Building A Swing Arm Belt Sander

[Guitarnut]

Originally Posted by Warnz

Hi Mark

+1 on the radiused profile without the flat spot.

Rather than going through the hassle of the rotating lower arm (another point to introduce "slack", and require more bearings etc), why not just have a pin that you can lock the swing arm assembly at a suitable location through the supports for gauging. If the bed is at 4' you could lock it at say chest height (90 degrees) and would (IMHO) be better as it would have no effect on any of the other tolerances.
Another reason is that with the lower arm not being fixed as such you will loose some strength where it would normally attach to the drop arms.

My plan was to use bushings instead of bearings since the section would be locked in place during machining but you make a good point here. Simply swinging the arm out would accomplish most of what I want and place the neck in "playing" position. As I recall, Dan Erlewine always rotates the neck to playing position to work on a neck in his Neck Jig. The only trouble I can see would be mounting the neck to the arm at that angle...gravity working against me. Seems it would be easier and more accurate with the neck flat on it's heel and headstock. I'll have to do a wood mockup and see what works best before I have the arm welded up.

Wish I had your abilities with the 3D stuff

It's all just points and polygons. Much easier than it may look.

Mark

[Guitarnut]

After some actual measuring...I was guessing yesterday...the Shopsmith quill is only 38" off the floor...a full 10" lower than I guesstimated. That's a game changer on the swing arm design. Running a 12" radius with the arm face up at 180°, this places the mounting plates at about 60". That's perfect for mounting the neck. And it's at a good level for truss rod adjustment and sighting under a straightedge. Then I can swing it 90°, check it in playing position and then down to sanding position. Should work out great.

This won't work with tighter radii as the frame won't clear the sander when swung 180°. And I plan to make better use of 9.5" and 7.25" radii. So, there is some merit to the rotating section and I'll need to consider it from both directions.

Many thanks to Warnz for his input on this.

Mark

[macaroonie]

Originally Posted by Guitarnut

Well, if I went that way, it would just be too easy. And, I wouldn't get to build anything.

I'm just concerned that you may be over engineering to accomplish a simple task. That in itself of course creates multi opportunities for dimensional errors / lash / judder etc to creep into the equation and spoil the job. Thats why commercial woodworking machines are built robustly to say the least.
If you are not into compound radii a guided roundover cutter is the boy for you , thats one about2.5" perhaps 3" in diameter. Do your boards in two passes , one for each E

I got a 1" rad !/2" shank off the shelf for £40 and its a joy to use but they will do them with the shallowest of profiles if you hunt about.
Might be worth getting a quote for a custom jobbie.

In this scenario your error is restricted to your height adjustment and the solidity of your router mount.

[flatfive]

Originally Posted by Guitarnut

Since I'm waiting on parts and materials to arrive...

You saying you have nothing else to do? You know what I'm
talking about.

Not having a Shopsmith I shouldn't be too interested in this
thread, but the pictures are so cool!

[Guitarnut]

Originally Posted by macaroonie

I'm just concerned that you may be over engineering to accomplish a simple task. That in itself of course creates multi opportunities for dimensional errors / lash / judder etc to creep into the equation and spoil the job. Thats why commercial woodworking machines are built robustly to say the least.

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PARADE

It's not always about the destination, my friend.

Being serious, I plan to use the sander for much more than putting a radius on a fretboard. I have plans for a fence, and a rig for thicknessing wood bindings, headstock veneers and such. It will also be great for cleaning up scarf joints, tapering neck heels and a whole host of other tasks my ROSS is too confined to do. I think if I'm even a little careful when setting it up, it will be accurate and robust enough for the job.

If all goes to plan, it will fold up and tuck between benches when not in use.

Next on my list is a robotic buffing station like Music Man uses...

Mark

[Guitarnut]

Originally Posted by flatfive

You saying you have nothing else to do? You know what I'm
talking about.

Not having a Shopsmith I shouldn't be too interested in this
thread, but the pictures are so cool!

Hey Glenn, you have me there. I know I have lots of outstanding projects. One of these days I'm going to surprise everyone, myself included, and knock them all out...promise.

Mark

[Warnz]

Originally Posted by Guitarnut

Next on my list is a robotic buffing station like Music Man uses... Mark

There's just no holding you back

[macaroonie]

Originally Posted by Guitarnut

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PARADE

It's not always about the destination, my friend.

Being serious, I plan to use the sander for much more than putting a radius on a fretboard. I have plans for a fence, and a rig for thicknessing wood bindings, headstock veneers and such. It will also be great for cleaning up scarf joints, tapering neck heels and a whole host of other tasks my ROSS is too confined to do. I think if I'm even a little careful when setting it up, it will be accurate and robust enough for the job.

If all goes to plan, it will fold up and tuck between benches when not in use.

Next on my list is a robotic buffing station like Music Man uses...

Mark

Don't say I didn't tell you It would be a very good idea to have a farm gate style diagonal brace on the swinging frame in such an orientation that it will resist the ' snatch ' that the abrasive will have.

