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45 degree
4

45 degree

45 degree

(OP)
In a design for a scraper that is to skive off flooring, such as linoleum, tile etc, I am trying to prove that a 45 degree angled blade is the best choice for wear and capability.  The blade will be flat to the floor and the leading edge is 45 degrees.  Does anyone know how I can prove this to be true?  Calculations or any other means would be very helpful.  Thanks
Jim
 

RE: 45 degree

Not completely satisfied that this is correct.  Yes - it will allow both the horizontal and vertical forces to be about equal.... but that may not be correct for the situation..

If you had say a 30 degree slope that would allow for more "shoving" or "pushing" power and maybe just enough "uplift" to break the bond.  It does not take much to break the bond --- but obviousy depends on many unknowns...

Will this be power or man driven.

 

RE: 45 degree

Usually, you let the engineering decide what is the best angle, rather than decide the angle and try to make the engineering prove it.  I'm with Mike.  It depends on the bonding forces, available 'pushing' power, friction coefficients, etc.

<tg>

RE: 45 degree

(OP)
The pushing power will come from hydraulic driven wheels, giving high pushing force.  

Lets assume that the bonding of the material to be removed to be high also.  If it were not, any angle would work (other than 90).

We can probably disregard the friction (although I realize it is there).  I am trying to determine that when using the blade, the leading angle could be more or less than 45 degrees but to get a compromise between its wearability and its usefulness, 45 would be equally good for both.

Jim

RE: 45 degree

You would probably save a lot of time and gain a lot of functionality by supplying three blades, 30 deg, 45 deg, and 60 deg and letting the operator select and use the one he likes best.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 45 degree

At 45 degrees, you'd probably damage the underlying floor.

I would tend to go, floor to blade angle of 30° maximum.

You're trying to pry the linoleum/tile off the floor, not jack hammer it downwards. That's a whole different tool.

V

RE: 45 degree

I think you are oversimplifying the problem.  How ridged is the equipment that holds the blade flat to the floor?  What is the hardness of the base floor: is it wood or concrete?  The hardness of the floor covering material should be considered as well.  The problem becomes oversimplified if you assume that the blade is infinitely ridged.  Wouldn't the flexibility in the blade along with the angle and relative hardness of the materials involved tend to drive the blade into the floor base material or cause the blade to climb into the floor covering?  That is why I like waross answer where you could have several blades to accommodate the various conditions where the tool could be used.  

RE: 45 degree

While a 45 may be appropriate, I think that a look at the rake angle data for various materials for cutting tools might improve your chances of being close on the first try.  See Machinery's Handbook.

Griffy

RE: 45 degree

(OP)
Before I go any farther, you need to know that this design was implemented, before I came along.  I have been charged with finding a way to prove that the 45 degree lead angle is what will resist wear as well as skive the floor effectively.

The underlying floor is generally concrete and the overlay can be just about anything.  The blade is ridged enough (1/2" thick) to be considered ridged.  The blade can ride up and over the overlay, on occasion.

I have read in the cutting tool section of Machinery's Handbook but the application isn't exactly the same.  The blade I am working with sits flat on the floor and the 45 degree leading angle separates the overlay from the concrete.

I understand this may seem to be oversimplified with all of the variables present, but I had thought there may be some known rule or way to calculate edge wear and/or edge effectiveness, for knives, scrapers, chisels etc.

RE: 45 degree

I would think that you don't want the blade to be flat to the floor.  I would think you'd want a small, maybe 5-10 deg angle there.  45 is probably too blunt for the blade edge, too.  

It will probably matter also what flooring you're removing - is it flexible, ie, linoleum, or rigid, ie, tile?

RE: 45 degree

Getting a little off topic since you're just wanting a proof of the 45 degree angle, but it seems to me that a serrated edge would perform better due to the concentrated force at the points and then the gradual lifting of the flooring.

<tg>

RE: 45 degree

Go look at a wood plane and see what angle the blade sits at.  This might be a good starting point, from which you may have to deviate in order to optimize the cut.

