jetting drill bits?

Umm, simply drilling jets can give unusual results. You can find that a smaller hole might flow more fuel than a slightly larger one, because of surface features inside the hole. If you really want to try, just purchase the drills from MSC Corp, what size(s) do you need?

Also remember that you will need to get them turning pretty fast to do a decent job of drilling the hole inside of a reasonable time, around 10K rpm or so.

A dumore drill press works well for this, even better is a Boley lathe.

Jim

Jim, just curious, what is a Boley lathe? Never heard of one. Bill.

Thanks, Chris. Bill

Not Jim, but it's a really tiny watchmaker's lathe:

Actually, sorry, I think those are the bigger Boleys on that page. Here are the tiny ones:

Sets of wire-gauge twist drills from 61-80 are readily available from the usual online sources, if not the local hardware store. A hobby shop may have them, exorbitantly priced, no doubt. Most lawnmower carbs I've seen only have holes in the castings, not removable jets, hence the need for getting the whole carb. You aren't prepping a Hemi for racing, after all. Getting AT the jet to drill it out might be a problem. Drag-racing lawnmowers are we???

Stan

A drill bit is generally just a drill bit.

Now the size..thats another story.

What size(s) do you need?

Gunner

"I think this is because of your belief in biological Marxism. As a genetic communist you feel that noticing behavioural patterns relating to race would cause a conflict with your belief in biological Marxism." Big Pete, famous Usenet Racist

Don't know any local source. But while ordering, you should also get a set of jet reamers. They are quite cheap and will help you to get the right size.

Nick

I probably should have said 'watchmaker's lathe' instead. Boley is only *one* company that makes/made them, and they are invaluable for doing small work like drilling a five mil diameter hole in a brass jet, that sort of thing. The idea is that the spindles turn at high speed and run on very accurate bearings or bushings.

I'm not going to go out on a limb here and make the statement that anyone trying to prototype or reproduce carb jets will not be able to do so without one (the overall level of resourcefulness of posters here being what it is) but it makes the job a HELL of a lot easier.

Levin Stark Rivett Boley Ames

That sort of thing. Seriously. A cursory check on ebay will show that one could tool up to drill small holes with a used watchmaker's lathe pretty inexpensively. If you look closely at the photo of my office at work, you will see a somewhat truncated boley lathe in the far upper right corner:

I don't use it often, but when I need it it's invaluable, for modifying miniature rf connectors.

Jim

================= FWIW -

I worked at Carter Carburetor in the mid to late 60's. The bulk of the carburetor jets were made on genuine Swiss screw machines (with a few Escomatics thrown in). The set-up people and operators were the "cream" of the machine shop personnel, the machines were kept in the best repair, and only the best tooling/materials was used. In spite of all this, it was impossible to produce jets of a given flow rate although when checked with pin gages these were identical. The procedure was to run the parts and then sort the production using high accuracy air gages.

I understand that ball point pens and many solid state electronic components are still like this. You make the parts and sort for the characteristic of interest, for example line width and diode break-over voltage.

I was on the fuel pump side of the Carter operation, but many conversations with the carburetor technicians about "tuning," indicated [and I have seen] in many cases the use of a sizing drill or reamer to "open-up" a jet 1/2 thou for increased air or fuel flow frequently resulted in *LESS* not more flow [apparently] because of changes in the surface finish or raising a minute burr etc. [There was as many explications as there were techs/engineers.]

All this is not to say you can't make jets, just that it is some what of a black art, and you will need some sort of flow meter to see what you made. This will be even more critical for the tiny hole sizes you will be dealing with, as you attempt to tweek and tune.

Unka George (George McDuffee) ============================= When you give power to an executive you do not know who will be filling that position when the time of crisis comes.

Ernest Hemingway (1899-1961), U.S. author. "Notes on the Next War: A Serious Topical Letter," in Esquire (New York, Sept. 1935; repr. in By-Line Ernest Hemingway, ed. by William White, 1967).

Philistine. It's the principle of the thing, not the size of the motor. You can be sure that the guys who prep the hemis spend as much time on their *lawnmowers* as with the top fuel machines....

:)

Jim

Acetylene torch tip cleaners make good jet reamers. Probably wouldn't try it on a car, but a 4s dirt-bike or lawnmower, chances of success are good.

Dave

While there are jet drill bits, ordinary jobber's bits can be used if you take and ease the sides of the bits a bit so they don't cut. Get a full set of number and metric and inch bits and you'll have a bit for every thou practically in the sizes used for gasoline jets.

-- Yeppie, Bush is such an idiot that He usually outwits everybody else. How dumb!