Concrete body for cnc router

I have read through a lot of the polymer concrete thread and have done searches but cannot come to a consensus as to if what I want to try will have a chance of working. I have read of other people wanting to do similar things as well as how machines used to be built using similar methods of casting concrete. The information might be here somewhere, vbut I cant seem to find exactly what I'm looking for.

I have a 4x4' Gerber router and want to start on a 4x8 (maybe a 5X8) self built machine. Being that I already have a router, I would like to utilize it for the new build. I could build a mdf router pretty easily but really need a machine that is more capable. Cost is a factor. I just looked into buying a Chinese machine but have decided that there was just too much risk in getting it here.... too many if's! I actually have a second build which is on the back burner, a cnc woodworking lathe using an old Hardringe lathe. I have a cabinet shop and am in the process of getting a semi custom product into stores that are mostly cnc'd. The 4x4 machine works great, but is a pain to have the limits less than the sheet stock being used. That and I am concerned about down time when the machine needs repair and would like some redundancy.

Here is what I propose:

The machine will be a moving Gantry router. I am better designing as I go with things so am just putting this together in my head right now before designing parts in Cad.

I would like to build a shell out of mdf, or more likely Extira board (if it remains permanent) so I can use the existing router to map everything out precisely. I would like to use this as a form to pour a fortified concrete (not polymer concrete). I would reinforce the concrete with both rods as well as tensioned cable as they do on bridges and decks, but on a much smaller scale. I did concrete work years back so have the concepts down for large scale stuff! I would like to do this for the gantry as well as beams to support the y axis. I could either remove the shell or keep it so the machine could be finished easily. I was thinking of embedding 80/20 t slotted beams into the concrete for not only a straight reference point to build from but for ease in assembly and adjustment during the final build. I've contemplated doing a build entirely out of 80/20, but feel it will not poses the build quality and rigidity I want. Overall the gantry would weigh between 375 and 450 lbs depending on the final design with a 5X10" main beam on the Gantry.

I want a heavy machine to cut down on vibration and increase rigidity over what most other methods people are using. I wont be rolling it around the shop! Though I cut mostly wood, I would like the ability to cut non-ferrous metals at a normal speed. High speed is nice, but I rarely cut at over 200 ipm as it is and am fine with that goal with the new machine with maybe 400 ipm rapids.

The Gerber I have is driven by 1" cog belts which work extremely well. After pricing them against rack and pinion, I find it is more cost effective and will make for a simpler build overall, so am leaning towards that and either a gear box or timing pulley system to get the best torque curve from the steppers.

What do you guys think about the direction I'm going with the concrete? Should it work?

Here are some links while reading various stuff trying to brainstorm I came up with this line of thinking:

Machines That Make | MtM | An MIT Center for Bits and Atoms Project

The Multimachine $150, 12" Swing, Metal Lathe/Mill/Drill

Looking forward to hearing your opinions!

Thanks, Jay

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I was thinking of embedding 80/20 t slotted beams into the concrete for not only a straight reference point to build from but for ease in assembly and adjustment during the final build.

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I think the different expansion rate of aluminum may cause it to break free from the concrete if it's subject to large temperature swings.

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Originally Posted by ger21

I think the different expansion rate of aluminum may cause it to break free from the concrete if it's subject to large temperature swings.

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Thanks Gerry! I also just remebered that the aluminum will react with the concrete and cause problems. I guess since steel has a similar expansion rate as concrete I would be best off drilling out the mdf forms with the cnc and installing steel anchor points directly into the pour for bolting 1/2" steel plates to for assembly. I got a bit over zealous writing the post and came up with using 80/20 without thinking it through entirely!

I'm most concerned with the viability of building the concrete structure. In theory as far as I can see it should work just fine and solve the issues I see in going with a rectangular tube design or similar with rigidity and vibration.

Jay

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I want a heavy machine to cut down on vibration and increase rigidity over what most other methods people are using. I wont be rolling it around the shop! Though I cut mostly wood, I would like the ability to cut non-ferrous metals at a normal speed. High speed is nice, but I rarely cut at over 200 ipm as it is and am fine with that goal with the new machine with maybe 400 ipm rapids.

