Backhoe Build A Backhoe For PT425... It Could Happen

[J_J]

David, I was trying to compute cylinder size from your 36,000 lbs, or 18T. Are you using a 4 in bore cylinder with a 1.25 in shaft? Using 3000 psi, I compute 37,680. What I am getting at here is, that is an awesome force to put on the dipper. I have bent the 1 in pins that hold the press table on my hydraulic press trying to push out the 2 in rollover pin from the tilt arm assembly using a 20T jack. You might not damage anything, because I suspect that much force will just lift the backhoe off the ground. You are probably doing what I do, using what ever is available.

 

[MossRoad]

Yes, I was computing a 4" bore on the lift and the dipper and a smaller cylinder for the bucket, as it will have a lower ratio on the leverage. I haven't purchased any cylinders as of yet. Those ones that I got for free are very small diameter and also way too long.

What I could do is buy a 3" bore for the dipper, and if it is too weak, use it for the bucket. The plans call for all cylinders to be 3" bore X 16" stroke cylinders. However, it also has 12" of lever on the dipper stick and I only have 8". Maybe I should lengthen the bracket above the dipper to increase my leverage point out to 12"? I could do that with not too much trouble.

The plans call for 3" X 3" X 1/4" wall square tubing and I am using 4" X 4" X a bit larger than 1/4" wall square tubing. It should be able to handle the load. I think, like you said, I will probably lift the backhoe or toss the tractor around before anything bends.

Another problem I will have is locating cylinders locally at decent prices. TSC has some that I will be looking at on Thursday or Friday. I will also be picking up a 1" X 14" grade 8 bolt that I ordered through a local bolt company. It will be about $15.00 and used for the main boom swing pivot pin. I have a 12" in there right now, but it is

 

[MossRoad]

Well that was weird... every time I hit the space bar in that last sentance, it made a post! Made about a dozen duplicate posts, all the same except one more word. Hmmmm.....

I'll report it to the authorities!

Anywho, the 12" bolt isn't long enough to get a nut on, so that's why I ordered the 14" bolt. I need to get grease zerks and a tap as well.

 

[MossRoad]

Spent some more time on it this evening. Welded up the pivot box assembly. It was just tack welded and I was finally satisfied with the position of everything. Also started cleaning up some of my horrible welds. Yikes, there's going to be a lot of grinding and re-welding on some spots. Other spots have perfect welds.

So far:

The main frame is complete.
The boom pivot box is complete.
The boom is complete with the exception of some grinding so the dipper can rotate all the way through its range of motion.
The dipper is complete.

Still to do:
Add wheels
Add a hitch
Fabricate outriggers
Fabricate the boom swing mechanism
Fabricate the bucket linkage
Add a bucket
Add the hydraulics
Add a seat
Test and add counter weights.
Lots of grinding, sanding and painting.

Bought a few more bolts and nuts.. $30.00
One 3" bore X 10" stroke cylinder.... $90.00
Ring hitch and receiver tubing....... $40.00


Running totals:
Time = 23.0 hrs.
Approximate Cost = $380

 

[MossRoad]

Spent two more hours on it tonight. Cut out several of the brackets that will be used to hold hydraulic cylinders to the boom and dipper stick. Drilled some 1" holes. Those bi-metal hole saws still work great.

Marked some holes on the dipper brackets for the hydraulic cylinder. 10" of travel will give me a good range of motion. I have two more holes to drill, then I can pin the cylinder in the retracted position and tack the brackets in place. Then I can double check the range of motion. If that goes well, I will next work on the boom cylinder length calculations. I might even use math!

The neighbor saw me using my torch on the 1/2" diamond plate to rough out some brackets. He wanted to try out a metal cutting circular saw from Sears. It has dual, counter-rotating blades. I think it is called a Twin Cut. I saw him cut through a pipe with it last fall like butter and he wanted to see how it did on the 1/2" plate. The first cut went through 3" in about 25 seconds. Very fast. Chips were flying everywhere. Second cut, the saw went just as well. I was amazed. Third cut, the saw motor started smoking. We decided to stop our experiment. Searches of the Sears website don't show it anywhere, so I wonder if it is manufactured any more. I went back to torch and bandsaw. If I had the extra $300, I'd pick up one of those Milwaukee metal cutting circular saws... but I don't have the extra $$$ and I'm trying to do this on the cheap.

Running totals:
Time = 25.0 hrs.
Approximate Cost = $380

 

[toy]

Spent two more hours on it tonight. Cut out several of the brackets that will be used to hold hydraulic cylinders to the boom and dipper stick. Drilled some 1" holes. Those bi-metal hole saws still work great.

Marked some holes on the dipper brackets for the hydraulic cylinder. 10" of travel will give me a good range of motion. I have two more holes to drill, then I can pin the cylinder in the retracted position and tack the brackets in place. Then I can double check the range of motion. If that goes well, I will next work on the boom cylinder length calculations. I might even use math!

The neighbor saw me using my torch on the 1/2" diamond plate to rough out some brackets. He wanted to try out a metal cutting circular saw from Sears. It has dual, counter-rotating blades. I think it is called a Twin Cut. I saw him cut through a pipe with it last fall like butter and he wanted to see how it did on the 1/2" plate. The first cut went through 3" in about 25 seconds. Very fast. Chips were flying everywhere. Second cut, the saw went just as well. I was amazed. Third cut, the saw motor started smoking. We decided to stop our experiment. Searches of the Sears website don't show it anywhere, so I wonder if it is manufactured any more. I went back to torch and bandsaw. If I had the extra $300, I'd pick up one of those Milwaukee metal cutting circular saws... but I don't have the extra $$$ and I'm trying to do this on the cheap.

Running totals:
Time = 25.0 hrs.
Approximate Cost = $380

Moss you mentioned drilling holes with bi-metal hole saws, I have some of those bi-metal hole saws but haven't had to use them in that thick of material . I have a question when the hole saw is breaking through the back side do they grab like a twist bit does. I drilled some 1 inch holes with the twist bit and they were a bear when they broke out the other side but the millwauky drill could handle it but I thought it was going to throw me out in the yard. After that I ran into a sale on hole saws and bought some. I already had one the size to drill the lock in a garrage door but I didn't think they would hold up for drilling that thick of material.

 

[MossRoad]

I am using a small, weak drill press to drill with them. They work very well. The thickest stuff I have cut is a tad over 1/2 inch. Takes just a couple minutes. No cutting fluid required. Drill press on slowest speed. If I had a "real" drill press, it would take less time. The bits are only about $5.00. I burned one up after about a dozen holes. The second one seems to be lasting longer. I am not forcing it like I did with the first one.

I still use regular bits, but only when necessary in pieces too akward or large to get into the small drill press. You are correct about breaking through the back side on regular bits. The hole saws don't seem to have that problem.

 

[RegL]

Can you use those hole saws in a Hand held drill? I've bought some big bits and they are very expensive. They are dull now and I bet they would cost more to get sharpened than the hole saws are to purchase.

 

[MossRoad]

The problem with a hole saw in a hand drill is that you have to keep them in line or you will bend the teeth in towards the center. Once you do that, the blade doesn't cut very well. While you would think the pilot bit would keep it nice and straight, it doesn't always work that way. I think that's how I killed the first one. Now I try to use the drill press if at all possible. If not, I use regular bits.

 

[J_J]

David, If you haven't already made up a test set of cables for the cylinders, I would highly recommend it to check out the cylinders in the open and closed position. Sometimes you can use air to force the cylinders to open and closed. The QA hydraulic circuit would be ideal for this test set. You don't even have to tack any of the brackets for these test.