relative4

I'm dealing with a V-brake boss that has been slightly mushroomed. Does somebody make a tool to machine it down to spec, or do I need to go at it with a file?

relative4

Please disregard, I just realized the boss is replaceable. Duh.

dsbrantjr

A file, used intelligently, will also work; I have done this successfully. The mushrooming is usually right at the end so little metal is needed to be removed. Go slow and check frequently. It is not necessarily a disaster if you take a little too much off the end.

JohnDThompson 

Bicycle Research makes a tool for this purpose:



But careful work with a file ought to do the job, too.

dsbrantjr

Interesting tool, I wonder how one gets it started straight, since the mushroomed part is generally right at the end. Is it piloted somehow?

Andrew R Stewart 

I usually just use a strip of production/emery cloth and shoe shine as the initial step. Andy

ramzilla

Dremel tool with cylinder shaped grinding wheel. Takes about 5 seconds. Polish with steel wool. Done deal.

WizardOfBoz

Yike's ramzilla, that approach can take a LOT of metal off in a hurry. The really precision metalworking guys (tool and diemakers, moldmakers) are super talented and have a lot of experience. They use a lot of small hand files and what are called "rifflers". And we have Andrew talking about emery cloth, and dsbrantjr talking about very careful use of files.

I've been fooling around with metal working and bike wrenching for a long time and I'd really avoid power tool stuff. Even though Dremel tools used to be made in my home town, and my Dad was VP of sales for a company (DuMore) that made flexible shaft tools and die grinders (which are Dremel tools on steroids).

But maybe you're a tool and diemaker, or are just way more coordinated that I am!

WizardOfBoz

Here's a picture of rifflers, btw. Made by Grobet (good brand), sold by Gesswein (no connection to me). The tips are about an inch long.

Andrew R Stewart 

Rifflers are not the file I would reach for to remove a mushroomed end of a brake boss. Too little flat surface width to nicely keep the file flat to the boss while also wrapping your stroke around the boss. Andy

leob1

Having worked in the machining industry, most tool and die makers would rather use a power too whenever they can, it just a matter of saving time. Some detail work requires the rifflers, but not mush.
IMHO, the emry cloth approach would be the quickest, easiest way to go.(after replacing with a new one)

WizardOfBoz

Which is why my Dad had a job back in the 60s! A modern Dumore Die Grinder below. A little like a Dremel, but the one shown will last a lifetime and has replaceable bearings and brushes, IIRC. Also can take nearly a 100% duty cycle. They do cost 3 times more though...

Andrew R Stewart 

In 45 years of hobby fabricating I've worn out a few Dremels and a couple Makita 1/4" die grinders. Were I wealthy I would go pneumatic. Andy (who now has one of these too)

WizardOfBoz

With pneumatic, you need to have an adequate compressor. My cheap Chinese compressor (I speak disparagingly, but it's lasted 10 years) is not up to the task. Hmmm. Were I wealthy, I'd install a Quincy compressor and could run all of the high-torque, high-quality pneumatics you can shake a stick at.

But before I install a $4000 compressor, I'd probably go for a DuMore. I have a Dumore flexible shaft tool from 1968 that still works well. If I needed to have a go-to Dremel type tool for high-duty cycle every day, I'd get a Dumore. The die-cast metal housings hold real, industrial quality bearings. You can replace brushes if they wear out. Made in the USA (Mauston, Wi, I believe, whereas the original plant was in Racine, WI). But they are 300 or 400 bucks for the small, 1/10 HP ones.

PS That Makita thing looks useful.

Patty Up North

Never seen one of those before. But I think that one could align it 'close enough' with a long M6 screw.

I would just file it, or put it in my lathe... If you have a belt sander or a bench grinder, it is easy to round it again.

But im also a precision mecanic, working metal for 10 years. I know not everybody has the tools or skills I have.
But carefully filing should be good enough.

dsbrantjr

Sometimes, if a few file strokes will do the job, it is faster than setting up a machine tool and safer (in terms of overdoing it) than a handheld power tool.

dsbrantjr

Sometimes, if a few file strokes will do the job, it is faster than setting up a machine tool and safer (in terms of overdoing it) than a handheld power tool.

Andrew R Stewart 

I'm trying to imagine the lathe and work piece set up that would swing a frame and keep the boss coaxial with the lathe spindle Andy (Who in the time it took to write this could have filed the boss's end down)

Mad Honk 

Andy,
It is a replaceable post so just unscrew it and chuck it up. Smiles, MH