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I used to work in pre-stressed concrete (multi-story parking structures) and I know how much fun it can be. It seems though that it might be a whole lot easier and ultimately dimensionally controllable to fill structural tube with concrete to gain mass rather than casting concrete in open or closed molds. Also when you get into the 350-450 lb range for a gantry it seems like you will need very large motors to get the accelerations you'll need for high rapids. You might want to look at the Mechmate site for performance/weight/drive comparisons.

Chris

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Originally Posted by OCNC

I used to work in pre-stressed concrete (multi-story parking structures) and I know how much fun it can be. It seems though that it might be a whole lot easier and ultimately dimensionally controllable to fill structural tube with concrete to gain mass rather than casting concrete in open or closed molds. Also when you get into the 350-450 lb range for a gantry it seems like you will need very large motors to get the accelerations you'll need for high rapids. You might want to look at the Mechmate site for performance/weight/drive comparisons.

Chris

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Thanks Chris,

I guess it depends on which way you look at it. I'm a cabinet maker by trade. Therefore I have all the tools I could ever need to work on wood. I do have a wire feed welder and some metal working tools as well as ingenuity when I need it! For me it seems that to weld up a frame isn't so much a problem as there will inevitably be a fair amount of welding anyhow. It's more of a problem to line everything up properly especially laying out holes and hardware in reference to one another. For me it would be much easier to build a wooden (mdf) form where I can lay out all of the connections to keep the machine true in cad, then cut them on my router. I want to utilize what I have on hand as much as possible. The shop next to mine is a machinist with quite the setup who I can have make me up just about anything for a fee. He made me up some parts when I updated my Gerber. I also have access to some machining tools myself through familly. If I'm smart about it, I shouldn't need too much more than what I have. To build a nice heavy tube frame, then fill it with concrete, sand grout, etc., wont save me too much on weight if any. If I'm going to build my own machine I want it to be robust. I know the y axis is going to need a big motor. I'm hoping to see what I can do with a 1200 in/oz which seems like the largest before they start costing big bucks with the electronics needed to push them. Simple wisdom tells me that since the gantry on my Gerber weighs about 200lbs and I just upgraded the y axis from a 250 in/oz to a 600in/oz which is more than enough now, that I should be right in the ballpark with 1200 in/oz to keep the speeds I have now on this machine. I am going to design the forms inside volume to keep the concrete and parts at right around 400 lbs by putting eliminating anything which is not structurally necessary.

Here is a general sketch of what I want to do with it:

<a href="http://www.flickr.com/photos/76412145@N08/7178025131/" title="router6-11 by jayscustom1, on Flickr"><img src="http://farm9.staticflickr.com/8006/7178025131_c3e554a86e.jpg" width="500" height="244" alt="router6-11"></a>

Jay

Here's one more view:

<a href="http://www.flickr.com/photos/76412145@N08/7363336536/" title="router6-11#4 by jayscustom1, on Flickr"><img src="http://farm8.staticflickr.com/7217/7363336536_60b81b5cd0.jpg" width="500" height="244" alt="router6-11#4"></a>

I'm trying to come up with a reason that structurally concrete wont work for this application.

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Originally Posted by jayty97

I'm trying to come up with a reason that structurally concrete wont work for this application.

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I don't see why it wouldn't work structurally. As with any material you just need an understanding of the methods of fabrication.

Chris

To quote a line, I remember from "This Old House" there are two kinds of concrete, concrete that is cracked, and concrete that is going to crack. I too, used to work at a company that constructed cooling towers for reactors. Stress cables were used for the assembly of all of the steel reinforcing which went into them. The concrete was cured overnight, by use of a large boiler, and steam vent system. This yielded a finished product which was very durable (they HAVE to be in a reactor), but also allowed some flex. These pieces were also poured into steel form beds, which featured massive vibrators which totally eliminated air bubbles in the concrete. It never ceased to amaze me, how a seemingly "Full" form bed of concrete would suddenly drop to less than half full, when the vibrators were turned on! These things were massive, when they were turned on, one could feel the vibrations on the ground up to 300 feet away from the forms! If you have access to something like this, to construct your pieces with, then it just might work. However, anything less than this, and the line from This Old House will come into play.