RE: 45 degree

Seems to me that the objective, once the leading edge is broken free, is to minimize the "lift" i.e., the bending upwards of the material already dislodged.  That would suggest that 45° is too high.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: 45 degree

If you have the time and money - try a few samples...

You might be in for a surprise.

RE: 45 degree

Come on, people.  Read the question!

Quote:

...this design was implemented, before I came along.  I have been charged with finding a way to prove that the 45 degree lead angle is what will resist wear as well as skive the floor effectively.
The OP is not asking how to find the optimum angle, but how to prove that the existing angle is adequate.

"Good to know you got shoes to wear when you find the floor." - Robert Hunter
 

RE: 45 degree

Quote (okjim):

Before I go any farther, you need to know that this design was implemented, before I came along.  I have been charged with finding a way to prove that the 45 degree lead angle is what will resist wear as well as skive the floor effectively.

Can't help you, because I don't think that's correct.

V

RE: 45 degree

Sometimes disproving it leads to better designs and the correct answer.

RE: 45 degree

KENAT,

You're almost as cynical as I am. wink

V

RE: 45 degree

Uh, jim, if your boss thinks that's what engineers are for,
....
you need to get a new boss.

Tomorrow.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: 45 degree

Alternative approach.

Try and find the truely optimum angle.

See how close 45 is to it.

Come up with some justification of why 45 is a reasonable approximation given other factors that can't easily be calculated or some such twaddle, or perhaps 45 is within X% of the theoretical ideal etc.

KENAT,

Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?

RE: 45 degree

(OP)
If a 45 degree blade edge angle is not ideal, finding what is ideal would get me farther down this path.  Also remember, 45 degrees does not have to be the best choice for blade angle, but a compromise between wear resistance and the blade's ability to do the work is.  
This may muddy up the discussion but....
We all know that if the blade was 90 degrees it would not wear as much as the 45 degrees but the 90 would not lift the flooring. I think that line of thinking is why 45 degrees was chosen originally. (anything less than 45 would wear quicker too)

Thanks for the Archard Equation suggestion, I will see what I can do with it concerning the wear.

RE: 45 degree

if the design works, why does someone want you to prove that it's the "optimum" ?  maybe there are service/customer problems ?? certainly, it doesn't sound very optimal.

 

RE: 45 degree

I like 30 degrees. There should be less pressure on the blade with less deflection and as a result, less wear. As the angle approaches horizontal, the cutting edge becomes more prone to bending and breaking.
I suggest that optimum service life between sharpening and repair may not be the same as optimum for best efficiency and least energy expended.
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 45 degree

So basically you've been asked to back-fit a justification for an existing design...

Why not just check out the competition, i googled "floor scraper concrete" and came up with http://www.floor-equipment.com/

Ring them up and ask if you were to buy/rent how often you would have to change blades. Ask the operators of your equipment what sort of lifespan the blades have.

It may be there is no theoretical answer - how thick is the lino, is there more than one layer, what adhesive is used will surely all play a part. Older lino floors may have asbestos in them and may require you to apply special precautions to protect the operators.

Regards, HM

No more things should be presumed to exist than are absolutely necessary - William of Occam

RE: 45 degree

2
Hello,

I did this about two years ago in order to take a lot of tile/linoleum off plywood subfloor. I bought a commercial scraper blade and reground it by trial and error.

I found the angle varied with the hardness of the glue. Hard glue required an angle above 35 degrees, but much higher dug into the plywood. Soft glue loosened well with something close to 30 degrees or a tad less.

I worked with the bevel down and found I needed a slight crown on the bevel so that I could "rock" the point up and down to avoid plowing - more of a problem with low angles.

I wound up doing a little bit on concrete and found that something like 45 - 50 degrees worked well since it didn't come to a dead stop every time I hit a concrete bump.

I think that if I had to do it again, I'd have tried pouring liquid nitrogen on the floor first to make all the glue brittle.

RE: 45 degree

Adhesives usually have a high shear strength rather than tensile strength.  My first thought would be to go around 20-30 degrees to break the bond then it would still have enough force to pry the flooring upward.

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