Chip suction system clogging on brand-new blanks?

[EmAtChapterV]

Back in the day, I used to have a terrible time with the chip clogging up in my suction system, before it reached the glass jar. I had been using 5/16" copper and latex tubing to the jar, and a 1 1/2" vacuum cleaner hose from the jar to the pump, which used 110 watts at full power.

In getting my Rek-O-Kut running again, I upgraded the tubing to 1/2" inner diameter and sealed off some air leaks with a redesigned jar lid, resulting in effective suction increasing to the point that I could run the pump at 50% power when starting the cut and 30% thereafter and not have any problems at all for twenty minutes at a time... or so I thought. Then yesterday I pulled out the first of the the brand-new Apollo dubs I'd ordered last month and tried to cut a side. Hello, my old nemesis, slowly-growing sock-like glob of balled chip at the end of the latex tubing inside the jar. I turned the suction power up to full, but it was no good, I couldn't dislodge the clog and it grew until suction was cut off and the chip dropped six minutes into the side. Argh.

Then it occurred to me that everything I'd been cutting until then was technically New Old Stock, made in 2001, 2002 at the latest. This fresh box had a date code of D13001, so I'm assuming it's barely a month old. And I had the exact same problem with the old stuff when it was new.

Does anyone have any advice on how to avoid this problem, besides ordering blanks a year or two in advance of using them? I do use talcum powder to lubricate the inside of the tubing, but in cases like this I wonder how effective it is.

[opcode66]

Baby powder. Or just straight talcum powder.

Take a bout a spoon full and gradually allow it to get sucked into your tubing from the point of the cutterhead. You might need to take off your head to do this.

It allows the chip to travel down the tube without getting snagged up on the bends in your tubing. It also allows the material pass with less friction. Therefore less static. Therefore less chance for static build up which tends to make chip (especially plastic chip vs lacquer) stick together in a little ball and clog up the tube. Also, it is important to make sure that the connection to your chip jar is good and that there is absolutely no blockage at that linkage point. I've had chip make it to the top of the jar and get stuck and bunch up which eventually decreases suction and then you dropped chip.

[Serif]

Have you tuned the heat by ear with the new blank? Cool chip might be heavier since it is not yet as vaporized as hot string. If there is a lot of out of phase when you get to the 6 minute point, there might be some depth angle obstruction in case the position of the nozzle is not ideal.

Since you already use talcum powder, and if no clog exists in the tubing, other factors must be afoot vis a vis the fouling. My mentor said that chip suction is in some ways more art than science. He did indicate however that most of the time the chip is going to drop during fast pitch, such as lead in, and that if it doesn't drop there it is less likely to do so during the slower pitched grooves. Your drop at 6 min + is not supporting this theory, but there was no claim at absolutes.

I believe that best results are obtained when the nozzle is less than 1/16" above the blank and sits no further than 1/4" or so from the front of the stylus - with the nozzle on the incoming side of the stylus.


Keep trying, it will only give you more information to watch and notice. Let us know if this is resolvable and how so....


- Chip Swarf

[EmAtChapterV]

I haven't had the problem re-occur yet during test cuts, even starting with a regular lead-in on the b-side. I suspect it may have had something to do with the a-side being the top of the first dub out of the package - the shrinkwrap was very sticky and obstinate, and looks like it might have left a bit of residue around the outer diameter where the cutting stylus dropped. I'd watched to make sure the chip was picked up from the disc surface when starting the cut, but by the time I noticed it wasn't making it all the way into the jar, I'd already finished the lead-in and started the music, and was committed to the side. Now I know better. I haven't tried cutting another complete side yet, I'll post results when I do.

I also discovered that the new blanks like a lot more stylus heat than the NOS ones at inner diameters. I'd had it set to a 450 mA happy medium, but found the results rather dull and muffled on the new blank. I managed to get a 3 dB improvement at 12.5 kHz at 5 inches diameter by increasing the current to just over 600 mA, the limit of what I'm comfortable with. (At around 700 mA the heating wires start glowing red - noted on the DIY control panel as "BBQ Time" - and high frequency response was still increasing at that point!)

[Serif]

That's one way to tune the heat. The method I was alluding to (which is widely used) involves cutting unmodulated grooves and listening to the pickup (riding the just-cut groove) cranked up loud enough to hear the Gaussian hiss. When the heat is increased above the minimum setting there will usually be a noticeable drop in hiss at some point. The point where the hiss disappears first is the right spot, since too much heat can cause both electroforming-vexing horning and possibly swarf fire. Also, the heat builds during the side, so the same heat can be invoked via attenuation of the current during an LP after it's half way through, or so... I wonder if Complete attenuate heat during a long side... D. care to weigh in?

