Ferrofluid Tweeter in a Lathe - Any Concerns?

[bmwman91]

I have some Seas Prestige 27TAFNC/G tweeters on order right now for an upcoming project. Due to space constraints, they must be mounted from behind, and I plan to do the modifications on a lathe. The rear screw boss will be held with a collet while I modify the plastic housing. I will be removing the mounting flange and adding a step to the front so it will lock into place when mounted from behind.

I know very little about the construction of tweeters, and this one has ferrofluid fro VC cooling. I am just wondering if the centrifugal force from being in the lathe could cause anything to get messed up (fluid separating into parts, getting into places it doesn't belong, etc). Any input is appreciated! Thanks!

(obviously, the tweeter can be damaged many other ways on a lathe...and THAT is totally up to me)

[Ed LaFontaine]

I think your concern is well placed.

The fluids I have experience with around a lathe are the ones I use for finishing. They don't stay where they are very long. They usually wind up on the wall behind the lathe, out in the shop or on me.

Can you remove the fluid with the intent to replace it after turning?

I'd consider that.

I have turned tweeters, though without the fluid. It doesn't appear the faceplate is easily removable. Look into that as well. I think the part you want to change has nothing to do with the fluid.

[Loren42]

You can call the manufacture if you want the real scoop.

The other option is to put the lathe on a very slow speed. Plastic is easy to cut and a slow speed generates less heat.

Place some masking tape over the dome.

You could also do the same operation on a mill with a rotary table.

[turboyam]

Originally Posted by Loren42

You can call the manufacture if you want the real scoop.

The other option is to put the lathe on a very slow speed. Plastic is easy to cut and a slow speed generates less heat.

Place some masking tape over the dome.

You could also do the same operation on a mill with a rotary table.

+1. fluid will be everywhere in the motor if you spin it.
See if you can take it apart or go the milling/ rotary table way.
Cutter has to be fresh and fast spinning for a nice finish.

[exurbia]

A very low speed on the lathe and a high rake on the HSS tool might work. But, very low speeds and that acetal that seas use don't always go together. Most of these plastics require a relatively high surface speed around 50-90SFM. Make sure your clearance angle is steep, as close to vertical as possible is good. I used to machine a lot of plastics, nylons, etc.
The best bet would be to set your tweeter up on a vertical mill and use a fly cutter. this would give you true concentricity without the hassle of setting up a rotary. Another possibility is to me the most obvious and sets up the tweeter for grinding on a spindle, precision finish and no chips or swarf.
All of this is assuming that you have a nice fully equipped machine shop.

[bmwman91]

Thank you all for the wonderful input. I am happy to see that I am not the only one who has thought about machining tweeters!

If I can get the plastic casing off, I will just do that. I am assuming that it won't come off without wrecking the tweeter though, so that is why I was considering turning it fully assembled. If the ferrofluid is going to end up everywhere except where it belongs, I will either use a grinding wheel, or mount it on the rotary table & mill it. The M4 screw boss on the rear will probably be really useful for setting up the cuts, except the one where I cut IT off! I have access to a pretty complete machine shop, so I will come up with something. For now though, it sounds like the lathe is OUT!

Thank you!

[Loren42]

Originally Posted by bmwman91

Thank you all for the wonderful input. I am happy to see that I am not the only one who has thought about machining tweeters!

If I can get the plastic casing off, I will just do that. I am assuming that it won't come off without wrecking the tweeter though, so that is why I was considering turning it fully assembled. If the ferrofluid is going to end up everywhere except where it belongs, I will either use a grinding wheel, or mount it on the rotary table & mill it. The M4 screw boss on the rear will probably be really useful for setting up the cuts, except the one where I cut IT off! I have access to a pretty complete machine shop, so I will come up with something. For now though, it sounds like the lathe is OUT!

Thank you!

I usually mount a lathe chuck on the rotary table. Would that work?

[bmwman91]

Originally Posted by Loren42

I usually mount a lathe chuck on the rotary table. Would that work?

Brilliant! I should be able to get the smaller chuck onto it. Parts come Tuesday. I will try to get some pictures of my shenanigans posted up here.

[bmwman91]

Here was the final result.

I started out making a fixture from some D2.5" 6061 aluminum bar scrap. This was 10x more work than the modification operation on the tweeters (as usual)!


This is how it goes together.




On the rotary table...


The tweeters, post-mod...


The application for these is in the factory door-pods for a 1991 BMW 3 series (E30).




I am probably going to put some 1/8" open celled foam between the tweeter & grill to hide them a little more. It is nice that I was able to keep the diffuser on there too.

[Loren42]

Awesome job!