ferrofluid?

[synths]

i need damping fluid of presto 6n w 1d head
(the stuff that goes in that metal canister next to head)
I read about the magnetic properties of ferrofluid-
but i fail to see how this applies to the use I am using it for-

help me understand-

is it that the density of ferrofluid is just right for this/
what other substitute will do?

[cuttercollector]

Ferrofluid as I understood it was to aid in conduction of heat away from voicecoils. I guess it might have an application in cutter heads for the same reason.
I think what the thing on the Presto is for is to provide resonance damping but I'm not sure whether that is to do with the resonance of the head assembly or warps in the disc being cut.

[Steve E.]

first I tried glycerine, which is what was suggested in the 6N manual. But apparently glycerine comes in a couple of viscosities, and mine was too thick.

So now, on emorritt's suggestion, I'm using mineral oil. Seems OK. I bought both at the same pharmacy.

[synths]

thankx-

my bad-
ferrofluid goes inside head for damping-

silocone, or medium weight oil
or the like will work for the canister

[grooveguy]

I've thought long and hard about using Ferrofluid in a cutterhead and decided against it, at least with Presto and similar "moving iron" units. Ferrofluid works well in a loundspeaker because the voicecoil moves parallel to the magnetic structure and the gap is open at both ends. In a cutterhead, the armature is pulled toward the magnetic structure, and if anything is in the gap, it's going to be compressed. Maybe the viscosity is such that it can bleed out of the way at low frequencies where the displacement is greatest, and at high frequencies there is very little displacement so perhaps it doesn't matter. But it won't help draw heat from the voicecoil, as it does with a loudspeaker, and that's what Ferrofluid was all about. It's not a means for damping resonances, etc.

The oil-filled cylinder off to the side of the cutterhead is what's know as a "dashpot." It does help damp vertical cutterhead resonance, which was a particular problem in the old days with "standard groove" recordings and their deep cuts. The cutter could actually go into vertical oscillation at a low frequency... 20 to 100Hz. This is not such a problem with microgroove recording, however. The oil had a viscosity very similar to '3-IN-ONE" oil. I used 20-weight motor oil in a Presto dashpot that I fitted to a Rek-O-Kut lathe, which did have a severe vertical oscillation problem. That was with the Astatic, horizontally-mounted head, howeverl. Cutters with a vertical profile (like the Presto 1D, Audax, Fairchild, etc.) never seemed to have the same problem.

[Cutterwoller]

Olive oil works well, I use it and have no problems.

[grooveguy]

Lewis: Olive oil should work just fine, until it turns rancid. What's more, olive oil has no cholesterol and is full of mono-unsaturated fatty acids, so it's healthy for your lathe!

[Cutterwoller]

I should have mentioned that it should not have been cooked first! Mine has never gone rancid, thats 6 years on the trot. Extra Virgin of course! Or try 3 in one, the damping fluid in the dash pot is not to essential, but for the head you need to use the right stuff, definatly not olive oil in the head!

[piaptk]

A dashpot also helps to gently drop the head onto the cutting surface, correct? To keep it from impacting as hard? This woul dbe the only reason I needed one.

How much fluid do you put in there? How full do I fill it?

[petermontg]

A dashpot also helps to gently drop the head onto the cutting surface, correct? To keep it from impacting as hard? This woul dbe the only reason I needed one.

How much fluid do you put in there? How full do I fill it?

3/4 full is what a presto manual will tell you. but am guessing this is just a rough guidline.

[JayDC]

I need a dashpot :/

[petermontg]

I need a dashpot :/

I think Markrob might have the info for having one built. I think its posted here somewhere.

If i come across one on my travels jayDC ill send it your way.

[petermontg]

I need a dashpot :/

I think Markrob might have the info for having one built. I think its posted here somewhere.

If i come across one on my travels jayDC ill send it your way.

Ah it was you that started that thread. silly me

[JayDC]

yeah I know, I guess I'll just build one, kinna wanted an original one though..