THe only thing I see is all your weight and strength is up top, which I think may negate some benefits of the concrete. If the machine will be stationary, why not just build two concrete walls with steel inserts for the linear rails? Would be a heluva lot cheaper than buying all that steel?

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Originally Posted by adprinter

To quote a line, I remember from "This Old House" there are two kinds of concrete, concrete that is cracked, and concrete that is going to crack. I too, used to work at a company that constructed cooling towers for reactors. Stress cables were used for the assembly of all of the steel reinforcing which went into them. The concrete was cured overnight, by use of a large boiler, and steam vent system. This yielded a finished product which was very durable (they HAVE to be in a reactor), but also allowed some flex. These pieces were also poured into steel form beds, which featured massive vibrators which totally eliminated air bubbles in the concrete. It never ceased to amaze me, how a seemingly "Full" form bed of concrete would suddenly drop to less than half full, when the vibrators were turned on! These things were massive, when they were turned on, one could feel the vibrations on the ground up to 300 feet away from the forms! If you have access to something like this, to construct your pieces with, then it just might work. However, anything less than this, and the line from This Old House will come into play.

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Thanks!

What I have been looking into are some of the concrete mixes out there that are commonly used in concrete counters and furniture. These don't have as much of a tendency to crack with the inclusion of fiberglass strands in the mix as well as fortifiers. It shouldn't be too hard to get most of the bubbles out in a pour this small. There are guys out there building amazing things out of concrete. I think the basic concepts of larger standard reinforced concrete pours are a bit different than what i want to tackle. There are a lot more things that will come into play with a large pour like the ones you are talking about as far as stresses, temperature fluctuations, etc.

There absolutely could be cracking, but I think by using the right mix as well as the right reinforcements a piece this size could be made to not want to crack in a fairly controlled environment.

I would love to hear from someone who actually does concrete counter tops and furniture. That might be able to shed some light on this (unfamiliar to me) other side to concrete!

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Originally Posted by louieatienza

THe only thing I see is all your weight and strength is up top, which I think may negate some benefits of the concrete. If the machine will be stationary, why not just build two concrete walls with steel inserts for the linear rails? Would be a heluva lot cheaper than buying all that steel?

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I absolutely agree with that.... but I am building this in a rented commercial space so will likely move it at some point. Otherwise, it would be concrete all the way to save on cost. The main body of the machine, anything where motion would be involved, would be concrete which I would hope would give the majority of the benefits of going with concrete as a build material. I have an old Hardinge lathe here (waiting on a convert) which is a high quality lathe, the mass is all up top where the machine does the work. The base, though not light weight is pale in comparison to the lath itself. I know there is going to be some cost in welding up a frame in 1/4" thick 4" square tube, but I'm not sure I have a choice. My main reason for thinking about concrete is in the gantry. Most machines I have seen seem like they could use more rigidity in this are. Concrete done right should provide that... I hope!

I have no doubt that this concept could be made to work with a proper understanding of the materials and you seem to have that in spades. The thing that concerns me about the idea is that you'll still have a bunch of variables in the frame to stand part of the build (if I understand correctly you'll have cast concrete sitting on a steel tube frame) Next, if you cast hardpoints into the concrete for mounting the rails and so forth, they'll have to be pretty precise so that you're not chasing alignment and height problems. I'm aware that you can cut some precision molds on your other machine but it just seems like a long way around to gain mass/rigidity. In addition to that, if you ever want to move the machine, there will be no possibility of breaking it down into smaller components to effect a relocation. Maybe this wouldn't be a problem if you have access to the right lifting gear and transport. Have you thought about doing this in steel with deep side beams on the x-axis/bed and then look at filling the RHS with some sort of dampening material that won't be structural? I know steel aint cheap but it does give you the possibility of trueing and tweaking to get the machine set up right.

Just some ideas to kick around :)

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Originally Posted by jayty97

I absolutely agree with that.... but I am building this in a rented commercial space so will likely move it at some point. Otherwise, it would be concrete all the way to save on cost. The main body of the machine, anything where motion would be involved, would be concrete which I would hope would give the majority of the benefits of going with concrete as a build material. I have an old Hardinge lathe here (waiting on a convert) which is a high quality lathe, the mass is all up top where the machine does the work. The base, though not light weight is pale in comparison to the lath itself. I know there is going to be some cost in welding up a frame in 1/4" thick 4" square tube, but I'm not sure I have a choice. My main reason for thinking about concrete is in the gantry. Most machines I have seen seem like they could use more rigidity in this are. Concrete done right should provide that... I hope!

