Building A Swing Arm Belt Sander

[CptRyg]

It's starting to look familiar.

$17 a bearing? Do they have their own motors?

[Guitarnut]

Originally Posted by CptRyg

It's starting to look familiar.

$17 a bearing? Do they have their own motors?

I had no idea what the loads would be so instead of light duty, I went with something more robust. Bearings are the one thing I won't have to worry about on this project.





Mark

[Guitarnut]

I forgot to include these in my post last night. Nothing special but I thought it was important point out how I used the axle to make sure all was centered.

I marked the flanges and drilled for flat head screws. Then predrilled one hole into the hub, set that screw to hold everything in place and then predrilled and set the other 3 screws. Since I lathed everything to it's physical center, the axle kept it all lined up.





If you remember from earlier in the thread, the center bore on the flanges didn't go to plan. I ended up recentering them to the offset bore and you can see this in how some of them line up with the hubs. They all spin clean and true despite the awkward appearence.



Mark

[Warnz]

Hi Mark

It's looking good :)

You won't have to worry about the bearings, I think they will outlast the frame!

I can see that the hubs are centered but looking at that picture makes my eyes go funny.

[macaroonie]

Hey Mark thats all looking relly good. Couple of points as always. Could you change your bearings over for a 3 bolt flange type ( Pic ). The O/A diameter should reduce and with some luck fit right inside your profile without fouling anything.



These are usually smaller overall than the equivalent 2 bolt.
You also get what are known as cushion or pillow bearings that are normally meant to go in the middle of drive shafts but in your application would suit pretty well. the mounting block is meant to sit flat but for your project could be away from the outside end of the roller mounted to a 90deg section , hence leaving the roller area clear to remove the belt.

Looking at what you have now I think it is screaming for a single sided mounting. A bit of custom welding should see that done without to much drama.. Some 1.5 box section and some 3/16 flange plates with whatever the Shopsmith needs to hook up to.

Earlier you asked about the live end of your roller. I would lean towards up and away simply because the friction is moving away from you and will be less likely to snatch.

Just my 0.02 M

[Guitarnut]

Last night I moved things forward quite a bit.

I started by getting the aluminum adjustment brackets marked and drilled. I didn't notice it when I was cutting them, but the edges were not square to the back of the channel...probably a slight error when they cut the end of the channel. I had to have all of the holes in line with each other so I marked lines down the center by using a known square block of wood and tucking it into the inside corner of the brackets.

I used a fence to keep things consistent and a C-clamp to hold the brackets tight. first the ends...



Then the faces. using an 1/4" bit first followed by a 3/8" bit.



Then I bolted everything up.





Then I clamped it up again to check alignment.

[Guitarnut]

Originally Posted by macaroonie

Hey Mark thats all looking relly good. Couple of points as always. Could you change your bearings over for a 3 bolt flange type ( Pic ). The O/A diameter should reduce and with some luck fit right inside your profile without fouling anything.

Attachment 116435

These are usually smaller overall than the equivalent 2 bolt.
You also get what are known as cushion or pillow bearings that are normally meant to go in the middle of drive shafts but in your application would suit pretty well. the mounting block is meant to sit flat but for your project could be away from the outside end of the roller mounted to a 90deg section , hence leaving the roller area clear to remove the belt.

Looking at what you have now I think it is screaming for a single sided mounting. A bit of custom welding should see that done without to much drama.. Some 1.5 box section and some 3/16 flange plates with whatever the Shopsmith needs to hook up to.

Earlier you asked about the live end of your roller. I would lean towards up and away simply because the friction is moving away from you and will be less likely to snatch.

Just my 0.02 M

Hi Mac. Always thinking on my behalf...appreciat it!

The bearings were special ordered so I can't return them. As for the frame being one-sided, I'm feeling pretty confident in the current design. The belt will always be changed when the sander is attached to the Shopsmith so I think the combination of the back panel and the live roller being chucked into the SS will be plenty steady to support the whole rig when the front panel is swung open.

This is V1...who knows what refining I need to do...good to have everyone's ideas at hand for revisions.

Mark

[Guitarnut]

Since I am where I am with the bearings and longer adjustment arms, I've been thinking about a solution for belt change outs. It's clear that taking an adjustment arm off as I had planned is a lot more involved than it need be. So, while chatting with my neighbor as he worked on his F150 power steering pump, I noticed the tensioner pulley in the serpentine belt path. Hmmm.

If I added a passive idler pulley that would remove easily and not interfere with the tensioning of the adjusters, I could create enough slack to slip the belt over the longer adjuster arms.

The axle for the pulley would ride up in a notched plate that lets it return to zero when under belt tension and drop down on it's own, out of the way, when tension is removed. It doesn't need to be anything more than a piece of PVC pipe on all-thread with simple bearings in the ends.

Something like this...

[Guitarnut]

I mocked this up with 3/4" pipe but 1" would work better with these bearings. With 1" pipe, I could flip them and insert them into the pipe.



