Mag Drill for Line Boring

[sierradmax]

So here's my problem. I have a bobcat with some bad bushings. Pins are easily replaceable but the bushings are tough to replace. You have to cut the welds, remove bushings and re-weld new.



Another alternative is line boring but I'm having difficulty finding a company to weld & bore 1.25" holes. Seems a bit too small for the machinery normally used.

I have 4 bushings that need to be replaced and two lift arm rod links. Essentially, $1,100 in parts new, minus labor to install. I'm curious if there it a mag drill that can use 1.25" bits or cutters with a throw of over 4.5"? This way I could puddle weld the holes, set the mag drill on one side and drill through both existing bushings for a clean, straight hole.

 

[iajonesy]

Could you install the new bushings and then hand ream them to size? They should come just slightly undersized and welding them in will cause a little bit of distortion, so a good sharp hand reamer or expansion reamer should do the trick.
Just my thoughts.

Mike

 

[Jim Johnstone]

I'm surprised you're having trouble finding a shop that will bore them, boring and fitting bushings is daily work for the machine shop I work at. My concern with trying to use a mag drill is finding a way to mount the drill to the fabrication that will be truly square to the hole. Any distortion on the surface you attach the mag drill to, will translate into the hole being out of alignment.

 

[txvwnut]

I'm surprised you're having trouble finding a shop that will bore them, boring and fitting bushings is daily work for the machine shop I work at. My concern with trying to use a mag drill is finding a way to mount the drill to the fabrication that will be truly square to the hole. Any distortion on the surface you attach the mag drill to, will translate into the hole being out of alignment.

This^^^ and also to properly line bore the holes you would need a bit long enough to do both holes at once to insure for proper alignment across the loader frame at the pivot point.

 

[Bobcat753]

Since you are in RI give these guys a call. It's not cheap but they have the right equipment.
http://boston.craigslist.org/gbs/hvd/5774433837.html

 

[Jim Johnstone]

Any decent machine shop can do that bore. 4.5" isn't even line bore territory in my mind. I've been doing a set of 16 frames for scissor lifts at work. I have a 2" bore with 0.002" tolerance on the diameter and there are 3 holes in line, one at 0" the next at 12" depth, the next at 24" depth, and the customer needs to be able to slide a 2" ground rod through all 3 holes for holding a hydraulic cylinder.

1.25" hole 4.5" deep...that's a job for a reamer.

 

[sierradmax]

I did call them. They said they couldn't do 1-1/4"

 

[sierradmax]

Any decent machine shop can do that bore. 4.5" isn't even line bore territory in my mind. I've been doing a set of 16 frames for scissor lifts at work. I have a 2" bore with 0.002" tolerance on the diameter and there are 3 holes in line, one at 0" the next at 12" depth, the next at 24" depth, and the customer needs to be able to slide a 2" ground rod through all 3 holes for holding a hydraulic cylinder.

1.25" hole 4.5" deep...that's a job for a reamer.

What tool would be required so I'm not talking jibberish with a machine shop. Would the loader arm have to be removed so it could be positioned on a Bridgeport or mill?

 

[Jim Johnstone]

What tool would be required so I'm not talking jibberish with a machine shop. Would the loader arm have to be removed so it could be positioned on a Bridgeport or mill?

Ideally yes. What is the overall size of the arm? 4.5" is doable in a bridgeport, but I'd rather stick that on a decent size vertical cnc or a horizontal boring mill.

1.25" can be done either with a boring tool, but that is getting on the small size for that deep of a hole, you would definitely get some cutter deflection or chatter. I would use a shell reamer on a Morse taper arbor personally.

 

[2oolhound]

Cut the welds?

I'm a novice and haven't done this type of work on similar equipment but what I'm seeing here and the way I've always encountered bushings is there are 3 components.
1 - Pin
2 - bushing
3 - bushing boss ( the steel lug that is welded in in this case).

#3, the bushing is usually friction fit into the boss so the movement and wear occurs only on the inside of the bushing and pin unless it is left too long before servicing.