But the weight of the string could be different if the string is heated more than less. I had a relay on the Chip pump which would cut off after a few seconds to make the pull go from high to low, once the suction had been established. But I now have a variac on the table which can leave it pulling high for longer and makes the whole variety of suction strength available at the operator's position, rather than having to walk to the other room to adjust the box-mounted rheostat. I think the low setting is just to be quieter and to keep the pump cooler than running it always high. But, I don't know if the vacuum can ever be too strong if using something like a standard job shop vac, such as the Ametek used in the Lee boxes.

Hopefully your chip issue was only due to the top blank in the new stack.


- Chuck Spindle

[EmAtChapterV]

Here are some silent grooves, then 12.5 kHz at approx 60V/7W at 33 1/3 rpm at 5 inches diameter, with stylus heat increasing in 100 mA increments from 350 to 750 mA.



I had the chip dump again last night, on the second of two new blanks. It wasn't even clogging up, things were going great until it just snarled out of nowhere halfway through the second side. I'm now revising the suction nozzle to try to pull the chip more from the center side at 90 degrees from the stylus, instead of 45 degrees from the back. It's challenging when the design of the lathe means the only practical suction access is from the back side of the stylus (front side of the head) and there's less than a quarter inch of lateral clearance between the stylus and the center clamp at 3 7/8" diameter.

[EmAtChapterV]

Third new blank, third failure. Zero success rate so far. It wasn't even a clog or a snarl this time, the chip just dumped completely out of nowhere. Plenty of suction pulling through the vacuum, nothing out of the ordinary, but suddenly there was chip going all over the disc surface. This was after realigning the suction tube and fine-tuning stylus heat multiple times on the unused space of one of the failed blanks. And yet every single NOS disc always cuts perfectly. At this point I'd go back to Transco if they were still in business.

[Serif]

It's quite interesting that the vintage blanks aren't dropping chip when using the same technique on the new blanks does cause it to drop.

What are the numbers 60V/7W referring to?

The cutting level is usually defined in terms of the velocity or possibly acceleration. Velocity, in cm/sec, and acceleration, in cm/sec/\2.

The cutter doesn't want to see more than 6 Watts per second, according to ABG. So, a brief transient of high frequency which is a fraction of a second's duration in the loud attack portion of the sound can require as much as 600 Watts, but most of the time the power consumption is much lower in a head during modulation. The Ortofons can supply 550 W/ch. which is not shabby. Still, no more than about 5-6 Watts are used with Miami bass lines soloed or, say, 808 booms that are loud - full displacement wiggles of the lowest frequencies cut. Less power than that is required in the low midrange, and less, still, as one sweeps up through the midrange. Almost no power (relatively speaking) is required around the cutting head's resonant frequency, which is usually 1 or 2 kHz. Above that, there is a steep slope of power required for the realm of acceleration, which is any velocity that is faster than the standard (usually 1 kHz = 3.54 cm/sec/channel/RMS). This is half of the trouble with treble and why fidelity that is high is a big deal. The other part is pickup cartridge trackability.

So, while 7 W sounds mild compared to 600 W, it is too much power to sustain for more than a half a second, since 6 Joules is the max throughput. 1 Joule = 1 Watt * 1 second. Thanks to James Prescott Joule.

Not to sound like a broken record, but the AES Anthology on Disc Recording is quite specific in recommending having the chip suction nozzle be positioned on the side of the stylus which is towards the incoming revolving blank surface, rather than the out-going surface with the new groove. So, if the back of the cutter is on the still-uncut side, then one should try to have his nozzle pointing at the back of the cutter, rather than the front, which is the side one sees from the front of the lathe and where the brand name badge usually goes. Also, it can be picked up satisfactorily from the side (as you might mean by 90 degress offset), like with the Neumann heads, but those have a captive mini nozzle (captive inside the head) which keeps the suction trained on the stylus quite closely and goes up and down with the head depth. Whereas, on my system, the nozzle is independently supported from the head. But, it is in the preferred position for best pickup and to preclude excessive build up of chip smut on the jewel. By having the nozzle on the other side of the stylus, aimed from the front side of the cutter, it pulls the string against the stylus, rather than away from it, in order to clear it off. That's how the jewel smut would build up most.