[Warnz]

Originally Posted by Guitarnut

This won't work with tighter radii as the frame won't clear the sander when swung 180°. And I plan to make better use of 9.5" and 7.25" radii. So, there is some merit to the rotating section and I'll need to consider it from both directions. Mark

It would work for the smaller radii if you were not fussed about the 16" rad, and if you really wanted it you could always make a dedicated frame for the larger radius.

Another option would be a demountable frame as in the MM videos, although I couldn't see how that latching system worked.

[Guitarnut]

The PVC sheet came in yesterday along with the aluminum plate for the bed. The sanding belts should be here today.

My plan on the rollers, now that I have the PVC sheet in hand, is to use a 3.25" hole saw and cut out 6 discs per roller. I'm planning to use an oversize saw because the hole it leaves is 3.25" so the resulting disc diameter is under that by the thickness of the saw x 2, or about 3.125". After cutting the discs, I'll drill out the centers to .500" and slip them, three at a time, onto a piece of .500" rod, applying PVC primer and then cement and clamping them together. Then it's just a matter of chucking them up in the Shopsmith and lathing them to 3". This will also center them on the axle.



Once they're the proper size, I'll glue them in and stop collars will hold the axle in place.





Then that assembly can be lathed to create the taper on the roller bringing the ends down by about .0625". Very subtle. You can just see the bow in this render and it's slightly exaggerated.



Mark

[Warnz]

Hi Mark

How are you going to prevent the rollers rotating on the shaft?

[Guitarnut]

Originally Posted by Warnz

Hi Mark

How are you going to prevent the rollers rotating on the shaft?

I still need to figure that one out. I need to pin them somehow or go with all-thread instead of a smooth axle. That way I can jam them with nuts/washers before I glue them in. That would mean trimming the axle to length afterward but that's doable.

I was thinking something along these lines. If I'm careful, I can pin both sides of the hubs for added strength. I may have to find a slower adhesive though. That PVC cement is almost instant bond.






Mark

[CptRyg]

Probably not up to your standard but my axles are threaded rod. I have nuts and washers on both sides of the hubs and they aren't going to be doing any slipping.

[Guitarnut]

Originally Posted by CptRyg

Probably not up to your standard but my axles are threaded rod. I have nuts and washers on both sides of the hubs and they aren't going to be doing any slipping.

Haha! Standards? I'm making this out of a lot of scrap and salvaged parts. It looks much better in the renders than it will in the flesh.

Good to hear about the all-thread. That's one of the options I'm considering.

Mark

[CptRyg]

Simple/Effective/Cheap = my standards. Wish I could say that about my women...

[Warnz]

This project takes me back to my Robot Wars days. You would be surprised how we used to lash things up to keep them going, even McGiver would have been proud of us :)

The advantage of using bar stock is that if the need arises to drop the rollers out, you can release the grub screws on the locking collars and withdraw the shaft without dismantling the rest of the machine.

If you are machining your own locking collars, machine them with a flange, then you can just screw through the flange into the roller hubs. Make them long enough and they will act as spacers between the hubs and the bearings.

Also if your using a grub screws you will need a "flat" on the drive shaft for them to act on and probably a bit of threadlock to prevent vibration loosening them.

[Guitarnut]

Originally Posted by Warnz

The advantage of using bar stock is that if the need arises to drop the rollers out, you can release the grub screws on the locking collars and withdraw the shaft without dismantling the rest of the machine.

That's a good point. If I put keys inside the hubs, I'm screwed for ever removing the rollers. I think I'll just key the outsides.

If you are machining your own locking collars, machine them with a flange, then you can just screw through the flange into the roller hubs. Make them long enough and they will act as spacers between the hubs and the bearings.

Nothing that fancy. I'm using drill stops...$3 a set at Lowes. Although, I might be able to find a flange with the right bore and I can drill and tap it for a set screw.

Also if your using a grub screws you will need a "flat" on the drive shaft for them to act on and probably a bit of threadlock to prevent vibration loosening them.

I plan to put a divot in the axle with a drill bit to hold the set screw. I can do it while I'm drilling for the pins.

Mark

[Warnz]

Sounds like you got it sussed

You guys are so lucky (Lowes, HD, etc) with decent tools and wood in stock, I am a Brit currently living in the middle of France. The only wood I can get hold of easily is Oak or Pine, even getting MDF to make my first set of templates was a task in itself

In saying that, the Oak is of really excellent quality, most of these mills out here have been family run for donkeys years and a lot of their stocks have been air dried for 50-60 years or more.

I have friends that come over from the UK on a regular basis so I am hoping that they can get what I need at a reasonable price and bring it over for me. That or Ebay.

[CptRyg]

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

This is my concept in the works for the swing arm.

Swing arm pivot bar with the adjustable radius bolted through.



The bar will pivot on these shorter threaded rods. The habs are cut from mdf with the 1 1/2" hole saw. The resulting diameter happens to be the exact fit for the ID of this square bar. The result is a pretty solid fit.

[guitarbuilder]

even getting MDF to make my first set of templates was a task in itself

I'm just saying this because it bears repeating. You don't need to use MDF. Plywood, plastic, or solid wood will work fine too for templates. Heck, You don't even need to use a template although I do like them for pickup and neck cavity routs.