[treegezer]

Hello everyone, first time posting. I am with a student group at ASU and we are looking to build a machine that could cut foam plugs for canoe hulls that would later be used as forms to make concrete canoes. I have been lurking for a while now and have come up with a basic game plan.
Build a gantry that would roll along the floor on an angle iron track pulled along by a steel cable pulley system. The gantry would then have a y and z axis carrying a router.
I am not familiar at all with CNC machines. So I am looking at using the 200oz/in steppers and controller kit from hobbycnc as hopefully that will reduce the complexity of the project. I plan on building the gantry out of ¼” plate and ½” box tube and using drawer slides for the movment.

Any other suggestions? Pointers? What software?

I know it wont have much accuracy but the way we do it now ( cut each section individually approx 200 sections with a hotwire and laminate them together) isn’t any better. I would be extremely happy with .25in accuracy. I plan on building this over the next three months so I am sure I will have more questions.
Thanks in advance,
Stuart

[mxtras]

Software? = Mach 3 - without a doubt. It's free for a fully working version, but is limited to 1000 lines of code and 25Khz step frequency in 'free' mode - $160 fixes those limitations if they are a problem. For many, these limits are not an issue.

I would look at the weight of the gantry and the rolling resistance of your guiding and possibly reconsider your 200OzIn motor selection - that seems a bit weak, but I could be off. I guess that depends on your accel and speed.

Scott

[wizard]

Hello everyone, first time posting. I am with a student group at ASU and we are looking to build a machine that could cut foam plugs for canoe hulls that would later be used as forms to make concrete canoes.

There is just something about the concept of floating concrete vessels that bothers me. I know they work but it just doesn't seem right.

I have been lurking for a while now and have come up with a basic game plan.
Build a gantry that would roll along the floor on an angle iron track pulled along by a steel cable pulley system. The gantry would then have a y and z axis carrying a router.

Not to be negative here but how do you expect the router to handle the profile of a canoe with just three asxis? The problem as I see it is the length of the tool and the diameter of the router, combined I don't think you will have the clearances to go deep enough. Granted I'm thinking about an conventional canoe and the 3D shapes they have.

I am not familiar at all with CNC machines. So I am looking at using the 200oz/in steppers and controller kit from hobbycnc as hopefully that will reduce the complexity of the project. I plan on building the gantry out of ¼” plate and ½” box tube and using drawer slides for the movment.

Somebody will have to do the math on this. That is figure out the wieght of the gantry and the required torgue to get the work done in a reasonable time. It is foolish to assume you can get good results by randomly selectiong components.

A packaged system would allow you to get on line quicker there is no doubt there. Just make sure it will do the job.

Any other suggestions? Pointers? What software?

Yes EMC. It is free which always helps and if you get the BDI install should be trouble free. Being open source there are no limitaitons to the software what so ever. Further due to continous development it has come a very long way.

I know it wont have much accuracy but the way we do it now ( cut each section individually approx 200 sections with a hotwire and laminate them together) isn’t any better. I would be extremely happy with .25in accuracy. I plan on building this over the next three months so I am sure I will have more questions.
Thanks in advance,
Stuart

Well you are doing concrete over foam so the accuracy thing is understood. For the Y & Z you shuld be able to get by with simple leadscrew drives. The cable drive I don't know about, if it was me I'd get a long length of light timing belt or chain.

Have you considered just getting smarter about your section laminations? I'm thinking why not CNC the sections. Yeah you still end up with alot of sections but your accuracy should be much better and the sections should blend to gether better. This would require a much smaller machine which you should be able to get on line quicker. Further if the sections aren't to thick you should be able to manage the 3D profiling with off the shelf hardware. I don't know how thick the foam is that you are using but if it is 2 to 3 inches this ought to be very doable low cost.

Personally I see the long machine taking you way to long to build and get working. Do a small router and you have a machine operating much faster. Another plus with a small machine would be the abiltiy ot keep the swarf contianed.

Thanks'
Dave

[Art Ransom]

Whers are you located?

