Electric Discharge Machining

[White Horseradish]

The trouble with $200 motorcycles is that they usually need a ton of elbow grease, and occasionally have very tricky problems.

I've been working on this FJ600 for a couple of years now. Mechanical stuff done, electric squared away. All I have left is the damn carburetors. Couldn't get them tuned for anything, so figured on replacing the last two things I haven't yet - pilot screw seals and throttle shaft seals.

One pilot screw turned out to have been completely stripped from factory. So, I tried to drill it out. And broke a left-hand drill bit in it. So, I have a steel bit broken off in a brass screw that is in an aluminum body.

I've heard EDM is the way to go with something like this. Anybody ever have that done?

[tokugawa]

Post a pic, lets see what you have to work with. 

[Fly320s]

I can't help.  I just wanted to say I read the title as Electric Discharge Machinegun and now I have the disappointment.

[mtnbkr]

Is a replacement carb expensive? 

Chris

[White Horseradish]

Is a replacement carb expensive? 

Chris

New, I doubt they are available. It's a 30 year old bike.

I bought another set on eBay, but it has three different screws completely buggered.

[Nick1911]

The problem with using EDM on this is that the equipment is not super common.  Which means it's not cheap to have done.  But - a halfway competent machine shop should be able to deal with this using just a mill.

There's a particular way you can grind a piece of round carbide into a spade-point drill.  In a mill, clamp your work, line up your carbide drill, and run the mill as fast as it will go.  Peck away at the drill bit.  You'll probably have to resharpen the carbide a few times.  The "engineers black book" has a page on it.

I learned it from an old machinist teaching at the local community college.  I've used this technique to drill straight through very hard HSS taps.

[Brad Johnson]

Brass in aluminum? Should be able to apply gentle heat and swell the aluminum away from the brass.

Brad

[Nick1911]

Brass in aluminum? Should be able to apply gentle heat and swell the aluminum away from the brass.

Brad

Try reading the first post again.

[Brad Johnson]

Try reading the first post again.

He has a steel bit broken off in a brass screw that's in an aluminum body. Slot the bit and screw with a dremel. Gently heat the aluminum body to swell it away from the brass screw while applying torque with a screwdriver or, better yet, an impact driver (carb body properly supoorted, of course).

Brad

[Nick1911]

He has a steel bit broken off in a brass screw that's in an aluminum body. Slot the bit and screw with a dremel. Gently heat the aluminum body to swell it away from the brass screw while applying torque with a screwdriver or, better yet, an impact driver (carb body properly supoorted, of course).

Brad

Correct me if I'm wrong, but aren't pilot screws in an FJ600 carburator down in a hole?  I'm not seeing how you're going to cut a slot in it for a flat blade driver to apply torque.

[Brad Johnson]

Correct me if I'm wrong, but aren't pilot screws in an FJ600 carburator down in a hole?  I'm not seeing how you're going to cut a slot in it for a flat blade driver to apply torque.

If that's the case then, yes, the slotting technique will not work.

If memory serves the FJ used Mikuni carbs. They were common in Japanese bikes for decades and are still around. Sourcing a replacment body should be easy and probably a lot less expensive than machining the existing carb body.

www.mikunipower.com

Brad

[birdman]

Dissolve the drill bit.

Use Alum, dump a bunch in water, put part in.  Steel will dissolve (dunno about brass) aluminum won't be touched at all.

[tokugawa]

This is useless without pics.   

 How are we supposed to solve your problem without being able to laugh at the screwup? 

[HeroHog]

AvE did a YouTube of this not long ago. Worked quite well!

[HeroHog]

found it: https://youtu.be/fqZYgReuywM

[230RN]

In the video, why would they ask what you wanted all that alum for?  Is there some pernicious use for it?  (I'd have just told them I cut myself shaving a lot.)

I wonder what the surface of a piece of steel would look like treated for a short time with alum.  Like sandblasting?  (Without actually having a sandblaster.)

[Nick1911]

That alum trick is pretty cool.  Probably the lowest cost/overhead way of dealing with this problem.

For those that are curious, here's some pics of a shop ground tap disintegrater.  This one isn't perfect, but I grabbed a fairly large one so you can get an idea of the geometry.  This is ground on the shank of a broken end mill.  Remember, if you're going to grind carbide, you need a silicon carbide grinding wheel, not the standard aluminum oxide wheel.

Ideally you want it symmetrical, and you want the curve of the tip to blend into the the straight walls of the shaft.

[230RN]

What do you use for coolant/chip removal/lubricant?

Or do you just shove it in there dry and keep pushing it in and pulling it out?

Terry

[Nick1911]

No coolant.  It runs dry, and HOT.  The heat is part of the process.  The carbide will glow dull red.

Chips look like fine powder.  This obviously won't remove them, and doesn't have any flutes, so you have to manually clear chips while you peck.

It's not exactly a production line process, but it does work and has saved many parts.