Mark

[Warnz]

Hi Mark

Great progress, I think the idler pulley would serve better on the non drive end, then the belt angle at the drive end would be more shallow giving more contact area on the drive pulley.

[Guitarnut]

Originally Posted by Warnz

Hi Mark

Great progress, I think the idler pulley would serve better on the non drive end, then the belt angle at the drive end would be more shallow giving more contact area on the drive pulley.

Excellent observation. I hadn't considered that. It makes sense that I would want maximum wrap on the drive end.

Mark

[macaroonie]

Originally Posted by Warnz

Hi Mark

Great progress, I think the idler pulley would serve better on the non drive end, then the belt angle at the drive end would be more shallow giving more contact area on the drive pulley.

Yes

[macaroonie]

Originally Posted by Guitarnut

Since I am where I am with the bearings and longer adjustment arms, I've been thinking about a solution for belt change outs. It's clear that taking an adjustment arm off as I had planned is a lot more involved than it need be. So, while chatting with my neighbor as he worked on his F150 power steering pump, I noticed the tensioner pulley in the serpentine belt path. Hmmm.

If I added a passive idler pulley that would remove easily and not interfere with the tensioning of the adjusters, I could create enough slack to slip the belt over the longer adjuster arms.

The axle for the pulley would ride up in a notched plate that lets it return to zero when under belt tension and drop down on it's own, out of the way, when tension is removed. It doesn't need to be anything more than a piece of PVC pipe on all-thread with simple bearings in the ends.

Something like this...

If you can spring load it that would be good. Same layout just with some loading. You WILL have to muck about with this.

PS see idler wheel on reel to reel tape machines Revox , Teac etc.

[Guitarnut]

Originally Posted by macaroonie

You WILL have to muck about with this.

You're right there. I need to lay it out and test it. If I cut everything shorter and it doesn't work, I'm starting over.

Mark

[macaroonie]

Look here Mark



the two little idler rollers with the curved slots at each side are spring tensioned. They keep the tape at an even tension across the tape heads. Nice and simple really. In practice they do not shuffle around much except at fast spooling. They buffer tape stretching due to the motors accellerating

You can figure a variation of that I'm sure. 4-6" swing arm and then mess with the spring tension. Use a longer spring rather than a short stiff one as you will need the stretch to release the belt

[CptRyg]

This is preeb's belt sander that I just stole from his latest post. Notice that there is no robust bracing to counter the belt travel. I've added a cross brace to mine but otherwise all I've got is what you see here with the 1/2" threaded rod.

You may be at risk of over-engineering this part of the project.

[Guitarnut]

Originally Posted by CptRyg

You may be at risk of over-engineering this part of the project.

That ship sailed a long time ago...

Mark

[Guitarnut]

I finally had things ready for assembly...or so I thought.

Here's a pic of the interior of the sander. I don't think I mentioned the threaded plates on the back side of the adjusters. Actually, they didn't exist until yesterday. If you look at the original design, I had the slots for adjustment in the arms. First time I cut the pieces for the side rails, I cut the slots in the rails by mistake...again, so I thought.

On the second set of arms I caught my mistake and cut the slots in the arms only to find that the adjusters didn't adjust.

Then I realized that the first set of rails were correct...good thing I didn't trash them. The bracket, arm and whatever fastener was tightening the joint needed to be mobile. So, I machined the 4 threaded plates so they could slide along with the arm. Using nuts on the backside wouldn't work because the belt would be in the way. They had to tighten unaided by a tool.



So now that the adjusters actually adjust, I put everything back together. It worked pretty well. Except that the adjusters came off the bolts when completely tensioned. I'll need to make a slight change by moving the bolt holes back .75" on both ends. I'll also need to lengthen the slots in the same direction. I may go 1".

I'll also turn the adjustment bolt around so that the extra thread doesn't block the bolt heads on the arm brackets.







The belt went on pretty easily with the ends of the arms still square. I plan to shape them which will shorten the belt path a few inches when the adjusters are loose.



Mark

[Guitarnut]

I made the modifications mentioned above. Now the adjusters have plenty of thread even when the arms are fully extended. The extra thread gives me the opportunity to make a "home" position as so wisely suggested by Macaroonie. By setting a nut and jam nut on the end of the bolt at when the arms are extended and the belt is tensioned, I can simply slide the arms back into position after a belt change. Then do whatever adjusting is needed.



I also rounded off the ends of the arms...almost looks intentional.



By reversing the bolts, I have plenty of room to get a socket on the adjusting bolts...the extra thread now hangs over the bolts that mount the rails...which won't need to be accessed unless I'm taking it apart anyway.

Here is the adjuster/arm all the way back for belt change out, with the home position in place.



And, here they are slid back to operating position and the jam nuts threaded back down..



I'm hoping for a live-run test this weekend!

Mark

[oigun]

schwing!!! I cant wait, bijoetivoel!