need help with cutter setup

[shotline]

I'm using a 3/32 round cutter for two woodruff key slots on a 4" bolt. I'm having a hard time repeating from part to part. Not exactly sure how to center the cutter. Any ideas/ help on setting this up?

I was also wondering if an endmill would be a better way to go.

Thanks in advance!


Sorry if this is the wrong area to post, I'll move it if it is

 

[Metalfixer]

More information would be helpful. Are you using a vertical milling machine? Woodruff keyseat cutter, like 5/8" diameter by 3/32" face width? Are the bolts 4" long, I can't imagine a 4" diameter bolt.
I use a vertical mill with a keyseat cutter,holding the part in an indexing collet holder or chuck, or dividing head or vise if the slots are inline.Bring the cutter to touch the diameter of the part on top,move table to clear the cutter when you raise the table. raise table 1/2 the diameter of the part, plus 1/2 the face width of the cutter.Position the cutter at the location you want and use the machine dials to cut the correct depth. Stops can be used for repeat setups.

 

[shotline]

I don't have the parts in front of me... so this is an estimate, I the the bolt is 1/4-20 x 4". The cutter is custom cut, about 1/4" dia. Some history...before me about 60 were cut and 5 cutters broke, the shank is ground down to 1/8 or smaller. Which makes it very delicate. It's not my choice, but I'd like to try a 10-$20 end mill. The bolt is held in soft jaws. The cutter is tricky to measure, but I could measure the slot to get the tool/kerf size? I'm running at about 200 rpm with a mister. I doesn't make chips, more like granuals or sand. I've traversed the cutter across the soft jaw and it works much better. It seems like plunging the kerf in( 0.130") isn't the way to go. I've looked at some of the worn out cutters and the kerf is rounded and burnished. In two days I can get some exact info on the current setup.

Thanks for the response, I appreciate it.

 

[Metalfixer]

I would look more at a modelmaker's line of tools.

http://www.sherline.com/

Cutters that small require a more delicate touch than my Bridgeport would provide with me at the controls, someone else may have the skills.

 

[ornerynorsk]

200 rpm is very slow for a cutter of that size. Is your cutter HSS. What grade and material are the bolts?

 

[shotline]

The cutter(s) are both HSS and Carbide, 200 rpm was suggested by the tool maker. The bolt is an of the shelf grade 3, I don't know the alloy. It works, but too many things don't feel right on this one.

 

[ornerynorsk]

I'm old school tool and die,trained under WWII era Journeymen. For the most part toolmakers will normally tell you SLOW rpm on form cutters, keyseat cutters, and the like. But, my years in the shop post-apprenticeship say that these tools can and should be run close to normal milling rpm ranges, which would put your cutter right around 800 to 1000 rpm on that bolt. That's on the low side to allow for any alloying elements in the bolt as well as less side clearance in a cutter of that type. Chip per tooth feedrate becomes irrelevent as you will be hand-feeding very slowly, relying on feel and sound more than anything.

Your mist coolant is just the ticket for a deal like this.
Good luck.

 

[shotline]

Thanks for all the input. That project is on hold for now. Ornerynorsk-thanks for the speed tip, It does work at faster speeds. Also, I tried a 3/32 4 flute end mill and it seemed to walk around so stopped. Could that be the wrong application of the cutter and or material? And what about drilling a pilot hole for the end mill? There's a change the project maybe re-enginered in the future to adress these issues.

 

[4JawChuck]

You use two flute end cutting cutters for keyseats, not four flutes. You should plunge into the work and then make the seat, if you need to come out you start at the end of the keyseat and work out with the two flute.

Four flute cutters will cut oversize because of vibration.

 

[ornerynorsk]

4jaw, any endmill, regardless of the number of flutes, will "pull" as it's cutting. 2 flute cutters are actually ground with more chip clearance, and will deflect more than a 4, 6 or 8 flute at a given chip load. This is why woodruff cutters are ideally suited for keyseat cutting because any deflection in the cutter will not cause the critical dimension (width) of the keyseat to vary.