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I've done three concrete countertops. Nothing special with the concrete, but I did add "milk" normally used to bond new concrete to old as a precaution (forgot what it's really called.) I used melamine for the forms, and made the bullnose form out of PVC pipe cut in half. The slab was reinforced with welded wire mesh. I affixed the slab to the cabinets with silicone; this took up some unevenness and allowed the slab to "move."

I didn't use a vibrator, though a quarter sheet sander might work well. I just rapped the form with a hammer to get the juice to the bullnose and "top" and it worked fine. Since I finished the tops with wax, I deciced to wax the forms as well to make removing them easier.

I would like to suggest that you consider your potential product sales plan needs vs your router desire.

It really takes nothing for a router build to use up a year, and 3 - 4 months is aggressive. In the meantime, you will still need to be knocking out production.

Consider to take advantage of others that have good quality cnc wood routers to outsource a few parts to other local cnc router shops, and keep the interesting ones in-house. That can triple your capacity pretty quickly, but you do need to really nail down the specs on those parts if you want them made "correctly". This might take a few times, so staying power is a must, as is careful documentation of what you want. Keep it local though - not further than you can drive in a day.

Once this is complete, THEN go back and start building another cnc router. This will save you at least one stress induced illness, and if you are married, might allow you to stay that way.

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Originally Posted by jayty97

Here's one more view:

<a href="http://www.flickr.com/photos/76412145@N08/7363336536/" title="router6-11#4 by jayscustom1, on Flickr"><img src="http://farm8.staticflickr.com/7217/7363336536_60b81b5cd0.jpg" width="500" height="244" alt="router6-11#4"></a>

I'm trying to come up with a reason that structurally concrete wont work for this application.

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Keep in mind that concrete is designed for use in compression, not tension. The bottom of that X beam is in tension, so it will likely crack, unless it is under heavy pre-stress tension, and even then, you can find cracks in well-engineered setups.

If you are really convinced to go concrete, consider this:
- Pour a pad of self leveling epoxy to make a dead flat area
- make a mold using steel channel on the floor, then your mdf sides to the top. Use the floor as the bottom of your router and add some spoil board on top of it.
- Use self leveling epoxy to level the top of the concrete and a bridge between the sides to level them to each other.
- Mount your rails on some ground flat steel plate and then fasten them to the top of the epoxy / concrete sides.

When it is time to move, take the parts that are valuable, and crash the concrete walls down.

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Originally Posted by harryn

I would like to suggest that you consider your potential product sales plan needs vs your router desire.

It really takes nothing for a router build to use up a year, and 3 - 4 months is aggressive. In the meantime, you will still need to be knocking out production.

Consider to take advantage of others that have good quality cnc wood routers to outsource a few parts to other local cnc router shops, and keep the interesting ones in-house. That can triple your capacity pretty quickly, but you do need to really nail down the specs on those parts if you want them made "correctly". This might take a few times, so staying power is a must, as is careful documentation of what you want. Keep it local though - not further than you can drive in a day.

Once this is complete, THEN go back and start building another cnc router. This will save you at least one stress induced illness, and if you are married, might allow you to stay that way.

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I don't really understand why it takes so long for some to build a machine. I'm not knocking anyone. A lot of people put a lot of time into creating their babies. There are a lot of extremely smart people here. That is why I posted this as I value those opinions! I am more concerned about shear functionality. A few years back i needed a small machine to do custom lettering in wood parts. I didn't have the money for a machine nor any knowledge of working with cnc equipment, never mind building it. It took me one week to start cutting parts on my new build. I found an old wire wrapping machine from the 70's locally which gave me a good base. I purchased some ball screws from Rotton, a set of linear bearings from Ebay used and a motor and driver kit from hobby cnc which I soldered together myself. The machine which I still have and am going to beef up into a mill did what i needed and gave me the cnc bug.