[treegezer]

Remember we are making a plug not a core. The foam is a positive casting of the hull. So as long as the hull has no tangent line steeper then the angle between the bit and the collar of the router we should be alright. Am I correct in this assumption? If not could we some how tell the software that the 4th axis is controlling the pitch of the router and not a typical lathe like situation?

With some rough calculations a the 200 oz/in motors would require a 10:1 gear reduction to drive a 6 in spool to move a 50lbs gantry.
EMC looks nice since we run an ubuntu system in the shop.

We are using a 2in foam. However cutting the sections is only half the battle when laminating to produce the plugs. Indexing them and gluing them together is a long process. I cant find the actual numbers at the moment but we have done some calculations on laminating a large block using only full ½, and ¼ sheets of foam vs the cross sections we do now and we where able to save 3 or 4 sheets of foam due to waste along with less foam adhesive which gets expensive quick.

To clarify our design choices here is a little background. We compete in a southwest regional conference each year for the American Society of Civil Engineers where cost in material and labor is around 30% of the total scoring rubric. Currently all the teams produce and form hulls the same way. It takes about a day and a half for 3 guys to build a plug from raw sheets this includes cutting two sheets at a time as the hull is symmetrical end to end. So, the advantage of having to report little labor cost is large not to mention the reduction of actual costs.

As far as swarf goes when we hand build hulls we still have to run a planer. To contain the particles we enclose the area in plastic. Place a large fan on one end blowing into the enclosure and another on the other sucking it into a trash can and attach the exhaust of the planer to a shopvac. It works very well and could work with this setup too I think.

If it was for personal or multi purpose use I agree I would cut the sections on smaller table machine and laminate them. However unless there are other issues I believe this may be the optimal solution.

Whers are you located?

I am in Tempe, AZ
More questions:
Are the hobby cnc drivers adequate?
What kind of bit to cut Expanded Polystyrene Insulation?
Anyone have a better source for large foam sheets or blocks? ( Buying insulation from Home Depot currently)

Thanks for the comment and keep them coming. I am learning a lot and may be tempted to build a small table for personal use.

[jeffs555]

So as long as the hull has no tangent line steeper then the angle between the bit and the collar of the router we should be alright.

Every canoe I have seen is close to vertical near the gunnels, so a fourth axis to tilt the router would probably be necessary.

[jeffs555]

I am not familiar with cutting foam, so not sure if this would work, but what about using a hot wire cutter and using it like a draw knife. The long axis could drag it along the side of the plug, and the other axes could tilt it and move it to cut the profile. It would take many passes, but the waste cut off would be solid sections, not the fine dust that a router would create.

Another option would be to cut out sections like you are doing now, but with a cnc machine they would be much more accurate. You could cut out locating holes, and stack the sections on a couple of 2x4's to make laminating easier and more accurate.

[andy_ck87028]

Every canoe I have seen is close to vertical near the gunnels, so a fourth axis to tilt the router would probably be necessary.

Previously on this forum, I have seen suggestions to solve this problem simply by tilting the table. Assumedly the CAD software has to be able to generate G code based on a model that has been spun by the same number of degrees as the table tilt.

That would still be multi-pass but an easy solution none the less.

Andy

[pen25]

4 axis would be sweet to do think others have used 4 axis to build thiers. also rather then cable check out the plasma section and look what someone did with 40# chain. i also like the idea of hot wire to cut the plug. if it were a neg mold then it would have to be routed.

[wizard]

Remember we are making a plug not a core. The foam is a positive casting of the hull.

To be honest you lost me a bit here. I was imagining a core around which the concrete was cast. You seem to be describing a molding technique wheere the concrete is cast in the mold????? I was thinking more along the lines of making a conventional canoe.

In the end it doesn't matter as the problem would be the same.

So as long as the hull has no tangent line steeper then the angle between the bit and the collar of the router we should be alright. Am I correct in this assumption?

Exactly! Granted I can't say I have a huge amount of back goround in canoe making but every one that I've every seen has some complex curves transitioning into vertical surfaces. So how would a verrtically mounted router handle that? With a real CNC spindlle and an extension you might cover the surfaces but even here a 3 axis machine is not really the best choice.

