Presto 8dg refurb. (Lathe porn)

This is where record cutters raise questions about cutting, and trade wisdom and experiment results. We love Scully, Neumann, Presto, & Rek-O-Kut lathes and Wilcox-Gay Recordios (among others). We are excited by the various modern pro and semi-pro systems, too, in production and development. We use strange, extinct disc-based dictation machines. And other stuff, too.

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Stevie342000
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40423Unread post Stevie342000
Mon Feb 08, 2016 1:59 pm

sameal wrote:Is anybody using an overhead lamp when cutting on these?
Not currently but was going to rig something up that was akin to the angle poise lamp used on a Scully. For sheer coolness and completeness of the era of course.

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sameal
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40429Unread post sameal
Mon Feb 08, 2016 7:18 pm

Well, i mean, yeah of course! Keep with the era!

But i thought it served a functional purpose aside from shedding light on the matter.

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Stevie342000
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40430Unread post Stevie342000
Mon Feb 08, 2016 8:19 pm

sameal wrote:Well, i mean, yeah of course! Keep with the era!

But i thought it served a functional purpose aside from shedding light on the matter.
I thought it served a dual purpose to provide light and to warm the material that you are going to cut. Depends very much on the type of lamp you intend to use. What do people use?

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audiocarver
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40433Unread post audiocarver
Mon Feb 08, 2016 8:47 pm

Well, in my room, I have LED track lighting and they are pretty bright on the lathe now for general lighting. I like them because they are cool.

I was going to hang above the lathe, but not on all the time, was something like a 500W photo flood lamp to serve as sort of a Buchmann-Meyer light.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40435Unread post grooveguy
Mon Feb 08, 2016 10:29 pm

With regard to the light, I know that a good number of trolls heat the blank as it's spinning, ostensibly to 'soften' it. But the temperature it reaches is minuscule compared with what's developed at the "cutting edge"; even a 'hot stylus' pales in comparison to heat generated in the microscopic region of those tiny stylus burnishing facets. In fact, I wonder if the heat lamp does more to encourage the disc material to reflow back into its original state. Just don't know. Have never tried it myself, although Ernie Knight of Diacoustic Lab recommended it to me in the early 1960s.

As for Buchmann-Mayer, I know that Oliver Read (The Recording and Reproduction of Sound) used a bare 500W photo-flood bulb at six to eight feet from the disc. The original paper is quoted to reference a light source "...with parallel rays of light," which might have been discussed in high school physics when I was asleep; does that refer to a point source or a diffused source of light? I know those little LED "Pin Spots" you can get on eBay for not a lot of money put out a well-collimated beam; the spot it projects on my neighbor's garage door across the street is not much larger than the lens of the light itself.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40443Unread post Stevie342000
Tue Feb 09, 2016 5:52 am

Those led lights would be useful if using a microscope as the light beam is focussed not diffused. I would imagine heat lamps fell out of use when heating the stylus became the standard as did diameter disc equalisation or compensation.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40541Unread post sameal
Wed Feb 10, 2016 7:02 pm

I just noticed something. My 45rpm switch activates the "puck" drive plate, which i read on the 8gv is the 78 rpm motor.

Did somebody swap switches on me?

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audiocarver
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40544Unread post audiocarver
Wed Feb 10, 2016 8:54 pm

They might have.

The switches are supposed to be electrically interlocked in nature so that when one motor is selected, you can not select the other two and so on. That power supply on the side of the 78 motor should only be turned on when the 78 motor is turned on.

There is also a mechanical interlock inside the transmission as well. Whenever one switch is on, and that motor is turning, the other two motors should not be mechanically engaged at the same time either because inside the transmission, there are clutches that dis engage them mechanically. The puck on the 78 motor should do just that for the 78 motor.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40545Unread post grooveguy
Wed Feb 10, 2016 9:21 pm

Hold on, though. Aren't the two geared drives 33 and 78, and the 45 uses a puck?

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40546Unread post Prestofan
Wed Feb 10, 2016 9:33 pm

Originally the gear driven lathes were 33 and 78. 45 became a rim driven attachment. Some later models had gear motors for 33 and 45, and then 78 as the added rim type drive. Fortunately, the design of the shaft allowed the attachment motors to be added with a solenoid to engage the added motor against the edge of the vibration isolation gismo.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40547Unread post audiocarver
Wed Feb 10, 2016 9:42 pm

On my 8GV, the 33 and 45 are gear driven with the 78 rubber idler rim driven.

