Plug Cutter-Posted Here as ET People Dig Deep

[kaptainkosmic]

jim, i have a plug cutter that I made several years back. Here are my conclusions about it. Pinpointing must be deadly accurate! the teeth will really tear up a merc dime!. works good in nice grass with moist dark soil. soil will stay together and you can replace plug so that no one can even tell you were there. doesn't work well in sandy soil because soil pours out of bottom and plug falls apart.

for the handle on the bar that pushes out plug make a stop so you can't pinch your fingers or you will!

i don't use mine at all any more. in theory its a great idea, in reality it didn't quite pan out for me.

of course this is just my opinion and i'm no expert but i did spend some time dancing with this rascal!

hh steve

 

[diggernash]

You all have good ideas. Have you went to a local golf course and looked at what they use for cutting holes to move the cup around? I know the greens are probably the ideal soil consistency, but it might be something good to look at for ideas.

Being from NE Georgia, I have seen times that a full size pick will practically bounce on our good red dirt. I don't know if you can make a plugger that will cut through those conditions without mechanical assistance.

Jarrett

 

[Hungry]

I just used a 5/16" round file to make the teeth. I also extended the shaft through the knock out washer about 2" to locate and keep the cutting tube centralised when you start cutting

 

[Erik in NJ]

My God, no wonder you're having trouble getting the plug out! The TargetBuddy only cuts a plug about 4-3/4" deep - looks like yours does about 9". I would imagine that the force required to eject the plug increases exponentially with length, even if it's linear, your small handle doesn't look like you can prop the unit upside down and put your weight on the handle to pop the plug out. Notice the large flat disc on the TargetBuddy for this. I also think that the narrower the tube the tougher it is to eject the plug as the compression of the soil to diameter ratio is greater. That is, a larger diameter like Jim and I want to produce - 6" should in theory eject the plug easier that 4" or 3" etc.

You did do a nice job on the build though!

 

[BK]

the ground, What if you need to dig a fat hole for a deep target? What about cutting through roots?

 

[Erik in NJ]

That's why I recommend at least a 6" cutter - you don't push it, you twist and it slices through roots like a hot knife through butter -- at least the unit Jim and I are envisioning.

 

[zincpenny]

Interesting idea. FWIW I have 10 years experience in the cutting tool industry for machining and have applied these principles to your design.
Few things that I think.

1. The more teeth or serrations you have then the more resistance to rotation.
2. The larger the teeth or serrations you have then the more resistance to rotation.
3. If you sharpen the edge from the OD inward at 45 degrees then the soil on the outside will be pushed outwards and the soil on the inside will NOT be pushed inward. It will be exactly the same size as your ID and should create minimal resistance. This is assuming that the cylinder has no taper.
4. If you make the teeth too long you may eventually start bending them and that will definitely create much resistance.

Things to consider:

1. Instead of having the pipe go straight into the center of the cutter make it "U" around the center. That way you can apply the vertical force with your foot and leave the strength in your hands for the rotational force.
2. Or instead of the whole rotating cutter idea just cut the cylinder so that it is at a severe angle maybe 60 or so degrees. To give you a visual idea think about how a doctors needle has an angle on it such that it almost comes to a point to ease entrance. This way you simply step on it pressing it into the soil then pull it out rotate it a bit and then step on it again. Doing this 3 or 4 times should result in a somewhat free plug.

just a few thoughts... hope it kinda helps.

 

[grumpyolman]

Thanks zincpenny! Never even thought about maybe tapering like a needle. 45 degrees bevel on the teeth is no problem and it makes sense to me. Now the biggy. How many teeth? I see the 2 effects you describe clearly. Any thoughts on the TPI for something 6" in diameter and 3/32 thick? If this thing ever works and there is a hobby interest in using them, I will a sample to a lot of folks. Jim

 

[zincpenny]

I think that you could get away with a fairly dense pitch AS long as the teeth are small and not too aggressive. Actually, the tooth design that Kaptainkosmic posted (looks like a "wave" type) on his plug cutter looks to be a desirable mixture of pitch, size and shape. The teeth on his design look like they will displace the soil rather than dig into it. Also, they are not very aggressive so should not require a ton of force when rotating.

That being said I think the "wave" teeth may be your best bet. With a density around 2-3 per inch and a depth of 1/8"-3/16".

One other thing... did you ever consider using a lubricant like paraffin wax or a Teflon based spray. It may sound a little silly but you would only have to apply it a few times through out the day. I think its worth a shot... it may help that sucker slide right in the ground.

 

[wcorney]

There are some other factors involved (thickness, sharpness), but the general idea is that you have a force (pushing down with your foot) that is transferred into the edge of your cutting tool. The edge of your cutting tool's circumference is 3.14 (pi) x the diameter of your tool. So you can see that if you had, say a 3" diameter tool versus a 6" diameter tool, you would need double the force to achieve the same cutting pressure to the ground.

Having the bottom of your tool at an angle versus flat would help a little to provide more pressure initially (less circumference against the ground), but once you have the entire tool's edge engaged, you are back to the same problem.

Wayne