I guess I could have spent longer on the build to get things pretty, but shear necessity has a tendency to light a fire under the posterior... amazing things can be accomplished by the shear need to get them done. The machine still works great though it is currently being taken apart for some upgrades after 3 years in use. She isn't pretty, but for this, function defeats form any day!

I am fine for a while with my new product with the equipment I have now. That is why I'm throwing around ideas, not frantically building a machine! I do want to keep things in house. I almost have to since it's a semi custom product with no two the exact same. Currently I'm a one man show and everything i do is 100% custom. this product I'm working on, if I can start scaling it, will allow me to grow and start taking on employees since the skill level involved in processing will be far less than my normal every day work, which I've given up looking for in someone else (at least at a reasonable cost)!

Jay

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Originally Posted by harryn

Keep in mind that concrete is designed for use in compression, not tension. The bottom of that X beam is in tension, so it will likely crack, unless it is under heavy pre-stress tension, and even then, you can find cracks in well-engineered setups.

If you are really convinced to go concrete, consider this:
- Pour a pad of self leveling epoxy to make a dead flat area
- make a mold using steel channel on the floor, then your mdf sides to the top. Use the floor as the bottom of your router and add some spoil board on top of it.
- Use self leveling epoxy to level the top of the concrete and a bridge between the sides to level them to each other.
- Mount your rails on some ground flat steel plate and then fasten them to the top of the epoxy / concrete sides.

When it is time to move, take the parts that are valuable, and crash the concrete walls down.

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As this whole thing is just concept at this point, I'm not sure of where I want to use the concrete yet. Originally I just wanted to do a concrete gantry. I'm now thinking that may still be best. I do want the machine to be movable and don't want to be tied to the floor with anything more than bolts. That being said, I'm looking at tried and true designs of larger industrial routers. The biggest difference in design that I see are not only beefier parts, but how the gantry uprights are made. Most companies seem to use cast iron. My machine has cast iron. It seems as though they all seem to make an extremely rigid structure at this point. That is where the concrete part came to mind. I couldn't use cast iron, but i could make a perfect mdf mold for not just the Gantry uprights, but the bridge as well as a solid unit. I understand that concrete has great compression strength and poor tensile strength. That is why we use rebar. With some of the new fortified reinforced concrete mixes, combined with more conventional reinforcements, I am under the impression that a relatively small structure such as a router gantry could be poured with much success seeing as though there are people using this method to create some abstract pieces of outdoor furniture which are not only relatively thin, but have extremely high tensile strength. I did concrete form work for some time and understand the dynamics of standard concrete pours, but It seems that there are smaller scale methods which may be able to be applied here like this that take a different line of thought.

http://static.concretenetwork.com/ph...ings_52976.jpg

I am now leaning towards a conventional steel frame with only the gantry being concrete may be the best combination. I do like the concept of using self leveling epoxy and may be able to incorporate that into truing thing up.

Thanks, Jay

Here's one of my projects. I designed and built the mechanism in 3 days. It has been working in the customers house for almost two years now. I like thinking outside of the box, this time it was sideways! I could have made it faster.. a lot I would do different if I did it again, but I think it is pretty cool nonetheless!

http://youtu.be/TMYdgeL9PV0

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Originally Posted by jayty97

Here's one of my projects. I designed and built the mechanism in 3 days. It has been working in the customers house for almost two years now. I like thinking outside of the box, this time it was sideways! I could have made it faster.. a lot I would do different if I did it again, but I think it is pretty cool nonetheless!

video 2011 03 10 10 52 50 - YouTube

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It would be nice if while the TV was disappearing a nice piece of artwork was emerging to take its place. Nice job though.

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Originally Posted by OCNC

It would be nice if while the TV was disappearing a nice piece of artwork was emerging to take its place. Nice job though.

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The funny thing is, that's exactly why we did it! The woman made an intricate needlepoint years back that she wanted to display over the fireplace. Her husband wanted a TV... after 5 different designs of all sorts, I presented them with this. Great people trusting me to pull it off!

Sent from my GT-N7000 using Tapatalk 2

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jaty97 Wrote: I don't really understand why it takes so long for some to build a machine.

