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Rim Sander ala Tim McKnight!
http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=3154		 Page 1 of 2
Author:  Shane Neifer [ Wed Sep 07, 2005 3:54 pm ]
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Well....My top is ready to brace and I want some go bar dishes. I knew that eventually I would also want a rim sander. And since you have to spin the discs to make dishes with a router sled I thought I may as well just build the rim sander and have it spin the discs! So I printed Tim McKnight's post in the jigs and fixtures section and then asked Tim what he didn't like about his machine. He just said that getting the belts tight was a bit of a choir and thought that maybe a chain drive would be better. I am not into chains so I stuck with belts but I think that the system I came up with will make tightening and keeping tight those belts not so problematic. I am not finished the sander yet as I have to build the chuck to hold the dishes but I will do that very soon. So here is the sander.



I thought you might like the electric guitar 'speed knob' knobs! The undished discs are in the shop, four in all two each for the back and top, one to fasten sand paper to and the other for the go-bar deck. They are 2 ply of 3/4 MDF, just like Tim's except I went to 24 inches in case I want build an acoustic bass.

Here is the motor tightening mechanism, quite simple really!



And here is the idea to tighten everything up. I stole the idea from the idler pivot that is on my 12 speed drill press. The shaft and two middle pulleys are in a box that pivots so when the motor is tightened the center block pivots and everything comes tight. You cannot grab that spinning shaft and stall it out. It works GREAT!



My sander is probably a bit slower than Tim's. My math with his pulleys says his turns at about 155 rpm and mine turns at about 127 rpm. Mine is also probably turning in the opposite direction as Tims because my motor is upside down and is held in place with a pivot pin (3/8 bolt, with no nut). My motor is 1/2 hp washing machine motor that a friend of mine who owns an appliance repair business gave me. I have a cover for it that I took off to show these pictures. My pulleys are 2" on the motor to a 6" then another 2" to another 6". Some thoughts for the future are to construct my moulds so that I can set them on a frame on the sander deck and lower them onto some stops. This will give me cosistent results everytime but it just an idea for now.

Thought I would share my long weekend project!

Cheers
Shane
Author:  BlueSpirit [ Wed Sep 07, 2005 5:21 pm ]
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Very Nice, and I like your idea about the stops for consistancy. All that in a weekend? WOW!
Author:  Mario [ Wed Sep 07, 2005 5:34 pm ]
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The dish RPM is easy to accurately calculate. Devide the motor's RPM's by the ratio.

In your case, 2" to 6" yields a 3:1 ratio, and double reduction multiplies it twice. 3x3 is 9, giving you a 9:1 ratio.

What's the motor's rpm's? If you're running the typical 1725(1750?) motor, you're rpm at the dish will be 191(or 194). Too fast, and you'll not have enough torque to do the sanding(there's a LOT of friction with all that sandpaper against the guitar's rim).

When I designed and built this machine, I ended up gearing it with a 16:1 ratio, using a 1-1/2" on the drive and a six inch at the driven(4:1 ratio), with the double reduction. With the 1725 rpm motors, this brings it down to 107 rpm. Much more torque availble(78% more torque with 16:1 than with 9:1), and way more importantly, much safer. Your speed is dangerous for spinning such a large dish!

You can keep the 6 inch pulleys, but change the drives to 1-1/2" pulleys, please. Trust me; I had mine geared like your's is currently, at first, and it just about tossed my dish across the shop like a frisbee the first time it came up to speed. I made this an important point when i shared this machine on the MIMF, where Tim saw it and took it to the next level with its own cabinet.

Doesn't Tim mention and explain this? I haven't read his write-up on it, but the gearing, and proper reduction, taking the motor rpm's into considerations, is of utmost importance!

Also, be aware that your open frame motor will spark in use, especially while under load. This machine wil make a lot of fine dust, while under load. Fine dust and sparks don't mix well... Try to enclose the motor(but keep it vented at the same time..) if you haven't yet.