If I'm understanding this correctly since the bosses are being cut out and re-welded in couldn't you take the new bosses, fit the bushings and ream them to size then get an extra long rod the same dia. as the pins and fit the bushed bosses along the rod and then weld the bosses in place? The rod will keep them aligned. You would have to align and stabilize the bucket and locate the bosses equally from reference points (other pin points) on each side so in the end the bucket is on straight.

 

[Bobcat753]

I'm sorry, I didn't fully understand your post. 1.25" is very small for a line bore. Have you contacted Bobcat and asked about the repair procedures? I know for the end of the arms which connect to the bob tach are special. My local dealer has custom jigs they use with a mag drill.

 

[sierradmax]

loader arm is about 400+ lbs. More cumbersome than anything. 4'x8'x3'. It's the two middle bushings at the back of the loader (right in the picture)
https://www.purplewave.com/auction/121228/item/E5771

There's no boss or sleeve here pressed on, just steel bushings welded to the loader arm. What's in the picture above has to be cut off. And that's just one of 4.

 

[Jim Johnstone]

loader arm is about 400+ lbs. More cumbersome than anything. 4'x8'x3'. It's the two middle bushings at the back of the loader (right in the picture)
https://www.purplewave.com/auction/121228/item/E5771

There's no boss or sleeve here pressed on, just steel bushings welded to the loader arm. What's in the picture above has to be cut off. And that's just one of 4.

Ok I understand better. I thought it was a single arm with a 4.5" deep hole. What you've shown there is an ideal job for a horizontal boring mill. For comparison, this is what I doing right now as I type this:


I could do the same to your part. Once it's fixtured, bore/ream the hole from one side, spin the table 180 degrees and do the same hole inline from the opposite side.

Barring that, a custom jig that locates off the existing holes would work, but then you need to have a jig made.

 

[pamike]

Trying to find a general machine shop that is willing to bore that is going to be tough/impossible. Not to mention you have to pull the entire boom off the machine. Cutting off the bosses and welding new on is the standard for most mfgs. Line boring it is another option if you can find someone... Personally I would just like with the wear until its bad enough to spend the money on to repair it right...

 

[lazer50]

I was the main welder/fabricator for a major recycling steel/scrap company.i made repairs like your situation on a regular basis.granted they were on lugged tub trucks.the trucks that drop the tubs with the swinging arms.but the principle is exactly the same.the only wear should be in the bushing itself and the pin.to cut the weld i used a carbon arc torch.the welds come off neat and clean this way.to get the bushing out i would weld a similar size piece of round stock to bushing,spray a penetrating oil in there,heat the area around the bushing.i used a rose bud torch.then drove old bushing out.i made a point to install new bushing while still hot,shouldn't be any need to drill or bore unless im missing something.the new bushings should be sized to fit the bore when the old are driven out.the process i explained although routine for me wasnt simple by no means.this maybe a task an equipped weld shop could handle.a carbon arc torch is not something everybody has nor is a rose bud torch.the machinery i repaired was larger in scale and had to be done correct or the arms would bind and or would wear out fast.but that procedure is what i used and it worked well.the hardest part was driving the old bushing out but it was overhead and they where 3 inch by 8.

 

[sierradmax]

Trying to find a general machine shop that is willing to bore that is going to be tough/impossible. Not to mention you have to pull the entire boom off the machine. Cutting off the bosses and welding new on is the standard for most mfgs. Line boring it is another option if you can find someone... Personally I would just like with the wear until its bad enough to spend the money on to repair it right...

I agree, and I still will continue to use the machine but at some point this winter, I plan on going through the machine and this will probably be the largest repair.

Here's a parts diagram of the loader. Parts 12 & 19 are the weld-in bushings, 12 being the outer bushing & 19 being the inner. It's clear that the loader arm has holes cut to accept the bushings. The outer could be cut off and a new one welded rather easily but the inner is tight. There's 2.75" between plate where bushing #19 is welded inside. I would assume a machine welded the original.

