Test Stand

[one.man.band]

In the process of designing a saw test stand to test different saw muffler designs, and maybe my chain sharpening ability. The idea for the stand is based on the attachment below. (Originally, was leaning towards a simple prony brake. Could not come up with a solution for gearing a disk or drum brake without investing lots of money for a custom made gear).

Looking at the photo of the test stand, there are some things that I would like to change:
1. not use a zip tie for holding throttle wide open. would like something safer in case the saw ever dropped of the stand.
2. idea for timing device. the photo shows a lever actuated timer, most likely coupled to a stop watch/clock which is AC powered. i would like this unit to be portable, and not rely on an extension cord.
3. the gauge used to calibrate the down-force of the saw at 9 pounds is definitely out of my budget. idea is to balance the saw teeter-tooter style with weights. then hang a weight of ten pounds directly under saw.
4. do not know the customary size diameter log being cut. the photo shows about a 12"?. the height of the stand will be based on this.

could use some ideas pro/cons etc.

 

[trappermike]

I'm trying to figure out what you are trying to build,something to test a saw's power,or test chain cutting speed?

 

[one.man.band]

...originally, my thought was to build a very simple brake style "dyno" (using the term dyno very loosely), that would give a good idea of peak torque. chain driven to a small diameter disk or drum brake. holding saw speed at a constant rpm (say 10,000 or 11000), then apply brake pressure. brake pressure could be measured using an inline gauge. the brake pressure reading where the saw could maintain a drop in rpm's to say 9000 rpm could be recorded. the more brake pressure the saw could handle, would give a estimate of any gains or losses with different muff or chain mods. gave up on this idea (for now at least). the issue is adapting a chain gear to a disk that can stay together at this rpm.

the test stand, using timed cuts, would not be as accurate as above, but by using the same saw, and testing only one change at a time, over a series of many cuts, would hopefully give me an idea of any power gains/losses. the data from the 'chain test' above shows there is a +/- 5 second difference between cut times from one cut to the next. don't know for sure, unless i try.

project update: the local scrap/recycling yard does not sell metals by the pound anymore to joe shmo's. since, i have to mock up the stand anyway, am currently gathering lumber and steel brackets.

 

[trappermike]

I saw a very simple "Dyno" a guy built and it worked in that he could run a saw on it and get a "Reading" of a saws power,he could compare 1 saw to another,or check to see any power increase mods made.
He simply built a rig he could bolt a saw onto,the saw bolted to a bar(He had various little spacer bushings to adapt different saws to the bar),on the end of the bar he had a larger sawchain sprocket from an Atom drill attachment which drove a high pressure water pump,mounted after the pump was a pressure guage and a valve(Tap) to restrict the flow and load the motor,he also had a tach to monitor rpms. With this he was able to put saws under load and gauge the power at various rpms by the water pressure the saw could produce. In theory you could take the peak pressure reading made by the(New,stock) saw at what rpm and call it the torque peak and compare that to the factory spec,then calculate a conversion factor number to convert your pressure reading to a torque reading. Then you can use the horsepower formula to calculate your pressure-torque number by rpms to calculate a horsepower figure. Of course your final horsepower and torque readings will not be exactly true as done on a real dyno but it will provide relative numbers for comparison which is all you need!
Add a head temp. gauge(Used to be a motorcycle acc. and sensor fit under spark plug),and an ex. temp. (To accurately gauge fuel mixture)gauge available from a snowmobile shop,and you can really monitor the engine.