Facing bit with pilot?

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Little Scrapper

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I have two 3/8” OD x 1/4” ID bushings welded perpendicular in to a 3/4” tube 6” apart. I need to mount a bracket on it and would like to find the right tool that can spot face the weld/bushing so I can mount the bracket appropriately. Something with a 1/4” pilot? Do they make such a animal?

could take my time and file it flat old school but was thinking this could be pretty nice if I can find such a thing.
Thanks!

FE6DEE27-D543-4204-93F6-20B106B0AB4A.jpeg
 

ScaleBirdsScott

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McMaster has these badboys:


or this


Is that what you're talking?
 

Aviacs

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I didn't actually look at SBS's links, but assume typical inter-changeable pilot counterbores.
To add to what he said - it is typical to just turn up the size pilot you need, & reduce one end for a snug fit in the counterbore.
The pilot should be larger than its shank so the counterbore completely machines the face. (IOW, pilot can't be smaller than shank or it will prevent the cutter from doing so). Those things are not necessarily the easiest to use free-hand, but if the work is secure & you keep the drill speed dialed down with a careful touch, it should go well.

I'm thinking there has to be a way to rig a chainsaw bar file contraption to the bottom or beside the hole, with a coarse flat file, to accomplish the same task. :)

smt
 

cvairwerks

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Pilot size and shank size have no real relation. Pilot should closely fit the hole diameter and not interfere with the cutting lips. A reverse c’bore, the shank is the pilot.
 

BJC

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Do they make such a animal?
Yes, a spotfacer with a pilot will do the job.

I’ve found some, in the surplus tool vendors at Sun n Fun / AirVenture, that I use to square the face of spacers. If you want to pay the price, they are available at Search results for Spot facer

If the bushing has limited access, such as the lower face of a Cassutt wing bolt bushing, a reverse, or back spotfacer works.

What are you building?


BJC
 

Little Scrapper

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I think the biggest issue is holding a drill and expecting it to remain rigid so I can produce a decent flat spot. I’m starting to think it won’t works. And 80sd2 isn’t exactly the easiest on cheap bits. In the photo attached I did find things like this and I can certainly turn a custom arbor on my lathe but by the time I’m done I have a feeling I might be better just hand filing it like decades of people have done before me.

It’s easy to overthink things like this, I may have done that to myself. I’ll just file it. I do appreciate the responses.
 

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BJC

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I think the biggest issue is holding a drill and expecting it to remain rigid so I can produce a decent flat spot.
That is not a problem with a pilot. Use a back spotfacer on a 1/4 rod or drill bit and the cut surface will be square to the bore.

I bought this spotfacer for about $5. The pilot keeps it square in a round hole, even when used in a hand drill.

0E720B92-E231-4C7E-87E4-6B98B3DFD022.jpeg

Very handy to have.


BJC
 
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Pops

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Have no idea what you are doing, but is that persision really required ? If not, maybe just a few seconds with a good file and a straight edge.
 

MadRocketScientist

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Have no idea what you are doing, but is that persision really required ? If not, maybe just a few seconds with a good file and a straight edge.
Hey don't spoil our fun, there is a good over-engineering discussion going on here. ;) :p I would like the spotfacer but the file and a square would have to do since I don't own one.
 

Little Scrapper

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Have no idea what you are doing, but is that persision really required ? If not, maybe just a few seconds with a good file and a straight edge.
in my case I want to mount a bracket but many tube and fabric airplanes have bushings in a round tube with welds that need to be ground flush or flat.

I have no issues using a grinder and file but thought maybe people had a better way. I’m always up for trying new ways.
When a bolt or bracket is tightened against something like a welded bushing it’s pretty important all surfaces mate well. So I figured some type of spot facing tool would be worth asking about.

BJC seems to have found one. I just can’t seem to find one that cheap.
 

Stephen Asman

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Well, I don't weld, but here is how I would approach the problem. I'd make an aluminum disk by by using a bi-metal hole saw on a piece of 0.25" plate, this has the added benefit of leaving a 0.25" hole in the center of the disk. Then drill and tap the disk from the edge on opposite sides (6-32 should work) put a couple of divots on a 0.25" rod, slip the disk over it and tighten the screws. Then attach an abrasive to the face of the disk, mount it in a hand drill and go for it. You might need to replace the abrasive material too frequently to make this practical but it would be 90 degrees.
 

Aviacs

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Pilot size and shank size have no real relation.
You might have misunderstood.
The shank of the pilot must be the same size, or smaller than the pilot. If the pilot is smaller than its own shank, the cutter won't cut. A 1/4" shank pilot can be used with pilots from 1/4" on up to the limit of the cutter diameter. But it won't work with pilots less than 1/4" ground on a 1/4" shank. Mostly i was pointing out why C-bores and other piloted tools use small holes. The hole in the tool is not a limit - It is expected that larger pilots will be used with them.

For instance, looking at BJC's example, a person could find a dowel or other rod to fit the hole size, and cylindrical grind or turn the pilot shank size on it. Then pull it through by the pilot, (as a reverse spot facer) so long as remembering to run the drill in reverse. Also, used in that manner, all the power is going through the 3/16" stub, so include a flat for the ss, & it still can't take much force without twisting off

A big factor is that cutting geometry of counter bores is somewhat aggressive. So regardless which side the approach is from, it takes a controlled, careful touch to get started to avoid grabbiness.

smt
 
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BJC

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Well, I don't weld, but here is how I would approach the problem. I'd make an aluminum disk by by using a bi-metal hole saw on a piece of 0.25" plate, this has the added benefit of leaving a 0.25" hole in the center of the disk. Then drill and tap the disk from the edge on opposite sides (6-32 should work) put a couple of divots on a 0.25" rod, slip the disk over it and tighten the screws. Then attach an abrasive to the face of the disk, mount it in a hand drill and go for it. You might need to replace the abrasive material too frequently to make this practical but it would be 90 degrees.
I’ve done something similar, for truing a face on a hole in fiberglass.

I silver soldered a washer to a bolt head, then put adhesive-backed sandpaper on the washer. Be careful not to wallow out the hole when sanding.


BJC
 

Pops

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Part the bushing off in a lathe for a good true surface on each end. When I weld a bushing through a 4130 tubing, I install a longer bolt in the bushing and bolt a scrap piece of bushing stock to each end of the bushing I'm welding as a heat sink so the edge of the welded bushing will not be disturbed from the welding.
 

Little Scrapper

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Part the bushing off in a lathe for a good true surface on each end. When I weld a bushing through a 4130 tubing, I install a longer bolt in the bushing and bolt a scrap piece of bushing stock to each end of the bushing I'm welding as a heat sink so the edge of the welded bushing will not be disturbed from the welding.
That is a excellent suggestion! Thank you! It already welded but next time I’m definitely gonna try this!

Appreciate everyone else’s respose as well
 

cvairwerks

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I've been in the aircraft production world for over 30 years now. There are times that the pilot diameter has to be smaller than the shank. Pretty tough to have to spotface over a shallow counter bored hole and use a pilot the same size as the counter bore. I've even had reverse spotface and countersink cutters that were on shafts larger than the locking part of the shaft due to design requirements. Really depends on what needs to be done, as how the tools are made.
 
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