Making didgeridoos with ShopBot

[didgeridan]

Hello, I'm new to this forum and I have a question regarding a potential application for the ShopBot. I make these Australian wind instruments called a "didgeridoo" which are basically hollowed logs. Traditionally the dimensions (length and diameter) of the inside were random and each didgeridoo ends up sounding a little bit different, but the instruments I make are carved according to precise dimensions for a precise tuning. They tend to be from five to seven feet long and have natural, and therefore, irregular shapes. The basic carving process entails cutting the log in half lengthwise, hollowing out the inside, and then glueing the two pieces back together.

Please see the photos I have attached to be able to picture the process to which I am referring.

I would like to begin making these precision-tuned instruments on a Shopbot CNC router to which I will soon have access. So that I can continue to carve irregular shaped pieces, I envision taking the two pieces, after the log has been cut lengthwise through the bandsaw, and laser scanning each piece. The scanned file would then be imported into the CNC router's CAD software and combined with the dimensions to be carved by the router.
I'm looking for a low cost solution to be able to laser scan the pieces to be carved. I understand that most scanners are very expensive, and therefore, out of the question for me. One possible low-budget solution is to use the David
Laser Scanner (david-laserscanner.com). Does anyone here have experience with this? Do you think it would be accurate enough? (The interior dimensions of the instruments I make have to be within a millimeter accuracy in terms of lengths and diameters to result in the pre-determined sound spectrum.)
I also looked at the NextEngine scanner (nextengine.com) as another low-budget solution, but it looks like it can't handle objects as large as a 6 or 7 foot long didgeridoo.
Another alternative is just to use the ShopBot's Digitizing Probe to scan the object, but I understand this takes quite a while. Can someone who has used the digitizing probe give me a ballpark idea of how long it would take to scan in something like the two log-halves that I included as an attachment to this posting?

Your input will be greatly appreciated.
However, please do not respond with general advice directed to beginners about how to make didgeridoos, how they are traditionally made, etc. I have plenty of experience in this area, and am asking specifically about ways to make them with the ShopBot. (I only say this because I put out a similar question on a router forum and most of the advice I got was in this vein.)

Thank you,
Dan




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[ron brown]

Daniel,

Interesting project, I see this more as taking the lines off a boat than art scanning.

For scanning 'art' and furniture projects, many points may be needed. For what you are doing, quite a few less might be better. I would THINK a few points, say "10 per station" and "stations" placed ~10cm apart (~4" for the metrically impaired) would be enough, and accurate enough to put the half logs in a CAD program and do your 'modeling' from there. You may find you can space the 'stations' further as you develop a feel for what is needed.

I see this as 'fairly fast' after a good technique is developed.

Ron

[billp]

Daniel,
You might contact the folks at Next Engine. I have used one, and I believe that with the proper software you can "stitch" smaller files together to make a contiguous object.
As Ron points out above you'd need to practice almost any technique for awhile before you could generate files/products with any semblance of "speed".

[myxpykalix]

Let me ask a few uneducated questions in order to try to help.
When you hollow out the log does the inside have a symertrical shape all along the length or is the inside shape determined by the outside shape of the log?
I would take a picture of the end of the log, take that shape then do a 2 rail sweep for each side taking into account the shape of the log accounting for any bends or whatever. I don't think you would need a laser scanner to do this on a bot.

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[knight_toolworks]

myself even if you can get the piece of wood into a usable format then you have to toolpath it and the wost is trying to hold it in place and accurately place it. since the wood is not straight or even I think the shopbot is the wrong tool.
I would ask how are you hollowing them out right now?

[didgeridan]

Thanks for your responses.

From Steve Knight:
..................................................
"even if you can get the piece of wood into a usable format then you have to toolpath it and the wost is trying to hold it in place and accurately place it. since the wood is not straight or even I think the shopbot is the wrong tool.
I would ask how are you hollowing them out right now?"
..................................................
I use an angle grinder with a wood carving disk. Lancelot, Kutzall,Arbortech, etc. These work great as far as removing wood fast, but for carving precise dimensions, it is very tedious. I've attached a diagram of the interior to give you a better idea. The inside is divided up into 20 segments, each with a specific length, beginning, and ending diameter. The diameters are converted into circumference, and then, when I am carving, I have to carve 1/2 circumference into each side of the log. It is painstaking cutting and measuring repeatedly, and takes a long time to be precise.
So, for doing this on a ShopBot, maybe it will only work well on pieces that are perfectly straight? I guess holding it in place would still be a problem, though. Any ideas?

