453 Bobtach pins and bushings

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OldMachinist

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A couple of weeks ago I decided it was time to replace the pins that hold the Bobtach to the lift arms. As you see they where pretty worn compared to the new on in the middle.


On my 453F there are no factory installed pressed in bushings. The service manual says if the hole wears out you have to cut the old welded on bushings off and weld new ones on in the right location. I really didn't like the idea of trying to get things all lined up by welding in new bushings so this what I came up with.

I decided I would like to bore out the hole on the old bushings and fit them with replaceable bronze bushings. The alloy 932(SAE660) bronze bushings I used have plenty of load capacity (4,000 psi) for this machine but for larger machines you could step up to alloy 954(4,500 psi) or you could make steel ones. I used bronze because most of the future wear would be in the bushing ($2 each from McMaster Carr) and not on the pins ($35 each from BobCat) and changing the bushings as needed would be simple.

Now I could have taken the Bobtach into the machine shop I retired from on a weekend and done this real simple but having time on my hand I wanted to figure out a way a person with some tools available could do this at home. I checked the original welded in bushings and found they where made from cold rolled stock and that the bores were concentric with the outside diameter. I made two guide bushings from 4140 steel on the lathe that slide over the outside diameter and drilled and tapped three setscrew holes to lock them on. I bored them to be a slight press fit so that I could tap them on and off with a lead hammer. As you can see I notched them out to slip down past the gussets. My pins are 1" in diameter so the first bushing has a 1 1/16" bore and the second has a 1 1/8" bore.


I used my bucket as a fixture to hold the Bobtach and magnetic drill square to each other. The bucket was shimmed level and then I placed small welds to hold the Bobtach in place after it was lined up. I used a 1 1/16" shell reamer first then changed the guide bushing and finished the hole with a 1 1/8" reamer. Then I ground the welds off flipped the Bobtach 180 deg. and did the other side. The reamers and arbor cost me about $125. The new bores ended up being concentric with the outside diameter within .005" and right on size for a press fit for my bushings.



I also reamed out the welded in tilt cylinder bushings on the Bobtach and both ends on the tilt cylinder while I was at it. Now all they all have replaceable bushings


I ran a small brake cylinder hone in the tapered pinholes on the lift arms to make sure the pins would seat proper. These holes had no wear just a little rust but on any tapered mount hole must be clean for it not to start working around and get loose. I used delrin washers I also bought from McMaster Carr to take out some of the side play of the Bobtach. When I reassembled it every lined up perfectly.

All together I spent about $250 and it took 6 hrs. which included making the bushings. In the future I figure it will take me no more than 1 hour to replace the bushings.

 

Tazza

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Very nice!
I machined my bobtach out by line boring it. The previous owner drilled the tapered pin and bobtach out to hold a 1 1/4" bolt!!! i used an old rail drill i bought from auction, cut a taper on a length of chrome bar which i installed a piece of tool steel as a cutter. The rail drill has a low RPM and moves in at a very low speed too, worked great. A magnetic drill sure would be handy!
My setup was this:
15-04-06_1652.jpg

Driven by the big yellow thing and a tool steel cutter. This setup only worked because the previous owner got the end of the holes drilled out.
3 pictures of it http://users.tpg.com.au/tazza_/Bobtach/
 

Fishfiles

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Very nice!
I machined my bobtach out by line boring it. The previous owner drilled the tapered pin and bobtach out to hold a 1 1/4" bolt!!! i used an old rail drill i bought from auction, cut a taper on a length of chrome bar which i installed a piece of tool steel as a cutter. The rail drill has a low RPM and moves in at a very low speed too, worked great. A magnetic drill sure would be handy!
My setup was this:

Driven by the big yellow thing and a tool steel cutter. This setup only worked because the previous owner got the end of the holes drilled out.
3 pictures of it http://users.tpg.com.au/tazza_/Bobtach/
Old Machinist , you got 'er done , Tazza thats some set u you got there , -------my magnet on my Black and Decker mag drill counked out ,the part is no longer available from B&D , seen a few on ebay but they go high , took it to a few electric motor rewinders and they didn't want to fool with such a small job , so they say , tried to break the mag casing in two to see the windings and see if I could possibly rewind it myself , but it is frozen up pretty good and no where to grap it , I think she is done
 

skidsteer.ca

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Old Machinist , you got 'er done , Tazza thats some set u you got there , -------my magnet on my Black and Decker mag drill counked out ,the part is no longer available from B&D , seen a few on ebay but they go high , took it to a few electric motor rewinders and they didn't want to fool with such a small job , so they say , tried to break the mag casing in two to see the windings and see if I could possibly rewind it myself , but it is frozen up pretty good and no where to grap it , I think she is done
I'd sure like to learn more about machining. I steped out and bought a used 14 40 lathe and I'm just learning as I go. Need to invest in a good book or two. But line boring is something else I could get some use out off on out skidder cradles and center pins. And i'd love a mill someday too.
When I did these pins on my 553 and 853, I cut the bosses out and welded in new ones. By the time I did the 853 I had the lathe so I made my own. Tazza pointed out to bush them so I added that too. (Wish I'd have though of that for the 553, but I'll likely never wear it out anyway) Sure did lots of careful checking and tack welding, but it turned out good. Definely more then 6 hours though.
Before I had my own shop I worked with a mechanic out of his shop on our equipment in the off season.
He introduced me to a Mag drill when we decided to double up the wheel studs on our Clark skidders from 10 to 20. We had to drill the stud holes on 10 planetary hubs (2 skidders by 4 hubs plus 2 spares) or 100 holes and also on 13 wheels, so another 130. Though 3/4" steel on the wheels and 1" cast material on the hubs. John bought a new mag drill for the job and it just shocked me how that thing made a hole so slick. It took longer to move it to the next hole then to drill it.
It used a fancy hole saw bit, so to speak with flutes up the side so the chips could get out. It bored those 230 holes and the cutter was still like new. 1000 times better then any drill bit.Definitely on my tool list.
Always great to see a thread like this
Ken
 

Tazza

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I'd sure like to learn more about machining. I steped out and bought a used 14 40 lathe and I'm just learning as I go. Need to invest in a good book or two. But line boring is something else I could get some use out off on out skidder cradles and center pins. And i'd love a mill someday too.
When I did these pins on my 553 and 853, I cut the bosses out and welded in new ones. By the time I did the 853 I had the lathe so I made my own. Tazza pointed out to bush them so I added that too. (Wish I'd have though of that for the 553, but I'll likely never wear it out anyway) Sure did lots of careful checking and tack welding, but it turned out good. Definely more then 6 hours though.
Before I had my own shop I worked with a mechanic out of his shop on our equipment in the off season.
He introduced me to a Mag drill when we decided to double up the wheel studs on our Clark skidders from 10 to 20. We had to drill the stud holes on 10 planetary hubs (2 skidders by 4 hubs plus 2 spares) or 100 holes and also on 13 wheels, so another 130. Though 3/4" steel on the wheels and 1" cast material on the hubs. John bought a new mag drill for the job and it just shocked me how that thing made a hole so slick. It took longer to move it to the next hole then to drill it.
It used a fancy hole saw bit, so to speak with flutes up the side so the chips could get out. It bored those 230 holes and the cutter was still like new. 1000 times better then any drill bit.Definitely on my tool list.
Always great to see a thread like this
Ken
Ken - i have found the best source of information is being shown or told what to do. Reading books doesn't always get the info across as well. I had a GREAT machinist mate that would tell me what to do and then proceed to show me on his lathe. Small things that i never thought about but sooooo simple after being shown. Like machine new gland nuts for rams, just how do you measure the depth of the pressure seal groove? So simple, just work off the graduations on the cross slide and double it (double because you cut in 1mm you actually remove 2mm of material). Little things like that i didn't understand or at least think about at the time, so simple when told about it. Then you have the *art* of grinding your tooling correctly... i'm still working on that one...
You then need to understand tolerances, just how much should you leave for a press fit etc. Warping when you weld, crush from a press fit. Most of this i still don't understand but i do get by. My metal lathe is probably my most used piece of equipment. I have a mill, but i haven't had a chance to set it up and do any real work with it, i need more things for it like an indexing head, i have a few gears to make, great first job isn't it? i never seem start with something simple :)
Speed is something you will pick up later on, its best to take your time and get it rite.
One great thing i use on mine is thread cutting, its no where near as hard as many people may think.
Fishfiles - that was just an 5hp B&S powered rail drill i got at auction just for the engine, i needed to do some line boring and when i spoke to my machinist mate he said you need low seed and slow feed and i was like HELLO i know just what will do that. It was dirt cheap with a few other engines, its paid for its self with this one job. I'd like to throw an electric motor to it to make it quiet and lower vibration but its been used once in like 5 years. They use them with the yellow bit you see in the pic as a clamp to grab the rail way track. They then drill 1 1/4" holes through the track using the machine. It has some serious power, i was cutting about 1/8" with each pass with no problems, no chattering, hole was spot on.
 