If not could we some how tell the software that the 4th axis is controlling the pitch of the router and not a typical lathe like situation?

This is certianly one way to do it. The problem is software. By that I mean finding software (low cost or free) that can handle the hardware configuration. EMC is flexible in this regard but I don't know if there is a kinematic solution available for that machine configuration. I'd suggest getting on involved with EMC and some of the low cost CNC software forums to see what the feedback is.

There is I believe a solution available for the fourth axis being rotary. That is nice but then that would be a very long axis and more machine complexity. The only good thing is that foam is nothing in the way ow weight or machine reaction forces.

With some rough calculations a the 200 oz/in motors would require a 10:1 gear reduction to drive a 6 in spool to move a 50lbs gantry.
EMC looks nice since we run an ubuntu system in the shop.

Yep there is even a page floating about the internet with scrips and stuff to do the install. I'm not a fan of ubuntu so can't comment on it. There is a fair amount of interest in ubuntu and EMC so that is good.

Please understand that there are two versions of (maybe three) of EMC. One called EMC1 or the original stable version, one called EMC2 which is fairly along in development, and the BDI install which is EMC1 that is maintianed as a seperate project.

We are using a 2in foam. However cutting the sections is only half the battle when laminating to produce the plugs. Indexing them and gluing them together is a long process. I cant find the actual numbers at the moment but we have done some calculations on laminating a large block using only full ½, and ¼ sheets of foam vs the cross sections we do now and we where able to save 3 or 4 sheets of foam due to waste along with less foam adhesive which gets expensive quick.

I understand all of the above but do realize that a bit of design effort could help with putting all the pices together. You could route keying slots and sequence numbers into the panels for example.

Even better if you have a machine that can handle full sheets of foam you could turn the panels out length wise. This should drastically reduce the problem with mate up of the parts. You still end up with a modest router compared to doing the canoe in one shot.

Taking the above idea a bit farther you could make a rotary fourth axis economically on this size of machine and do 3D sections of the canoe lengthwise. An 8 foot axis is far more doable than a 30 foot one.

To clarify our design choices here is a little background. We compete in a southwest regional conference each year for the American Society of Civil Engineers where cost in material and labor is around 30% of the total scoring rubric. Currently all the teams produce and form hulls the same way. It takes about a day and a half for 3 guys to build a plug from raw sheets this includes cutting two sheets at a time as the hull is symmetrical end to end. So, the advantage of having to report little labor cost is large not to mention the reduction of actual costs.

As far as swarf goes when we hand build hulls we still have to run a planer. To contain the particles we enclose the area in plastic. Place a large fan on one end blowing into the enclosure and another on the other sucking it into a trash can and attach the exhaust of the planer to a shopvac. It works very well and could work with this setup too I think.

If it was for personal or multi purpose use I agree I would cut the sections on smaller table machine and laminate them. However unless there are other issues I believe this may be the optimal solution.

Interesting competition! The idea that the canoes are symmetrical leads me back to thinking about a smaller machine to do half the canoe.

I am in Tempe, AZ
More questions:
Are the hobby cnc drivers adequate?

I don't realy know but with a 10 to 1 reduction I'd be concerned aobut the top speed you could realize out of your servo/stepper. If you are being scored on saving labor the machine will need to operate reasonably fast.

Look up Gecko drives as these are about the best you are going to get for stepper control in a reasonable price range. They also have servo controls.

The problem is that you will want to move reasonably fast through the foam to prevent melting and burning. So you may need a larger drive to keep you speeds up.

What kind of bit to cut Expanded Polystyrene Insulation?

I don't know for sure which would be best but a couple fo things to consider. One is that HSS might be better than cabide if it is extremely sharp. Two you don't want to have the helix on the mill pulling the foam up. Look into Onsurud, hope I spelt that right.

