Motor needed to drive McDonald lathe feed screw

[cheapthrills]

Any recommendations on a new production motor to drive this feed screw? I've been looking for a similar application in the search button with no luck. It would be nice to have a variable speed knob and on/off. Thanks in advance for your help!

[rootz]

i used a brushless dc motor. You can check maxon motors "swiss quality". There are also suitable controller where you can set speed, direction and brake via pot/switch.
nice looking little lathe!

[cheapthrills]

Thanks Rootz. Last night I came close to ripping out a motor from a turntable in the basement. I found Maxon brushless dc motors on ebay, but there are so many options! Ideally it would be nice to have a digital reading of the adjustable speed.

The feedscrew has three different settings as shown in photo.

[tragwag]

that's quite a nice looking overhead!
I haven't seen one before, where does it come from?

[cheapthrills]

According to the gentleman whom I purchased it from, this type of lathe was used in the motion picture industry where disc recording was needed for making playback discs for production work. It was made in Hollywood, California probably in the 1950's. I looked high and low for a lathe that could be used with a modern direct drive turntable. I'm a newbie, but from what I've seen so far this one is simple and elegant.

I would also like to say that as a newbie, I've found loads of information using the search button and browsing other posts. There's incredibly cool stuff in here! If you feel the same please donate to the forum!

I hope to ad my story to the forum once I get things cleaned up and running.

[cheapthrills]

[sakuszi]

nice machine

[tragwag]

wow! yes it does seem very well designed.
is there a name plate or serial number somewhere?
for research/history sake?

[cheapthrills]

Nothing is labeled on this one- only a lonely R
Still looking for a motor as I have no clue as to the amount of torque or speed to use for feedscrew

[markrob]

Hi,

That's a really nice looking lathe overhead! Here are some tips I hope will help.

1. Move the head to the outside location (at the start of a record).
2. Mark the starting position of the head.
3. Turn the hand crank and count ten turns.
4. Measure the distance the head travels.
5. Now you know the feedscrew pitch (distance per turn)

I see that you have 3 pulley diameters to play with. Maybe settle on the middle one to start. Measure its diameter.

Let's say you want to cut 150 lpi. At 33.33 rpm, each turn of the platter occurs in 1.8 seconds (60 secs / 33.333 rpm). 150 platter turns would happen in 270 seconds (150 lpi x 1.8 sec/rev). If, for example, your feedscrew moves 0.01" per rev for each pulley turn (use the number you find above), then the feed screw would have to turn 100 times to move 1 inch and it would need to do that in 270 seconds. That would equal 22.22 RPM (100 turns * 60 / 270 seconds). Now you can find a motor and pulley that, along with the one on the lathe overhead, gives you the feedscrew rpm you need. Most motors will run with no problem over a 25:1 speed range. So if you fine a nice DC motor that has a shaft speed of 1000 rpm, you can run it down to 40 rpm with the proper controller. You'll want to scale the motor so that you can cut a wide range of LPI from say 10 to 250.

To determine the torque needed, wrap some fishing line around the middle pulley and hang weights off of the line until you find the lowest weight that causes the feedscrew to turn. Using the diameter you measured, calculate torque as (diameter / 2) x weight. This is the pulley torque. If you measure diameter in inches and weight in oz, you will have the torque in oz-in. To be safe, I would double this value. The actual motor torque will be scaled based on the pulley ratio you use so if the motor turns 10 times faster than the feedscrew, the torque required will be ten times greater than what you measured.

I hope this helps you out. Good luck with your project. Keep us posted.

Mark

[cheapthrills]

Lots of great info Mark!

[tragwag]

mark that's an super helpful, thorough post, thanks for that concrete info!

[Gridlock]

Mark the torque wizard. I feel like I "been told"