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

Post: # 40646Unread post sameal
Sun Feb 14, 2016 4:01 pm

Ill take a look at all of that next crack i get at it.


One other option im thinking of is getting them re-worked by terry's rubber rollers or possibly trying lord manufacturing. There still around apparently.

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

Post: # 40647Unread post sameal
Sun Feb 14, 2016 4:33 pm

Looks like the center of the armature shaft is about a centimeter up from exact center of the hole in the motor mount.

(Picture is side ways.)
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audiocarver
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40673Unread post audiocarver
Mon Feb 15, 2016 4:32 pm

You know, I think my lathe has those Lord shear-type couplings between the motor shaft and worm shaft. Maybe yours is the same?

I know Presto used Lord for the rubber base mounts on most of their studio model lathes.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40675Unread post grooveguy
Mon Feb 15, 2016 5:20 pm

Hey, Sameal,

I think you ought to look at factors other than alignment; something doesn't sound right with regard to that transmission. The motor may spin freely with nothing connected, but does it have full torque, I wonder? A bad or wrong capacitor can make the motor very weak. It will look fine with no load, but won't power the gearbox. Can you operate the gearbox by hand, from where the motor is supposed to connect? Do the gears and the turntable turn freely with little or no effort when you spin the input shaft by hand? That should turn easily with one finger... after all, it is a speed step-down and a power step-up.

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

Post: # 40678Unread post sameal
Mon Feb 15, 2016 8:51 pm

As far as motor torque, thats a good question. How would i measure that?

All the caps were changed in the presto. The only difference is the new cap is 5mf and the old one is 3.75uf.

The gearbox spins freely from either worm shaft without the motor connected. The filter disc also spins.

When i put everything back together, it locks up.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40680Unread post grooveguy
Mon Feb 15, 2016 9:47 pm

That's crazy; just doesn't make sense at all. That motor ought to be strong enough that you'll have a hard time stopping it with your thumb and index finger. Could be a bad winding on the motor, I guess; any way you can swap the 33 and 78 motors? I just don't know the 'G' version on the Presto personally.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40685Unread post audiocarver
Mon Feb 15, 2016 11:46 pm

Here is a crazy idea......is the motor spinning the correct direction? :?

The transmission is direction specific because of the clutch on the worm shaft to disengage the electric motor while not in use.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40686Unread post grooveguy
Mon Feb 15, 2016 11:50 pm

Excellent point! Wouldn't be the first time a motor was disassembled and the end bells reversed.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40688Unread post Stevie342000
Tue Feb 16, 2016 2:53 am

If the capacitors on the motor were 3.75uF then you need to replace them with the exact value of the motor will not synch correctly it was discussed recently on another forum.

Pretty sure Mouser has the motor run capacitors as well. You may need to use more than one capacitor in series or parallel to get the value you want. There are on line calculators that you can use.

If the motor is not synching then you will loose torque.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40690Unread post sameal
Tue Feb 16, 2016 6:49 am

The 78 motor will spin about a half spin and seize, when i disconnect power its still seized. I have to remove the motor from the adapter and then each will spin free. I can't turn the adapter with my hand at all when that happens. The motor has to be at least pulled half way out of the lord adapter to release tension.

The 33 motor will turn all day, with a snag in the filter disc rotation. If you loosen the motor bolts holding it to the mount, the motor physically hops up and down when the filter disc snags.

Sounds like a worm shaft problem, but both of those spin fine when nothing is on them and theres nothing bent that i can see.

Both motors will turn the filter disc when engaged.

I feel like the lord adapters hardened in a bent position.


The torque issue may be a real thing, but i dont think its causing the 78 side to physically bind to the point i cant move it by hand, nor do i think its causing the 33 hop.

I need to setup a video channel.

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

Post: # 40695Unread post sameal
Tue Feb 16, 2016 9:51 am

Is there a relatively inexpensive torque meter anybody knows about?

Id like to test the old caps vs. The new.


And whats the little gauge people use to see if somethings bent? Looks like a round of the day gauge with a "feeler" on it that moves the needle when pressed.

I sound very primitive right now.

Im gonna go back to carving stone wheels.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40696Unread post Soulbear
Tue Feb 16, 2016 10:34 am

Hi Sameal,
For testing for run-out and if things are running true engineers often use a Dial Test Indicator similar to this :-
25mm-Digital-Indicator.jpg
I got mine from digitalmicrometer.co.uk for around £40/$60 The scale is switchable between imperial and metric measurements with an accuracy to 1/2 a Thousanth of an inch. Hope this helps :wink: :P :D Soulbear
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40697Unread post Soulbear
Tue Feb 16, 2016 10:58 am

Hi Sameal,
Forgot to mention that the older analogue Dial Test Indicators (D.T.Is) tend to be clockwork, but work work fine, and have been used for many years prior to the advent of the these digital gizmos, so you might pick one up off the bay for less than the price I quoted. Be aware though that one U.K. company which will remain nameless want an eye watering £260-ish for a D.T.I. similar to the one I've just posted the link to :wink: :P :D Soulbear

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

Post: # 40831Unread post sameal
Mon Feb 22, 2016 11:21 am

Anybody see a problem with getting the lord bushings re-rubbered?

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 40832Unread post grooveguy
Mon Feb 22, 2016 11:43 am

Only that it seems the slower and probably much more expensive way to go. Just for my own info, I downloaded the latest Lord catalog from their site and see what looks to be the very same shock-mount plates and flex couplings that I've seen in recording and other mechanical equipment for decades. I'd lean on them first, with a clear couple of snapshots of the parts you want to replace, asking for their direction in finding an equivalent.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 41071Unread post sameal
Thu Mar 03, 2016 7:08 pm

So i sourced the bushings from lord, their "Shear bushings" and the number is from mcmaster-carr. The mcmaster-carr number is: 6410K55.
The lord manufacturing number is: J-1211-2-12

The difference is night and day in feel. The old bushings hardly flex, the new bushings feel much better.

Mounting them soon.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 41095Unread post sameal
Fri Mar 04, 2016 4:12 pm

And im happy to say, i got my 78 & 33 1/3 back.

Onto the 45.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 41122Unread post sameal
Sun Mar 06, 2016 2:38 pm

So the next mission seems to be all the bushings in the machine. They are all made by lord thankfully, but pretty much every one looks to be deteriorated.

Then the 45 puck.
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 41438Unread post sameal
Fri Mar 18, 2016 8:34 pm

Id like to take a post in this process thread to thank len horowitz of history of recorded sound in culver city.

If your considering any lathe work, i would more then recommend len horowitz. He has been extremely helpful with my lathe to this point, and i would be struggling very much without his help on this.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 41442Unread post Gridlock
Sat Mar 19, 2016 12:32 am

Sameal....you are very correct (Seconded) ....he also was very good to assure me the k8 is his favorite for 78 s
<\\\\\\\\\\\\\\\\\\\\\[[[[[[[\/]]]]]]]\\\\\\\\\\\\\\\\\>
Recordette Sr.......Presto K-8

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