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Help needed making a 12" Disc Sander

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Forum topic by tyka posted 05-11-2011 02:47 AM 5326 views 1 time favorited 6 replies Add to Favorites Watch
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tyka

142 posts in 2154 days


05-11-2011 02:47 AM

Topic tags/keywords: question

I just started putting together this 12” disc sander using a pump motor and the 6” disc from my Delta combination belt/disc sander. The MDF disc is temporarrily held with two 1/4” bolts to be replaced with recessed Allen bolts. I tried using four screws from the back spaced evenly on the outer edge of the 6” disc but got a worst reading.
Before I go further I was wondering if a .030” wable is acceptable. I get a smaller deviation towards the center. The Delta 6” disc has a .010” wable. Is the 3400 rpm going to be a problem? Any comments would be appreciated.

-- Paul, Plantagenet, Ontario


6 replies so far

View GaryK's profile

GaryK

10262 posts in 3449 days


#1 posted 05-11-2011 02:55 AM

I would think that you can “sand” out the wobble.

-- Gary - Never pass up the opportunity to make a mistake look like you planned it that way - Tyler, TX

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tyka

142 posts in 2154 days


#2 posted 05-11-2011 03:14 AM

GaryK.
Similar to sanding an MDF drum on a drum sander to make it evenly round. I didn’t think of that, makes a lot of sense. I’m going to try it. BTW I love your dyed wood glue test. Tks again for taking the time.

-- Paul, Plantagenet, Ontario

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Druid

1299 posts in 2256 days


#3 posted 05-11-2011 06:44 AM

Hi Paul,
You didn’t mention if the disk has any vibration as it runs. If it is off balance, you might want to consider temporarily mounting the disk on a lower speed motor if you have one. Use the final hardware that you mentioned for mounting the 12” disk to the 6” disk (so the balance and alignment do not change), and I think the extra screws are a good idea to keep that 12” disk under control. Get rid of the wobble as Gary suggested, then work on final balancing before remounting the disk back onto the higher speed motor.

-- John, British Columbia, Canada

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tyka

142 posts in 2154 days


#4 posted 05-11-2011 02:11 PM

Hi Druid,
Thanks for your help. I don’t seem to have any vibrations, although I have to clamp it to the bench, otherwise it walks away (3400 rpms is quite fast). I’ll ad the screws, keep the bolts and make a temporary table to sand the disc . If this doesn’t help I’l try a 1/2” – 5/8” disc. This one seems to make the motor labour a bit when it starts and takes forever to stop when I power off. It acts like a flyweel. Tks for the tip.

-- Paul, Plantagenet, Ontario

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tyka

142 posts in 2154 days


#5 posted 05-12-2011 03:21 AM

Gary,
The sanding did the job. I now have .003” variation on the outside face. Tks.

John,
I must have been blind. I have serious vibrations. I don’t have another motor but can see it well when the disc slows down to about 1000 rpms after I turn the switch off. I have no vibrations witht the 6” disc alone. I’m going to try a 1/2” disc. The 3/4” disc is just to hard on the motor even if it’s a 1hp motor. It doesn’t have a capacitor or a starting winding. I might have to ask you how to balance the disc at one point. Tks.

-- Paul, Plantagenet, Ontario

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Druid

1299 posts in 2256 days


#6 posted 05-12-2011 07:05 AM

Hi Paul,
Your comment about it “walking away” kind of confirms the off balance issue. Unfortunate about not having another slower motor (there’s one running the fan in your furnace, or in the washing machine . . . no, better not). Well, now that you know there’s a balance issue, the first thing is to decide if you are keeping the existing disk. If you are going to a ½” one, it’s a fresh start. Either way, you need to start by making sure that all of the hardware is the final configuration that you will use. Of course, make sure that all bolts/washers/nuts are identical, and accurately spaced equally from the center of the disk, as well as at equal angles (say every 90° or whatever you decide) around the disk. This will distribute the weight of the hardware evenly.
A very rough balance test would be to spin the mounted disk by hand and let it stop by itself. Take note of whether or not the rotation stops and then moves backwards to a final stop. This is a clear indication of one side being heavier. When it stops, make a reference pencil mark at the lowest point on the disk, then repeat the same hand spin several times. If you are always seeing the disk stop at approximately the same position, you will need to take some material off by drilling shallow balancing holes into the rear side of the marked area. Repeat the same hand spin tests, and balancing holes until you get random stopping points that are evenly spread around the disk. Then your disk should be far more balanced for your initial power test.
Then true up the disk as Gary recommended. If you end up having to remove a fair amount of material, you should retest for balance again. You want this disk to run true and well balanced for safety reasons. If you work out the speed at the rated rpm of the motor, you will find that the outer rim of the disk will be traveling at slightly over 120mph !!!

Waiting to hear about your successful results. Enjoy.

-- John, British Columbia, Canada

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