As for the stylus heat tuning, again, there is no need or want of modulation during the test cut for determining the best stylus heat for the given blank. The test grooves are unmodulated and only the hiss of the smooth groove walls should be listened to, involving stereo crankage, as needed. Use the pickup cartridge to play the just cut groove in order to listen to this hiss. So, there should be two styli in contact with the lacquer disc at the same time - et enregistreur, et lecteur. Then slowly raise the current such that the hiss gets noticeably quieter. Keep on increasing to verify that you have reached the point of no returns, so to speak. Then return to the point just where that quiet zone starts. The heat will build while cutting a long side, so one might benefit from lowering the current after the trolley is half way or more through the effective radius provided the best heat for the given blank to be most hiss-free is already rather high.

As for the position, the nozzle should be placed somewhere between 1/32 and 1/16 inch above the lacquer surface. It should also be positioned around 1/4 inch from the stylus - perhaps even closer. Not close enough to perturb the stylus, but not far away enough for there to be any hope for the string to foul.

Also, there might be a bad batch. Sterling Sound once bought a vintage Neumann just to use for testing batches of blanks while not in a paying session on the clock...

Transco are now owned by Apollo, of course. They use old machines, just like cutters. Might be worth calling them with courtesy to inquire about this if you aren't able to sort it in the next several tries.

- Serif

[EmAtChapterV]

Hi Serif,

The Presto heads have a fairly steep inductive reactance - BBC research archives list a 1B (nominally listed as 500 ohms around 1 kHz) as going from 85 ohms at DC up to 1800 ohms and climbing around 8 kHz. Mine is a 500 ohm 1D, measuring 92 ohms DC. At its nominal rating, 60 volts would be 7 watts, a recipe for catastrophe but only at 1 kHz. At 1800 ohms though, it'd only be 2 watts. I have a 63 mA fuse in line with the head, which has only popped once, on a loud cymbal crash after an afternoon of high-frequency response tests. What spurred me to put the fuse in the circuit in the first place was a malfunctioning op-amp in the recording EQ deciding to generate and send spurious 14 kHz tones through the amp to the head at around 150 volts. The head obediently cut these signals and never so much as blinked, but I nearly had a heart attack when I saw and heard the cutter power meter unexpectedly peg off scale hard right with a little "tink" sound. Someone else here has noted that Presto heads are really difficult to blow, for which I'm very grateful.

I am trying to remove the chip at a 90 degree angle from the side, like in Westrexes (Westrices?) and Neumanns. I'd originally had it offset about 45 degrees from the inside trailing edge, where the chip would go naturally anyways were there no suction. This served me well from 1999 to 2006, and from last November up until earlier this month when I tried to cut new blanks. Yesterday evening and today I've been going over the tubing with a round file and ultra-fine-grit sandpaper making sure there are no nicks or burrs anywhere, before trying again. Barring that, redesigning the system to remove the chip perpendicularly from the cutting face of the stylus will require the services of a machine shop. (New bolt holes tapped in the side of the cutter carriage for support, and some seriously intricate and circuitous bending of copper tubing.)

[Serif]

Presto without "chango." That's some nice imperviousness. I've envied the Westrex's lack of need for Helium. The 90-degree sounds good if the proximity is good. But I think everyone from Scully to MossBoss have suggested that the ultimate shape for the nozzle should be that of a flattened oval so that the angle of approach can be low. I have in another thread noted that I hear three "notes" made by the vacuum at the same pump speed. If the trolley is far enough to the right that the chip tube nozzle is not over the platter will be one pitch. Then another, if one moves the trolley just enough so that the nozzle is over the platter, but not yet over the blank. And the third pitch when the nozzle is positioned somewhere over the blank, since its surface is higher up than the surface of the platter. That makes it closer to the nozzle which make more intimate contact, and faster Bernoulli.

The solution I got was custom made by Island Audio Engineering. It was a flattened oval entrance that is adjustable in length and position. But the Scully manual suggested a Venturi nozzle, which normally seems to imply a convergence leading to a narrower opening leading to a divergence before remaining at hard normal "tube diameter." The fore and back pressures are possibly decoupled from each other while maintaining optimal velocity. But then flatten the convergent flange of the nozzle piece. Let it be a Hoover-like cow-catcher for all swarf, hot or cold. Sticky or dry.

I named a blog after the Scully manual's use of the word, Venturi, but I have not seen an actual one in the field and the photo in the manual is too grainy and not close up on the object for any detail to be gathered.

http://home.fuse.net/injanius/Venturi_Tube.html

I love closeups of "living string." I think Taloowa have such an one.

servus,
Serif

[jjgolden]

Something else to try/observe,
When you get a new box of dubs, Open them up and let them "Air" out for a few days if possible before use.
There are times when the lacquer arrives softer and needs to cure/dry out a bit more.

[audadvnc]

I had chip spillage happening a few weeks ago, similar to your situation. I suspect that static electricity may have been a factor, as it was late winter and everything was very dry.