Looking for some HELPPPPPP!!!! Machining down some gears

teamsouth · Apr 17, 2007

Hi, Im trying to machine some gears for a buddy of mine who races. The whole less rotating mass thing. Anyway they are transmission gears in a motorcycle transmission. All I can say is that these things are like rocks. So far i have had the best result with m2 cobalt. Nothig lasts very long, maybe a couple cuts. Ive tried m5,carbide inserts,micro 100 brazed tools. I am using flood coolant on them otherwise i get cherry red shavings,and i have to be honest..they hurt like hell when they hit ya..
I've tried turning as slow as 100 rpm and as fast as 235..varied feed rates and still get poor tool wear..Is that just going to be the nature of this beast or am i doing something wrong here??? This project of course a freebie is going to end up costing me a fortune..LOL

Thanks for the help and letting me ramble

CHris

lenny baledge · Apr 17, 2007

Maybe a toolpost grinder?

Lenny

joeby · Apr 17, 2007

I am certainly not going to be of any help here because I don't think you will have much luck turning them without specialized tooling.

I don't know what type of material they use to make transmission gears; but could they be powdered metal?

I had to modify a drive coupler for a friend and it gave me the same trouble as you seem to be having. I tried everything I could think of, with no luck at all. I am sure that you could get inserts that would deal with it.

I finally gave up and took the hub into work. I ground the diameters and EDM'ed the holes.

Fortunately, this fellow understands that if I can't get the job done with what I have, it either doesn't get done or he buys the tools necessary to get it done (or I cheat and take it to work).

Kevin

Lumpsmith · Apr 17, 2007

I've had good luck using Carbloy 883 brazed tooling,its not made for cutting heat treated steel but will do a reasonable job.
You need to make the cutting edge a negative grind,and it will chip if you have an interrupted cut.
I use it to cut down the shanks on end mills so I can use them in my bridgeport mill.

drof34 · Apr 17, 2007

Many long years ago, we used to get several gears at a time off some concrete trucks. These gears run open, usually dry and they got very hard. They were about 14" Dia. with about a 12" face and about 1.5" tooth depth. we had to machine all the teeth off and build them back up and recut the teeth. Sometimes we would have three or four people at the time working on them and it was taking about three days each to do one. We tried all kinds of tools(carbide K-6=C2), feeds and speeds. We finally got it down to a day and a half each by turning as slow as it would go useing the slowest feed rate the 24" Monarchs had which was about 12 RPM with a .002" feed rate. However we were useing 1" SNG K68 in a B type configuration with a depth of cut of about 7/8". It took nearly all day but the tool held up and you had accomplished some thing after the cut. The slow RPM and slow feed meant the tool wasn't taking such a beating. Two passes would do it. If you use uncoated carbide you should hone the edge of the insert to deliberately dull it.

Just guessing but I would imagine about a 1/4" depth of cut on those motorcycle gears would be adequate. Worth a try.
:confused:

Jim W.

teamsouth · Apr 18, 2007

Well, I have to say,Im glad i'm not the only one thats had this problem..LOL. Drof I will definitely try your idea out tomorrow and see how i make out. Lump i will also try out the tooling u describe as at this point it cant hurt. The funny part is now it's a battle of wills, mine against the metal and since I hate to lose im in for quite an adventure i think. Thanks for all the knowledge and ideas, i knew this forum would have some great ideas to try.

eKretz · Apr 18, 2007

Use ceramic inserts or CBN (cubic boron nitride). Like buttah. You can likely pick up a ceramic insert for ~$15 or less brand new. Don't bother with CBN for a freebie, too expensive.

If you've never used it, don't get overenthusiastic with DOC and feed. Light cuts in the neighborhood of .02"-.03" and feeds in the neighborhood of .005" per rev are a good starting point.

hello113 · Apr 18, 2007

i have done the gears for some of the racers around here ,i start out with them in a old (junk)dv59 and a hand grinder get them close and then put them in a lathe with a tool post grinder the finish them off... kinda crude but works well

teamsouth · Apr 18, 2007

Thanks for all the replies I really appreciate it. Although i havent gotten back to them today as soon as my gear cutting starts again i will let you know how it goes..

@hello..actually i thought about that but I just didn't want to have to get that involved in it ya know. Its taking away from my normal work...Boss will only take it for so long then i will get the look.

Chris

gar · Apr 18, 2007

If this is a turning operation and not an interrupted cut, then you could try CBN bits. Expensive, but cut Rockwell 60 quite well. Check on required surface speed. Chips will be red or white hot.

.

Peter from Holland · Apr 18, 2007

I take a blunt insert, any will do
And then I make cherry red shavings When a piece chips of the insert you have a sharp edge again
It is mentioned on this board before so I am not the only one doing it this way

teamsouth · Apr 18, 2007

The biggest problem is tht the insert has its biggest problem cutting the gear part. I guess it is not blunt enough and usualy breaks when it it the gear if that makes any sense.

With the ceramic should i flood with coolant still?? never used them inserts

Chris999 · Apr 18, 2007

Try ceramic inserts first, not really recommended for interrupted cuts, should be fine if you keep the depth of cut low at the correct speed. I've used them on case hardened gears. Use them dry, makes a nice show of glowing chips. ceramic is 1/4 the price of cbn, better place to start unless you have a generous budget.

http://www.productionmachining.com/articles/010602.html

http://www.mmsonline.com/articles/090402.html

http://global.kyocera.com/prdct/tool/ceratip/repert/ceramic.html

drof34 · Apr 19, 2007

Go easy on dulling the tool. The purpose is not so much to dull the tool as it is to get rid of the sharp edge which is very fragile and breaks easily. A couple of strokes with a green (carbide) hone at a 45 deg. angle is all that is needed, just enough so that it won"t scrape a fingernail. This should only be done on uncoated carbide.

You probably can't or don't want to this but one other thing that might help is if you can make the depth of cut far enough below the bottom of the tooth depth that no slack appears in the tool as it cuts pass each tooth. In other words the tool is always cutting.

You probably won't be able to do this very well on a Taig or any other similar lathe.

Jim W.

boslab · Apr 19, 2007

most of the gears in question are made out of nitralloys and heat treated by Nitriding, ion Nitriding or a host of company names like tuffriding and such like, i was at a heat treatment house having a couple of extrusion dies hardened,most of the companies work was gears and camshafts for bikes and cars, although to be fair i had to modify the die with the addition of a small screwgroove to locate a drill when fabricating, it took 2 hours and half a box of threesquate diamond swiss files to cut 0.25 x 0.25 x 45 degree groove, even then i dont think i got through the hardend skin, the dies went in with a batch of gears for 72 hours hardening, most of the guys i know modding gearboxes make new gears with straight 'gashed' gears for strength rather than helical which has a narrower tooth they tell me but these are for rally cars so it may not be the same for bikes.
good luck
regards
mark

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