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

Post: # 48270Unread post grooveguy
Mon Oct 30, 2017 4:48 pm

You are coming along famously, Sameal; keep us posted!

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 48489Unread post sameal
Sun Nov 19, 2017 4:25 pm

Working on a ton of stuff, i reaalllyy need the cutterhead back to complete, so in the meantime, an homage
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 50323Unread post sameal
Sun May 13, 2018 8:09 pm

Made some real progress with a swarf tube holder. I just cut a piece of lexan out to run the tube through and got a longer screw for the dashpot bracket. Mounted pretty good.

I might soon attempt a cut.
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 50324Unread post grooveguy
Sun May 13, 2018 10:31 pm

You are indeed chugging-along nicely, sameal. I am green with envy over that 8D.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 50325Unread post sameal
Sun May 13, 2018 11:25 pm

Thanks!

I really like the 8d series. I think presto did a good job on them. Built well, and takes modification pretty well too. Not that they saw that coming.

I got a lot more planned for it, hopefully some kind of arduino cutting computer, a button panel, metering.....

Ive been working on the vacuum box, made it enclosed in a rack box with a temp gauge that fits in the lathe cabinet with the chip jar and i made a more removeable scope light power supply situation, because i ripped the cable last time i moved it.

Im hoping to try a cut soon. I know it will shed light on a bunch more stuff ill need to revise.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51095Unread post symatic
Thu Aug 23, 2018 8:09 am

I've only just spent the time properly reading this thread - amazing!

I'm really interested in this because it's the closest thing to my 14B that I can find.

your pitch control system and dashpot assembly are of most interest to me just now - I have no idea how mine are supposed to work! but this looks at least a little bit similar.

On another thread i saw a video with the inner workings of an 8D that had a very complex looking system of belts and pulleys going from the main drive mechanism over to the pitch control drive shaft.
I assume this is the original way of turning the pitch drive shaft - off the main drive shaft. originally I thought it was as simple as a belt going from one to the other, but now seeing that video, and your entirely separate motor, I'm thinking I need to look at something more complex.

I might have to buy the 8D manual just to get a rough idea of whats going on with my lathe - at least the drive mech looks to be the same.

Oh and thanks so much for listing that part number for the bushings - I wouldnt have known where to start looking for those but mine are definately in bad condition. in fact the entire base plate for the mechanism is a bit bent..... i think it's workable for now but it'll need fixing one way or the other eventually

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51124Unread post sameal
Sun Aug 26, 2018 11:46 am

symatic wrote: your pitch control system and dashpot assembly are of most interest to me just now - I have no idea how mine are supposed to work! but this looks at least a little bit similar.

On another thread i saw a video with the inner workings of an 8D that had a very complex looking system of belts and pulleys going from the main drive mechanism over to the pitch control drive shaft.
I assume this is the original way of turning the pitch drive shaft - off the main drive shaft. originally I thought it was as simple as a belt going from one to the other, but now seeing that video, and your entirely separate motor, I'm thinking I need to look at something more complex.

I might have to buy the 8D manual just to get a rough idea of whats going on with my lathe - at least the drive mech looks to be the same.

Oh and thanks so much for listing that part number for the bushings - I wouldnt have known where to start looking for those but mine are definately in bad condition. in fact the entire base plate for the mechanism is a bit bent..... i think it's workable for now but it'll need fixing one way or the other eventually
Well, on the 8d/g series without variable pitch it is just a belt and a couple varying size pulleys from platter to overhead in that little hide a door on the front of the plinth.

If im thinking correctly, that variable pitch system in the video you saw was for the ultra rare 8dv. Ive seen maybe two of those systems in pictures only. To recreate that particular system would be more expensive then going with an arduino/motor setup.

Your welcome on the bushings. It was a pain finding all that stuff in the mcmaster carr manual, so i figured id pay it forward for other people in a similar situation.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51386Unread post sameal
Sun Sep 23, 2018 12:08 pm

I built a lift solenoid for the presto carriage. It does work, but either the solenoid i have is crappy or 12v 500ma is too weak to drive it strong. Every fourth cycle it seems to jitter and not fire.

Then, because this lathe was modified to hold a giant 2b head, the smaller heads not only do not sit in the correct place to use the space of the blank properly, they also weigh a lot less and can't utilize the dashpot or spring assembly correctly. So a plate had to be made to accomodate smaller cutterheads.
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51387Unread post grooveguy
Sun Sep 23, 2018 12:54 pm

Hey, sameal, good progress! With respect to the lift solenoid, I've used those a lot in tape transports and know that they really like to provide snap action, although you should be able to servo one, or at least contour the current into it for more gentle operation. My old Nikon point-and-shoot camera is sitting here on the desk, and it occurred to me that the mechanism for poking-out and retracting the lens assembly might be useful to similarly raise and lower a cutterhead. It uses a tiny motor and probably a screw or cam to provide linear action.

