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Galaga_Mike

Making Radius Sanding Beam: 3D Printing? Milling Machine?

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I've made a few guitars using my Stew Mac 8" sanding beam and I see the huge benefit of using a longer beam. This would level and radius the board/frets at the same time. Their aluminum one is very nice but I would need to refinance my house to buy it.

I started thinking about ways of making one. I am familiar with the method of gluing together MDF layers, but that seems messy and inaccurate. Does anyone have any experience or comments one:

A) Using a 3D printer to make a long radiused sanding beam.

or

B) Using a small CNC milling machine to cut one out of hardwood. I'm not sure of the tool marks and cleanup would make this impractical.

Edited by Prostheta
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It depends on whether you want to build one or build a bunch of them to sell. I make my own radius blocks, and have made a few as long as a fretboard. Maybe this will get your wheels spinning:

http://www.projectguitar.com/tut/radius.htm

I built something similar to that, but with the router in a vertically mounted swing. I also have a method for producing them in numbers - and even with compound radii, but never got around to making them for anyone but myself. One thing you'll have to consider is that with a piece of wood that long, warping will be a factor. That's one reason I think you don't see the long ones in wood.

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Acrylic would be great. I've also considered a foam core covered in fiberglass, but it seems too labor-intensive, and I think more weight is helpful. My most successful solution so far has been mdf with some sort of metal core. But I don't like working with mdf. Laminates would make sense too.

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I ran these 12" radius blocks on the CNC a while back out of sapele. I think I did a 20" beam, then cut it into an 8" & a 12". I found the 12" long one works well. Anything longer seems cumbersome to me. I use multiple blocks with different grits to save time & sandpaper.

I supply the students in the guitar building class I teach with an 8". I even burn my logo into it to "fancy it up". :rolleyes: I'm not sure what one of the 12" would go for...I thought about offering them in poplar or maple...

12inchblock.jpg

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You don't think the poplar would have a risk of the radius coming out of true? The fretboard stock would be a lot harder, I'd be afraid the edges would rub grooves into poplar.

SR

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Laminating is a good idea to produce stable blocks as long as you leave the laminates to settle and readjust any tensions before truing them up and gluing. MDF at the very least is stable and you can paint the surfaces in epoxy to harden it further and prevent water ingress.

Equally - if you have access to a thickness sander - you could make a set of 30-40 long 3mm (1/8") x 50mm x (beam length) strips of phenolic, drill them through at regular intervals (~100mm) and insert bolts through to make a long sandwich. Square this up in a thickness sander, then progressively make the block shorter by an amount corresponding to the radius you are aiming for, removing one outer pair each time. Putting them back together you should - in theory anyway - have a stepped block which is sufficient to work as a coarse sanding block, and you can "tune" using the easily affordable short blocks. I guess you could line the inner surface with a stiff-ish material like thin plastic and epoxy it across the stepped radius.

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If you check Search you will find several builds similar and/or better, plus they tend to appear in build threads a lot. Too much flex in the centre for my liking.

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If you check Search you will find several builds similar and/or better, plus they tend to appear in build threads a lot. Too much flex in the centre for my liking.

I was thinking about that. Using 1/2" plywood doesnt seem to be the best option. Albeit expensive, would using metal (thinking steel legs, and aluminum supports) and lexan compensate for the instability?

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Probably but it seems an overly large and complicated system for anybody that isn't building more than a few instruments. It is brute and perhaps a little ungraceful for my liking whether it works or not.

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Probably but it seems an overly large and complicated system for anybody that isn't building more than a few instruments. It is brute and perhaps a little ungraceful for my liking whether it works or not.

Working hard to make it easy ;)

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Meh, no. Overcomplicated.

Actually, the main reason I want to build one of those is for the multi radius capability. Doing it with blocks seems to be... "iffy" for a newbie :-/

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I beg to differ. You have instant access to a sanding beam, fret caul and radiused levelling beam! That contraption would be better serving to make concave radii for beams.