Don't mean to be scaring you, but I'd hate to hear you lost your shop and/or home because of this oversight...Mario38603.1175115741
Author:  DaveF [ Wed Sep 07, 2005 9:17 pm ]
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Instead of stops I put a lip over the dish on opposite sides. This way I didn't need to change my molds. When the mold sits flush on the lip everything is level.
Author:  Josh H [ Wed Sep 07, 2005 10:22 pm ]
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I would love to build on of these machines, but I do not have the space. So I guess I will keep "spinning" the mold by hand. Takes a while but it works.

Nice work and good tips guys.

Josh
Author:  John Kinnaird [ Wed Sep 07, 2005 10:25 pm ]
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My word. Everything looks so clean on the inside. It looks like you wiped up all the glue spills and sanded the interior. Very guitar like. Exterior is pristine as well. Impressive attention to detail. I do second mario's concerns about speed and dust and sparks.

John
Author:  Tim McKnight [ Wed Sep 07, 2005 11:58 pm ]
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As Mario pointed out, my design was adapted from his machine so I will tip my hat to Mario and also to an unknown small shop picture I saw before Mario's machine. They had converted an old potters wheel into a motorized sander. I actually went that same route as I too had a potters wheel that I converted. After my dissappointments with it's shortcommings I saw Mario's pictures and built mine. I also credited Mario in an article that appeared in Guitar Maker Magazine a few years ago.

Shane, I like what you have done with the tensioning system and now you have taken this design to another level. I also concur with Mario and John ... consider changing the motor to a TEFC NEMA rated design which is MUCH safer. Appliance motors are just not safe for this application.

John Hall at Blues Creek Guitars has some really nice sanding discs too. I started out using strips and squares of sandpaper and while they work they are also quick to peel up, snag and tear.
Author:  John How [ Thu Sep 08, 2005 1:23 am ]
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I installed 4 threaded rods in the top of my sander to hold the form centered over the revolving disc. They also have adjustable nuts and washers on them so that I can set the height of the form over the disc controlling the sanding depth. When the form rests on the washers/nuts, the sanding is complete and I can take the sides off put in the linings and then set it back on the sander to sand the linings to the same depth.
Author:  Shane Neifer [ Thu Sep 08, 2005 1:57 am ]
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Thanks Mario for your comments. Tim did explain it and I took it to heed. My motor is dual speed so I have it set at 1140 rpm, leaving my dish RPM at 126. That will work I think because it is a bit slower than Tim's. Also I do have a motor cover, it's off for the pictures.

Thanks again

Shane
Author:  Mario [ Thu Sep 08, 2005 2:24 am ]
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126 rpm sounds good, but you may still not have enough torque. If that happens(and it will, unless that motor has a lot more torque than I think it does), you'll need to change the pulleys, but at least now you'll know which direction to go.
Author:  Shane Neifer [ Thu Sep 08, 2005 2:25 am ]
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Great idea John, I think I will use it!!

Shane
Author:  Dave-SKG [ Thu Sep 08, 2005 2:26 am ]
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It's a great machine Shane...I guess I'm finally have to retire my "wheel of death" and make one of yours. Any recommenations for parts supplier(s)?
THANKS!
Author:  letseatpaste [ Thu Sep 08, 2005 2:55 am ]
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Harry Fleishman attaches his dish to the back of his bandsaw on the bottom wheel shaft. He calls it the "wheel of minor injury." I used it during class, it was nervewracking at first, but quick and effective.