Anyone have a better source for large foam sheets or blocks? ( Buying insulation from Home Depot currently)

It always pays to look into the big yelow catalog - McMaster-Carr and then the big blue catalog - MSC. You should have these catalogs on hand when attempting this porject anyways, though I don't see them as big foam suppliers. It may pay to check the yellow pages for local plastics and contruction suppliers and of course boating suppliers. Try looking up this stuff on the net.

Thanks for the comment and keep them coming. I am learning a lot and may be tempted to build a small table for personal use.

Addictive isn't it!

[pen25]

the 4th axis could be scalable. so instead of only doing 3foot plugs you could scale to the size of the boat. lazer guides are cheap now days and would allow the scaling to be sone pretty acurately. that would allow you to use hotwire outside. if you look at things like a cnc paint gantry. since its foam you wouldnt need to exactly have to have something heavy duty and would allow you to mount a router as well. i would use a trim router as its lighter..

[vacpress]

there is an inexpensive(free?) way to generate 4 and 5 axis toolpaths... it is a lite version of 3D Studio Max and some add on.... I cannot remember the names, sorry. I do know there is a thread or a few here about it, and searching google for 'rainea cnc' may find someone who uses it, and i think he may be the wreiter of the plug in also...

[vacpress]

also, i think something like this needs budget constraints outlined for anyone to give good advice. if your budget is 5,000 or more, lots of things are possible.. if it is 'uh,... about. like $75?' then you are gonna be using 2x4s for the frame and strong rope for the linear actuation cables...

[vacpress]

ok. i am feeling benevolent, and waiting for paint to dry on a wall i just finished...

rainnea's site:
http://www.rainnea.com/cnc_toolkit.htm

The free version of 3D Studio is GMAX, and the toolpath generation addin is 'CNC Toolkit'

I think there are multiple people succeding in using this to drive 4 and 5 axis machines...

you can also consider looking at his machine as a prototype and just make it way bigger. i would consider making it 15' long and 6' wide instead of 3x3x30.. despite how 'cool' this long machine would be, i think far cheaper and better results will be attained with a smaller footprint.. its pure vanity, since we all know this could be done in a sections just as easily, maybe easier, and then put together...

i think you should consider a hot foam cutter cutting 1-2' thick sections... i think it can tilt just right and cut alot of the geometry in 1 pass? i dunno.. you need more variables answered.. 3 months eh?

[treegezer]

To clear up the confusion with the plug here is a detail.


I have seen 2" router blades so theoretically based on the 48 hour number given by jeffs555 with a 2" pass instead of the 1/4" pass it could be done in 6hours. Doesn’t matter much as only man hours are computed in scoring.

I considered the hotwire method but was unsure of the software to do such operations. I have see a similar commercial machine. Sounds like it could work but I would need bigger steppers. At least on the long travel to keep the foam from melting.

Now I am not to sure about the 4 axis option ether as it sounds like EMC and others may not support it. Is there a name for this setup?

How would I go about cutting through 2 2" sections on a smaller table? Run the tool path multiple times? I am envisioning 2 4x8 sheet laid on top of each other to allow several section to be cut each load. It still would require loading around 10-15 times. How would I make keys in the foam if they sit flush to each other? Would I not ether a) have to mill down the face of the entire sheet minus the keying area or b) add material as a key and cut a pocket? As of now we cut section drill holes in them with a template and use shock cord as a clamp to hold the sections together while the glue sets.

Right now sounds like a lathe type 4th axis to manufacture small 3' sections might be my best bet. Or maybe a hotwire setup.

One more question wizard mentioned needing larger drivers to keep speeds up what does that mean? Is a driver only able to run at full speed for a certain duration? Also how do you calculate driver requirements? Based on stepper sizes?
Some one mentioned budget. We are fairly well funded and would not be scared off by $3,000+. We also have a machine shop and machinists at our disposal in the research support services department. I have been meaning to go pick there brains also. However, I wanted to have good idea of what was possible before I showed my ignorance to them.

Thanks for all the comments. Sorry for all these lame questions.
Stuart

[pen25]

my suggestion is read through the fourms and see what others are doing for thier plugs. I know there are several who make kyaks and what not.

[wizard]

To clear up the confusion with the plug here is a detail.

