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I have a 6x48 belt sander that is just too small for building guitars. The platen is too short to radius a fingerboard and the belt is too narrow to flatten out an 8” board. Buying a 6x80” sander is too expensive and its still only 6” wide. So I decided to "roll my own sander" and thought you guys might be interested in seeing it as I go.

The shafts, pillow blocks, and motor are from roof ventilators that went bad and were replaced. All the steel for the frame and the aluminum for the platen was scrap that I collected over the past year.
As a matter of fact almost everything is scrap and I haven’t invested any money into this project so far.

For Starters,
The drums are made up with copper pipe and ½” PVC sheet. The pipe shown in the pics are 9” and I have since cut them down to 8”.
The picture doesn’t show it but I have notched the keyway slots in the PVC donuts and I will use a set screw to hold it on the shaft. The copper drum will be attached to the PVC donuts with screws. I know that aluminum would be a better choice for the donuts but it would be much harder to machine and besides the PVC is more than adequate for the task at hand.
That’s all for now…I will post as I move along.

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Rich S

"The inconvenience of poor quality will linger long after the thrill of a bargain has been forgotten"

I am *REAL* interested in seeing how you get this built. I have been working with a desk top belt sander (4x24) and I know it is also too small. PLEASE keep this thread updated with pictures and details as you go!

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Reguards,

Ken H

Here are the guide plates. One will be fixed while the other is adjustable for both tracking and tension.

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Rich S

"The inconvenience of poor quality will linger long after the thrill of a bargain has been forgotten"

Lookin' good! I can't wait to see how this turns out. We'll be having folks around here building their own machines before you know it. It's fun eh?

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

I have a question. Have you crowned your pipes, to make the belt track to the center?

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

At the price of copper today, I'd have gone looking for something else to make the rollers of!

They also may prove to be too small. As the sanding belt gets longer, the tension needed also increases, thereby also adding friction, compounded by the fact that you'll now be able to sand longer/larger pieces, thereby requiring even more power, thereby requiring a larger drive drum to increase the surface contact area. Don't underestimate why the big machines are so sturdy, and expensive.

Keep us posted on the progress!

Don…Yes it is fun…kinda’ like building a CNC, but with a huge fudge factor.

Waddy…I am going to put 0.030” of Nickel on the copper and then turn the crown one of the drums and leave the other flat. Hopefully things will work out this way, if not I can always crown both drums to correct the problem.
I think the ideal way to crown the drums would be to spin it on a lathe and push the center section of the pipe outward to create the crown, I just don’t have anyway of doing this and besides the pipe is “L” class, so the sidewall may be to thick to push it out anyhow.

Grumpy…I had the copper pipes lying around in a scrap bin so I used them. If I were to buy the pipe today it would have made making the drums cost prohibitive. I like the copper because it is so easy to plate nickel on them.
I have considered the friction and I realize that it may be the down fall of this whole project. I have a 2 HP 1725 RPM motor to drive it and I plan to gear it down to a slower speed in order to gain more torque when I need it. I hear what you are saying about drum size and I may have to increase them to gain surface area. I won’t know until I try it. Sort of the no math way of doing things, but it's fun.

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Rich S

"The inconvenience of poor quality will linger long after the thrill of a bargain has been forgotten"

Hi, Rich

I'm glad to see someone else making a belt sander. Here is a picture of mine with the belt removed- I made it about 15 years ago and use it all the time :



I made the rollers out of cherry ( happened to have some scraps) that I glued up into square blanks, and drilled 1/2 inch holes most of the way through. I epoxied in 1/2 inch shafts ( roughed them up with a file first so the epoxy could "key" onto them). Then I turned them right on the sander, with a makeshift tool rest and a couple of borrowed lathe tools. I don't have a lathe myself.

It was easy and quick( and fun) to make the rollers that way. They are about 2 1/4 inch diameter, with the driven roller cylindrical, and the idler roller slightly barrel-shaped : it's about 0.030 inches larger diameter at the center than the ends. The tracking works fine. You can't see it in this picture, but there is a screw adjustment that tilts the idler roller for tracking.