From Jack Jarvis:
..................................................
"When you hollow out the log does the inside have a symertrical shape all along the length or is the inside shape determined by the outside shape of the log?"
..................................................
The inside shape is determined by the outside shape of the log, unless there is enough excess wood on the log that I can carve a symmetrical shape on the inside.


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[ron brown]

I'm going to make a few assumptions and statements here. I'm assuming you have a good CAD program, you know how to use it and the ShopBot will get the points needed to 'loft' the 2-half logs. Now, I haven't 'done' the logs, but I have lofted many boats in CAD and by hand and my eyes sometimes cross when I think about how many planimeter takeoffs and calculations I have done. I now let RHINO, my CAD program, do them.

I think a bit of scratch paper and the information collected on the lofted form would allow for fast and accurate machine carving.

For holding down, I'd have the tendency to glue tabs on the 1/2 logs. I would get 'screw locations' and drill them when doing the 'takeoff'. These 'tabs' would be cut to 'height' at the same time. When flipped, 'posts' would be cut to length, placed under the tabs and the log halves secured.

Now, I haven't personally built a didgeridoo. I have done every action and procedure mentioned at some time with either the ShopBot and/or CAD software and possibly by hand.

If someone cannot figure out how THEY can do a procedure doesn't mean is can't be done or you aren't using the proper tool. If every thing has to be straight and square before one starts, human reproduction would stop immediately. Fortunately, with determination and desire, things can be achieved.

Ron

[didgeridan]

Thanks Ron.
Umm...well, I haven't ever used CAD or a ShopBot. I'm a fast learner though, and determined to take my didge-crafting to this level. Maybe we could back up a little for some more generalized advice, like, what would be a good CAD program to learn on for this application? What software does the ShopBot use?

As for the scanning, from what has been said, it seems like maybe the ShopBot's digitizing probe will be suitable instead of needing to use a laser scanner.
I'm having a hard time visualizing what takes place once I have a "lofted" form imported into a CAD program. I realize I'm going to have to learn CAD for this, but maybe someone could give a run-down, in general terms, of what is involved in combining the dimensions to be carved with the digitized form.
..............................................
"For holding down, I'd have the tendency to glue tabs on the 1/2 logs. I would get 'screw locations' and drill them when doing the 'takeoff'. These 'tabs' would be cut to 'height' at the same time. When flipped, 'posts' would be cut to length, placed under the tabs and the log halves secured."
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Is there any chance you could draw some kind of quick diagram so I can visualize what you are saying?
Again, thanks for the input.

[ron brown]

As things evolve, so so my thoughts of 'how' I might do such a project

First, I would glue blocks to the side:
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And scan. Then, I would place the posts I mentioned.
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As the posts and and blocks are identical, there is now a 'plane' at the top of the posts. the '1/2 log' is still secured to the table. At this time (log scanned, everything secured) I might mount a piece of plywood to the bottom of the posts and some wedges to take up the gaps in several places.

This would be allowed to cure and the bottom of the ply would be 'indexed' so it could be flipped and registered in the position for carving. Your machine will then be 'free' to scan a part or two while you worked on dimensioning carvings.

This last rendering is the part 'flipped and green inside placed to represent the carved 'stuff'.
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By now you should be thoroughly confused as I have just gone through several hundred if not a thousand hours of learning curve.

I like RHINO for my CAD work and use VECTOR for tool-paths.

The only reason I don't shoot flies with a battleship gun is I don't have it at my disposal. I do believe in using more tool than one needs as I HATE to unlearn one CAD program and learn another.

Hope this helps,

Ron

[rb99]

Cool!

I wonder how Khalid would do it?