Thanks for the pic that clears up a lot. In boat making that would be considred molding the hull over a form.

I have seen 2" router blades so theoretically based on the 48 hour number given by jeffs555 with a 2" pass instead of the 1/4" pass it could be done in 6hours. Doesn’t matter much as only man hours are computed in scoring.

If you expect to CNC a profile I think you will need ball nose cutters. Atleat that is the common way to do profiles.

I considered the hotwire method but was unsure of the software to do such operations. I have see a similar commercial machine. Sounds like it could work but I would need bigger steppers. At least on the long travel to keep the foam from melting.

I honestly believe that hot wire wouldn't do the trick if you need 3D profiles. Round sections yes it might work. In fact for round sections it might work without any CNC at all.

Now I am not to sure about the 4 axis option ether as it sounds like EMC and others may not support it. Is there a name for this setup?

You will have to look into the resources for EMC but I'm pretty sure it supports a 4 th axis for the milling configuration.

How would I go about cutting through 2 2" sections on a smaller table? Run the tool path multiple times? I am envisioning 2 4x8 sheet laid on top of each other to allow several section to be cut each load. It still would require loading around 10-15 times. How would I make keys in the foam if they sit flush to each other? Would I not ether a) have to mill down the face of the entire sheet minus the keying area or b) add material as a key and cut a pocket?

There are a number of ways to cut the keys. One easy one would be to cut 2" square pockets to stuff some of the trimmed waste in. In other words the pockets would be filled with plugs cut from the waste to key each panel together.

Another option would be to cut slots in the periphery to lay in very long strips to align the panels. This Would almost be like traditional boat building.

I'm still of the opinion that laying the panels length wise might save you alot of time and materials. This would especially be the case if you cna cut a full 4 by 8 sheet. Think of it this way, if the canoe is only 18 inches wide you will only need to cut 9 maybe 10 panels in two inch material for each 8 foot section of canoe. Start with a panel on either side of the center line and add panels as needed. Since you have a mirror imaged canoe, the amount of NC code that needs to be developed should be very manageable.

As of now we cut section drill holes in them with a template and use shock cord as a clamp to hold the sections together while the glue sets.

Interesting but I do wonder how you keep the stucture straight and square. Seems like a long "bench' is in order. That is fix the panels to a rigid support and glue up from there.

Right now sounds like a lathe type 4th axis to manufacture small 3' sections might be my best bet. Or maybe a hotwire setup.

Personally I would find away around the 4th axis, it is a time to "market" issue. While certianly the right way to do things it does ad more expense and complexity.

The Hot wire setup is very interesting as youu could elminate all of the CNC issues up front if the canoe keeps the same profile throughout the majority of its length. The biggest problem wourld be keepig the wire tensioned and the associated safety issues of hot wires. Here you could go back to the lathe idea and build a fixture to hold hte canoe form between axis. Rotate the form by hand and have a section of canoe done in a few seconds. Asumming the sections are gluee previous to mounting in the fixture.

One more question wizard mentioned needing larger drivers to keep speeds up what does that mean?

To go faster requires more torgue and thus a larger motor which leads to a larger driver. That is one aspect.

The other issue is the unique environment in which a stepper operates. To get th ecurrent flowing as fast as possible in the motor windings manufactures resort to increasing the supply voltage significantly above the nameplate rating and then current limit. More advanced drives such as the Geckos handle this technology well and will drive a stepper faster than can be accomplished with a simple step controller.

Is a driver only able to run at full speed for a certain duration? Also how do you calculate driver requirements? Based on stepper sizes?

Driver requirements are based on the current and voltage ratings of the motor. Look up the Gecko drives on the internet. Once you find the web site you should find documentation that explains drive sizeing and configuration better than I can. There is also a Gecko Yahoo group worth looking into.

Some one mentioned budget. We are fairly well funded and would not be scared off by $3,000+. We also have a machine shop and machinists at our disposal in the research support services department. I have been meaning to go pick there brains also. However, I wanted to have good idea of what was possible before I showed my ignorance to them.

