power question

[jwest22]

hi, I have this problem that I have no idea how to solve, I’m trying to do some calculations for a project, so, does anyone have any ideas what calculations you might use to work out what force is required to push a wood working router through material, I want to apply these calculations to many different routers so I suppose the wattage or rpm isn’t important?

 

Any suggestions, thanks

[Externet]

It would need a lot of force to push the router through material at 0 Watts or 0 rpm; so it has to be very important.

[jwest22]

valid point, lets say 1kw and 25000rpm

[J.C.MacSwell]

valid point, lets say 1kw and 25000rpm

 

Even a light touch will put it through in that case...

 

...so you need the speed as well.

 

Also note that the force will not be directly in the line of travel and there will be a torque as well.

 

Can you do an experiment?

[Flashman]

There are many parameters involved, it will vary by material and either thickness of material or depth of cut.

 

Torque may or may not be so important since some edge moulding bits have a bearing on the bottom.

 

Also important may be the cutting angle of the bit, this is often selected by material.

 

Then of course in practical usage, cut quality comes into it, you can get a powerful high speed router and ram it through a material as hard as you can, and get a ragged cut with charred edges.

 

These pages may help you in defining your problem fully and getting towards an answer...

http://www.westone.wa.gov.au/toolbox8/furniture/toolbox/shared/resources_mw/tools_mach/tools/cut_speed.htm

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

[John Cuthber]

I think the power from the router goes into breaking the wood.

That energy is the work of fracture and there's some data on it here.

http://www.nature.com/nature/journal/v252/n5479/abs/252116a0.html

That tells you how much energy is required to expose an given area of fresh timber (by cutting away the stuff in front of it).

If you multiply that by the rate at which fresh surface is exposed (the cros-sectional area times the velocity) you should get a power.

That should be roughly the router's power requirement.

The question then is what hapens as you change the force on the router.

Imagine you push it so hard the thing stalls.

Since nothing moves thewrok done is zero. However, because the motor is still using electricity, the efficiency falls to zero.

Another scenario is that the force pushing the router through the timber is zero. Since no wood gets cut the efficiency falls to zero again.

Somehere in between there is a "sweet spot" where the efficiency is high.

If the router is geared to give a slow RPM it will be harder to stall. But you will be able to force it through the wood harder. You will take bigger chunks of timber out and the cut will be rough.

On the other hand if the router's gear is very high it will not be able to take as big a cut- but it will do it more often so you will still be able to push the tool through the material reasonably quickly.

[jwest22]

OK, so lets say I'm cutting with a 6mm diameter cutter at a depth of 6mm with a 1kw router @ 25000rpm, the material is pine at a rate of 0.02m/s.

 

John, this gives (correct me if I'm wrong) rate at which fresh surface exposed: (6e-3*6e-3)*0.02 = 7.2e-7

 

that multiplied my the mean 0.92 times 104 J m-2 gives 6.624e-3 (watts?)

 

so, thats how much power is required to cut through said material?

[John Cuthber]

Interesting isn't it?