I've never had a belt-slipping problem. As far as roller diameter, that really won't effect belt slipping. The force it takes to slip the belt depends on the roller force ( the tension in the spring that keeps them apart) and the coefficient of friction between the roller and the belt. The roller diameter doesn't enter into it, as long as the roller is large enough so the belt flexibility allows it to wrap around and contact it a full 180 degrees.

My platen is just formica on a couple of layers of hardwood plywood. I expected this would wear out quickly, but it's held up well for a long time and a lot of use. I've probably gone through about a hundred belts so far on this machine. It's got formica on the bottom surface also - so I can turn it over and get a new surface if I need it. But, I haven't even done that yet.

I've got a pretty small motor ( 1/4 HP) powering it, but that seems to be enough. I had some multi-diameter sheaves I used, so I can vary the belt speed by just shifting the belt. That's been convenient. By slowing the belt speed way down and using a fine belt, it works well for sharpening tools ( and kitchen knives)

One of the great things about making your own machines ( I've also made an 18" bandsaw with plywood wheels and an oscillating spindle sander) is that if anything goes wrong, you know you can fix it.

Good luck with it

Phil

The roller diameter doesn't enter into it,

Sure it does. Larger roller, larger surface contact area between roller and belt.

Your sander is a little wee thing, and doesn't ask for much. But when I made an extension for my 6x89 sander and converted it to 6x108, the change was dramatic, and I had to modify a few things in order to raise the tension, which in turn stressed the motor mounts and knocked it out of alignment, etc.....

Just like a longer scale will need more static tension to bring the same mass string to th same pitch, so does the belt length change. Only here, the change isn't a tenth of an inch, it's many, many inches....

I hope it works, I really do, as I want/need to make myself a second, dedicated to a certain task, sander, and I'll watch this thread to see where it goes. I'm merely warning y'all that engineering and physics may come around and try to play the spoiler if things aren't beefy enough.

I disagree.

A larger roller does mean more area - but friction force does not depend on area, only on the normal force and the coefficient of friction. With a larger roller ( and, the same initial belt tension) the force per unit area between the belt and the roller is lower.


This might help to understand what's happening:

The belt will slip on the drive roller when the ratio of the tension in the top of the belt to the tension in the bottom of the belt exceeds this value:

e^(f*theta); [ this should be read as "e raised to the ( f x theta) power ]

where e is the naperian number ( about 2.72), f is the coefficient of friction between the belt and the roller, and theta is the wrap angle in radians. (Note that the drum diameter does not enter into this calculation .) This formula is from my old copy of Shigley's "Mechanical Engineering Design" but you could probably find it somewhere on the web. It's also pretty easy to derive.

As an example, for a friction coefficient f=0.5 ( a conservative value) , and a wrap angle of pi radians ( 180 degrees) this number (maximum tension ratio) is about 4.8. To continue the example, if you tensioned the roller separation spring at 10 pounds, you will, initially, have 5 pounds of tension in both the top and bottom sections of the belt.

As you sand something and load the belt, the tension in the lower section will stay constant at 5 pounds ( it's controlled only by the tensioning spring at the idler roller) , and the tension in the upper section of the belt ( between the sanded part and the drive roller) will rise. If you load the belt enough so that this upper belt tension reaches 4.8 times the lower belt tension of 5 pounds ( about 25 pounds) the belt will start to slip on the drive roller.

If you're still convinced roller diameter makes a difference, try this: Take a length of rope and a 5 pound weight and find a tree with horizontal branches of different diameters ( and similar bark surface). Hang the rope over a small branch ( with the weight hanging free) and see how hard you have to pull down on the other end to get the rope to slip on the branch( and lift the weight) . Now, do the same thing with a larger diameter branch. It will take the same force to drag the rope over the larger branch - as long as each branch is large enough to allow the rope to flex completely around the branch to get the same 180 degree wrap. You could try this in your shop with dowels and string, instead, if that were easier.

Phil

I don't think we have enough engineers on the forum!!

