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Drive motor for rotary welding table

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Str8jacket

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#1
Gday, i am looking at building a rotary welding table to do some repairs to some shafts and other bits and pieces.

The mechanical side is easy but i am stuck on what sort of drive motor. I have looked at sewing machine motors and pedals but cant find one with reverse. Also vague on specs for torque. I dont want to much but it needs to be enough to turn 20kg icluding table and chuck.

I can get a 0.18kw 3 phase motor but it seems over kill. And costs more. Bigger.

I have looked at little stepper motor kits but am unsure how to control start stop forward reverse. I dont want to spend a long time trying to get it going.

Or i can buy a small rotary table on aliexpress for $500 AU an be done with it.

I rhink i can build a beefier one for that money but the time is something i dont have lots of.

Any suggestions?
 

hman

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#2

Keith Foor

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#3
What speed are you looking for?
Are you going to use a reduction of some sort or expecting the motor to be direct drive and directly spin the table?
I have seen rotisserie motors for grills used with pretty good success but they are single direction setups.

If you are starting from scratch, you may locate a cheap dividing head and pull the dividing ring and crank off it, drive it with a variable speed reversable drill and figure a way to remove the trigger setup and mount it in a foot pedal. It would have reverse, variable speed and if a battery drill was used in the 12 volt size they typically have a brake that when you release the trigger the motor quickly stops. That may or may not be important to you.
 

Silverbullet

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#4
Almost any WHEELCHAIR motor will work perfect. Being dc reverse is just switch wires. A potentiometer will vari speed . Id venture to guess under $100.00 for your electric parts, the steel and chuck is more. Bearings too. With those motors theres a freewheel lever to spin by hand if you want . Just what I plan on using for mine.
 

Dave Smith

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#5
a very simple way is wrapping a rope around your shaft and hook a weight on and use the gravity to rotate the shaft till the weight hits the ground ---you can get many rotations each time and regulate the speed with a simple drag setup---it can work on vertical shafts or horizontal shafts and forward and reverse by the direction you wrap the rope--for each wrap of the rope around the shaft, will give your project one full turn-for more turns just lift the weight up and go again---you can make a couple simple wooden pulleys with a chain running around them like a drive belt and then have a hook on your weight to hook into the chain on either side for direction needed---several different weights can also determine your speed---for vertical shafts coil around shaft direction you want it to turn and run it horizontal over to a pulley on side and then the weight gravity will turn your shaft---no motor required---just some chain or rope with tied loops some very simple pulleys a bolt through your shaft to hold the end of the coiled rope end--a simple foot operated drag to control speed can also be very simple---no money required to rotate your projects efficiently in all directions---hope you get the picture--ask any more questions if you don't understand---Dave *note you really just need about a three or four foot small nylon rope with a loop on each end and a peg on each shaft to start your wraps and a simple 20 to 40 lb weight with a hook on the top---wrap your rope on the shaft several times and hang your weight on the other looped end
 
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Uglydog

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#6
Dave Smith,
That's brilliant, simple, elegant and affordable!!

Daryl
MN
 

Str8jacket

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#7
Thanks for the replies guys, awesome suggestions. I am not sure how your idea will go on my job this time Dave, the shafts are only 3/4in thick and a foot loot long. If i ever have some bigger stuff to repair that is going to be my first approach.

I think a DC motor is the best bet. The table is only going to be enought for say a 10-15kg hub to sit on or shafts the size of the one i mentioned before.

I was thinking of using a trailer hub but mounted on a hollow tube so i could have it similar to a lathe headstock if needed.

There are some electric scooter motors that i found that have a bike chain sprocket. They may have a bit to much grunt though. Wheelchair motors seem expensive over here.

I have a few Doga 24v windscreen wiper motors that i think will do, need to work out the current draw so i can get a power supply to suit. Adapting a drive to the stub shaft will be the hardest bit.

A free wheeling clutch would be nice but not sure where to find one? Bike hubs free wheel one way. Belt drive was going to be the way i was going initially to help isolate the electrics
 

Ulma Doctor

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#8
i believe it may have been mentioned before, but a transformer and PWM board may be the cheapest, simplest, and most robust answer to the powersupply issue.
i'd consider a footswitch, then maybe a potentiometer or other fixed resistor to control speed if the PWM was not available or desired
 

Dave Smith

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#9
I see that you are still over thinking---and making it too complicated for a simple task----maybe you could take some pictures of your table for us to help you better---also how many rotations do you need to fix your projects, one, several or continuous ---are you welding them while rotating them ?----if you are determined to go with a motor then some of my suggestions would be---- a variable speed reversible drill(could be electric--cordless--or pneumatic)---an air motor which would be easy to control speed and direction easily----an air ratchet or air impact gun would also be very efficient and probably already in your mechanics tool box but a little noisy maybe----I would still just use a simple small nylon rope and a weight for best results and no money investment---there would be no noise--just nice simple rotation----five wraps around your shaft would only take about an inch of space on the shaft and give you five full rotations of your project---ten wraps would be about 2 inches and give you ten full rotations--speed control would be very easy-----Dave
 

f350ca

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#10
I built one using a 110 volt dc gear head motor salvaged from a blue print machine. That drives a gear reducer. You need a lot of reduction to get the speed slow enough if you end up welding or cutting large diameters. I have a variable ac power supply, a bridge rectifier between it and the motor gives me dc. I made an adapter for the output of the gear reducer, 1 inch unc thread that fits a 3 jaw, 4 jaw and 12 inch face plate for a wood lathe. They're extremely useful. Welding sprockets to hubs, building driveshafts, building up shafts the list goes on and on.
Im surprised a sewing machine motor isn't reversible, would have thought they were dc.
A windshield wiper motor should work, Im currently building a bandsaw blade sharpener, and using a 12 v geared motor from some sort of golf bag cart to advance the blade. Im going to use a battery charger transformer after the 110 v variable supply to give me 0-12 v.
Variable power supplies are available for wood routers. Not sure if they're ac or dc output.

Greg
 

Mad Monty

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#11
I love Dave Smith's simple, elegant solutions. And yet if I can find an excuse to make something more complicated - I guess I've got the Rube Goldberg gene - I can't resist; after all, we're on the Hobby-machinist website, right? So I'm a fan of treadmill motors, cheap, reversible, easy speed control, use a footswitch (or two if you want to reverse without taking your hands from the tools). $50 used motor, $15 router speed control from HF (or heater control even better - slower minimum speed), $5 full-wave rectifier and $10 footswitch and $? lazy Susan from Amazon, and voila!
Two comments on other ideas: First, I've tried wiper motors and security camera motorized mounts set to scan back and forth to turn a wash pot full of solvent back and forth, and it was really too much for either to handle continuously, plus the wiper was a little jerky at the end of travel. I don't think the wiper sweep comes close to a sine function, more militaristic as in "hurry up and wait". Second, potentiometers alone often don't work out because you need pretty high current ones, $$ and hard to find; don't work with most AC motors and DC motors have low torque with them. (Motor speed controllers use very low power potentiometers in a circuit that pulses the current at a high enough value that it maintains torque even at low speeds.)
 

Str8jacket

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#12
I picked up a pwm dc motor control for 20 bucks to try with a big 24v wiper motor i have already. If it doesnt work i will worry about it then. Its foing to have to wait now as i have too much work lined up. Plus i just spent a fortune on some fabrication equipment:):chunky::grin big::grin:
 
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