How can I machine this part?

[scubasteve_911]

Hello everyone,

I need to machine this part for a school project this year, but I am a bit uncertain how to do it. The final part will be composed of three different materials: brass, delrin, and adhesive. The back brass peice will be turned on a lathe with a precise OD and ID. The ID of the cylinder has a step near the rear of the part. Then, another cylinder of delrin will be placed into the part and adhesive will hold it. I plan to keep the setup on the lathe to help guarantee the parts true. After this is machined, I wish to adhere the brass to the delrin, then machine down the brass.

I am now pretty lost on how to create the slots. These slots are about 1mm wide. I know I can get endmills that are small enough, but their flute length is pretty tiny. I need to go in about 1/2" into the part, which is far beyond their length. My plan was to use a rotary axis and tilt the mill's headstock. I wanted to dial in the right angle, then take several plunges and increment either the X or Y for depth cuts into the brass.

I heard that brass and delrin machine beautifully, so I was hoping this was possible. Can anyone give me a reality check? Do I need to increase the slot width? In my case, the slot width is better kept small for the part. This part isn't to scale and it was just a concept that I came up with and I have been using it in FEM for simulations.

For those curious, it's a capacitive sensor to measure spindle runout. It will be integrated into a radial magnetic bearing for control. It's for my degree project in the electrical engineering program.

Thanks !

Steve

[Chuck Reamer]

Are they blind slots or do they go from one end to the other?

If they are not blind use a slitting saw to cut them.

[scubasteve_911]

I'm an idiot, I didn't even post my drawings ! SORRY!

[HuFlungDung]

Machine the inside slotted piece as a seperate 'bushing'. This way, you can do the slotting operation with a slitting saw and a dividing head setup.

If the handling of all these parts is a major headache while you prepare to do the bonding, then stop the slotting operation slightly short of the end, on the outside end. This will keep the segments associated but seperated by a small web.

Now, if you wanted to make the inside 'bushing' longer than necessary, you could after bonding, just face the outer end off, completing the seperation of each segment.

[scubasteve_911]

HuFlungDung,

Thanks! So, I should turn the inside piece of brass to it's proper OD and a rough ID. Mount it to the indexer, then slit the slots into the piece. The slits won't run all the way down, so that there is a peice holding it all together. Then, I can bond it to turned down delrin (in brass), and simply turn down the unneeded retaining piece? At this point in time, I can finish off the inside to a nice finish to account for the milling operation?

It is extremely important to get a good finish, which is the reason I chose brass. It also nearly matches the thermal expansion coefficient of delrin.

Thanks again! Hopefully, I interpreted your post correctly. I am an amateur machinist and more of an electrical engineer, so bare with me, I'm a little slow :P

[HuFlungDung]

Yup, I think you got it. You might want to make the ID an accurate (but undersized) bore, so that you can insert a dummy mandrel inside to squeeze it firmly within the delrin bushing while the glue sets up.

[scubasteve_911]

Yes! Great idea, that will minimize deflection that would certainly affect the quality of the sensor.

I will post my final project on here when I'm finished next may, maybe someone might find radial magnetic bearings useful. These sensors are far superior and easier to use than comparable several thousand dollar systems. Plus, I can make them for about 15$ plus about 100$ in electronics

Steve