Old School Sawmill Edger

[Brian Rupnow]

You just have to stop and admire a milling machine with such insane headroom. I don't use that head-room very often, but it is just wonderful to have it when you need it. I will have to put a tension pulley on that timing belt, but things worked out remarkably well. I will add an outboard bearing to that long shaft that comes all the way thru the edger to drive the large timing belt pulley.

 

[Brian Rupnow]

So here we are guys---almost ready to rock and roll. I picked up my Lovejoy couplings this morning, and I have adjusted the height of all the components to be (hopefully) in line with each other, shaft-wise. As you can see, I have a bit of work to do yet, as the couplings need to be drilled and tapped for set-screws, and the wooden blocks under the clutch have to be drilled and glued together. I strongly believe that there were so many frictional losses with all of the o-ring drives and shafts on the first set up two weeks ago, that the gas engine didn't have enough power to drive the edger. I don't know this for sure, but it is what I think. Wish me luck. In another day or so we will be ready for the next test.

 

[werowance]

good luck

 

[Brian Rupnow]

Yesterday and today have been a voyage of discovery for me. I have tried three different engines on this set-up, one being my throttle governed engine as seen in the previous post. Next up was the hit and miss side shaft engine, and then the Rockerblock engine. All of these engines have a 1" bore and a 1 3/8" stroke, and none of them have the power to drive the edger. This surprises me, but surprises are what you get when designing and building from scratch. Where do I go next?---Good question. I do have a twin cylinder engine that I built a few years ago, but it has a hand operated throttle. The perfect engine for this job would be throttle governed, whereby when there is no load on the fast idling engine, it does just that--sets there on a fast idle. As soon as it senses a load coming onto the engine, (because of the engine slowing down) it fully opens the throttle and holds the throttle open until the revs come back up to the "set point". One of the problems with using my twin cylinder engine to run the edger, is that the "off" side of the crankshaft is not accessible to attach a drive coupling to. I can probably work around that, but there is the issue of tuning the twin into a throttle governed engine. I have to dwell on this one for a while before deciding what I'm going to do. The edger itself is a success. I will post more of this after it becomes a little clearer to me what to do. Merry Christmas to all of you.---Brian

 

[CFLBob]

I have to say I'm a bit puzzled by the inability of the engines to drive this. When the motor is slowed down by the gear box, doesn't that gear ratio reduce the horsepower required to drive the saw by that same gear ratio?

Maybe numbers help: say it takes 1 HP to drive the edger and you reduce the speed of the drive shaft by a factor of 16. Doesn't that reduce the power required out of the engine by that factor of 16? (Minus any losses in the gears) So a 1/16HP input from the engine would drive the edger properly, and depending on frictional losses, a 1/8 to 1/4 HP motor should drive it.

Of course, I don't know what the HP of the engine is, but the displacement ((pi/4) * bore squared*stroke) is just over 1 cubic inch, so that seems like it should be capable of delivering a half HP. Much more than 1/16 or 1/8.

Unless I'm all wrong in what I think I remember about the HP going down by the gear ratio. If it goes up by the gear ratio, you'll never get there.

One of my favorite proverbs: research is what you're doing when you don't know what you're doing.


Merry Christmas, Brian. No answer required here.

 

[billco]

Yesterday and today have been a voyage of discovery for me. I have tried three different engines on this set-up, one being my throttle governed engine as seen in the previous post. Next up was the hit and miss side shaft engine, and then the Rockerblock engine. All of these engines have a 1" bore and a 1 3/8" stroke, and none of them have the power to drive the edger. This surprises me, but surprises are what you get when designing and building from scratch. Where do I go next?---Good question. I do have a twin cylinder engine that I built a few years ago, but it has a hand operated throttle. The perfect engine for this job would be throttle governed, whereby when there is no load on the fast idling engine, it does just that--sets there on a fast idle. As soon as it senses a load coming onto the engine, (because of the engine slowing down) it fully opens the throttle and holds the throttle open until the revs come back up to the "set point". One of the problems with using my twin cylinder engine to run the edger, is that the "off" side of the crankshaft is not accessible to attach a drive coupling to. I can probably work around that, but there is the issue of tuning the twin into a throttle governed engine. I have to dwell on this one for a while before deciding what I'm going to do. The edger itself is a success. I will post more of this after it becomes a little clearer to me what to do. Merry Christmas to all of you.---Brian

I am sure the answer will come to you
Merry Christmas

 

[Brian Rupnow]

I am looking at my twin cylinder opposed as perhaps being a candidate to run this edger. The only issue is that it has a manually controlled throttle on it. I want a governor controlled throttle, and am looking in to the possibilities of changing it over to governor controlled.

 

[Cogsy]

The engines I've used with a throttle governor don't normally hold the engine at any sort of idle but rather limit the engine from over-revving while allowing full throttle as RPM drops. For the ones that are required to slow down to some sort of idle, there is normally either a manual or electronic control such that when the machine is 'kicked into gear' the throttle is opened for max engine power and then the governor takes over to limit them. My thoughts are if you set your engine at any sort of idle condition and try to maintain it, you won't be getting anywhere near full power from your engine.

I'm also surprised your other engines won't run the edger as I also would have thought they'd have enough power and I'm wondering if it's a similar issue. I recall during some of your builds where you've gotten an engine running before adding the hit and miss mechanism and you manage to make them run fairly slow even without the hit and miss. I'm thinking some settings (likely the carb) allow this 'idling' condition of the engine and if you don't change the setting even after you attach the hit and miss mechanism then again you won't make full power. In my mind, if you disconnect the governor on a hit and miss engine it should rev up to the point of exploding fairly quickly as you need it to be making a large amount of power with every hit.

