Thanks: 0
Likes: 0
Needs Pictures: 0
Picture(s) thanks: 0
Results 16 to 30 of 40
-
11th May 2012, 05:43 PM #16anne-maria.
Tea Lady
(White with none)
Follow my little workshop/gallery on facebook. things of clay and wood.
-
11th May 2012 05:43 PM # ADSGoogle Adsense Advertisement
- Join Date
- Always
- Location
- Advertising world
- Age
- 2010
- Posts
- Many
-
11th May 2012, 05:56 PM #17Member
- Join Date
- Oct 2008
- Location
- Birchgrove NSW
- Posts
- 66
Derek,
I defer to the people who really know, but I don't think your conclusion is correct. Fence Furniture was making the comparison at the two different rpm I used and came to the same conclusion as me, about 45%.
For the same angular velocity (rpm), according to my calculator:
a 6" wheel at 2850rpm has a tangential velocity of 3.5625 metres per second,
an 8" wheel at 2850rpm has a tangential velocity of 4.7500 metres per second.
The 8" is faster by 33%, just as 8 is 33% larger than 6.
Yes, 6 is the base for these % comparisons.
If we want to talk about slower, the base becomes 8.
Either way, the 6" speed is 0.75 of the 8" speed.
Regards,
Mark
-
11th May 2012, 06:02 PM #18Jim
- Join Date
- Feb 2008
- Location
- Victoria
- Posts
- 3,191
FF your circumference are not accurate (not that it makes any difference when working with ratios) as you have been using radii and not diameters. Eight inch wheel has a circumference of 16 times pi making it nearly fifty not 25.
Cheers,
Jim
-
11th May 2012, 06:04 PM #19Jim
- Join Date
- Feb 2008
- Location
- Victoria
- Posts
- 3,191
-
11th May 2012, 06:09 PM #20
Hi Jim, there's a bit of confusion going around atm! This time it's your turn - circumference is Pi times diameter, area is Pi times radius squared. And yes it does make a very big difference in ratios when squares or square roots are involved, but not in this case. As Mark said earlier it's "linearly proportional".
-
11th May 2012, 06:10 PM #21Jim
- Join Date
- Feb 2008
- Location
- Victoria
- Posts
- 3,191
Derek, the water-ski-ing analogy doesn't affect anything. The maths are simple. Circumference is in a linear relation to radius. Double the radius and you double the circumference, hence with two wheels, one twice the radius of the other and the same revs, the smaller has half the circumferential velocity of the other.
Cheers,
Jim
-
11th May 2012, 06:14 PM #22
Yes I understand that Jim, but my calcs are spot on.
-
11th May 2012, 06:15 PM #23Jim
- Join Date
- Feb 2008
- Location
- Victoria
- Posts
- 3,191
-
11th May 2012, 06:17 PM #24
Funny, that's exactly the emoticon I thought I would see! It's too easy to get your head locked into a path with this stuff.
-
11th May 2012, 06:19 PM #25Jim
- Join Date
- Feb 2008
- Location
- Victoria
- Posts
- 3,191
-
11th May 2012, 06:27 PM #26
If you are referring to Simple Harmonic Motion (the tracing of the motion of a fixed point on a circumference when viewed from a profile), and the associated mathematics - I LOVED that at school. It was part of three subjects that I did for the HSC (waaaaay back in 73) - Science, Maths, and the Mechanics strand of Industrial Arts. By the time we got to IA I was doing it with my eyes shut (literally - all 3 studies were within a few months of each other, so I was happy naps).
An example of SHM is the vertical path that a cyclist's feet trace. And just as a bit of whimsy - the sexiest maths I ever studied was Integration by Parts - just a beautifully elegant solution to an unsolvable problem.
-
11th May 2012, 06:29 PM #27.
- Join Date
- Feb 2006
- Location
- Perth
- Posts
- 27,794
If everything else is constant, the heating effect on a tool being sharpened depends on v^2 .
This is because KE = 1/2mv^2 , a doubling of speed produces a 4 times greater KE, while a 50% increase in speed produces a 2.25 times more KE and more heat.
Of course the overall rise in temperature also depends on contact time and pressure so for higher speed grinders, compensations can be made using a shorter contact time and less pressure. Likewise grit size and type, (and to a lesser extent the type of steel) can be used to advantage.
Even when taking all this into account, local (ie immediate contact area) heating effects are still greater for higher speeds. just how much this is, difficult to say.
-
11th May 2012, 06:32 PM #28
Does it help if you blow on it Bob?
-
11th May 2012, 06:34 PM #29Jim
- Join Date
- Feb 2008
- Location
- Victoria
- Posts
- 3,191
FF. no what I was referring to was the fact that in theory the part of a wheel in contact with the road (unless it is skidding) comes to a stop for a fraction of a second and accelerates to twice the speed of the car at the top of its travel.
Cheers,
JIm
-
11th May 2012, 06:37 PM #30
Similar Threads
-
Ugly but effective!
By burraboy in forum DUST EXTRACTIONReplies: 1Last Post: 30th July 2011, 11:08 PM -
Frustrated by sharpening jig set-up time
By rsser in forum WOODTURNING - GENERALReplies: 10Last Post: 26th November 2010, 02:01 PM -
Simple but effective - WIP
By Billyboydes in forum BANDSAWN BOXESReplies: 20Last Post: 2nd October 2009, 08:13 AM -
simple but effective - x-mas
By keju in forum SCROLLERS FORUMReplies: 10Last Post: 14th November 2008, 01:55 PM