Help me understand "Downforce"

[orezok]

Help me understand how downforce is generated on a PHD. I know it works, but I just don't understand it.

Per the attached picture, A is attached to the lift arms and B to the 3 point connection. A & E are a fixed distance as is B & E. These cannot change. If a separating force is applied to the cylinder points C & D, then the only possible reaction is for point A to move away from point B, since point B is definitely an immovable point on the tractor.

Point A moving could only occur if the lift arms were in a "float" condition.

How does this result in downforce on the auger bit?

 

[Couple of Achers]

Help me understand how downforce is generated on a PHD. I know it works, but I just don't understand it.

Per the attached picture, A is attached to the lift arms and B to the 3 point connection. A & E are a fixed distance as is B & E. These cannot change. If a separating force is applied to the cylinder points C & D, then the only possible reaction is for point A to move away from point B, since point B is definitely an immovable point on the tractor.

Point A moving could only occur if the lift arms were in a "float" condition.

How does this result in downforce on the auger bit?

Your lift arms are always in a float position. There is no down pressure on your three point. Now I don't know for sure it that's what makes it work or not. But your lift arms can be picked up at any time from any position, with the exception of them being all the way up.

 

[rus_geek]

Added a point F to your drawing to form a diamond/parallelogram/whatever, where F is the point where the lift arms attach to the tractor.

Now, when you extend the cylinder, you are increasing the angle BEA, so you will also be increasing the angle BFA. Given that points B and F are fixed, the only way to increase that angle is for point A to move downward. Since A and E are a fixed distance apart, when A moves down, E moves down, pulling your auger downward.

Clear as mud?

-rus-

 

[orezok]

OK. I think I got it per attached. The cylinder force is actually pushing the lift arms downward.

.and incidently if it was clear as mud I wouldn't have a problem, but it's caliche!

 

[MtnViewRanch]

Orezok, not sure of your reason for asking other than to understand how it works. You said that you know that they work, just not how. I just wanted to let you know how well that they do work. I have a lot of DG (decomposed granite) at my place. Before I bought my down force kit, there were holes that I just could not dig without water. I would get down about 30" and then have to put 20 gallons of water in and come back another day to get down to 42". After a few of those holes, I bought a down force kit for my PHD. Have not had a problem since, can't say that any hole has taken longer than 2 minutes with the down force kit. No longer have to use water, just drill the hole when and where I want or need to.

Just thought that I would put the info out there as it has worked for me.

 

[orezok]

Orezok, not sure of your reason for asking other than to understand how it works. You said that you know that they work, just not how.

I have similar dirt to you up here in the high desert. I am planning on building my own using my my top link for the cylinder, but using it in a "pull" location rather than "push". By doing that I don't have to change any hoses.

The next thing I have to calculate is the proper geometry so that I don't overload the auger. Do you know what size cylinder you have and what the pressure regulator is set at (i.e. what downpressure you are generating)?

 

[wftree]

Now for real down force try this.

Take a John Deere 450 Dozer and just place the blade on the gear box and gently lower it.

THE RESULT! I completely destroyed the point on the auger, GONE. When I brought it out of the hole and touched the end, luckily with gloves on, the gloves smoked!

Thank God I did not ruin the auger but I did have to buy a new point!

I guess that was a little to much down pressure

wftree

 

[rus_geek]

wftree - you know those augers were never meant to drill through bedrock, right?

 

[MtnViewRanch]

I have similar dirt to you up here in the high desert. I am planning on building my own using my my top link for the cylinder, but using it in a "pull" location rather than "push". By doing that I don't have to change any hoses.

The next thing I have to calculate is the proper geometry so that I don't overload the auger. Do you know what size cylinder you have and what the pressure regulator is set at (i.e. what downpressure you are generating)?

I honestly don't remember what the diameter is, I think that it is 2", but I will have to double check. Remember that the hydraulic for the down force kit is a one way hydraulic. DO NOT use a double acting hydraulic, you will end up with big trouble. (bent parts) The cushion valve is set at 1500lbs.

Any other questions, just ask.

 

[wftree]

I tend to think I have a good idea, and in my head it all works out perfectly. In the real world thing can go wrong.

wftree