Mini excavator stick end boss machining

[Cmark]

We have a stick from a 6T mini excavator in the workshop and we're cutting out the boss from the end, machining a new one and welding it in.
Now we've done plenty on bigger machines where we bore the boss on the lathe to finished size and, with decent pre/post heat, weld them in without any problem, but we're having some doubts about this one. It's only 100mm OD and 50mm ID and we are concerned about distortion from the welding and feel we may have so leave it undersize and finish the bore once it's welded in.

So the question is, does anyone have first hand experience of welding smaller bosses like this and can comment on whether or not distortion is a problem?

 

[redneckracin]

If you have the capability to machine it afterwards why not just play it safe and plan on machining it afterwards? That sounds better than doing it twice to me?

 

[Theweldor]

Keep in mind that on a mini, it will not take as much weld to hold it in as a large machine. I have replaced stick bosses up 330's and not had a problem with machining to size before welding them in. I have 2 line boring systems, but it is a waste of the customers money to try and build up more than 4 or 5 passes to bring it back to size. They usually have a stroke when they see the boss hit the ground and I tell them do you have a prefered machine shop or would you rather I machine up a new boss for you. If you have a prefered machine shop have them call me. I will give them the dimensions.

 

[Cmark]

If you have the capability to machine it afterwards why not just play it safe and plan on machining it afterwards? That sounds better than doing it twice to me?

Purely time and money. It's about ten times faster to bore the boss in the lathe than to set up the stick on the mill, but if we need to do it, we can. Just asking to see if someone's been down this path before so we don't have to do so.

 

[Nige]

Never done anything that small but if it's a known fact that a structure can be pulled and twisted by welding why not machine the nose end up first, install the bushes in it, then slide the pin through it. As you are welding keep checking that the pin is still a sliding fit. If necessary stop welding on one side and weld on the other to pull the assembly back to "shape" again. If the process works on something the size of a walking dragline then it ought to work on the stick of a mini-ex. The other factor you'll need to take into account is to make sure the axes of all three pin bores are in line.

 

[Cmark]

From experience we're pretty much on top of the X,Y,Z alignment issues. We also know that with, say a 200+mm boss we can keep the bore within about 1/2 thou ovality with careful welding. Stick end bosses are a bit more tricky insomuch as they are only welded round half their circumference.

 

[redneckracin]

Good point. Just was stating the obvious i guess!

 

[td25c]

Never done anything that small but if it's a known fact that a structure can be pulled and twisted by welding why not machine the nose end up first, install the bushes in it, then slide the pin through it. As you are welding keep checking that the pin is still a sliding fit.

I like that idea ! Simple approach to the task wins every time .

No need to " over think it " .

 

[Cmark]

So the results are in. With careful pre/post heat and not concentrating the weld in one spot for too long, distortion was around eight tenths". Thanks all for the input.

 

[Nige]

Glad to hear that it worked out well for you and thanks for the photos.

For our US audience can you confirm if “eight tenths” is millimeters and would be by my calculations about 0.032”

 

[Cmark]

Millimeters? Wash your mouth out with soap young man!

 

[Nige]

So you're talking about distortion of a little over 3/4" then…?
I prefer to work in Christian Units myself.
TBH I wouldn't expect that much on a set of 994 lift arms, let alone a mini-ex stick. So long as it all works I'm sure you're happy with it but you can understand my confusion.

 

[Delmer]

"eight TEN THousanthS" ??? in machinist speak?

Just assuming because I didn't see the line bore rig in the pictures.

 

[Cmark]

Lol. Okay, yes, I mean eight tenths of a thousandth of an inch or 0.0008"
Like a lot of people of the Commonwealth of a certain age, including I'm sure the above mentioned honourable member for Doncaster, I was edumacated in the metric system whilst working in a world populated by people using imperial. The result being that we can work in either, but end up with some weird sort of hybrid. For me it's feet and inches for measuring people, millimeters for medium size things, miles for long things, thousands of an inch for teeny tiny things, and don't even get me started on pressure, mass, volume and torque.
Besides, all my machine tools are imperial.

 

[Theweldor]

I would dare say that is "Well within Tolerance"

 

[Nige]

I would dare say that is "Well within Tolerance"

I would have to agree.
I must be still recovering from jet lag for not picking up on the "8 tenths". Just goes to prove I was never a machinist I guess.....

Like CM I had to work in both Imperial and metric growing up, and can convert from one to the other pretty well in my head. Just that certain units seem to make more sense such as psi for pressure. I can easily get my head around 250 psi or 4000 psi but I have no concept of what pressure is involved if someone tells me 1725 kPa or 27500 kPa.

 

[TVA]

I grew up and lived in ex Soviet Union, and most widely used unit of pressure was atmosphere! Which I think is 14.7 psi.!
When my kin and my people complain about imperial system not being useful or comfortable, I say: it all depends! I like meters and millimeters, ( but there also decimal measurements in imperial system used by machinists), also like the Celsius scale for temperature ( mostly because at 0 water freezes and at 100 it boils, at least close to it depending on altitude)!
But when it comes for pressures: I can kinda work with BAR, but I like PSI the best! But when it comes to using Kw for heat transfer - kill me now, please!!! That’s something that little old abacus inside my noggin is not capable to process, if rather use BTUs!!! Same for KPa and rest of them!!!

 

[hosspuller]

How about that cute blonde girl ?? the 8 1/2 stone one …standing a bit shy of 17 hands