Presto 8dg refurb. (Lathe porn)

[sameal]

Hi!

I decided to start a thread on my presto 8dg adventure. Its already been a procedure picking it up, and moving it only to discover it cant really fit in my home studio. So with the advice and guidance as well as space of a local studio here in milwaukee, National recording, ill be undertaking this on site there. Much thanks to national recording, and many other sources and people that have thus far, and will hopefully soon guide this project along.

Onto the porn! Storage shots

[sameal]

Did westrex install security screws? I removed the head today and had a hell of a time doing it, as they had security type screws i couldnt find a bit for.

Probably gonna dump the security screws, makes no sense from a service standpoint.

Shots of the motor:

[grooveguy]

Hey, I remember that lathe; we had one at the college I attended, back in the 1960s. Even that long ago the lathe hadn't been used in years. It was in pristine condition, but had the ol' Presto 1D cutterhead. Nice piece of machinery, but could use a 1.5:1 pulley arrangement under the top plate to afford microgroove operation; that's something I did to my RCA 73A back in the 1970s. Good luck with this!

[Jccc]

nice score! keep us posted on how it runs

[sameal]

Hey, I remember that lathe; we had one at the college I attended, back in the 1960s. Even that long ago the lathe hadn't been used in years. It was in pristine condition, but had the ol' Presto 1D cutterhead. Nice piece of machinery, but could use a 1.5:1 pulley arrangement under the top plate to afford microgroove operation; that's something I did to my RCA 73A back in the 1970s. Good luck with this!

Im really hoping to find someone who can machine the variable pitch box that some of these came with.

I got time however, theres some serious work coming up with this guy.

[sameal]

I also picked up a controller made by len horowitz.

In another stroke of luck, i found all the hp equipment needed to adjust that controller for pennies on the dollar.

That stuff in itself is probably gonna take time to ingest.

[dimi751]

I'm drooling !

I love this lathe, actually one if my favourites !

[sameal]

Well much time has passed, but much has been discussed. The westrex head is confirmed to be a late serial 2b, in mostly good shape. Soon to be sent off for repair.

And hopefully a 8dg manual coming in from alan graves.

[Stevie342000]

Well much time has passed, but much has been discussed. The westrex head is confirmed to be a late serial 2b, in mostly good shape. Soon to be sent off for repair.

And hopefully a 8dg manual coming in from alan graves.

Not the manual for the 8DG but for the 8N which would be slightly earlier but it may help you in your mission. I forgot about this was just on the bbceng.info website and saw it just now.

http://www.bbceng.info/ti/non-eqpt/TI_R4_Presto%20Recording%20Equipment.pdf


Steve in the UK

[audiocarver]

Wow Steve, that manual is more comprehensive than the original Presto manual!

I like how it gives tips on swarf removal and general recording chain setup.

[Stevie342000]

Wow Steve, that manual is more comprehensive than the original Presto manual!

I like how it gives tips on swarf removal and general recording chain setup.

The BBC were nothing if not thorough, it contains the modifications that the BBC made to Presto equipment as well. It was all part of the lease lend agreement during the war. I do not remember if there is the modification to the Presto amp in this think it is the later 92A (the one with 807 tubes in it) but that is modified to be used the BBC Grampian cutter head.

The swarf issue is why the Grampian head has bit of a cut out around the cutting stylus so it forces the swarf to curl and throw it away from the cutter head. They used a blower at back of stylus and a sucker at the centre you need less suction, which makes for quieter operation in service.

As for the recording chain it follows standard procedures and methods set up and used by RCA or Western Electric, they were the original licensees of equipment, people like Blumlein were employed in the UK to circumvent the Western Electric patents, EMI had to pay a fee for every disk recorded. During his tenure at EMI he invented a new cutter head, full cutting chain, as well as developing stereo disc recording on 78s, the EMI television system adopted by the BBC and of course he was working on Radar when he died.

Glad it helps
Steve in the UK

[sameal]

Thank you very much! I will download this as soon as i get back.