Luthor

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Ken - i have found the best source of information is being shown or told what to do. Reading books doesn't always get the info across as well. I had a GREAT machinist mate that would tell me what to do and then proceed to show me on his lathe. Small things that i never thought about but sooooo simple after being shown. Like machine new gland nuts for rams, just how do you measure the depth of the pressure seal groove? So simple, just work off the graduations on the cross slide and double it (double because you cut in 1mm you actually remove 2mm of material). Little things like that i didn't understand or at least think about at the time, so simple when told about it. Then you have the *art* of grinding your tooling correctly... i'm still working on that one...
You then need to understand tolerances, just how much should you leave for a press fit etc. Warping when you weld, crush from a press fit. Most of this i still don't understand but i do get by. My metal lathe is probably my most used piece of equipment. I have a mill, but i haven't had a chance to set it up and do any real work with it, i need more things for it like an indexing head, i have a few gears to make, great first job isn't it? i never seem start with something simple :)
Speed is something you will pick up later on, its best to take your time and get it rite.
One great thing i use on mine is thread cutting, its no where near as hard as many people may think.
Fishfiles - that was just an 5hp B&S powered rail drill i got at auction just for the engine, i needed to do some line boring and when i spoke to my machinist mate he said you need low seed and slow feed and i was like HELLO i know just what will do that. It was dirt cheap with a few other engines, its paid for its self with this one job. I'd like to throw an electric motor to it to make it quiet and lower vibration but its been used once in like 5 years. They use them with the yellow bit you see in the pic as a clamp to grab the rail way track. They then drill 1 1/4" holes through the track using the machine. It has some serious power, i was cutting about 1/8" with each pass with no problems, no chattering, hole was spot on.
Very innovating work by both of you guys. I bored my bobtach on a big milling machine and fitted aluminium nickle bronze bushes which are holding up extremely well to date.
Hey Old Machinist I guess you could me an "old machinist" too after 35 years in the trade.
 

Tazza

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Very innovating work by both of you guys. I bored my bobtach on a big milling machine and fitted aluminium nickle bronze bushes which are holding up extremely well to date.
Hey Old Machinist I guess you could me an "old machinist" too after 35 years in the trade.
Its amazing just what you can do with the gear on hand. If you need a job done, you generally find a way.
I do like the idea of using a mag drill. I would like to clean up the holes on my 751 where all the pins go through. They will only be slightly worn but i'd still like to clean them up so there is no slack left. Just not sure how i'd hold a reamer with the drill and ream the hole out. A few ideas do come to mind but i think i'm over complicating the job. If it works, i'll make sure i take pictures as i think it will be quite easy and effective.
 

latrobe

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Its amazing just what you can do with the gear on hand. If you need a job done, you generally find a way.
I do like the idea of using a mag drill. I would like to clean up the holes on my 751 where all the pins go through. They will only be slightly worn but i'd still like to clean them up so there is no slack left. Just not sure how i'd hold a reamer with the drill and ream the hole out. A few ideas do come to mind but i think i'm over complicating the job. If it works, i'll make sure i take pictures as i think it will be quite easy and effective.
Nice job OldMachinist, After I get my water pump fixed I'm sure I'll have to do the same thing to my 853 because the joint is very loose. I was wondering though about how much press fit you used on the bushings and how much of a slip fit between the pin and bushing. Great pictures too, thanks for sharing.
 
