Fluted Knob Fail

[lcorley]

I'm trying to make a fluted knob as shown in the left picture. My plan was to use the hex bolt head (right pic) as an index in the mill vise and cut the flutes with the edge of a 1/4" mill. I would rotate the assembly to the next bolt head flat after each cut. I was very pleased with this plan till I tried it. The torque from the end mill happily spun the knob off my "fixture".

Hmph.

I guess my next approach is to make an aluminum v-block to hold the knob and index the points of the hex bolt against an index mark on the v-block. Any other suggestions? Comments welcome.

regards,
Leon

 

[Bill Gruby]

Keep the bolt as short as possible and use a JAM NUT instead of the one you did. Get the knob as close to the edge of the milling vice as you can. This will eliminate almost all vibration. Tighten the vise as tight as you can and try again. The regular nut is why it spun off. You have a sound plan, just the wrong stuff.

"Billy G"

 

[John Hasler]

Another approach: start with a piece of hex stock. Mill flutes in the flats. Turn the piece down on the lathe leaving just the flutes.

 

[jpfabricator]

Apply the feed from the other side of the knob. On the left side of of the knob so the rotating force is trying to screw the nut/knob on insted of off.

Sent from somewhere in East Texas Jake Parker

 

[TTD]

The torque from the end mill happily spun the knob off my "fixture".

I had the exact same thing happen to me when I made the knobs for some indicator holders (3/8" end mill). I switched to a ball nosed end mill and turned the workpiece like you see in pic below and it worked perfect...just make sure the knob is good and snug first.

 

[Round in circles]

Keep the bolt as short as possible and use a JAM NUT instead of the one you did. Get the knob as close to the edge of the milling vice as you can. This will eliminate almost all vibration. Tighten the vise as tight as you can and try again. The regular nut is why it spun off. You have a sound plan, just the wrong stuff.

"Billy G"

Billy , I'd try and not only use the jam nut principle I'd also fill the whole thread with nuts to stop movement in the chuck jaws , turning down a nut or the bolt length to make the final quality fit if needed. ( basically making the bolt into a hexagonal bar to fit the chuck jaws ) .

Then take it to bits put some Loctite on the threads , reassemble and make the flutes when the Locktite has set .

The six flats of the nuts will give you six flutes on the knob or make a thinner nut so you can rotate the knob 30 degrees & then you can get 12 flutes on it .

Once made , a bit of dunking in boiling water will see the Loctite loosed enough to undo it .

 

[Round in circles]

I had the exact same thing happen to me when I made the knobs for some indicator holders (3/8" end mill). I switched to a ball nosed end mill and turned the workpiece like you see in pic below and it worked perfect...just make sure the knob is good and snug first.

Hi Todd ,
Did you make a packing washer to get the knob,s 45 degree positions accurately set/held or turn some off the base of the knob?

 

[TTD]

Hi Todd ,
Did you make a packing washer to get the knob,s 45 degree positions accurately set/held or turn some off the base of the knob?

Hello David,
I'm pretty new at this whole machining game (about 1 yr) so I'm probably not the guy to be following any kind of advice from, but yes, I used some shims from a 3000psi regulator rebuild kit I had. Had to play around a bit before I found the right combination of shim thickness to "index" the knob the right amount, but finally got it "eyeball" close by lining up a line scribed in center of fixture with corresponding lined scribed on knob ....it sucks not having all the proper tools yet!

I won't clutter Leon's thread with my inexperienced jibber-jabber going into detail, but can show you here (just scroll down near bottom of page): http://www.hobby-machinist.com/thre...-first-project-with-milling-attachment.37673/

 

[kd4gij]

I have a piece of 1" hex stock with a 5/8" hole bored through it and made inserts with different thread sizes that I use for that type work. And as said run the mill on the right side so it tightens it.

 

[lcorley]

Thanks for all the comments/suggestions. What I ended up doing was making a v-block out of some scrap aluminum. I scribed a line on the block to use as an index against the points on the nut.

Then I was able to bring the end mill in from the side to make the groove.

It came out pretty good, although I had a little trouble with keeping the knob vertical in the vise.

The next one I'll take the advice and use locktite to hold the shaft in. That way I can use a jam nut (or group of them) to clamp and index.
It hadn't occurred to me how easy it would be to use heat release on the locktited joint.

regards,
Leon