Electric motor question

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Forum topic by Shane posted 09-15-2015 01:48 PM 917 views 0 times favorited 14 replies Add to Favorites Watch
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294 posts in 1811 days

09-15-2015 01:48 PM

I want to create this but I don’t know much about how the shafts work on electric motors. If I can’t find one that was originally used for a radial arm saw then the shaft won’t be threaded as a 5/8 arbor. So is there a way to do this with any random electric motor I can find on CL or should I just buy the next cheap RAS I see and rip out the motor?

14 replies so far

View Bill White's profile

Bill White

4931 posts in 3960 days

#1 posted 09-15-2015 01:57 PM

You can buy a threaded adapter that will fit a motor shaft.
It has set screws that secure it to the shaft, flanges and nuts to snug everything “spinny”.


View bigblockyeti's profile


5120 posts in 1720 days

#2 posted 09-15-2015 02:04 PM

Old craftsman radial arm saws can easily be had almost anywhere usually for under $100, sometimes much less if they’re damaged or in rough shape. The thing that really worries me about this setup is spinning a homemade 12” wood disc at 3450rpm. That’s a lot of energy and if it comes apart, it will do so very violently! a four pole motor spinning at under 1800rpm would offer more torque given the same horsepower and would be a more appropriate speed for most sanding duties.

View Shane's profile


294 posts in 1811 days

#3 posted 09-15-2015 02:07 PM

Well most of the used motors I’m seeing are sub 1800 rpm. Bill I’ve seen those adapters but they always say that they are a step down FROM 5/8 not to 5/8. Not sure where to get the right kind and I wonder if the screws would hold to the shaft under load…?

View SirIrb's profile


1239 posts in 1230 days

#4 posted 09-15-2015 02:38 PM

I would put a rheostat on it so you could keep the RPM’s down just in case. Just got done with my daily CL searches. Tons of cheap RAS’s on there. And a few not-so-cheap ones I would love to get to rebuild.

-- Don't blame me, I voted for no one.

View Shane's profile


294 posts in 1811 days

#5 posted 09-15-2015 02:39 PM

I guess I can put one of those adapters on any shaft and then just skip the buffing plate step and sandwich the plywood wheel between the washers …

View Tennessee's profile


2873 posts in 2514 days

#6 posted 09-15-2015 02:47 PM

I made one of those out of a standard 1/2HP motor years ago. But I agree, 3450 RPM is WAY too fast for plywood. I’d stick with a 1750 RPM.

Now I got one of those 3450 RPM Harbor Freight 12” units that I bought maybe 15 years ago, with the aluminum plate. They “sing” from the resonance of the aluminum every time you use it. Don’t use it much, anything with a face flying along at 3450 scares the heck out of me.

-- Tsunami Guitars and Custom Woodworking, Cleveland, TN

View JoeinGa's profile


7736 posts in 2007 days

#7 posted 09-15-2015 10:05 PM

Here’s how I built mine.

-- Perform A Random Act Of Kindness Today ... Pay It Forward

View rg33's profile


83 posts in 2002 days

#8 posted 09-16-2015 05:38 AM

I would slow it down with pulleys and a belt. More torque and less speed. regarding the shaft and couplers you could try DIY’ing something but by the time you get the material and figure out how to make it work you could have easily found something already premade here:

Check out the the power transmission section. They have just about everything imaginable to connect motor shafts etc.

View TTF's profile


154 posts in 3177 days

#9 posted 09-17-2015 06:29 AM

The RPM issue doesn’t seem to be problem so far (I’m the guy at the original link above). I could get a router speed control and slow it down I guess.

As for it flying apart – I had some initial concerns too. But the plywood has stayed very much intact. Buffing pad is still solid and the screws attaching to the wood are fine – there at 12 of them. Finally, the buffing pad screws on the arbor and then I put the original nut on top of that. The spinning of the disc just put more tightening force on it. I think its as solid as anything else.

-- Troy | | The more I see nature, the more I am amazed at the Creator. - Louis Pasteur

View TopamaxSurvivor's profile


18271 posts in 3676 days

#10 posted 09-17-2015 06:57 AM

If you have to put any money in the project, why not just go to Harbor Freight for $150?

Another $75 will get a Delta but I suppose there would be shipping on that one. They aren’t on every corner like HF is ;-)

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Shane's profile


294 posts in 1811 days

#11 posted 09-17-2015 10:03 AM

Yeah I suppose that’s my benchmark money-wise. My hope was to get a motor for less than $30 and spend less than $20 on parts. For $50 it would be worth it

View b2rtch's profile


4861 posts in 3048 days

#12 posted 09-17-2015 10:22 AM

Buy one at Harbor Freight and save yourself a lot of trouble and possibility a bad accident.
Something are just not worth it.

Get this one with a 20% off coupon:

-- Bert

View Woodknack's profile


11626 posts in 2380 days

#13 posted 09-18-2015 04:15 AM

I would put a rheostat on it – SirIrb
I could get a router speed control and slow it down I guess.- TTF

No, no, you can’t do that with an AC induction motor.

Shane, you are overthinking it. Elevenity bajillion woodworkers have built disc sanders and half of them made videos or blogged about it, you should have no trouble figuring it out. Joe made a nice one, he linked to it above. There are different types of electric motors, the 3 most common in woodworking are: AC Induction (stationary saws and machines), Universal motors (routers, shop vacs, hand held tools), and DC motors (smaller lathes, treadmills). Router speed control doohickeys will work on universal motors. DC motors need a PWM for speed control. AC induction motors need a VFD for speed control. For a disc sander you don’t need speed control and a 1750 ac induction motor would be simplest, followed by a dc motor. Universal motors are noisy and run at very high rpms.

-- Rick M,

View oldnovice's profile


6854 posts in 3368 days

#14 posted 09-19-2015 04:52 AM

Anyone interested in a 1/3 HP Siemens Micromaster drive/motor?
Variable speed, up/down ramping, reversing with the same ramping characteristics, 220 VAC, metric size and shaft!

If there is any interest I will locate the model numbers!

-- "I never met a board I didn't like!"

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