Pin Holes and Tubing, Drill bits

[jmanatee2]

Ok so I want to start the fabrication of the my backhoe thumb. I have build a lot of stuff with steel, just never gotten into anything with pins like a thumb needs.

I have two questions.

1st How are you all drilling a 1" or a 1.25" hole in like 5/16 or 3/8 plate? Must be just a big drill bit but where to buy a good steel bit that big? Also I saw a video on youtube where a guy (500passwords) built a backhoe and he drilled the holes close to size and then used a reamer for final sizing.

2nd I have an idea, if I use a 1.25" pin I can get a foot or two of tubing with an inside diameter of say 1.30" (a little bigger so the pin will slip in) and cut off say .5" section to add support to the plate, strengthen where the pin goes through. Problem is all the tube I have seen is not smooth inside it is ruff and has like a seem on one side. Does this mean I have to get it with the inside diameter like 1.20" and drill each bushing?


Looking for ideas, suggestions, help.

 

[SixHoeBob]

I just finished a thumb for my 9 ton track hoe. For large holes in thick plate I cut them out with a torch and then used a die grinder with a carbide burr. The cost per hole was very high. I progressed to laying out the hole locations on my steel, and marking them with a distinct center punch mark. Circle the mark with a white liquid marker, and clearly label the finished hole diameter. A good machine shop can drill nice holes for much less than your time. And they will look factory quality. For the main hinges I used seamless tubing, and solid rod for the pins.
Seamless tubing resembles very thick walled pipe, smooth on the inside.

For the design I cut the various pieces out of 1/4" luaun plywood. Drill 1/4" holes to mark the pin centers. As the project progresses you can use hole saw bits to enlarge the holes to match the seamless tubing and solid rod. It is easier to build the project full size in wood, and then transfer the patterns to steel.

When aligning the pins in the holes for welding, I used 8d nails for shims. Tack weld the entire project, and then if everything works out finish weld it.

Keep distortion and shrinkage in mind. I do not know how those two words apply, but I was told to keep them in mind

 

[jmanatee2]

Thanks for all the info... I am not one that likes to take anything anywhere but in this case it might be better to take it somewhere to get the holes drilled.

How many carbide burrs did you go through?

I will search for Seamless tubing.

Keep distortion and shrinkage in mind. I do not know how those two words apply, but I was told to keep them in mind

When you weld on one side of a piece of metal and it cools that side will shrink a little. the shrinkage will cause things to warp.

 

[LD1]

How you go about this project depends on what equipment you have at your disposal.

Drill press?
Mill?
Lathe?

You will have a hard time torching holes and trying to get them round with a carbide.

And drilling holes that big, I'd suggest a drill press. Large bits can be purchased OR ordered at almost any indusrtial supply place. Fastenall, MMC, Grainger, MSC, etc.

Drill bits drill a tad undersized. On a bachkoe, it is important that everything fits TIGHT and not sloppy. That is why a reamer is usually ran, to true up the holes.

But on a thumb, I dont see that being as important.

If you have a lathe, drill the holes and turn the pins/bushing to fit.

If you dont have atleast a lathe and drillpress, you'll have a hard time getting things to fit "right".

 

[jmanatee2]

How you go about this project depends on what equipment you have at your disposal.

Drill press?
Mill?
Lathe?

You will have a hard time torching holes and trying to get them round with a carbide.

And drilling holes that big, I'd suggest a drill press. Large bits can be purchased OR ordered at almost any indusrtial supply place. Fastenall, MMC, Grainger, MSC, etc.

Drill bits drill a tad undersized. On a bachkoe, it is important that everything fits TIGHT and not sloppy. That is why a reamer is usually ran, to true up the holes.

But on a thumb, I dont see that being as important.

If you have a lathe, drill the holes and turn the pins/bushing to fit.

If you dont have atleast a lathe and drillpress, you'll have a hard time getting things to fit "right".

I have a small lathe, OK drill press, Plasma, Oxy

I will check the above listed for Bits... thanks for the leads.

 

[jmanatee2]

WOW 1" bit from Fastenall $825

I have to be looking wrong

 

[LD1]

http://www.mcmaster.com/#catalog/117/2439/=bj6jcg

edit: first link didnt work

and heres an MSC link


http://www1.mscdirect.com/eCommerce...02g9y?refinement=4293208501&searchandizedOk=Y

 

[jmanatee2]

McMaster-Carr

edit: first link didnt work

and heres an MSC link


Reduced-Shank Drill Bits and other Metalworking & Multi-Purpose Drill Bits at MSCDirect.com.

Great thank you....

 

[LD1]

http://www.fastenal.com/web/search/...ll-bits/deming-drills/_/N-gj4y3tZjuevwe&Nty=0
Nothing even close to $800

 

[jmanatee2]

Deming Drills | Fastenal
Nothing even close to $800

This is the first one I found and scared the heck out of me.

I see now that I was looking in the wrong area...

opps forgot to post the link
http://www.fastenal.com/web/products/detail.ex?sku=3159245