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andy_b
08-09-2005, 12:39 PM
sorry for the on-topic post.
http://bbs.homeshopmachinist.net//smile.gif

does anyone know of a source for slitting saws? i need to machine a new throttle shaft for an old tractor. the shaft is brass, 0.250" in diameter and 3" long. there is a throttle plate that passes through the center of the shaft. the plate is approx 1.1" diameter and 0.055" thick. i need a way to cut the slot in the shaft for the throttle plate to fit in it. the cutout on the original shaft looks like it was cut with a slitting saw about 2" diameter (one cut was made from each side to give a total cut opening length just equal to the diameter of the throttle plate).

i'd like to buy a used cutter since i only have one use for it (at present), but didn't really see any on ebay. i'd buy a new one if it wasn't $50 or some crazy amount. i'm also open to other suggestions. i was thinking of trying it on the shaper (a bit overkill using a 20" shaper to cut a 1.2" slot 0.055" wide). any ideas on how to set it up so the chips don't clog the slot and break the cutter off in it? also, i don't think i can set the shaper for a 1.2" stroke.

if worse comes to worse i can drill a hole at each end and cut the slot by hand with a small jeweler's hacksaw (i forget the correct name for it).

andy b.

SGW
08-09-2005, 12:42 PM
MSC www.mscdirect.com (http://www.mscdirect.com) should have it.

chipeater
08-09-2005, 12:48 PM
Try Victor Machinery:

http://www.victornet.com/cgi-bin/victor/subdepartments.html?did=120&id=sT4np2zM

Look under Screw Slotting Saws or Jeweler's Saws. It looks like you'll have to choose between 0.051" and 0.057", though.

Steve

Evan
08-09-2005, 01:17 PM
Is it strictly necessary to maintain the original design? If not why not just mill a flat on the shaft to attach the plate to?

andy_b
08-09-2005, 01:33 PM
MAN YOU FOLKS ARE FAST!!!!!!

Evan,
i'm not an expert on materials' strengths (heck, i don't have any idea how to even calculate it). do you think the 1/4" brass shaft would hold up with that much material machined away? the body of the carb is brass. one end of the shaft just rides in a machined cavity in the carb body, the other passes through the body and is connected to the governor linkage. i don't really think airflow would be affected enough in this situation to worry about, so my only concern is strength of the shaft.

thanks for all the replies thus far!

andy b.

Evan
08-09-2005, 01:36 PM
I've seen lots of carbs with a flat milled on the shaft. I don't think it would be a problem for strength. Give a slight radius at the ends of the milled flat so it won't crack at that point.

Don't forget that the plate adds considerable strength to the assembly when screwed in place.

[This message has been edited by Evan (edited 08-09-2005).]

SGW
08-09-2005, 02:25 PM
I wouldn't think there would be any load to speak of on the shaft, so strength shouldn't be much of an issue. Milling a flat would certainly be easier. And if you try it and it breaks in use...just make it again! One of the great benefits of home shop machining.

Evan
08-09-2005, 06:33 PM
I just did an approximate stress calculation on a brass shaft 1.1" long. I assumed 15,000 ksi modulus of elasticity for brass and a resulting thickness of about 0.2" with the plate in place. Since it has an area of about 1 sq" if the engine draws a full vacuum the pressure on the plate will be about 14 lbs. If we count this as a point load in the center of the shaft (it isn't) the maximum deflection will be around 0.0005".

The shear strength of low lead brass is about 36300 psi so the strength of the remaining material in the shaft in shear will be around 800 lbs.

It should be strong enough.

Mcostello
08-09-2005, 11:07 PM
Make sure of the relationship of the plate to any idle gas feed holes as some carbs pull additional fuel from the passage to help avoid a stumble or hesitation. Don't remember where I have seen this tho'.

GRH
08-10-2005, 09:39 AM
Travers tool has .057 wide.I have used their saws with good results.

http://www.travers.com/index.asp

Item #10-215-057

2-3/4 x .057 x 1" bore @ $7.19

seems cheap enough.

Graeme

Rustybolt
08-10-2005, 03:15 PM
Andy. Let me look through my pile of slitting saws. I have one close I'll give it to you get me your address. Id there any hole preference?

IOWOLF
08-10-2005, 03:40 PM
Mill a flat on it and be done,Most of the ones I have seen are flat like Evan said.