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Reverse spot face

Need help figuring out how to spot face the tapered face of a rolled steel channel C10 x 40

Backgoround:

A test fixture I built years ago....

welded up from two steel channels C6 X ~12 (back to back to create a "spaced" I beam)

a pretty rough little beast but I had the top surface fly cut to remove remove some of the welding induced geometric irregularities.

I came back with a rather crude (quick & dirty) drill jig to place a repeating hole pattern (3/8" @ 6" O/C) through one set flanges

I used a MagBase drill to drill the 3/8" & later to reverse spot face the underside of the channel flange so I didn't have to deal with tapered washers.

Later I modified the test fixture, re-drilled it with a proper (12' long) drill jig. I bumped the bolt hole from 3/8" to 7/16" to cleanup the hole mis-location problem that resulted from the crude (quick & dirty) drill jig.

Since the spot face already existed & was big enough o accept a 7/16" washer....I was good to go.

Now...I'm rebuilding a new test fixture using the drill jig that produces a repeating 7/16" hole pattern.

I also want the reverse spot face on the under side of the channel flange but I cannot find a reverse spot face with a 7/16" shank

I need ~1" OD spot face to accept the 7/16" bolt washer.

I cannot find any spot facers that have 7/16" pilot.

How do I generate this feature?

I was thinking about using a 3/8" pilot with bushing out to

7/16"....no dice.

Now I'm thinking about using a 5/16" pilot & bushing to

7/16" ......only can find a bronze bushing though

suggestions

Bob

Reply to
BobK
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Shouldn't be a big deal to find a reverse spot face that has a shaft a bit larger than you need and grind the shaft to the diameter that you need. I had a situation where part of the repair called for a 1.25" dia spot face over a .250" pilot hole. We just had the tool shop grind a .375" standard shaft down to .2495" and used that to do the spot face.

Reply to
cvairwerks

Wohlhaupter and similar spotfacer/boring heads will spotface underneath, but they have 3/4 in tool holders. Suggest you turn down the business end of a toolholder to under 7/16th, or make a new one (3/4 to 7/16th) out of heat treatable stock.

Bob Swinney

Reply to
Robert Swinney

Might be easier to use tapered washers. You could align the holes and hold the tapered washer in place with a bolt, and then tack weld the washers in place.

Dan

Reply to
dcaster

...

...

Or, cut a strip from the tapered edge of another piece of channel, say

12' long by an inch or two wide, and place inside the edge of your channel, to complement the angle and produce a flat surface.
Reply to
James Waldby

I like it! A $3000 solution to not wanting to deal with a $12 box of tapered washers (estimating on the prices, but I figure I'm close)

Me. I'd just order a package of tapered washers.

Hey! Waddya know! $12.15 for a pack of 25 at

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Cheers Trevor Jones

Reply to
Trevor Jones

Why no dice on the 3/8" shank tool? Easy to bush to 7/16", no?

Or, take a look at the APT or similar inserted-blade type counterbores. You can get them with reverse blades as well as the regular blades.

John Martin

Reply to
John Martin

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