Update:

I have contacted alan graves and i think a manual is awaiting my arrival at home this weekend. Im hunting down a cutterhead amp so i can ship the cutter, amp and electronics to be repaired and calibrated.

Soon as im able to get that manual, ill be trying to get the platter to spin.

I replaced a bunch of security screws for easier service.

[sameal]

Well i had a chance to recap, oil, and start the motor assembly.......

The 45rpm motor starts up perfectly. But the solenoid doesnt draw the puck into the rim to drive it.

The 78rpm worked for a moment. Now it just hums when the switch is on. The 33 motor always just hummed.

Sigh.

[Stevie342000]

Well i had a chance to recap, oil, and start the motor assembly.......

The 45rpm motor starts up perfectly. But the solenoid doesnt draw the puck into the rim to drive it.

The 78rpm worked for a moment. Now it just hums when the switch is on. The 33 motor always just hummed.

Sigh.

My advice is to first clean the solenoids, take them to bits completely - not sure what you need to clean them with but a google search should elicit the information needed. Your post suggests that they are not bottoming out properly hence why it is not engaging correctly.

They get full of grime and do not forget not all places have been smoke free over the years and there have been a number of years which have passed since it was a new solenoid.

Which brings me to my next point, if that does not work then just replace the solenoid but from other groups I am on cleaning should work.

There may be a method to adjust just how much the solenoid pulls as well, it has to be enough to grip but not too much, there will be a sweet spot you got to find it. Anything on the manual about that adjustment?

[sameal]

I think i saw a youtube video of a guy pulling apart these bodine motors and scrubbing up the copper coils a bit.

The two motors that hum had their 3.75mf cap replaced with a 5mf cap.

I dont think the cap is the problem though. But i do have the old 3.75's i could test with, if there not blown. I replaced them without testing, mostly because they were original, and sat around doing nothing for what could be decades.

My other thought was the on/off switches feel real loose in operation. I think those are just round of the day electrical light switches.

[audiocarver]

Can you rotate the motors by hand? Sometimes they seize up after sitting for years and decades without use because the old oil has varnished up.

The rubber idler roller only drives the big flywheel in 78 speed only. When the 78 switch is selected, it turns the power supply on, as well as the motor, to engage the solenoid to in turn engage the rubber idler wheel against the large lower flywheel. Check that cap on the power supply unit.

The 33 and 45 speeds are direct drive via an internal gear in the transmission.

[sameal]

I believe i tried turning the 78 motor by hand, in place, in the assembly and it was very hard to move. I can pull the motor and try it outside the assembly.

I should have done that first. Hindsight is 20/20

The cap in the 45rpm supply was replaced as well. 40uf @ 250v if memory serves me. There is an old selenium rectifier in there, that i have no idea of the condition.

[sameal]

Yep. Both motors are pretty seized.

Anybody know how to get these apart?

[grooveguy]

Don't bang on them or force anything. "Back when I was a kid," the procedure was to soak motors like that in paint thinner, which was pure mineral spirits in those days. Just immerse and soak. After a few hours, you can remove the 8-32 screws holding the motors together and pull the bells off the ends. Then clean everything, re-lubricate, wait for the thinner to evaporate from the windings and re-assemble. But 'those were the days.' A family member who works at a hardware store says that paint thinner ain't what it used to be, so I would be very careful about soaking anything in what passes for paint thinner now. The old stuff would not attack the wire enamel or, for that matter, even the 'friction tape' that was used to insulate connections inside the motor shell itself. So I guess this is more of a what not to do than a what to do. Please be careful, you have a beautiful machine there. Don't ruin it. Best of luck, we'll be praying fore you!

[sameal]

Dont worry. I got kids gloves on handling this machine, with the scarcity of parts and all. Ive done a few repair jobs, nothing quite this intense maybe, but i got some experience.

If it gets real thick, there is a few places around that work on these motors. Itll be a pretty penny im certain, but thats how it works.

I used "pb blaster" very sparingly, and wiped up excess immediately when removing the the motor, as the shaft was absolutely stuck in the attachment for the gearbox.


Im thinking a full teardown is in order.