RIB

[knight_toolworks]

have you thought about using the bot to make jigs so you could use a hand held router with different radius bits to do the final work? myself I think that may be a faster solution then doing it on the bot. don't get me wrong I do so many things but sometimes the bot is not practical for some jobs or will just be slower.

[bill.young]

With a boatbuilding background like Ron, I'd agree with using Rhino to generate the surface...you basically just want to make very lumpy boats!

Here's a rough demo that I think might work for you. I did steps 1-3 manually by just making up lumpy cross-sections, but I think probing would give you what you need.

1) probe the outside of each half as a series of cross-sections in dxf format.

2) import the cross-sections into Rhino

3) Offset the cross-sections to the "inside" by the wall thickness you need.

4) use the Loft command to create a surface

5) save in a format that will let you generate a toolpath. Maybe Aspire could generate the toolpaths?




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[bill.young]

Oh yeah, I left out the "rotate everything 180 degrees" step so that the open side was up...it was easier to see this way

Bill

[didgeridan]

Thanks for all the good info. I'll definitely be referring to your posts when I start working on this project.
Steve, yes, I've thought about a jig and a handheld router to do this. Hadn't considered using the shopbot to make the jigs, though.

[beacon14]

My biggest concern would be the wood moving. You could spend hours making a toolpath and holddown jig, then by the time the cut is half done the wood will have twisted or warped. Maybe the only benefit of doing it by hand is not having to worry about that. If you need that kind of accuracy you might have to remove the waste, allow the wood to move, then re-probe and re-toolpath to the new shape before removing the last little bit.

[knight_toolworks]

I don't want to discourage you the bot can do pretty cool and very different things. but this just seems it would not save much time. something like this would not be something you would want to do till you get a fair amount of experience before doing it. then the time and experience and the cost of the hardware and software to do it I doubt you save much time. but the bot can make the jigs and that may really save you some time.

[rb99]

Perhaps you could use the arrow keys to manually control the SB to do the routing?

RIB

[didgeridan]

It's not too difficult to find logs that are straight enough to get a perfectly straight cut down the center (with a jig) on the bandsaw. Perhaps for pieces like this, the shopbot would be more practicable? Or, another thought is just to start with milled, square planks instead of irregular shapes. That should be fairly simple, right?

[ron brown]

Daniel,

A CNC machine will carve what you need. A good CAM program will define the toolpath and a good CAD program has the power to create the surface of the interior.

The question is do you have the mental ability and the desire to pull it off? When I first started playing with CNC, I figured it would take 'a couple of months' as I already THOUGHT I knew CAD well.

Several years later I showed the 'Texas Star'. Ted Hall asked me how long it took to design it. I had to admit it took 'only half an hour or so' .... after three or four years of thinking about it.

Ron

[didgeridan]

Just for time/work comparisons, at this point, with the tools I'm currently using, it tends to take about a week (two or three hours a day) to carve the interiors and glue the two halves back together. I realize it's going to take much more than a week to get this project going on the ShopBot, but, once I've got the kinks worked out, if I can get a didge done in less than a week, I would think that it's worth it. Also, I think the same amount of time spent on scanning, toolpathing, etc. might be more fun than the tedium and imprecision of carving with an angle grinder.
I never use green wood, so there is minimal warping. Even after carving out the inside, they usually don't warp by the time I'm able to glue them back together, except for on the larger, bell end, which I carve very last. It usually takes at least a day after hollowing out the bell end for warping to occur. So, I kind of thought that the CNC router would make it possible to avoid having any warping at all by the time the two halves are ready to be glued.

[zeykr]

With some engineering and programming, it seems that one might be able to place a probe of some type on the z axis along with the router and use it to follow the contour of the log - in a motion kinda like that of the copy machine. I can see where following the contour along the x,y would be pretty easy, but would take some more figuring to follow the change in log shape along the z. May not be able to do z with a stationary probe - might have to have it attached to a stepper as well. Move it in till it touches outside of log, then move cutter to within x distance of that point.

Don't think it'd be terribly expensive to do, a touch probe and a stepper motor and some mounting.