Small align bore?

[jcorsico]

I need some advice on how to drill/bore two holes. These holes are on the axle housing of an off-road machine. A mounting bolt goes between the two holes. Thus, the holes need to align. Plus, the holes need to have a good fit. Tolerances are -0.000" and +0.002". The existing holes were not made well, and have become oval. We need to bore the holes round, and then insert a bushing to restore a tight fit on the bolt.

How should I do this? Removing the axle housing from the machine and clamping it to a horizontal boring mill is not an option. This has to be done in the field.

I have seen people "line bore" or "align bore" similar mounting holes on large equipment, like excavators and bull dozers. This would work well for me, but my holes are only 0.750" in diameter. I need to bore them out to 0.875". I cannot find a line boring machine this small. The smallest I've found can cut a hole that is 1.50" in diameter.

Thank you!!!

 

[SIP6A]

. I cannot find a line boring machine this small. The smallest I've found can cut a hole that is 1.50" in diameter.

Well then build one.

 

[Garwood]

Reamer is the correct tool.

Sounds like a strange problem though. Have you researched bolted joint design to see if what you're doing makes sense?

 

[Gordon Heaton]

Is the location on a flange? If so, can you make a clamp-style drill/ream jig that you can fasten in place over the flange? (for a visual, it would look something like the slot in a quick-change tool holder but with screws to clamp it to the flange). BTW, -0/+.002 is a darn tight tolerance for mounting bolts on an axle housing!

 

[CatMan]

Reamer is the correct tool.

I'd hate to be the man trying to hold the drill, but agree with Garwood. Reamer is the correct tool. Specifically an alignment reamer or a bridge reamer. Used for a century to do basically what you're doing. Good enough for a field repair.

 

[eKretz]

How far apart are the holes? That is an important bit of missing information. If it's a dirt bike that's not so bad. If they are 3 feet apart a reamer isn't going to do the trick. For a short distance you might try a piloted reamer if you can find one with an interchangeable pilot; that way you could swap to a longer pilot that could reach the opposite side. You'd want both holes mostly round first ideally. You could also rigidly mount (perhaps clamp, perhaps tack weld) a plate with a hole in it outside the second hole to act as the guide for the pilot.

If it's a dirtbike axle I'm not sure it needs to be quite that tight though. It may be that way as new but for a field repair it may be more trouble than it's worth to get back to that level. As I think about it a little more though, it probably isn't a dirtbike since those have moveable carriers/tensioners that actually hold the axle, don't they?

 

[Nmbmxer]

I think a picture would be worth a thousand words in this case.

 

[trevj]

Cut out the holes with a torch, slide the bolts through, and goober the slack areas with JB Weld.

Honestly though, if you have room to ream it out for a bushing, ream it and put a larger diameter bolt through the whole lot!

If there is no room for a bushing, chop out the former 'hole', or weld it solid, then drill and ream back to size.

 

[jcorsico]

All - thanks very much for this advice. We decided to make a fixture plate which will hold a drill bushing, like Gordon suggested. We'll tack weld the fixture plate to one of the flanges, and then use a mag drill to enlarge the holes. We'll then use a long pilot adjustable reamer (https://www.mcmaster.com/adjustable-reamers/straight-blade-adjustable-size-reamers-8/) to get the holes into alignment and tolerance. Then add the bushings.

To answer some of the questions above:

1) The two bolt holes are 7" apart.

2) We need a tight fit on the bolt (hence, the 0.002" tolerance). The old holes were loose, and the bolt pounded them into an oval shape.

3) No, this is not a dirt bike. It's a piece of ag/construction equipment.

Thank you again!

 

[gbent]

You need to make a special long reamer. I usually start with shell reamers, but given your small diameter, you may just have to make an extension shank for a chucking reamer. You make the necessary bushings and go through the first hole to ream the second. Then use a different bushing to pilot through the second hole to ream the first. In steel, about 1/16 on diameter works well, cast iron you may get by with 1/8. Yes, you may have to buy several reamers.

 

[michiganbuck]

You said 0 to +.002on hole size. How much off-center and alignment error can your finished project tolerate?
Likely a bushing plate on one side coming out of a mag drill and intersecting an out-of-round hole with an angle nose reamer will still pull the reamer off to still not be perfectly straight for end-to-end alignment. How much are you willing to spend on the repair?
Better would be a located bushing plate on both/each sides of the part, a straight shank reamer 10" long with that straight shank going into the close side guide bushing first, and to be in the opposite side bushing for alignment while reaming. The reamer would need grinding the back taper going the other way (.0002-3 pr inch) and with the sharpened teeth on the other end of the flutes (toward the shank) end.