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Steve Walden
Aspiring Builder,
Bartlesville, OK

If you cant dazzle them with brilliance, baffle them with bull....

I dont know if I have been dazzled or baffled....

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Reguards,

Ken H

The surface area and coefficient of friction are the TWO variables to determine force. I learned that in high school physics.

Phil, would you have a shot showing the idler end of your sander??

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Dave
Milton, ON

Here are a couple of pictures



The carriage is an inch-thick baltic birch plate that's supported by a steel rod that slides in two bronze bushings that are pressed into two homemade baltic birch shaft supports. This lets the carriage move fore and aft (up and down in this picture) to tighten the belt. The spring at the top of the picture provides the tension on the belt by pulling on the carriage.

The roller is supported by two pillow block bearings that are mounted to the carriage. The one closer to the roller is a ball bearing unit, and has a set screw that locks onto the shaft and keeps it from sliding left and right. The bearing on the left is a cheaper bronze bushing unit. Both of these allow some misalignment - since the shaft has to tilt to provide tracking adjustment.

The second picture:



shows how the tracking is adjusted. I have to loosen the two plastic-knobbed screws, and then turn the knurled knob at the right to adjust the tracking. It seems every new belt needs a little adjustment to track right, but it's pretty quick and easy to do.


Phil

Many thanks Phil. Well done!

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Dave
Milton, ON

I have made some more headway on my sander. I finally found the time to weld the frame up and my upper carriage assembly is nearly complete. I need to order a tension spring, sanding belt and some pulleys. Looks like I’ll end up having to invest some money into this project after all.
As for the upper carriage assembly, I originally intended to use linear bearings, but I have decided to go a different route, I’ll post some pics of it tomorrow. Here is the frame.

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Rich S

"The inconvenience of poor quality will linger long after the thrill of a bargain has been forgotten"

Here are the pics of the carriage assembly. Next step will be the drums. I am going to increase the drum size from 2 5/8” to 3 1/8”. This will increase the belt speed from 2090 to 2488 Ft. /min.
I still haven’t figured out what color to paint the machine, probably end up black.

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Rich S

"The inconvenience of poor quality will linger long after the thrill of a bargain has been forgotten"

Dude! Way overkill on the slick-ness scale.

I love it <g>

How will you tweak the tracking?

I'd paint it a light color; dust shows up more, and is easier to vacuum off... Dark tools also absorb light from the shop, while white tools reflect it back.

Thanks grumpy…I am glad you like it.
Looking at the pic below, point (A) is the tracking adjuster, (B) locks in the adjustment, (C) is the tension adjuster and (D) is the pivot point and where the upper and lower plates of the carriage connect.

Thanks for the advice on color choice. I’ll stick to a light color.

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Rich S

"The inconvenience of poor quality will linger long after the thrill of a bargain has been forgotten"

I see how it works now.

May I suggest replacing the bolts with large star knobs? They can be had for the threads you have already, from Lee Valley and other sources. I think you'll find yourself tweaking tracking more often with the longer belt(it's been so with mine), so it would be handy to not have to stop, and reach for a wrench each time.

Other than that, this all looks sweet! How'd you make the new drums? Don't tell me you had copper that was even larger.....

How did you guess that I happened to have some 3” copper pipe lying around???

I made up some knobs and increased the holes from ¼-20’s to 3/8-16’s. I wish I had some bolts with the balls on the ends. The carriage is starting look real ugly now. I also made some caps for the open ends on the box steel.

I am thinking of a yellow similar to the Powermatic’s gold for the color.

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Rich S

"The inconvenience of poor quality will linger long after the thrill of a bargain has been forgotten"

3" copper....?

I just bought some 2", and it was $28/ft at retail!! Don't want to know what 3" is worth....

Copper prices are through the roof....

Yeah, ask my father and brother (electricians) all about it! When I put a new box in my shop to handle the CNC the main cost by far was simply the piece of wire connecting it to the entrance 20 feet away! Give me a call when you start working on that new sander. If it relates to another project we worked on together before then I might have some ideas for it!

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services