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1" spindle shaper?

We used to get our knives made for $27.00 per inch. Laminate some hardwood for stability.

I have a turret mill, so can swing the head in a 12" arch.

Would rather have the knives made with the 12" radius and 1 in 12+fret height. Plus I back the carbon boards with maple or mahogony.

Made the female fretboard mold (for carbon fretboards), with the bridgeport. It was a pain and time consuming. But free!

Have a freind with multiple cnc's. He only charges me 160.00/hr. He also taught me to draw on his computer, so I don't have to bug him to program small one-off parts. He could run a quite a few beams in Al. in an hour.

There are a LOT of small machine shops in Mi that are hurting now. Some don't mind easy set-ups/short runs?

JM

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Hmm. That sounds like an interesting idea. We have two production-level spindle moulders however I am not sure how much our terähuolto ("cutter care"?) department would charge to make a pair of balanced cutters that size. I guess the machining department could CNC and harden up a couple of tool steel blades but again that would be a higher cost since they are not directly associated with ours and favours are few and far between. The costs would likely exceed that of purchasing commercial equivalents in aluminium fairly quickly. To the hobbyist the aluminium (or other long non-wood) beams are a pretty high outlay however from a production standpoint the quantity required to make them worthwhile is reached pretty quickly, even factoring in shipping costs.

To be fair, if it were the choice between laying out cash to make convex cutters for the spindle moulder to cut wooden/phenolic beams or concave to mill boards directly, it would be the latter.

I always imagined that a flat aluminium beam say, 1/2" thick, milled with a radius and mounted to a wooden handle would be pretty economical.

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I tend to think in "production" mode.

Some of the "jigs" for radius' fretboards are kind of scary. Some look solid.

Going back and forth with the mill is acurate, and stable.But kind of slow. Better than a router , so I should be thankfull to have one!

Still requires "finishing. I set up another fixture for "convex" board/backers.

The spindle shaper, with power feed, would go through alot of board feet in a very short time.

It would be nice to have multiple fret cauls and beams with graduating sandpaper grades.

For my convex backers, I might just get some from one of our mills. 100' min covers the blade cost at Miliken millworks.

We used an overhead planer/shaper to do radius casing/molding.

It would be more cost effective to just buy the beams.

Marketing sanding beams to luthiers, would probably be harder than selling guitars?

Poor guys crown/cove molding trick; No offense if you've used it =)

Use the tablesaw with a fence/guide set up at 90 degrees to the blade. This is usually done at an angle for crown or cove but if you were carefull setting up your fence and have a 12" capable saw, it should work. RECOMEND feather boards and/or rollers, on top and outside of the work, to prevent any unwanted movement. Take a little each pass!

Powerfeeds work nice for this type of work. I wouldn't do it myself though. 7,8, 9, and 10" blades are common. (all measure diferent than stated dia.)

Let's see, 4 to 6 aluminum beams from Stewmac = ???$$$

JM

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You're right. More often than not in the cases of these tools it is economically impractical to make or sell them in the quantities that make it worth it.

I'm starting to think more and more in terms of repeatability and efficiency for my own purposes, so "production mode" isn't unfamiliar to me. It is easy to make many of something that is too expensive to cover costs or in quantities large enough to make dead stock and hence dead money. :-D

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I made some 8" block out of a router screwed to a jig I made the was adjustable to 12", 14", 16" and 20" radiuses. It worked decent but I ended up buying some of the stewmac blocks until I realized they aren't a perfect radius, there are imperfections in them (they are wood afterall) so I bought one of stewmacs fret leveling bars and basically only use that now. I rough in the radius with the 4" blocks and then use the fret leveling bar to finish it off, that way I have a perfectly level and more accurate radius than using a block after a few trys I was able to radius a board faster doing it that way than I could with a radius block. It also made doing compoud radiused boards a lot easier since you just had to section the board into thirds and radius each third then level them with the bar.

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