Yet another DIY table feed thread

[kd4gij]

Easiest way to figure out how much torque you need, is with a simple fish scale. Hook it to the handle of the axis in question, and slowly pull at 90deg to the handle (perpendicular to the tangent of the circular path of the handle...) and see what it takes to GET it moving. It usually takes more to get it moving, than to keep it moving. just don't yank the scale, and get the largest number

Then take this number, probably in oz, or lbs, and multiply it by the distance from where you pulled, to the center of the handle. E.g. the handle on my lathe is 4" from the center of the leadscrew. My granddads fish scale pulls 1lb, to get it moving. This tells me that the amount of torque that I need to drive that shaft is 4 inch pounds. Since motors are usually spec'ed in either oz-in of ft-lbs, a conversion is required. To convert to ft lbs, we would divide by 12, as we already have the correct force unit. If we wanted to convert to oz-in, we would multiply by 16. That gives us either 1/3 ft/lbs, or 64 in/oz.

This will tell you how much torque you need to move that axis. Now all you have to do is figure out how fast you want to move the axis, and you can figure out the horsepower required to do so!

Good Luck!

-Cody

you would need to do that test while taking a hefty cut in some steel to get a true reading.

 

[jmarkwolf]

One of the cutest little engagement/disengagement systems I've seen on a DIY table feed was an idler gear. There was a gear on the end of the worm shaft, and a gear on the end of the motor shaft. The shafts were parallel with gears adjacent. To engage the motor drive, he simply swing in a 3rd gear as an idler. Saw it on Youtube. There was no audio so no commentary.

 

[Codered741]

you would need to do that test while taking a hefty cut in some steel to get a true reading.

True. Though it probably be easier to just double or even quadruple the measurement you get. Be cautious, as too much power can be dangerous!

If I remember correctly, and you REALLY want to get technical, the Machinist Handbook has formulas for figuring out how force it takes to make cuts with certain feed rates. Not that I am recommending it, (note that I am not doing it) but it does provide an interesting guideline for figuring out what you really need. It usually amounts to double or triple what you need to just turn it, unless you are taking some REALLY deep cuts.

-Cody

 

[martik777]

I have used both a wiper motor and cordless drill motor:

The wiper motor has much more torque but is slower. You can speed it up by increasing the voltage

The drill motor has a wider range of speeds and would be preferred as long as it provides sufficient torque.

In either case, you should get a PWM (approx $8 on ebay) to control the speed and a DPDT (center off) switch to reverse.

Used cordless drills with bad batteries can be found for < $20 on craigslist.

 

[stern]

Thanks for all the info, especially the torque calcs. I will probably on use the feed to either very light cuts, but mostly just to move the damn thing LOL. I dont mind manually feeding during cutting, but moving to one side or the other takes a lot fo cranking, and my poor old arms are getting tired of it LOL
Once I get the min torque to move it, I double that and use it as my minimum. I do know cordless drills have more than enough to move it, so chances are I may use one of those (as long as the "guts mounting" doesn't get to crazy lol.

 

[prmindartmouth]

I used a window winder motor ( from Princess Auto) powered by a 115volt variac transformer that puts out 0 to 13 volts ac at 5 amps feeding through a rectifier (apparently not a good way, said one EE ) which uses a small chain drive. It works great. The text above shows it published in 2009. The "clutch" is just a screw in pin that works like the pin in a lathe's bull gear.

 

[stern]

View attachment 53531View attachment 53532I used a window winder motor ( from Princess Auto) powered by a 115volt variac transformer that puts out 0 to 13 volts ac at 5 amps feeding through a rectifier (apparently not a good way, said one EE ) which uses a small chain drive. It works great. The text above shows it published in 2009. The "clutch" is just a screw in pin that works like the pin in a lathe's bull gear.

Cool Do you have any data on the wiper motor you used, as I would love to grab the same one from princess auto and give it a try. If I can get it to move the bed I will grab an Ebay PWM motor control and stick it on

 

[iron man]

This is my home built power feed for my Grizzly 727 mill with the top off. I made a clutch by modifying a shaft coupler I shortened up the teeth. I did another one for something different and on that one I sharpened the teeth to a point you could engage or disengage that one with the motor running. The motor slides on a pair of rails with a lever and a cam controlled by a lever under the unit. This coupler is connected to my ICBM missile control surface motor it would probably be to small for a large mill but works well for this one.. Ray

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Here is a picture with the lid off you can kind of see the lever to the lower left of the photo with a little flashlite hanging on it. The motor is 38 volt DC with a PWM speed control built in. Ray

 

[iron man]

Complete setup.

 

[prmindartmouth]

Reply to stern: Here is the motor, followed by a couple of arrangement pictures. That exact motor may not be available but any similar one should work.