So costing two bushing plates (one large enough to hold the mag drill) One special ground reamer. likely two additional reamers, some method of secure clamping the bushing plates, and some form of measuring tools.
likely $500 for a fudge-up job and over a grand hiring out some of the work. The special reamer likely $100 altering a used tool.

The first reamer (the special) would likely just be large enough to make the bore round + .010, straight and on location, so .770 or what is needed and flat-ended (not having the normal reamer nose angle. It would be started at a slow feed rate. Very sharp HSS. and the nose end of the special reamer would become the driving end, perhaps grind a square at that end (You would want to retain the reamers center hole).

The special reamer could be used to make/ream the guide bushings, CRS would be ok for a one-up use (simple lathe job/part).

*A photo of one end of the part would make engineering a repair plan easier

Depending on how much cast iron is in the hole I could set/rig a flat plate at the end and with a die grinder attached to a v block make a centered straight bore to a few thousandth close. Likely a couple hours to repair .008 or so for each end with a die grinder set up and a caliper, and then ream to a lathe turned bushing.

Oil rig roughnecks are handy for this kind of fudging up a repair, seasons millwrights and toolmakers also could be a decent choice..likely be a two-day job. One day with a die grinder.

Might be better to lathe turn the part repair bushings and Loctite them in rather than going all the way to 7/8. OD and .750 ID.

 

[eKretz]

As I understand his plan, he will rough the holes with a drill and finish them with the type of reamer that he linked, which has an available long pilot. That should work quite well.

 

[whateg0]

You do you, but if the machine has been operating with the wallered out holes, and it apparently has been, I sure don't see the need for a tolerance of +0/-0.002 or whatever it was.

 

[whateg0]

Good enough for a standard-gage locomotive axle. GTTS.

Overkill for Ag use in the DIRT.

Unless "Agriculture" involves laser-trimming of 3-D printed aerospace-grade astroturf?

I've a friend who worked in aerospace. The stories I've heard about having to "massage" parts to get them to fit together has completely and utterly abolished any notion that "aerospace grade", or whatever description one wants to use, means anything more than expensive.

 

[michiganbuck]

We don't yet know how important the alignment or the value of the machine.
A wheelbarrow and an $800,000 cotton picker need different concerns.
Ref:https://www.tractorhouse.com/listin...690-cotton-pickers-slash-strippers-harvesters

 

[Garwood]

Sounds like you have a pivot pin, not a bolted joint. Very different critters. If you're using a bolt for a pin, that may not be a great idea.

I see a lot of ag equipment that's badly designed in one area or another. I get to fix it.

Crazy how all these small ag OEM's are out there and don't really understand how to make their own shit. Good enough to sell then it's the next guys problem.

 

[jcorsico]

As I understand his plan, he will rough the holes with a drill and finish them with the type of reamer that he linked, which has an available long pilot. That should work quite well.

Exactly! Tools ordered. Thank you again!

 

[gbent]

Crazy how all these small ag OEM's are out there and don't really understand how to make their own shit. The big ag OEM's are even worse. Good enough to sell then it's the next guys problem.

There, fixed it for you.

 

[jimg1955]

mag drill with rotabroach ,press new bushing,ream to size.

 

[trevj]

I've a friend who worked in aerospace. The stories I've heard about having to "massage" parts to get them to fit together has completely and utterly abolished any notion that "aerospace grade", or whatever description one wants to use, means anything more than expensive.

I worked on airplanes ranging from Grumman CS2F Trackers, Lockheed T-33's, jet trainers, and F-18's. The F-18 was the newest (other than the POS Bell 412) by a long shot, and even THAT was essentially locked in around 1977 or so, as far as the levels of 'Tech" were concerned, outside of the various Sparkie parts. We used to sit around and talk about what it would be like, to work on Combines, or other High Tech stuff!

People who tout anything as "Aircraft Grade" or "Mil-Spec", generally do not have any idea what that actually means, but they are selling stuff to folks that also are ignorant, so I guess it works...

We used a LOT of standard Adjustable Hand Reamers, with various extensions and double cone centering cones, to maintain almost "line bore" straightness while installing bushings in flight controls and landing gear parts.