Presto Model K7 Lathe

[pianimator]

Hello - I'm a new member to this forum because I just purchased a vintage Presto K7 Record Cutting Lathe. Does anyone have info on this model and/or can point me to resources regarding this lathe and where to purchase an adaptor to record at 33 1/2 and/or 45 rpms with this lathe? It currently records at 78 rpm. Thanks!

[rsimms3]

The one off of eBay? I'm not familiar with the K7. The K8 has a capstan on the motor shaft for the default 33rpm and then a slip on capstan to cut 78rpm. If it's the one from eBay, I see a brass capstan that looks like it would be for cutting 78rpm. If that comes off, you should be able to cut 33. First let us know, or post a picture, of the size of your current capstan, then you can figure out what direction to take for finding a way to cut other speeds. There is a K8 manual posted here on the site, that will give you an overview of how this type suitcase lathe operates.

[opcode66]

K8 Manual downlaod
http://lathetrolls.com/download/file.php?id=274

Posted here and originally supplied by rsimms3
http://lathetrolls.com/viewtopic.php?f=9&t=1161&p=27345&hilit=k8+manual#p27345

[pianimator]

Hi - yes, it's the one from eBay. I have not received it yet - just trying to get a leg up on what I'm getting into and what resources are available to me. Thanks for your responses - very helpful! I'll know more when I receive the lathe and post pictures, and ask more informed questions as they arise. Thanks for the link to the 8k manual!

[rsimms3]

If you haven't already - read, read, read. There's a wealth of information here on the board about cutting, impressing, and working with a K8. The K8s and 6Ns are the most plentiful and discussed Presto units around these parts from my observations. It looks like the tire (flat rubber belt) on the outside of the platter is in good condition, that's a big plus since a lot of them are dried, cracked, or have large indentations in them from storage.

[pianimator]

If it's the one from eBay, I see a brass capstan that looks like it would be for cutting 78rpm. If that comes off, you should be able to cut 33.

My Presto K7 arrived today! Everything seems to be in working order, though I'm waiting on a shipment of blanks to record. Where exactly do I find the capstan on this lathe? Should I heat the blanks before recording?

Thanks.

[pianimator]

Actually, I believe I understand which part is the capstan as I realize it should be rotating so that the platter rotates - so, newbie that I am, I think I know now what the capstan is (see photo). Of course, correct me if I'm wrong. Please tell me how to remove it and whether, once removed, I'll need to purchase another capstan to record a 33 1/3 or 45rpm.

Also, to set up for recording, the K8 manual states to connect a wire from the "binding post" to a water pipe or radiator for proper grounding. Is this an outmoded statement if I have modern AC outlets, or should I still connect a wire somewhere for grounding? I want to achieve as good of a recording from the get-go as possible, though I realize the learning curve may take awhile. I just don't want to be getting poor results if the grounding issue really is relevant today.

[rsimms3]

Yes, that brass piece is the capstan. If you lift the platter off of the lathe, you'll be able to see the side of it. It should have two "ears" at the bottom of it that put pressure on the 33rpm capstan from the motor to hold it in place. See picture -

capstan.png

Also, that knurled brass knob just above the capstan is used to hold the capstan against the edge of the belt on the platter so it spins at the correct speed. Since the rubber belt has give, if you push it against the belt harder it will have a different speed than if it is pressed against it lightly. It'll take some practice to get the right pressure. You'll have to strobe speed with and without cutting.

[pianimator]

Great info - thanks! Although, from your description, I still don't understand whether I remove the current capstan (for cutting at 78rpm) and replace it with one designed for cutting at a different speed (33 1/3 or 45rpm) or just readjust the current capstan to "rub" against the belt to slow it down. I don't have a strobe, but I do have a metronome. Perhaps placing a sheet with a mark on it and timing with metronome will work at calibrating the speed.

[rsimms3]

In my picture above, the two capstans on the left fit over the third one on the right so 78/45/33. The standard capstan is for 33rpm, it is attached to the motor shaft by a hex screw, you don't remove it. As I mentioned previously, you can take the platter off and should be able to see the side of the brass capstan to see if it has the ears on it. If it does, you work it off of the top of the 33rpm capstan inside of it. For the K series, the size of the capstan determines the speed hence the need for the knob and slider so you can move the motor and capstan to contact the rim of the platter.

[pianimator]

Thank you for the detailed explanation. Being new to this, how easy is it to remove the platter? The recording arm is easy enough to swerve away from the platter, but the playing arm is mounted pretty much right on the edge of the platter, and I fear damaging the playing stylus by lifting the platter & hitting it. I also am concerned about repositioning the platter back in place once I determine the capstan is as you describe. Will it be easy to remount the platter if I take it off to view everything underneath?

[pianimator]

I don't seem to be able to get what you are calling the 33 1/3 capstan, which is the thinnest "spindle" attached to the motor, to touch the platter's belt to drive the platter. I've loosened the thumbscrew to adjust the distance between the capstan and the belt, pushed it as close to the belt/platter as it will go, but it does not reach the belt. Am I missing something?

[rsimms3]

There are stops on each side of the slide, possibly the one needs adjusting. I've put an arrow to the one that may be keeping the capstan from engaging the side of the platter. Loosen this screw, turn the off set circle so that the thinnest part is toward the slide, and see if it will engage then. If it still doesn't reach, it may be that the K7 wasn't meant to cut 33rpm.



http://106.imagebam.com/download/hRKzA7yOSuACrvlTdRgTxA/41066/410652231/IMG_0849.jpg

[pianimator]

Yes. That makes sense and I did try that, but the capstan doesn't reach the belt. I guess the K7 is not meant to record at 33 1/3rpm after all. I'll take suggestions for a 45rpm adaptor, which I imagine from your earlier attached picture will work with proper calibration. I may experiment with trying to calibrate to a desired speed, perhaps "building" a DIY capstan.

Also, do I need to attach a ground wire as suggested in the K8 manual before cutting, or is that necessity obsolete with modern AC outlets?

Still waiting on blanks - should arrive Thursday.

Thanks for all your help!

[rsimms3]

You could take the knurled screw and the stop out so that it makes contact, but without a stroboscope you won't know if it is running at 33rpm. I would start by finding someone with a K8 and having them measure their capstan on the motor and what speed their motor runs. If your motor is the same speed, you could have a 33rpm capstan made and then adapter capstans made for the other speeds.

As for the ground, I've never heard of it being necessary but it couldn't hurt to run a ground to that post.