OP
OP
OldMachinist

OldMachinist

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Its amazing just what you can do with the gear on hand. If you need a job done, you generally find a way.
I do like the idea of using a mag drill. I would like to clean up the holes on my 751 where all the pins go through. They will only be slightly worn but i'd still like to clean them up so there is no slack left. Just not sure how i'd hold a reamer with the drill and ream the hole out. A few ideas do come to mind but i think i'm over complicating the job. If it works, i'll make sure i take pictures as i think it will be quite easy and effective.
Ken,
As Taz said experience is the best teacher for the art of metalworking but books do provide much of the theory that you still need to know so that no matter what the job is you can figure out a solution. After nearly 40 years of making parts and repairing equipment I still have to refer to several reference books from time to time. If you ever have a question about how to machine something just ask I'm sure with all the brainpower available on this forum we can find an answer.
Tazza.
The best reference book available for information on press and shrink fits and much more is the Machinery Handbook from Industrial Press. It's been in print since 1914. It contains more than 2,000 pages of information. I'm not sure what edition there up to but any one printed in the last 20 years should contain all the reference material you need.
If you do look to buy a magnetic drill make sure it is capable of holding Morse taper shank tools it will much more versatile. I also have some drawings of how to grind your high-speed steel lathe tools. I dig that out sometime and post it. In fact I have quite a library of reference material available. One of the things I learned a long time ago is not to try and memorize everything just remember where to find the answer.
 
OP
OP
OldMachinist

OldMachinist

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Ken,
As Taz said experience is the best teacher for the art of metalworking but books do provide much of the theory that you still need to know so that no matter what the job is you can figure out a solution. After nearly 40 years of making parts and repairing equipment I still have to refer to several reference books from time to time. If you ever have a question about how to machine something just ask I'm sure with all the brainpower available on this forum we can find an answer.
Tazza.
The best reference book available for information on press and shrink fits and much more is the Machinery Handbook from Industrial Press. It's been in print since 1914. It contains more than 2,000 pages of information. I'm not sure what edition there up to but any one printed in the last 20 years should contain all the reference material you need.
If you do look to buy a magnetic drill make sure it is capable of holding Morse taper shank tools it will much more versatile. I also have some drawings of how to grind your high-speed steel lathe tools. I dig that out sometime and post it. In fact I have quite a library of reference material available. One of the things I learned a long time ago is not to try and memorize everything just remember where to find the answer.
Store bought bronze bearings have the press fit and clearance made in them. For example my bearings were 1.127" on the outside diameter and I didn't measure the inside before I pressed them in but after pressing into a 1.125" hole they were 1.0005" inside. The pins from Bobcat were .9985" so there was .002" total clearance. The chart below should help.
 

jerry

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Store bought bronze bearings have the press fit and clearance made in them. For example my bearings were 1.127" on the outside diameter and I didn't measure the inside before I pressed them in but after pressing into a 1.125" hole they were 1.0005" inside. The pins from Bobcat were .9985" so there was .002" total clearance. The chart below should help.
Tazza, that rail drill looks like it is gas powered? That would be really handy for boring big machinery on site. Worked in the taconite mines for 20 years and we did a lot of big bores with homemade bars. After 43 years of machining I have found there is always more to learn. My Machinery Handbook is the 1941 edition and just as relevant now as then. It is surprising some of the oem tolerances and how loose they are. We made cylinders for a company for a few years and they wanted .015-.020 clearance on the bushings so that is what they got. Probably easy to assemble but not good.
 

skidsteer.ca

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Tazza, that rail drill looks like it is gas powered? That would be really handy for boring big machinery on site. Worked in the taconite mines for 20 years and we did a lot of big bores with homemade bars. After 43 years of machining I have found there is always more to learn. My Machinery Handbook is the 1941 edition and just as relevant now as then. It is surprising some of the oem tolerances and how loose they are. We made cylinders for a company for a few years and they wanted .015-.020 clearance on the bushings so that is what they got. Probably easy to assemble but not good.
We should kick some of this over into a new thread about machining??
Ken
 