Good luck with your build and I'll be following along as always.

 

[TonyM]

To get our small engines to rev slowly we adjust the timing and carburation so that they run at reduced power. Just enough to maintain rotation at the lowest speed possible. In order to produce more power we need to reset our ideas and settings to a faster revving engine in order to get the power more relative to its size . I'm with Cogsy. It may just need a tweek of the timing and carburation to solve this.

 

[Brian Rupnow]

Yes, you fellows are correct. When I first start and adjust my engines, I am setting up for the lowest speed possible when I video them, not the highest. I did use three different engines tweaked to give me a higher rpm before trying to run the edger with them, but they simply didn't have the power output I needed.

 

[dsage]

Horsepower = torque x rpm / 5252.
There is no way around that. The edger requires a certain torque (set by the friction of the mechanism and the job it has to do) and the rpm is set by how fast you want to do the job. Presumably you added the gear box to reduce the torque requirement of the engine but you also increased the rpm requirement. The formula still holds. The horsepower requirement didn't change.
In fact by adding the gear box you probably INCREASED the overall torque requirement because you added friction (in the gears etc). You can figure out the give and take on the whole mechanism.
Horsepower comes from the fuel. You need to burn more fuel and you can get more power (torque) from the fuel by higher compression and (as suggested) possible timing changes. Most model engines are built to be lazy and inefficient. Perhaps it's time to design / build a performance engine or take your best engine candidate and increase the compression (at least), improve the carburetor and run it at a higher rpm and add a governor.
You might be able to estimate the horsepower requirement by measuring the torque required on the input shaft with a piece of wood in the edger and a lever arm and spring gauge on the imput shaft (or a torque wrench if you have one that goes low enough). Then multiply that by the rpm you want to turn it (back to the formula). You also need to measure your engine horsepower and match one up.
Perhaps your next project should be a simple Prony brake engine dyno.
OR a simple dyno can be made from an electric generator (an electric hobby motor can be used) with a variable DC load on the output wires coupled to your engine. You can measure the voltage and current output of the generator with couple of meters. One horsepower approx equals volts x amps / 746 . (there are estimated losses that need to be added in there as well).
Where it would be cool to run your edger using one of your engines it is a very cool project in it's own right. I don't think it would degrade the project by running it from an electric motor.
Nice job.

 

[Brian Rupnow]

Before I dive into this one, I want to set up the twin cylinder engine and make sure that I can tweak it manually to give a high speed of 2000 rpm and a low speed of about 1500 rpm. I have a laser tachometer and can measure rpm quite accurately. Last night I lay in bed thinking about this. If I don't want the engine to ever exceed 2000 rpm, that can be accomplished by a hard-stop on the throttle linkage which doesn't really involve the governor. I would like to have a "mode" where the governor is disengaged so I can start the engine with the throttle closed and the governor completely "locked out" where the engine will run at about 850 to 1000 rpm . When I have the engine started and do engage the governor, I would like the governor to take the rpm up to around 1500 and hold it there under a "no load" condition. As soon as a load comes onto the engine and the flywheel shows the smallest inclination to slow down, I want the governor to immediately open the throttle fully, not incrementally, and take the speed up to full 2000 rpm and hold it there until the flywheels are no longer seeing a load and the engine can drop back to 1500 rpm until the next load is applied.

 

[CFLBob]

Horsepower = torque x rpm / 5252.

What units? Torque in ft-lbs or in-lbs? Or metric?

Thanks

 

[awake]

Brian, can you say more about how it doesn't work with the various engines - what the sequence or symptoms are? I believe you have a clutch between the engine and the sawmill, correct? I assume that the engine runs fine while the clutch is disengaged. But what sort of engagement is the clutch - is this a friction-type clutch that can engage slowly, or more like two castellated nuts that engage all at once?

I'm thinking about what happens with a manual transmission car or truck. The engine has plenty of horsepower to move the vehicle, but only if the torque is transferred gradually through a friction clutch. If the clutch is let out all at once, the engine dies. Could that be what is happening with the saw mill, or is it a totally different set of symptoms?

 

[Brian Rupnow]

Today, just for giggles, I removed my new engine "Thumper" from the edger and replaced it with an old 1/4 HP electric motor. It worked like a charm, putting boards thru with no hesitation, with both saws cutting. I had hoped that my new engine would have the power to do this, because at 1 3/8" bore it has almost twice as much surface area on the piston as compared to my other 1" bore engines. Sadly, it didn't. Before I tear the set-up down off my worktable I may add a manual ignition advance to the engine, but I don't have high hopes for it.

 

[CFLBob]

40 years as EE made me a fan of rules of thumb and other cheap and dirty mathematical approximations that can bound a problem for me. Simple equations I can solve that give me an idea of the performance I can get. Bear with me a second.

The displacement of your engine is (pi/4)*(bore^2)*(stroke). Simply the volume of the cylinder traced by the piston's movement. I don't know what the stroke on that engine is but a cheating approximation there is that it's close to the bore, which you said is 1.375. That's (pi/4)*1.375^3

That's 2 cubic inches. Another approximation is that you're doing good to get the same HP as the displacement. Yes, I know there's more involved when you get to power delivered than displacement, but displacement is certainly part of it.

That engine should be easily capable of 1/4 HP. It should be capable of more than 1 HP.

That tells me that it's likely to be down the road you're going down of advancing the ignition. Or something to make it "run harder" when it's under load.

 

[minh-thanh]

Add a suggestion: reduce the tension of the belts, reduce the friction of the parts, and reduce the thickness of the wood., maybe solve the problem !?