I suppose maybe the earlier lathes were 33 and 78 on the gears and 45 was rubber idler driven?

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40548Unread post grooveguy
Wed Feb 10, 2016 9:47 pm

That's good! Presto rated the SNR 10dB better with gear drive than with rim drive. They must have changed over in the early '50s when 45s displaced 78s as singles.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40549Unread post sameal
Wed Feb 10, 2016 9:51 pm

Unless its a mistake in the manual, or the 8dg is different then the 8gv, the plate with the supply "should be" 78 according to the 8gv manual.


My next issue, im right back where i started with the motors. I replaced every ball bearing, opened up and cleaned all the motors and filled the oil back up.

I can start the motor outside of the assembly and it runs great. I can also turn the shaft by hand now. I tightened the bearing cup so there was about 1 centimeter of play in the armature shaft back and forth.

I then with the motor out spun the worm shaft at the rubber isolator, spins free and good. I can also put the motor back in place and it spins great.

BUT when i tighten the motor to the mount it locks up on the 33 and has a hard time on the "supposed 78" (other gear)

Are the mounts bent? And how?!? Could i shim the mounts or motor with neoprene or something? Or should i get them bent back?

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40550Unread post sameal
Wed Feb 10, 2016 9:53 pm

grooveguy wrote:That's good! Presto rated the SNR 10dB better with gear drive than with rim drive. They must have changed over in the early '50s when 45s displaced 78s as singles.
Then could it be modified on my lathe? Or would it require new gears in the motor assembly?

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40552Unread post grooveguy
Wed Feb 10, 2016 10:08 pm

Yeah, I'm afraid it would take new, very different gears. What I'd do, if the lathe were mine (left arm available) would be to disconnect and discard both the 78 and 45 drives . Of course I don't ever figuring on cutting any 78s, even though I have the idlers and leadscrew for my Wretch-O-Kut that will do that. But with the Presto I'd take advantage of the low noise of a solitary gear drive, like the 33 (most used), and for the occasional 45 would either run the motor with an 81Hz power source (stable oscillator and a good Class-D amp with step-up transformer), or run my mastering source at 74% speed somehow. In other words, optimize the lathe for high quality 33 work and figure on a bit of inconvenience and maybe not quite so good quality when cutting discs for friends with juke boxes.

Having said that, back in the early '60s, most of my cutting hobby was taken up cutting 45s for guys at school with aftermarket record changers in their cars. Back then the large hole, yellow label Audiodiscs were a buck each(!) and I charged $5 to put a tune on each side. That was good money back then.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40554Unread post audiocarver
Wed Feb 10, 2016 10:12 pm

Well, all I know is, my 8GV is exactly what is shown in the 8GV manual.

I keep forgetting that 45 was the "new" speed back in the 1940s and 1950s. :lol:

It does mention about aligning the motor shafts to the worm gear shafts in the maintenance section of the 8GV manual. You may have to move the motor and mount around slightly to get a good alignment between the two.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40558Unread post sameal
Wed Feb 10, 2016 10:49 pm

I read that. Im going to play with alignment soon.

I still feel a rubber pad between the mount and the motor, and a rubber pad between the mount and the assembly would cut down on that adjustment.




I did drill out the cabinet holes for the table top studs a little more. Much easier fit.

Im thinking about drilling out access holes in the tray underneath each motor mount. Those attachment screws are a pain to get at. Having a hole through the tray you could get a T-handle allen key in there easy.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40625Unread post sameal
Sat Feb 13, 2016 6:34 pm

So it looks like the isolation adapter between the motor and worm shaft is bent.

Any way to fix that? Im sure there not available anymore.


No amount of plate adjustment fixed it. The 33 motor at its best adjustment had a "hop" in it that trips the platter rotation.

The motor armature shaft looks good, the worm shaft looks good, and everything spins free without any binding when the adapters are taken out.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40640Unread post sameal
Sun Feb 14, 2016 9:26 am

Just checked the motor mounts on a straight edge. There dead on.

Its gotta be the rubber? Isolators.

How am i gonna fix those!?

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40641Unread post audiocarver
Sun Feb 14, 2016 12:06 pm

I'm not sure how it can be, unless the rubber is hard and the coupling is formed bent? :?

Perhaps a "Lovejoy" type coupler would work in it's place? Maybe the Buna-n type rubber for maximum vibration isolation. You can look at McMaster Carr under shaft couplings to see if something would fit there.

You checked the motor shaft for 90* to the motor mount while the motor is screwed down to the mount right?

The worm shaft out of the transmission box is square or at right angle?

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