/st_136.html

http://en.wikipedia.org/wiki/Sine_bar



Here's another example. I want to mount the sign plate at 23.25 degrees...exactly.

Sine 23.25 = 0.3947438

0.3947438 x 5" = 1.9373" So the stack of blocks needs to equal 1.9373".

Keep your units straight. Degrees and decimal degrees or degrees/minutes/seconds. but don't mix and match, you'll be sorry


Very useful for all kinds of things...especially odd angles.

Dave

PS how about sensitivity to error?

Lets say, in our last example, our stack of blocks was off by 0.002" too big.

The side opposite would really be then 1.9393

1.9393 = sine ( angle+ error) x 5"
Sine (angle+error) = 1.9393 / 5" = 0.38786

ArcSine (0.38786) = 23.27 degrees actual versus 23.25 degrees desired, or about 1.2 minutes of arc

If your making cement mixers...you won't know, but if your doing something thats supposed to be accurate, accuracy counts when you make a sign plate.

Sine

 

[Maryak]

Cross head guides or Journals! ;D

Cross head guides I don't mind,( well the ahead ones coz you don't/cant move em, never had the pleasure of a double guide), journals are OK? but it's lifting the bottom half of the big ends in and out of the crankpit that takes the bloody cake.......... Not to mention how many shims of ??? ??? ??? size dropped in the process when you let go the lowering ropes and a couple are/were hung up and drop off just as you reach for them.

Best Regards
Bob

Apologies for the hi-jack, the above has little to do with the sign of anything but the times.

 

[steamer]

Cross head guides I don't mind,( well the ahead ones coz you don't/cant move em, never had the pleasure of a double guide), journals are OK? but it's lifting the bottom half of the big ends in and out of the crankpit that takes the bloody cake.......... Not to mention how many shims of ??? ??? ??? size dropped in the process when you let go the lowering ropes and a couple are/were hung up and drop off just as you reach for them.

Best Regards
Bob

Oh you have got to get the movie " The Sand Pebbles" ;D

Dave

 

[mklotz]

Sine bar/plate error due to stack height errors...

sin(theta) = h/L

where:

theta = angle
h = stack height
L = sine bar/plate length between rolls

Taking the derivative of both sides of the equation wrt h, we have:

cos(theta) * dtheta = dh/L

where:

dtheta = error in angle
dh = error in stack height

Solving for dtheta...

dtheta = dh/[L*cos(theta)]

Example:

L = 5"
theta = 15 degrees
dh = 0.001"

dtheta = 0.001/[5*0.966] =0.0002 radians = 0.012 deg =~ 0.7 arcmin

 

[steamer]

Hi Marv,

I believe you and I agree?

Dave

 

[mklotz]

Probably. I didn't check your calculations that closely.

The difference is that your approach requires more calculation than mine which uses a single formula to determine the error.

The formulary approach also makes it clear how the error changes with the angle to which the device is set. With the cosine of the angle in the denominator, the angle error due to a fixed stack error will grow with the angle - a 0.001" stack error will cause more angle error at 30 deg than at 15 deg.

I went back and checked your calculations and there is one problem.

You wrote:

ArcSine (0.38786) = 23.27 degrees

but the reality is:

asin (0.38786) = 22.82 deg

 

[steamer]

probably round off error...your point?

Dave

 

[mklotz]

My point is that with a (corrected) value of 22.82 deg, the resulting error is unrealistically large. To wit...

23.35 - 22.82 = 0.43 deg = 25.8 arcmin

which implies that a 0.002" stack height error is going to cause almost half a degree of angle error. Intuitively, that makes no sense.

The error can be traced back to this line from your post...

0.3947438 x 5" = 1.9373" So the stack of blocks needs to equal 1.9373".

If you check, you'll see that:

0.3947438 x 5" = 1.9737... (not 1.9373)

You did some digit transposing when you typed.

Continuing your analysis with this corrected value, we have:

asin(1.9757/5) = asin(0.39514) = 23.275 deg

so the angle error is 23.275-23.25 = 0.025 deg =~ 1.5 arcmin

As a check, let's see what my method yields...

0.002/(5*cos(23.25)) = 0.00043 radians = 0.025 deg =~ 1.5 arcmin

 

[steamer]

Thanks Marv....I'll try to keep my Dyslexic math in order.

Dave