That is not bad if you are just building a CNC machine as you will find that guys here spend a lot less. Then agian they are getting smaller machines then what you need.

If you already have a machine shop I'd take a look at what they have and see if something could do the job there. Even if it means altering how you wher egoing about this build.

Thanks for all the comments. Sorry for all these lame questions.
Stuart

Believe questions are not lame. If you can't ask questions you are not ready for the engineering world.

I do wonder about the contest itself and its goals and judging. If the goal is to build a CNC machine then anything discussed here has potential. If the goal is to build a process that reduces labor, for a canoe shaped like a half torpedo, then I'm wondering if CNC is the right way to go. I would have to think that the actual construction of the CNC device has to work into the equation someplace and I'm not sure if it would do so positively.

Dave

[treegezer]

We looked in to having the machine shop do the cutting however they didn’t like the idea. So the thought was to build our own machine.

The competition doesn’t really have much to do with process engineering or at least thats not the goal. The focus is to come up with lightweight highly plastic mix designs that fit in to some tight guidelines. As of late, the state of the art has lead to most teams being able to meet requirements with very light weight mixes with very little effort being done to mix designs. Barring any major changes to the specification, the same will happen this year. So in order to set ourselves apart we are trying to reduce costs and allow more time for experimentation. Labor being a big one. So the process engineering is kind of an aspect we have added.

Another aspect as to why we thought we needed to peruse CNC was we tend to build 2-3 smaller canoes to test different ideas such as pre-stressing, light-weight rebar replacement ect. Along with the fact, we pour 2 full size canoes as an insurance policy.

As far as the half torpedo comment goes our current hull design looks much different then that. I realize it would be trivial to setup up a human powered lathe and hotwire to make that shape.

I read in one thread about boat plugs that you could just have the spindel set at a fixed pitch to avoid a 4th axis. However, the more reasoning I hear for just cutting cross sections the better it sound. We do use a t-track to mount sections to. I forgot about that, it would be nice to have a key cut for them.

I think the case has been made for a 3 axis machine. I will hopefully draw up some plans after finals. Maybe somebody has built something of this size here on the forums already. I will take a look.

Thanks for all the answers guys. I really do appreciate all your help.

[JerryFlyGuy]

I've just come across this thread as I've been off the 'zone' for a few days. I think some of your parameter's are going to give you a bit of trouble. Currently I'm about 1/2 way through a 20 x 10 x 4 machine build, I'm not sure that your going to be able to build a gantry that is stiff enough w/ just 50 lb's weight, mine is over 800 lb's. If your main goal is to build a canoe, and not really build a milling machine, I think you'd be best suited to find someone who can mill it for you, rather than build your own machine to do it. I don't want to be all negative, but I'm just curious as to if this is part of your program or a side bar that is needed to get to the actual meat of the project.

As Vacpress has noted, a budget number would help us greatly in illuminating options for building your machine.
I can honestly say that my machine has gone from a $X projected cost to over double that[ and I'm no-where's near done it yet either.. there's still 50% again as much in stuff to purchase..and my initial number was well over the $5000 Vacpress stated], and not to mention its alot more work than I'd first thought. Its not an impossible thing to do.. it's just not a complete walk in the park Also its worth noting that I work full time designing mechanical/industrial equipment, and have access to machines and material's that others might not have so your projected price could vary greatly depending on your situation. If you have to rent certain tools etc..

I would also recommend sitting down and doing the nesc. calculations to get your design down-pat, know what your cutting force needs to be, how fast you want to accelerate your gantry, how heavy it is [ do some actual design on this as it will come out way heavier than you think..] then spec in the stepper size you need. You'll have more success via this route, over the TLAR design [That Looks About Right].

My 2 cents
Jerry [ still shaking grinding dust out of my hair..but 3/4 of my welds are now ground down and nice and smoooooth .. getting ready for priming!! ]

[izzlestar]

30 feet long? Wow, thats huge for a first machine. You would really be doing yourself a favor if you made a 10' long machine and cut the canoe in three sections, then glued them together? Seems much simpler to me than a 30' long machine. -Carl