Building A Swing Arm Belt Sander

[Guitarnut]

Originally Posted by CptRyg

Hope you don't mind if we share a build thread.

Well, technically, I haven't built anything yet.

Mark

[Guitarnut]

My approach to the swing arm is a bit different from CptRyg's. I got a great deal on some 6061-T6 aluminum square tubing. Three pieces 48"x1"x.125" and one piece at 48"x.75"x.125".

I don't have any way of welding aluminum so I'll use mechanical connections. As luck would have it, the wall thickness of the 1" tubing leaves a .75" internal spacing that will accept the .75" tubing...may need a bit of sizing. I'll notch the wider tubing and insert the thinner tubing. Then bolt it up.





If that's not sturdy enough, I'll add L brackets in the corners.





I'll have eveything in-house this weekend and get started on the build.

Mark

[Guitarnut]

I did a bit more work on the hubs and rollers. Warnz' input on this really got me thinking about using a flange. I looked thru the inventory of both local home improvement stores and several online but found nothing that would give me the outer strength I need with the proper .500" bore.

So, why not make my own?

By making the flange portion with a center bore large enough to accept the hub portion, I could glue it up just like a water pipe.



Then simply screw the flange to the roller hub. Screwing it on is a little bit more work than just gluing it all together but this way I can separate the flange and roller if needed. A cotter pin will keep it from spinning on the axle.



Mark

[mgdesigns]

Originally Posted by Guitarnut

My approach to the swing arm is a bit different from CptRyg's. I got a great deal on some 6061-T6 aluminum square tubing. Three pieces 48"x1"x.125" and one piece at 48"x.75"x.125".

I don't have any way of welding aluminum so I'll use mechanical connections. As luck would have it, the wall thickness of the 1" tubing leaves a .75" internal spacing that will accept the .75" tubing...may need a bit of sizing. I'll notch the wider tubing and insert the thinner tubing. Then bolt it up.
...
Mark

How about this stuff? I used it back about 20 years ago, and it works well.
http://durafix.com/

[Warnz]

Those hubs look rather nice

Did you manage to solve the issue with the glue going off too quick or have you not got that far yet?

[Guitarnut]

Originally Posted by mgdesigns

How about this stuff? I used it back about 20 years ago, and it works well.
http://durafix.com/

Thanks Mark. As interesting as that looks, I think I'm better off going with something I can back up and adjust if i need to. Welding of any sort is just not my thing.

Mark

[Guitarnut]

Originally Posted by Warnz

Those hubs look rather nice

Did you manage to solve the issue with the glue going off too quick or have you not got that far yet?

Thanks. They seem like a good solution.

I haven't done anything at this point other than planning and messing with polygons.

I have all of the aluminum, PVC and parts on hand now. Just a trip in the morning to HD for hardware and hole saws and I'm good to go. The build starts tomorrow.

Mark

[Warnz]

Looking forward to seeing this taking shape, hope all goes well.

I was thinking about how to insert the end discs into the tubes and the gluing problem. I know when I've jointed PVC pipe in the past I have used a lot more glue than necessary to get a bit of "location time". You don't get much but generally enough to give it a twist or two. Would it be worth shaving the discs to get a nice slide fit and file a couple of grooves on the mating face to give the excess glue somewhere to go? Failing that, get the depth stop set on the drill press and use that to push them in nice and square.

There again I might just be waffling. Good luck.

[Guitarnut]

Originally Posted by Warnz

Would it be worth shaving the discs to get a nice slide fit and file a couple of grooves on the mating face to give the excess glue somewhere to go? Failing that, get the depth stop set on the drill press and use that to push them in nice and square.

I had planned to lathe the discs to get the final fit. When they are fresh cut, they're too big to fit the pipe. I'll also need to lathe the hub portions of the flanges to fit them. I had thought about putting slits on them to act like treads on a tire to release air pressure in the pipe but I hadn't considered them for allowing the glue to flow.

Using the drill press to set them is brilliant! I was thinking the other way around...trying to come up with something to place in the pipe to stop the hubs solid and flat. I will definitely try the drill press. Thanks!

Mark

[Guitarnut]

After much planning and pixel pushing, it's officially a build.

I started off by gathering up all the goodies. I was surprised how much of the hardware I already had in the shop.



Then I cut out all the discs I was going to use for the rollers. There were 12 @ 3.25" for the roller hubs, 16 @ 1.75" for the flange hubs and 4 @ 2.25" for the flanges.





I cut the center bore in a flange disc and used it to size the pieces on the SS.



I chucked up 8 of the pieces that would be the flange hubs and using a flat rasp, milled the discs down until a flange fit snug on the end. Then just continued down the rest. Then I did the other 8.







When I placed the hub pieces on one of the 2.25" flanges, I could see there wasn't going to be enough area left to screw them down.



So, I needed 4 more 3.25" discs like I was using in the rollers. I must be living right, I had exactly enough PVC left to do it.

[Guitarnut]

I placed a 1/4" bolt in the vise and slid a disc on. Then applied PVC cement to the mating surfaces until I had 4 discs in place for each hub. After a minute, I slid them off and did the next.



After they set up for a few minutes, I cut the center bore in them. I wish I had thought this through a little better. The bit pulled off center a touch. Now all flanges were off center.



With a piece of 1/2' rod in the vise, I used the same steps as before and glued up the flanges.





When they had set up, I chucked them up in pairs on a piece of 1/2 all-thread. Knowing they were off center, I lined them up with their greatest offset. These needed to be smaller than the ID of the PVC pipe so I had some room to lathe them back down and center up the bores.

