# Pivoting motor mount for belt sander



## jwmelvin (Nov 2, 2021)

I have a Rockwell-Delta belt & disc sander, made for wood, and wanted to speed it up a bit. So I ordered a new motor pulley, to go from the 2.5" original to 4.75". In the existing arrangement, the motor was mounted under the table just attached to some fixed blocks. I wanted an easier way to accommodate a new pulley and maybe change the pulley in the future if I want. (By my estimates, the original sanding belt speed was about 2400 fpm, and will be about 4500 fpm with the new pulley.)

I looked around and made a plate on which to mount the motor, a couple pivots attached to the plate, brass bushings, and a bracket to position the bushings a few inches down from the bottom of the table:



I was happy that I was able to weld the bracket pieces without distorting them (I used great restraint, and had machined some registration features and surfaces). After painting and installing it, it is working well:



I included a threaded hole for a tensioning bolt, but it seems that the weight of the motor is fine for tension. At first, I used a traditional v-belt but the belt vibrated a ton, so I tried the link belt. It's a huge improvement. I imagine that the links offer a big advantage in damping to suppress the vibration modes in the belt spans between pulleys, but I'm not sure. Either way, I'm happy. Initial testing seems to show the belt will be better for my needs at the increased speed.

I still need to mess with the disc hub mounting to reduce runout; it's a bit loose on the shaft and secures with a couple set screws 90° apart in the middle of its length. I'm thinking of adding eight set screws, with pairs spaced as far apart axially as I can, with a pair every 90° circumferentially, so I can use them like a spider to dial in the hub on the shaft. One alternative is some shim stock, which may be okay. Or I could bush and rebore the hub for a better fit...


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## Doug Gray (Nov 2, 2021)

Nicely done.


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## markba633csi (Nov 2, 2021)

Curious to see how long the link belt lasts since the belt sfm is probably quite high
-Mark


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## jwmelvin (Nov 2, 2021)

markba633csi said:


> Curious to see how long the link belt lasts since the belt sfm is probably quite high


I don't see the spec listed on the fennerdrives.com site but retailers indicate 5000 sfm max for the A-size link belts. My link belt is running at ~2200 sfm so should be okay if that's the spec.  (My original post mentioned "belt speed" but meant _sanding_ belt speed, which is now ~4500 sfm.) 

I'm more concerned about the edges of the 12" disc, which will now be at about 10k sfm.


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## jwmelvin (Nov 3, 2021)

The belt sander seems pretty good at high speed. There's still more making noise than I'd like, but a full rebuild will have to be a future project. 

I thought also that some people may enjoy seeing some of my machining setups and progress shots; I welcome any feedback:









Also, today I repaired the belt-sander work rest by TIG brazing a plate on the front, which I then fly cut and surface ground (my first time playing with my grinder, a Rockwell Toolmaker):


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