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I think there would be ample scope to build a machine quickly, especially out of a kit. Even if one was just to use a kit for the motion parts (motors,drives etc) that would make the process much quicker. My build has taken a substantial amount of time because I went custom everything, from the design in Solidworks all the way through. Add to this I'm using industrial servos and drives etc etc etc. After all of the big stuff is sorted, you've still got wiring and limit switches, software setup.

Most importantly for me, when i am finally finished I'll be able to take a couple of steps backward and say "I made that!"

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Originally Posted by Benonymous

I think there would be ample scope to build a machine quickly, especially out of a kit. Even if one was just to use a kit for the motion parts (motors,drives etc) that would make the process much quicker. My build has taken a substantial amount of time because I went custom everything, from the design in Solidworks all the way through. Add to this I'm using industrial servos and drives etc etc etc. After all of the big stuff is sorted, you've still got wiring and limit switches, software setup.

Most importantly for me, when i am finally finished I'll be able to take a couple of steps backward and say "I made that!"

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I looked at some of what you are doing. It looks like you are definitely building your baby!

I have a lot of the parts already for this mechanically that I have collected over the years and have a good idea of what I will be using. The drive system and electronics are the least of my concerns. After my last rebuild of my Gerber what I didn't understand, now I do.. I've made my mistakes and am becoming very comfortable with this stuff.

I'm sticking with steppers for simplicity, cost, familiarity.. as well as they have done me right thus far and i haven't needed the benefits of servos. I like using what I have on hand and any shortcut I can take I will, just not at the cost of quality. I always look to see what i can find that is similar to what I want to make and I could make work. That being said, it seems as though the gantry is the most import and part of the build, especially the uprights. That is were i see a lot of machines have trouble with as far as rigidity.

With concrete I could make up an accurate form and pour in a weekend. Welding up steel is going to take a long time. I can weld, but its not second nature to me like carpentry is. My faith in making an accurate form far outweighs my faith in my metal working abilities. I have done a lot of experimenting with casting parts.. even new gears for the Gerber. I know I could pour a good part, but am only questioning that part in service over the long term.

Sent from my GT-N7000 using Tapatalk 2

Have you also given thought to using an epoxy-granite mixture of some type? I don't know how it'd work for a large gantry, but it's probably more impact and crack-resistant than regular concrete....

Concrete(standard) is generally regarded as poor material for machine tools,
compared to other materials.Reasons given include:a Poor Strength To Weight Ratio,its
dimensionally unstable(eg absorbs water),never really cures,Poor Strength compared to
alternatives,has virtually no tensile strength,is susceptible to cracking(lowering
strength),brittleness and its properties deteriorate over time.There may be damping
advantages from the use of concrete.I am only aware of around a handful of efforts to use
concrete in machine tools.


https://www.jstage.jst.go.jp/article...4_1_1/_article
Concrete Machine Tool Structures - Hand Tools - Concrete Construction

For a comparison of machine tool materials see page 136 of this pdf.

DSpace@MIT : Manufacturing and testing of composite machine tool structures

Remember to that a tube is much more structurally efficient than a bar of the
same material and this is not reflected in a direct comparison of material properties
alone,multiplying the strength advantage of steel.

For info on concrete(strength) variations see.

Types of concrete - Wikipedia, the free encyclopedia

(There are perhaps 3 commercial machine tool builders using essentially uhpc,~= to
epoxy granite in specification,pc in the above pdf)

On beam design see these.
Reinforced concrete - Wikipedia, the free encyclopedia
Basic Issues of Beam Design - Yahoo! Voices - voices.yahoo.com
Breaking a Plain Concrete Beam - Yahoo! Voices - voices.yahoo.com
Deflections of an Uncracked Reinforced Concrete Beam - Yahoo! Voices - voices.yahoo.com


Apart from the possibility of beam failure,I see the biggest problem being the concrete gantry being
to heavy.If its significantly heavier than say a steel alternative then you
will require heavier duty screws,rails,bearing etc and that will surely cost more than you
save by using concrete.If it was me I would use the steel in the gantry and table and use
the concrete in 6 or 8 pyramid shaped legs.