Looks like you're going high-tech/full-auto with your lathe; I'm still very manual. In the lathe I'm building right now I devised this cam arrangement to raise and lower the head. Again, all manual with a lever on the farside. To put it in perspective, that's a 4-40 screw that holds the nylon cam on its shaft. The mechanical advantage is such that a 180-degree rotation of the cam shaft moves the stylus up and down about 3/8". Thus it can be set-down very slowly.
Cam.jpg
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51388Unread post sameal
Sun Sep 23, 2018 1:41 pm

grooveguy wrote:Hey, sameal, good progress! With respect to the lift solenoid, I've used those a lot in tape transports and know that they really like to provide snap action, although you should be able to servo one, or at least contour the current into it for more gentle operation. My old Nikon point-and-shoot camera is sitting here on the desk, and it occurred to me that the mechanism for poking-out and retracting the lens assembly might be useful to similarly raise and lower a cutterhead. It uses a tiny motor and probably a screw or cam to provide linear action.

Looks like you're going high-tech/full-auto with your lathe; I'm still very manual. In the lathe I'm building right now I devised this cam arrangement to raise and lower the head. Again, all manual with a lever on the farside. To put it in perspective, that's a 4-40 screw that holds the nylon cam on its shaft. The mechanical advantage is such that a 180-degree rotation of the cam shaft moves the stylus up and down about 3/8". Thus it can be set-down very slowly.
Cam.jpg
I just hit it with 1.5A instead of 500ma, it seemed to like that a lot better.

That cam is pretty neat!

Im gonna try and incorporate some modern features as i find out what makes sense to use. My recent test cuts told me a lot, but mostly that i have a really long way to go still. I'm trying to put a button panel in with hopefully some kind of cutting computer in it and some meters. I've probably rebuilt the vacuum system ten times now, but it has a temp gauge and a fully enclosed case that fits in the cabinet with the chip jar.

Things are working better then i expected, but there's a lot of adjustments still. My first attempt at cutting actual audio failed, and my swarf plugged up. Im almost ready to try again though.

This poor stylus has been through it though!
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51389Unread post grooveguy
Sun Sep 23, 2018 2:28 pm

Those plunger-type solenoids need a lot of current to get them to pull-in with force. Some come equipped with a microswitch, so that once they pull in the current can be cut-back to a lower value just to hold the load. That type of solenoid has two windings, one high-current one plus the 'holding' one. You could do the same thing, either using a microswitch or an opto-coupler and two separate voltage supplies. There are also rotary solenoids that could be used to actuate a cam.

Your idea of a button panel is good, I was going to do much the same thing with the lathe I'm working on now. On mine, there is no way to disengage the leadscrew, so I'll need 'fast-forward and rewind' buttons to help in setting up to cut, and then afterward to 'park' the cutterhead out of the way. I'm keeping my lathe simple, maybe some basic logic to prevent stupid mistakes, but no computer as such. Unless you're cutting symphonies and want to get maximum minutes per side, variable pitch is pretty much overkill. Most pop music already has so much dynamics compression that your pitch computer wouldn't be doing much. I've never felt the need for automatic groove pitch control, or for a dashpot, for that matter. I know a dashpot was standard on the 8D, but the one we had when I was in school never had oil in it and it worked just fine. The RCA 73B lathe needed it because its horizontally-mounted cutterhead had a very high-Q suspension.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51433Unread post sameal
Sat Sep 29, 2018 10:44 am

Would you have a scematic of the dual supply for the solenoid?

On mine, the dashpot was modified to accomodate a 2b head. In that circumstance i think a dashpot is going to be needed. With the plate i had to craft for the smaller heads, they weigh a bit more as well. But i haven't cut actual music yet.

I got some sweet white noise!

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51434Unread post grooveguy
Sat Sep 29, 2018 12:16 pm

No schematic for the solenoid supply, but depending on the resistance of the coil, you surely could run it from two of those switchmode wall-warts or inline supplies, available in nearly any voltage for ten bucks or less. In that case you'd energize the solenoid from, say, a 24-volt supply, then when the plunger pulled-in a microswitch could simply switch to a 12-volt supply or maybe even lower. The main thin is to figure what current you need to actuate the solenoid (you mentioned 1.5A), and what current to hold the plunger in once it's pulled-in all the way (probably 0.5A). Depending again on the DC resistance of the coil, you can make these tests with one of those big adjustable power resistors. Then armed with those two figures, and the DC resistance of the coil, you select two supplies and wire them to the normally-closed and normally-open contacts of the microswitch as required.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51437Unread post EpicenterBryan
Sat Sep 29, 2018 7:25 pm

sameal wrote:Would you have a schematic of the dual supply for the solenoid?
I can work up a schematic for you with stuff you can buy cheap on E-bay. I did something like this to run a valve on my freeze dryer a year or two ago.