A couple days ago I just did my first rim profiling since then, I attached a crank handle to the dish and cranked it around. Took less than five minutes of sanding (and lifting the dish to check progress) to get the profile sanded in the ribs/linings.
Author:  John Kinnaird [ Thu Sep 08, 2005 3:04 am ]
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I just push my disk back and forth over the exposed edges of the guitar, while it is chucked up in the building form, until it make contact with the sides all around. After all it is like a ball and socket joint that works in every direction, rotation, or as in your shoulder in a straight line as well. It really does sand down pretty quickly like that and in the end lays perfectly flat on the edges of the rim of the guitar. I just mention that for folks that seem to feel like they MUST rotate the disk, a motion that I personally find troublesome when sanding.John Kinnaird38603.5044097222
Author:  letseatpaste [ Thu Sep 08, 2005 3:17 am ]
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It just seemed to me to go faster by rotating with a handle, it's not a necessity of course. Side to side or front to back should work fine like you said. I was just looking for a way to get more sanding done quicker without killing my shoulders. I bolted a flange to the base of my form with a piece of pipe sticking up a bit, so the dish rotated around that. I'll have pics of it on my blog tonight or tomorrow.

My top's going to be cylindrical instead of spherical so I'll be doing a front to back motion (with a cylindrical form of course).
Author:  Dave-SKG [ Thu Sep 08, 2005 3:48 am ]
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Harry's contraption was what inspired mine. We called it the "wheel of death" when I was there ( hence my name for it). Mine is very similar in that the wheel spins vertically rather than horizontal like most we have seen here. Mine is spinning way too fast so I use a foot pedal to shut it on and off/control speed as I go. Good old Harry...what a Guy!
Author:  Pwoolson [ Thu Sep 08, 2005 4:03 am ]
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[QUOTE=Tim McKnight] also to an unknown small shop picture I saw before Mario's machine. They had converted an old potters wheel into a motorized sander. [/QUOTE]

Tim, that was CFox. When I left ASL I looked everywhere for a potter's wheel and the cheapest one I could find was $400 used. So I figured out a way to motorize a dish. About two weeks later I saw Mario's design and really wish I would have waited.
Author:  Anthony Z [ Thu Sep 08, 2005 9:10 am ]
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Shane the thing that is nagging me from your pictures is what are you going to use to inlay your cool logo sketched on the side of your machine? Can you get Ablam that big? <VBG>
Author:  Tim McKnight [ Thu Sep 08, 2005 11:27 am ]
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Lutz Spruce would be nice
Author:  Shane Neifer [ Thu Sep 08, 2005 1:23 pm ]
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I was thinking maybe excavate and then inlay pebbles. Might be a bit heavy but hey it would be different.

Today I was processing Lutz SPruce into shop timbers. I will post pictures in the next few days, so I can get you some Lutz inlay wood if you need it Tim? I might someday try that though on an ebony headplate, especially some of highly figured, no good for guitar tops stuff. Thanks for another idea Tim!!

Shane
Author:  L. Presnall [ Sat Sep 10, 2005 3:51 am ]
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Say, are you talking about Mario Proulx? Or if not, which Mario? I'd like to see a photo of that sanding rig...I'm contemplating what looks like a "wheel of CERTAIN death and/or dismemberment"...putting the dish on one side of my buffer ...
Author:  Tim McKnight [ Sat Sep 10, 2005 4:57 am ]
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Yes, Mario Prouls. I believe his sander is incorporated into one of his work benches. You may be able to find some pics in the MIMF Library or maybe MP can post some here?

I would strongly advise against mounting a sanding dish on your buffer as it will spin wayyyyy to fast. I believe I remember someone mounting one on the outboard side of their wood lathe BUT it had a variable speed control which allowed them to run at a low SAFE speed.
Author:  L. Presnall [ Sat Sep 10, 2005 5:36 am ]
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Hi Tim, yes the site I saw is Kathy Wingert's...there's a link in the "radiusing sides" thread here on the forum...I dunno, hers may be geared down as well...I can't tell from the photo...
Author:  Don A [ Sat Sep 10, 2005 8:06 am ]
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How about just using a hand drill with a variable speed or adding a router speed controller? No reason you have to lower the mold onto the dish rather than the dish onto the mold. Not my idea, Lance suggested this a while ago when I said I wanted a dish sander but didn't have the room.
Author:  L. Presnall [ Sat Sep 10, 2005 12:21 pm ]
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Don, a hand drill? Elaborate...I'm curious but my Alabama education is getting in my way again!!
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