Tazza

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Maybe a new forum catagory for machining questions might be best.
I would agree, a thread dedicated to machining would be very handy.
LOL i like that one oldmachinist, just remember where the info is located, it sure does make sense.
Yes, the rail drill was petrol or gas powered. They used it out on the rail line so no *real* power was easily available. It works great but i think its a tad heavy with the engine. I'm thinking of pulling the motor and installing a small electric motor to it to lighten it a bit. I can then use it on its side without problems
 

Luthor

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I would agree, a thread dedicated to machining would be very handy.
LOL i like that one oldmachinist, just remember where the info is located, it sure does make sense.
Yes, the rail drill was petrol or gas powered. They used it out on the rail line so no *real* power was easily available. It works great but i think its a tad heavy with the engine. I'm thinking of pulling the motor and installing a small electric motor to it to lighten it a bit. I can then use it on its side without problems
Latrobe, the interferance fit for the bush should be around .001" per inch of diameter although I gave mine close to .002" total and pulled them in with a 20 ton hydraulic cylinder. As for the the bush to pin clearance I found from experience that you need about .005" diameteral clearance to allow for a coating of grease on the moving surface to avoid it from siezing up as my tilt cylinder rod end pin did when I only had .002" clearance.
 

Tazza

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Latrobe, the interferance fit for the bush should be around .001" per inch of diameter although I gave mine close to .002" total and pulled them in with a 20 ton hydraulic cylinder. As for the the bush to pin clearance I found from experience that you need about .005" diameteral clearance to allow for a coating of grease on the moving surface to avoid it from siezing up as my tilt cylinder rod end pin did when I only had .002" clearance.
There is an art to making a good bushing. I was always told .008 - .010" for clearance for earth moving gear but i always went .003 - .005 because i wanted my machine to be all tight, it does make installing pins a little harder if its not quite square.
 

Fishfiles

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There is an art to making a good bushing. I was always told .008 - .010" for clearance for earth moving gear but i always went .003 - .005 because i wanted my machine to be all tight, it does make installing pins a little harder if its not quite square.
I can confirm the hands on is a much better way to absorb knowledge than books , as I went thru a heavy equipment training program for 4 years , which sent me to book school by an instructor two nights a week for 3 hours each night , I worked a regular job under a journeyman during the day and went to a 8 hour per day , 2 week hands on every 6 months , no doubt you learn a lot more seeing and doing than reading about doing it ----------- I usually go for .005-.010" clearance
 

Luthor

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I can confirm the hands on is a much better way to absorb knowledge than books , as I went thru a heavy equipment training program for 4 years , which sent me to book school by an instructor two nights a week for 3 hours each night , I worked a regular job under a journeyman during the day and went to a 8 hour per day , 2 week hands on every 6 months , no doubt you learn a lot more seeing and doing than reading about doing it ----------- I usually go for .005-.010" clearance
Yes I liked the idea of a nice tight machine too but after having 1 pin and bush sieze I will never go less than .005" clearance again. In this case the bush had actually welded to the pin and I had to spend hours cutting it out and remaking everthing again.
 
OP
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OldMachinist

OldMachinist

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Yes I liked the idea of a nice tight machine too but after having 1 pin and bush sieze I will never go less than .005" clearance again. In this case the bush had actually welded to the pin and I had to spend hours cutting it out and remaking everthing again.
I bought a new pin on Bobcat manufactured bucket awhile back that had never been mounted. I cut the pin on mounting bracket off and made a new one to use the Bobtach. The original clearance from Bobcat on the steel bushings to the steel pins was .005" on the lift arm and tilt mountings. I figured I could go a little tighter with bronze bearings as dissimilar metals normally won't gall and seize up as long as they are lubed. Time will tell on that. I agree if you go back to the steel on steel set up you need more clearance.
 

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