I see from one of your photos that the solenoid has two wires, uses 12v and says it takes 2.1 amps. That is what is needed to move it. If you leave that kind of power on it you will find it gets really got. Perhaps 180 degrees in an hour. Not good. But you will find it might only take 1/10 that (200ma) to hold it in position once it has moved and it will only get to 80 degrees in an hour.

You can either do what you need with a voltage regulator for the hold voltage, or a current regulator. You will need a time delay relay, and another relay for your controller in addition to a 12vdc supply. I can go over that.

If you can do a quick check to get in the ball park on the holding voltage (or current) that would help. Set up a 12vdc adjustable power supply and measure current to the coil, and voltage across the coil when you apply full 12vdc power.

Then, adjust the voltage down and measure the current (and voltage) to find the spot where it kicks off. It may be as low as 50ma. Take that reading as the bare bones bottom line drop out voltage / current. Do the test again and adjust so the current is three or four times that and record the voltage. Three or four times the drop out current is a reasonable hold current to start with.

I'll have to find my notes on my project but as I recall tonight, it took about 2 amps to fire the valve but only 200ma to keep it in position. I bet your solenoid has similar needs.

So the quick version is that your controller is going to hit the solenoid with full current for a short period of time to move it, and then after 300ms or so switch to lower current / voltage for hold current. On my project after the valve switched and the current was reduced it only got to about 80 degrees after an hour (100 degrees lower temperature by reducing current after moving).

B

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51442Unread post sameal
Sun Sep 30, 2018 4:59 pm

EpicenterBryan wrote:
sameal wrote:Would you have a schematic of the dual supply for the solenoid?
I can work up a schematic for you with stuff you can buy cheap on E-bay. I did something like this to run a valve on my freeze dryer a year or two ago.

I see from one of your photos that the solenoid has two wires, uses 12v and says it takes 2.1 amps. That is what is needed to move it. If you leave that kind of power on it you will find it gets really got. Perhaps 180 degrees in an hour. Not good. But you will find it might only take 1/10 that (200ma) to hold it in position once it has moved and it will only get to 80 degrees in an hour.

You can either do what you need with a voltage regulator for the hold voltage, or a current regulator. You will need a time delay relay, and another relay for your controller in addition to a 12vdc supply. I can go over that.

If you can do a quick check to get in the ball park on the holding voltage (or current) that would help. Set up a 12vdc adjustable power supply and measure current to the coil, and voltage across the coil when you apply full 12vdc power.

Then, adjust the voltage down and measure the current (and voltage) to find the spot where it kicks off. It may be as low as 50ma. Take that reading as the bare bones bottom line drop out voltage / current. Do the test again and adjust so the current is three or four times that and record the voltage. Three or four times the drop out current is a reasonable hold current to start with.

I'll have to find my notes on my project but as I recall tonight, it took about 2 amps to fire the valve but only 200ma to keep it in position. I bet your solenoid has similar needs.

So the quick version is that your controller is going to hit the solenoid with full current for a short period of time to move it, and then after 300ms or so switch to lower current / voltage for hold current. On my project after the valve switched and the current was reduced it only got to about 80 degrees after an hour (100 degrees lower temperature by reducing current after moving).

B
I am always impressed with your ideas. I never would have come up with that.

Id actually like to ape that relay section you built for your controller. I think it'd work for what i got in mind with my controller. I have an arduino in place with a basic supplied program i got from another member that i think will be a decent template to tweak. Im thinking the lift section might happen outside the arduino realm....but maybe itd be nice to control in the arduino....i haven't figured that out yet.

Riding on the shoulders of giants i am. Thanks giants!

Anyway, i think my hold voltage might need to be greater then 500ma, because at 500 i got erratic firing of the plunger. Ill do some tests soon.

A schematic would be excellent sir!

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51476Unread post EpicenterBryan
Thu Oct 04, 2018 7:29 pm

Hi sameal,
Here is a schematic and a list stuff to buy on E-bay.
This will do what you want and be really inexpensive.
IMG_6358.jpg
I forgot to mark the diode. Be sure to add that. A 1N4004 will work fine.

First thing you need is a 5v opto isolated relay module like this... It will connect to your arduino and switch 12v into the time delay relay.

https://www.ebay.com/itm/352229186371

Next you need a 12v time delay relay like this....When the first relay is activated, it will provide 12v to this relay. The solenoid will fire, and the timer will start. After it times out, the second relay will drop the voltage to the solenoid down to 2.5 volts thus reducing current.