As an alternative consider there are many apparently successful builds in
steel including the mechmate and it is the material of choice for industrial router
builders(normalized I would think).This one looks good to me.

http://www.cnczone.com/forums/diy-cn...ext_cnc-6.html

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Originally Posted by shedbob

Concrete(standard) is generally regarded as poor material for machine tools,
compared to other materials.Reasons given include:a Poor Strength To Weight Ratio,its
dimensionally unstable(eg absorbs water),never really cures,Poor Strength compared to
alternatives,has virtually no tensile strength,is susceptible to cracking(lowering
strength),brittleness and its properties deteriorate over time.There may be damping
advantages from the use of concrete.I am only aware of around a handful of efforts to use
concrete in machine tools.


https://www.jstage.jst.go.jp/article...4_1_1/_article
Concrete Machine Tool Structures - Hand Tools - Concrete Construction

For a comparison of machine tool materials see page 136 of this pdf.

DSpace@MIT : Manufacturing and testing of composite machine tool structures

Remember to that a tube is much more structurally efficient than a bar of the
same material and this is not reflected in a direct comparison of material properties
alone,multiplying the strength advantage of steel.

For info on concrete(strength) variations see.

Types of concrete - Wikipedia, the free encyclopedia

(There are perhaps 3 commercial machine tool builders using essentially uhpc,~= to
epoxy granite in specification,pc in the above pdf)

On beam design see these.
Reinforced concrete - Wikipedia, the free encyclopedia
Basic Issues of Beam Design - Yahoo! Voices - voices.yahoo.com
Breaking a Plain Concrete Beam - Yahoo! Voices - voices.yahoo.com
Deflections of an Uncracked Reinforced Concrete Beam - Yahoo! Voices - voices.yahoo.com


Apart from the possibility of beam failure,I see the biggest problem being the concrete gantry being
to heavy.If its significantly heavier than say a steel alternative then you
will require heavier duty screws,rails,bearing etc and that will surely cost more than you
save by using concrete.If it was me I would use the steel in the gantry and table and use
the concrete in 6 or 8 pyramid shaped legs.

As an alternative consider there are many apparently successful builds in
steel including the mechmate and it is the material of choice for industrial router
builders(normalized I would think).This one looks good to me.

http://www.cnczone.com/forums/diy-cn...ext_cnc-6.html

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Thank you for the abundance of information on concrete. It will take some time to read through it all! I won't give up on the idea before reading something with comprehensive facts against it... I have my work cut out for me!

If at the end of the day, concrete wont work. Epoxy granite will just be too expensive to use for the kind of volume needed. I've seen a lot of the projects done on this site and know most have been out of steel. I really hate working with steel. For one it is very hard to get good straight stock. Two, it takes a ton of prep and oil to drill and tap which I try to stay away from using too much in my shop due to contamination problems I get with my woodwork, etc. Lastly, by using steel, I would have to lay everything out by hand. I really want to utilize my existing router for critical layouts and steel is just not possible with this machine without oil coolants. Aluminum though more costly would be manageable, but still there will be a lot of fabrication involved to make complex parts and recesses for a belt drive system.

Maybe for me I would be better off building a laminated Baltic Birch machine... I could vacuum laminate the parts and have extreme flexibility in designing and cutting the parts. A 4" x 10" BB beam would have very good dimensional stability using the appropriate construction methods. I know there are drawbacks with this as well, but utilizing what I have on hand is of great importance to me if I'm going to go forward with a build. Plus, though I'm a good all around mechanic my familiarization and comfort level working with wood is far above anything else. This is where the desire to explore concrete construction originated from.

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Maybe for me I would be better off building a laminated Baltic Birch machine... I could vacuum laminate the parts and have extreme flexibility in designing and cutting the parts. A 4" x 10" BB beam would have very good dimensional stability using the appropriate construction methods. I know there are drawbacks with this as well, but utilizing what I have on hand is of great importance to me if I'm going to go forward with a build. Plus, though I'm a good all around mechanic my familiarization and comfort level working with wood is far above anything else.

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This sounds like the best idea so far.

Hi Jay - Did this machine work out? Concrete or birch? I've been playing with UHPC and its got many advantages...Peter

I can understand how hard it's for a beginner to sand concrete or cement if you haven't done it before. During my research on this topic I found this blog very helpful https://writions.com/how-to-sand-concrete/