???Crankshaft for a wobbler engine???

[davidyat]

So I'm working on Bazmak's Cirrus V8 2X build. Working on the crank. Hog out a lot of metal on the mill, then over to the lathe for turning. Make the 5 central areas. Now on to the rod journals. With the offset jig, I get 2 journals made. OH, and by the way I'm using a 1/2 inch flat nose carbide bit. I'm working on the 3rd journal and the bit grabs and does this!!!:wall: Maybe I'm hogging out to much at one time??? Bazmak has been helping me and I'm hoping my THIRD crank won't turn out like this one. Take little bits at a time. I've always said, "I've never had a FAILURE in my life. Only learning experiences. I've learned, "Don't do that again!!" I'm heading out for the NAMES Expo up near Detroit today. Hope to learn a lot from some EXPERIENCED machinists.

 

[Cogsy]

Are you putting any spacers between the other webs as you machine the one you're working on? You want to minimise the ability of the material to flex in response to your cut. If you do that and take small cuts you should be fine.

 

[Jasonb]

Try a narrower bit like a parting tool and work it side to side, a full 1/2" wide cut is going to put a lot of strain on your part.

 

[davidyat]

Thanks. I,ll be using all the suggestions I can get.

Dave

 

[Hopper]

... I'm using a 1/2 inch flat nose carbide bit....

As already suggested I would use a narrower toolbit. I would also use HSS and make it razor sharp to minimize cutting forces. Last crankshaft of that size I did, I used a 3/32" wide x 1/2" deep parting tool blade ground on the end as a turning tool. Softly softly catchee monkee.
Plus the spacers between webs as suggested too. It looks very long and thin out in the middle there. Some kind of offset jig to hold it by the the OD of the crank webs so you are machining close up to the point of support could be good too.

 

[Cogsy]

and by the way I'm using a 1/2 inch flat nose carbide bit.

I completely missed this bit - as others have said, a much narrower tool is needed. My last 2 cranks I used a 0.093 HSS parting blade.