[Guitarnut]

Using the same method, I glued up the roller hubs.



I had very little room to size the roller hubs so I needed to keep the bores centered. I decided to use the pin register method. I clamped a board to the drill table, and ran a 1/4 bit thru it. Then I chucked up a 3/8" bit. I also drilled a small hole in each hub so I could screw it down to the board to keep it from spinning.





After I drilled most of the way thru each hub, I ran the 3/8" bit thru the board and used a 3/8" bolt for the pin. Then I flipped each one and finished the 3/8" holes.



Last was a 1/2" bore using the 3/8" pin as a guide.



After drilling them half way thru, I ran the bit thru the board and used a piece of 1/2" all-thread as the pin. Drilled one side, flipped them and finished off the bore. All nicely centered.

[Guitarnut]

I chucked up each roller hub and did just a touch of milling to get them to fit snug inside the PVC pipe. I'll do some hand sanding for final slip fit before gluing.





One last thing to do was the hole for the cotter pins.





I then cut 2 pieces of 3" PVC pipe at 6" long. The hub and flange assemblies are 2" thick, not counting the flanges hub...which I want outside the pips. So I knew I needed about 4" between them on the axle. To give the hubs a bit of inset, I went with 3.75" instead. I mocked them up on all-thread to check spacing.

[Guitarnut]

Enough of the plastic for one day. Let's cut some metal!

I had a piece of aluminum channel laying around and I thought it would be great for the project. It will be enough to make the brackets for the adjusters and also the plates that go on the swing arm...for mounting the neck.





After ripping the section I wanted for each purpose, I set the fence to 1.5" and cut 8 brackets.



Here they are after rolling all the edges. I put each one in the vise and eased the edges with a file.



More tomorrow...

Mark

[Guitarnut]

I made quite a bit of progress yesterday. I finished up the metal cutting and 99% of the wood cutting.

I started off by testing my idea for the mechanical joints for the swing arm. I set a fence on the band saw at the width of the larger tubing, minus the thickness of one wall. And set a depth stop to 3/4"...the outside width of the smaller tubing. Then it was a matter of two cuts to get the notch that would accept the smaller tubing.



Here's the test cut.



Here's frame fitted together. The joints are tight...it's standing with just friction in the connections.



While I had the bimetal blade on the band saw, I cut up the rest of the aluminum scrap into the two neck mounting plates for the swing arm and 4 plates that I can use for capping the bearings or axles if needed.



Fast forward about 2 hours and lots of measuring and cutting of birch ply. I only had 2 half sheets and a few scraps but I was able to get eveything I needed. Since my base needed to be 54"...wider than I could get from a half sheet of ply...I decided to go with an offset lap joint. I cut 2 pieces at 34" and 2 at 20" and made a lap joint with the top layer opposite the bottom. You can see the pieces in the background of this pic. The overlap is 14" and shoudl be plenty strong on it's own. In addition, the base will be supported by the Shopsmith way tubes and the folding leg on the other end.

I also laid out all of the pieces to the main body and started working out the placement of brackets and the reach of the adjusters.





The math I did early on determined a minumum distance between the rollers so I cut a shipping tube to 31" and wedged it between the rollers to tension the belt.

[jkingma]

VERY interesting project. Thanks.

[Guitarnut]

After shaping the adjuster arms and marking out all of the holes for bolts and slots, I was able to determine how much travel I would have in the adjusters. Here is the layout with them adjusted all the way back...



...and all the way forward. Total travel of 2". The area between the 2 marks on the lower board will be a 3/8" slot.



All of the holes and slots are 1.5" off the edge so I set a fence on the drill press to make sure everything would line up. I drilled all holes with a 1/4" bit and then followed with a 3/8" bit to finish them off. I don't have pics of the process but I used a 3/8" Forstner bit to make the slots for the adjusters. I don't have a 3/8" router bit and this was probably faster anyway than doing another setup with a router. The bit is stiff enough and stable enough in a drill press that I could make half cuts and clean the slots out nicely. A bit of smoothing with a file and they were good to go.



Then , time for some test fitting.









Even though the bearings I'll use in the final product haven't arrived yet, I decided to mock up one end with the lawnmower bearings to see what the roller fit is like. I'll need to recut the 2 adjuster arms but that's an easy task compared to having clearence issues later on.

I saw 3 things right away. The first is that the cut ends of the rollers need to be trued. I didn't mention this earlier, but I cut the rollers from either end of a pipe so I would have 1 factory edge on each. When I lathe the taper into the rollers, I'll clean up the edges as well.

The second is that the 32" deck is too long. Because it's 3/4" thick, it needs to be shortened to about 30.5". The pics below show it pushed back to the proper position.

The third is I need to ease the corners of the sides that are closest to the rollers. I'll cut a miter on them to create more clearence during belt change outs. The last pic shows them Photoshoped out.





Mark

[Guitarnut]

Originally Posted by jkingma

VERY interesting project. Thanks.

Thanks! Glad you're enjoying it. I'm starting to realize that as much as I like building guitars, I think I'm even more excited to build something I've never tried before. This would qualify.

Mark

[macaroonie]

Just a thought. Nyloc nuts on your rollers. Also you might want to consider this pic. Red being the travel of the sandpaper , green being a reinforcement.
As it stands there is potential for chatter as the frame can parallelogram from true with friction.

Good progress big guy !!



or this ( Purple )



These will ground any movement to your pivot point which we will assume is plenty rigid.
I only mention this because if you have ever used a hand held belt sander you will be aware of the considerable force generated by the friction of the abrasive. M

[Warnz]

That's some superb progress, looks like the plan is coming together.