 

[lazer50]

Sierra d max. I wanted to follow up and explain a few things you may or may not be aware of.a carbon arc torch is a device that holds a special cutting electrode.it hooks up to typically the stinger of a welder and an air compressor.as it uses high current to gouge the weld the air forces it out.although you could grind the old weld this method is fast and clean.a rose bud torch is used for high heat concentration on large areas.again these are tools an equipped weld shop should have.to follow up a little on your task at hand,if you take a look at the exploded view in the post above you can visualize the process i described in my previous post.with the size bushings your dealing and after looking at it myself it shouldnt be that difficult.

 

[johninct]

I don't thing a drill bit or cutter would work. I think that they will drill a nice hole but the drill bit will be drawn in and go to the area of least resistance so the hole won't be perfectly centered.

 

[Jim Johnstone]

I don't thing a drill bit or cutter would work. I think that they will drill a nice hole but the drill bit will be drawn in and go to the area of least resistance so the hole won't be perfectly centered.

Another reason why a mag drill won't do. If the OP needs them bored, a milling machine is the only way to do it.

 

[2oolhound]

I'm sorry, I didn't fully understand your post. 1.25" is very small for a line bore. Have you contacted Bobcat and asked about the repair procedures? I know for the end of the arms which connect to the bob tach are special. My local dealer has custom jigs they use with a mag drill.

More comments from the peanut gallery:
Looking at the drawing you can see the steel bushings have a shoulder machined in one end which drop into the bores on the loader arm. This locates the bushings fairly accurately and keeps the welded outer edge away from the bores in the loader arm to prevent distortion to them from welding and refitting. If bobcat has a mag drill jig for these as well, as speculated in bobcat's post, you would have to position the bushings and clamp them tight in the bores using an alignment pin through their centre holes in all 4 bushings then weld them into position. With a long alignment pin through the bushings you could lock the mag drill chuck onto the end of the pin and shim the mag drill base to the loader arm or ideally have an adjustable 3 point base on the mag drill to conform to the loader arm plane. Now switch on the base, install an annular cutter with a pilot that fits in the lower bushing hole and drill the finished sizes.

 

[sberry]

I weld stuff like that up all the time with wire feed and fit a hole saw in to re bore the hole, how close is it and how good does it have to be? If a hole is worn a 1/2 inch and still working bringing it within an 1/8 or so and sticking a new pin in it may out live the machine for a part timer.

 

[sierradmax]

This may be straying off topic or belongs in another area but what about the thought of machining oversized holes in the bushings & having clearance spacers machined

 

[Jim Johnstone]

This may be straying off topic or belongs in another area but what about the thought of machining oversized holes in the bushings & having clearance spacers machined

You mean opening up the existing locations larger and pressing in a new bushing?

 

[sberry]

Another fast and simple trick to this is shove a larger pin in the worn holes if they are fairly round, very fast, easy and cheap.

 

[crewchief888]

you are really overthinking this repair.

torch off the worn bushings, and weld in replacements, (line them up with a new pin)

or weld up the worn bushings, then use a die grinder to get a "round" hole again,
install a new pin.

it's not rocket science...

 

[johninct]

You mean opening up the existing locations larger and pressing in a new bushing?

Holes usually don't wear exactly round so the center of the new hole may not be the center of the original one.

 

[sberry]

I am with Crewcheif here. I do have rotary files and soon may make a vid of fixing and truing a hole with a hole saw to fix egg shaped hole. Now, this machine may be in such shape that this is the very worst and fixing it or dumping a grand or 1500 in increases the value but if it is for hobby maintenance use and the goal is to use it fix the thing up some. This is different than a late model machine in continuous service where the life of the useful repair will be utilized, maybe that is the case but I don't get that vibe.

 

[Jim Johnstone]

Holes usually don't wear exactly round so the center of the new hole may not be the center of the original one.

Totally agree, so boring and pressing in a bushing can be done, it's just more difficult. You need some other locating spots on the parts, like other bores that are still true.