One thing to note about these relays boards. Some times the relay connections are marked NC,COM and N0. Some times they are marked CB, COM and CK. Here is what manufacturer says:
[i"]When unconnected with the supply power, the state of the module is "NO" [ normal open ], CB and COM are conductive. CK and COM are unconductive.
When connected with the supply power, delay for 0-10s, the module will in the state of "NC" [ normal closed ], CB and COM are unconductive, CK and COM is conductive"[/i]


https://www.ebay.com/itm/253694964747

And here is the Buck (step down) DC/DC converter. This is adjustable down to 1.23v.

https://www.ebay.com/itm/202026317439

All the parts will cost you about $3.

Let me know how it goes.

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

Post: # 51482Unread post sameal
Sun Oct 07, 2018 9:46 pm

Thanks!

I got all the parts on order, ive been a bit busy to do any testing but i will soon.

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51484Unread post sameal
Mon Oct 08, 2018 9:55 am

I do have a quick question on the buck converter. Will it do step up conversion as well? It seems as it would.

Im asking because this arduino set up has a 12v motor into the motor sheild and my motor runs 35v i believe. So im thinking id put a step up before it in this diagram
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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51491Unread post EpicenterBryan
Mon Oct 08, 2018 9:04 pm

sameal wrote:I do have a quick question on the buck converter. Will it do step up conversion as well? It seems as it would.
No. That specific one is down only. You can buy one that is up, down or both. Each version has it's own application...
I don't know what current you need for the other motor you mentioned. Can you check that and post the voltage and current?

You can certainly use an up converter to go from 12 to 35/36v (Not sure what you really need). But remember, converting from one voltage to the other with these converters is not 100% efficient. They are really power converters. Power is current x voltage. If you assume conversion is 100% efficient (and these DC to DC converters are as low as 65 percent and as high as about 95% depending of the range of conversion), converting from 12v to 36V at 1amp on the 36V side means the unit is going to draw a minimum (100% efficiency) of 3 amps on the 12V supply side. So be aware of that with your 12V power supply selection. You may need a larger 12V power supply than you thought. That complicates the selection of an up converter that can handle that much power as an input on the 12v side. You may need one with a good heat sink like this:

https://www.ebay.com/itm/122037404647

Or it could be as inexpensive as this depending on the current needed at 36V...

https://www.ebay.com/itm/273404590211

I also notice you are using 12v on the Arduino board. That's OK if you don't use much extra 5V coming from the Arduino after the on-board regulator. If you do need a bunch of extra 5V, you should think about either driving the Arduino and other stuff directly with 5V, or inputting 9VDC to the Arduino.

So what 12V power supply were you thinking about using?

I'm starting to think you should start with a 36VDC supply (most have some adjustment too) and just use down converters from there...

Let me know what you find out about the motor you have.

B

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Re: Presto 8dg refurb. (Lathe porn)

Post: # 51492Unread post sameal
Tue Oct 09, 2018 9:02 am

EpicenterBryan wrote:
sameal wrote:I do have a quick question on the buck converter. Will it do step up conversion as well? It seems as it would.
No. That specific one is down only. You can buy one that is up, down or both. Each version has it's own application...
I don't know what current you need for the other motor you mentioned. Can you check that and post the voltage and current?

You can certainly use an up converter to go from 12 to 35/36v (Not sure what you really need). But remember, converting from one voltage to the other with these converters is not 100% efficient. They are really power converters. Power is current x voltage. If you assume conversion is 100% efficient (and these DC to DC converters are as low as 65 percent and as high as about 95% depending of the range of conversion), converting from 12v to 36V at 1amp on the 36V side means the unit is going to draw a minimum (100% efficiency) of 3 amps on the 12V supply side. So be aware of that with your 12V power supply selection. You may need a larger 12V power supply than you thought. That complicates the selection of an up converter that can handle that much power as an input on the 12v side. You may need one with a good heat sink like this:

https://www.ebay.com/itm/122037404647

Or it could be as inexpensive as this depending on the current needed at 36V...

https://www.ebay.com/itm/273404590211

I also notice you are using 12v on the Arduino board. That's OK if you don't use much extra 5V coming from the Arduino after the on-board regulator. If you do need a bunch of extra 5V, you should think about either driving the Arduino and other stuff directly with 5V, or inputting 9VDC to the Arduino.

So what 12V power supply were you thinking about using?

I'm starting to think you should start with a 36VDC supply (most have some adjustment too) and just use down converters from there...

Let me know what you find out about the motor you have.

B
I have the motor on a 24v 2.65a supply. I believe it's a 24v 1A motor.

It's currently running with a little pwm controller, but that's probably getting eliminated with the arduino

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