Max Milling Depth 3

[SpaciouS]

Wondering if there is a general rule of thumb for max milling depth? I'm designing a fiber optics cover that is about 4" inches tall. Due to design requirements it’s going to be machined aluminum. I'm debating on whether it should be designed in 2 pieces, each 2" tall and assembled, or 1 piece. If milling aluminum at a 4” depth does not require a special process or extra cost I would rather do that.

Thanks,
Sean

 

[BrianE22]

Depends mostly on the diameter of the mill that can be used. A 3:1 ratio (mill length/mill diameter) is pretty safe for HSS. A larger ratio can be used with carbide end mills.

 

[racookpe1978]

Consider the waste material and extra time:

You're OK with him buying a 4 inch deep casting and then machining out a 3-7/8 deep hole in the middle to get a 1/8 thick wall?

It might not be right - but that doesn't seem like the right process optimizer.

 

[KENAT]

So, while it would depend on shape, volume and various other factors, if it needs to be aluminum you may want to look into casting.

Processes like Rubber Plaster Molding can be competitive with machining at fairly low volumes. On a part I recently did I seem to recall the break even between cast & machined was somewhere below 30 parts.

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[MikeHalloran]

For low volumes, CNC can make billet parts competitive.

For extra deep pockets, plunge milling can be effective for roughing. I.e., move the milling cutter to a fixed XY position, and drive it in the Z direction to nearly full depth. That way, the cutter is stressed in compression, not bending. Then relocate the cutter and plunge again, and repeat.

Some mills have plunge cycles built in.



Mike Halloran
Pembroke Pines, FL, USA

 

[ornerynorsk]

You will not take a 3/1 depth of cut all in one pass, not by any stretch of the imagination. By taking a depth of cut of 1D per pass, you may go as deep as the tool shank will allow. Good chip flushing with either air or liquid coolant is essential so you are not re-cutting chips as they fill the pocket.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[SpaciouS]

ornerynorsk,

I understand there will be several passes, I was just wondering, because how thin the wall needs be with fairly tight tolerances, if there could potentially be any wobble with an extended shank. I'm guessing that a standard shank is shorter than 4" (I could be wrong).

Thanks,
Sean

 

[looslib]

What is the shape of your finished part? If it is a simple "U"-shape, try a horizonatl mill with an adjustable or fixed width wheel-type cutter. If you need to end up with thin walls, you can support the statring block from the sides.
If the quantity is high enough, have a die made for your shape and have the part extruded.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[SpaciouS]

Good idea but my space it very limited. I'm in opto-mechanical design, which tends to be extremely tight packaging and I have a couple very sensitive optical components I have to stay clear of as well as protect the fiber optics; pretty tricky volume of space. Flatness is of major importance to prevent ANY twist when fastened in places (or else it will affect optical properties). I don’t want to hand over a drawing to a machine shop with a ridiculous request. I plan on contacting the vendor once I settle on a concept, but for now I’m trying to do my homework. If it is possible to make out of one piece than I will approach as such, if it makes more sense to machine the cover in 2 manageable pieces and have it brazed, I can go that route as well.

Thanks,
Sean

 

[ornerynorsk]

Could you machine a baseplate and cover plate, wire edm the center section (similar to a motor housing w/endcaps) and have either or both gasketed and bolted or welded assembly? Or just have the whole thing sinker EDM'ed to final print?

A number of years back I machined a number of complex camera mount systems for aerial survey services. I fully understand the need for preciseness in the fit-up of all components. Gasketed housings work well when used with lips or bosses that retain your absolute geometry while providing the correct amount of compression allowance for the gaskets or o-rings.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[SpaciouS]

ornerynorsk,

We do use wire EDM a lot here to handle athermal flexure requirements, however I not know of anything done here with 'sinker EDM'. I just did a little research on that process, and though it's fascinating, it is a high cost solution. I have modeled 2 concepts, one being a mono part and the other being a 2 piece (base and top) that I would have vacuum brazed. That being said for the 2 piece design, wouldn't milling 2" deep parts sort of get me to the same place as sinker EDMing a base and a top?

Thanks,
Sean

 

[ornerynorsk]

Hello Sean,
Yes, it would. It comes down to a matter of what processes are readily available to you.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[SpaciouS]

ornerynorsk,

You've been really helpful. I appreciate your time...

Thanks,
Sean